Spread The News

In radio communications, spread spectrum techniques are methods by which a signal generated with a particular bandwidth is spread in the frequency domain, resulting in a signal with a wider bandwidth.  So, why would a radio communications engineer want to do this?  There are actually many advantages to employing spread spectrum in your design.  I […]

In radio communications, spread spectrum techniques are methods by which a signal generated with a particular bandwidth is spread in the frequency domain, resulting in a signal with a wider bandwidth.  So, why would a radio communications engineer want to do this?  There are actually many advantages to employing spread spectrum in your design.  I will not even attempt to explain spread spectrum techniques in this blog, but if you want to learn more about these techniques, ATI can help.  So, what are the advantages, you ask?

Crosstalk interference is greatly attenuated due to the processing gain of the spread spectrum system.

Voice quality is improved due to less static noise.

Lower susceptibility to multipath fading.

Increased security since a PN sequence is used to either modulate the signal in the time domain, or select the carrier frequency.

More users can Coexist in the same frequency band

Longer operating distances since higher transmit power is allowed.

Signal is harder to detect by those who are not supposed to be detecting it.

Signal is harder to jam.

If these advantages sound like something you would like to achieve, consider learning more about Spread Spectrum techniques in radio communications by taking the ATI short course titled Wireless Communications and Spread Spectrum Design.  You can learn more about this course, and register for it here on the ATI Web Page. 

And as always, a complete list of ATI courses, and a schedule of upcoming offerings can be found here on the ATI home page.

Submarine Movie Chat

Although I work for Applied Technology Institute now, I spent 40 years working in a career that had me riding nuclear submarines frequently, often for weeks at a time, doing tests and working closely with sailors in the US Navy.  Suffice it to say, I know a little about Submarines and Submariners.  Admittedly, I do […]

Although I work for Applied Technology Institute now, I spent 40 years working in a career that had me riding nuclear submarines frequently, often for weeks at a time, doing tests and working closely with sailors in the US Navy.  Suffice it to say, I know a little about Submarines and Submariners.  Admittedly, I do not know one one-hundredth of what is known by our many brave Submarine Sailors, past and present, but I but probably know more than most civilians.

So, what is the most realistic, and best Submarine movie ever made?  I am asked this question often, and although I have a quick and definitive response whenever I am asked this question, I decided to do a little research before writing this blog post.  I will reveal my top choice and my bottom choice, later.

When I googled the topic, I had hundreds of hits, so I decided I needed a systematic way to choose which sites I would visit.  I picked three sites.  First, I choose the Number 1 google hit, as google would want me to do.  Second, I chose the US Naval Institute, as I belong to this fine organization, and I trust what they say.  Lastly, I chose IMDB, the greatest movie site on the internet, which everyone should check out if they don’t already know about it. 

Here is what I found.

The two movies that appear on most top ten lists are Das Boat and Hunt for Red October.  These movies are not always Number one and two, but they are almost always on the list.

Many of the movies of the movies on top ten lists are foreign films.  Many are also older films from the WW2 era starring famous actors who are no longer with us.  There are many films in this category ( foreign and older ) which I have never seen before. In fact, based on the recommendation by a Navy Captain on the USNI site, before writing this blog, I decided to watch the 2019 UK-French film called “The Wolf’s Call”; more on that to follow. 

 Most of the movies on these lists make sense.  Even if I have never seen the movie before, the title and the picture on the box look like they would be submarine movie.  The one notable exception was a top- choice chosen by an officer in the US Navy on the US Naval Institute Site.  He chose “Office Space” as his top choice.  He justified his choice by saying “TPS reports, multiple bosses, a defective printer, coming in on Saturday, the oversight team of The Bobs that are There to Help, and the engineers are not allowed to talk to the normal people.”    A rather bizarre choice, but humorous and understandable to anyone who has served on a sub.

Some of the movies that people put on their top pick list were terrible movies.  My bottom choice actually appears on some of the lists.

So, after reviewing these sites, and after watching a new movie which piqued my interest, I will reveal my top choice and my bottom choice.  Top choice was, and remains, Das Boat.  (Honorable Mention goes to Hunt for Red October.)  Bottom Choice was, and remains, Crimson Tide.  My latest movie, The Wolf’s Call, did not impress me, in fact, it would be fairly low on my list.  I look forward to watching a few more of the submarine movies that I have not seen.  Who knows, I may find one that beats Das Boat.  Please feel free to leave recommendations in the comments section.

From IMDB, the tag line for 1981 film Das Boat is “The claustrophobic world of a WWII German U-Boat; boredom, filth, and sheer terror.”  I have seen this film many times, and I still enjoy watching it each time I see it.  This film is ranked as IMDBs second best Submarine Movie, and as IMDB’s 77th best overall movie.

 ATI has a submarine related course coming up in late September called SONAR Signal Processing.  You can learn more about this course, and register, here.

Another fun course offered by ATI is Submarines and Submariners.  Although this course is not being offered in the near future, you can read about it here.  If this course interests you, and you would like us to run it, or bring it your location for your staff, please let us know, and we can work with you.

Lastly, as always, a full listing of ATI’s courses can be found here.

Yeah, But What If?

Submarine accidents which result in the submarine careening to the sea bottom are spectacular in Hollywood movies and video games, but they do not happen often in real life.  In fact, for the U.S., we have not lost a submarine to the depths since 1968 when USS Scorpion was lost with 99 souls due ( […]

Submarine accidents which result in the submarine careening to the sea bottom are spectacular in Hollywood movies and video games, but they do not happen often in real life.  In fact, for the U.S., we have not lost a submarine to the depths since 1968 when USS Scorpion was lost with 99 souls due ( most likely) to an inadvertent activation of a battery or a torpedo.  Prior to that, in 1963, USS Thresher was lost with 129 souls due to ( most likely ) a piping failure during a deep dive.  Due to actions taken as a result of lessons learned from those two mishaps, the U.S. has not had a major submarine loss since then.  The safety record for U.S. Submarines since 1968 has been remarkable, and the envy of other countries.

Yeah, but what if?

To be prudent, the U.S. must assume that there will be submarine accidents in the future, even if they are not U.S. submarines.  For this reason, the U.S. continues to maintain a force dedicated to the rescue of downed submarines.  Undersea Rescue Command (URC) is the U.S. Navy’s official command for the rescue of sailors during a submarine casualty anywhere in the world.   If you would like to learn more about this command, you can read about it here.

The blog author has had some personal experience working with the Undersea Rescue Command, and all comments that follow are the authors personal opinions, and not an official opinion of the U.S. Navy or Applied Technology Institute.  In case you missed that, please go back and read it again.

Two significant issues that confront the Undersea Rescue Command are funding and localization. 

The funding issue arises from the fact that our submarines are so safe, and our safety record is so good, there is a hesitance to pay too much attention ( and funding ) to an organization which may not ever be called into service.  Unfortunately, there is not much the technical community can do about that; it will have to fall upon the Public Relations Office at U.S. Navy. 

Localization, however, is a problem which the technical community can help solve.  When a submarine goes to the bottom, the Undersea Rescue Command jumps into action, and reports to the vicinity of the accident very quickly.  Unfortunately, the Undersea Rescue Command cannot start their rescue mission until the precise location of the sunken submarine is known, and that is often a difficult problem.  Until the submarine is located, the rescue can not actually begin.  Often, in exercises, or in other countries, by the time the submarine is located, it has become a recovery mission rather than a rescue mission. 

So, how can we simplify the task of locating a downed submarine?  Some of the answer lies in the concept of operations, or things that a distressed submarine can do to facilitate the search for them.  Some of the answer lies in advances in sonars and sonar signal processing.  And the rest of the answer lies in innovative new ideas, for example, using AUVs or UUVs to find distressed submarines ( cool idea ). 

Applied Technology Institute is offering several courses in the coming months that will help you brush up on your skills, so that you can apply them to this problem.  You can find information about our Sonar Signal Processing course, and register for the course here.  Additionally, you can find information about our Passive and Active Acoustics Fundamentals course, and register for the course here.  Lastly, a full listing of ATI’s Acoustics and Sonar Engineering Courses ( including AUV and UUV courses ) can be found here.  If you are interested in a course which is not currently on the schedule, please let us know, so we can try to schedule an offering soon.

As I said earlier, the author has had the pleasure of working with the Undersea Rescue Command several years ago, and was very impressed with the hard work and dedication exhibited by all members of their team.  The following picture shows me and the rest of the JHU/APL Team that worked with the URC.  We are posing inside of the Pressurized Rescue Module which travels to the distressed submarine to perform the rescue.  Although no one would ever want to experience being on a submarine in distress, they should feel encouraged that a team as dedicated and qualified as URC is on the job.

How to Promote Your ATI Course in Social Media

How to Promote Your ATI Course in Social Media LinkedIn for ATI Rocket Scientists   Did you know that for 52% of professionals and executives, their LinkedIn profile is the #1 or #2 search result when someone searches on their name? For ATI instructors, that number is substantially lower – just 17%. One reason is […]
How to Promote Your ATI Course in Social Media LinkedIn for ATI Rocket Scientists   Did you know that for 52% of professionals and executives, their LinkedIn profile is the #1 or #2 search result when someone searches on their name? For ATI instructors, that number is substantially lower – just 17%. One reason is that about 25% of ATI instructors do not have a LinkedIn profile. Others have done so little with their profile that it isn’t included in the first page of search results. If you are not using your LinkedIn profile, you are missing a huge opportunity. When people google you, your LinkedIn profile is likely the first place they go to learn about you. You have little control over what other information might be available on the web about you. But you have complete control over your LinkedIn profile. You can use your profile to tell your story – to give people the exact information you want them to have about your expertise and accomplishments.   Why not take advantage of that to promote your company, your services, and your course? Here are some simple ways to promote your course using LinkedIn… On Your LinkedIn Profile Let’s start by talking about how to include your course on your LinkedIn profile so it is visible anytime someone googles you or visits your profile. 1. Add your role as an instructor. Let people know that this course is one of the ways you share your knowledge. You can include your role as an instructor in several places on your profile:
  • Experience – This is the equivalent of listing your role as a current job. (You can have more than one current job.) Use Applied Technology Institute as the employer. Make sure you drag and drop this role below your full-time position.
  • Summary – Your summary is like a cover letter for your profile – use it to give people an overview of who you are and what you do. You can mention the type of training you do, along with the name of your course.
  • Projects – The Projects section gives you an excellent way to share the course without giving it the same status as a full-time job.
  • Headline – Your Headline comes directly below your name, at the top of your profile. You could add “ATI Instructor” at the end of your current Headline.
Start with an introduction, such as “I teach an intensive course through the Applied Technology Institute on [course title]” and copy/paste the description from your course materials or the ATI website. You can add a link to the course description on the ATI website. This example from Tom Logsdon’s profile, shows how you might phrase it:   Here are some other examples of instructors who include information about their courses on their LinkedIn profile:
  • Buddy Wellborn – His Headline says “Instructor at ATI” and Buddy includes details about the course in his Experience section.
  • D. Lee Fugal – Mentions the course in his Summary and Experience.
  • Jim Jenkins – Courses are included throughout Jim’s profile, including his Headline, Summary, Experience, Projects, and Courses.
  • 2. Link to your course page.
In the Contact Info section of your LinkedIn profile, you can link out to three websites. To add your course, go to Edit Profile, then click on Contact Info (just below your number of connections, next to a Rolodex card icon). Click on the pencil icon to the right of Websites to add a new site. Choose the type of website you are adding. The best option is “Other:” as that allows you to insert your own name for the link. You have 35 characters – you can use a shortened version of your course title or simply “ATI Course.” Then copy/paste the link to the page about your course. This example from Jim Jenkins’ profile shows how a customized link looks:   3. Upload course materials. You can upload course materials to help people better understand the content you cover. You could include PowerPoint presentations (from this course or other training), course handouts (PDFs), videos or graphics. They can be added to your Summary, Experience or Project. You can see an example of an upload above, in Tom Logsdon’s profile. 4. Add skills related to your course. LinkedIn allows you to include up to 50 skills on your profile. If your current list of skills doesn’t include the topics you cover in your course, you might want to add them. Go to the Skills & Endorsements section on your Edit Profile page, then click on Add skill. Start typing and let LinkedIn auto-complete your topic. If your exact topic isn’t included in the suggestions, you can add it. 5. Ask students for recommendations. Are you still in touch with former students who were particularly appreciative of the training you provided in your course? You might want to ask them for a recommendation that you can include on your profile. Here are some tips on asking for recommendations from LinkedIn expert Viveka Von Rosen. 6. Use an exciting background graphic. You can add an image at the top of your profile – perhaps a photo of you teaching the course, a photo of your course materials, a graphic from your presentation, or simply some images related to your topic. You can see an example on Val Traver’s profile. Go to Edit Profile, then run your mouse over the top of the page (just above your name). You will see the option to Edit Background. Click there and upload your image. The ideal size is 1400 pixels by 425. LinkedIn prefers a JPG, PNG or GIF. Of course, only upload an image that you have permission to use.   Share News about Your Course You can also use LinkedIn to attract more attendees to your course every time you teach. 7. When a course date is scheduled, share the news as a status update. This lets your connections know that you are teaching a course – it’s a great way to reach the people who are most likely to be interested and able to make referrals. Go to your LinkedIn home page, and click on the box under your photo that says “Share an update.” Copy and paste the URL of the page on the ATI website that has the course description. Once the section below populates with the ATI Courses logo and the course description, delete the URL. Replace it with a comment such as: “Looking forward to teaching my next course on [title] for @Applied Technology Institute on [date] at [location].” Note that when you finish typing “@Applied Technology Institute” it will give you the option to click on the company name. When you do that ATI will know you are promoting the course, and will be deeply grateful! When people comment on your update, it’s nice to like their comment or reply with a “Thank you!” message. Their comment shares the update with their network, so they are giving your course publicity. If you want to start doing more with status updates, here are some good tips about what to share (and what not to share) from LinkedIn expert Kim Garst. 8. Share the news in LinkedIn Groups. If you have joined any LinkedIn Groups in your areas of expertise, share the news there too. Of course, in a Group you want to phrase the message a little differently. Instead of “Looking forward to teaching…” you might say “Registration is now open for…” or “For everyone interested in [topic], I’m teaching…” You could also ask a thought-provoking question on one of the topics you cover. Here are some tips about how to start an interesting discussion in a LinkedIn Group. 9. Post again if you still have seats available. If the course date is getting close and you are looking for more people to register, you should post again. The text below will work as a status update and in most LinkedIn Groups. “We still have several seats open for my course on [title] on [date] at [location]. If you know of anyone who might be interested, could you please forward this? Thanks. ” “We have had a few last-minute cancellations for my course on [title] on [date] at [location]. Know anyone who might be interested in attending?” 10. Blog about the topic of the course. When you publish blog posts on LinkedIn using their publishing platform, you get even more exposure than with a status update:
  • The blog posts are pushed out to all your connections.
  • They stay visible on your LinkedIn profile, and
  • They are made available to Google and other search engines.
A blog post published on LinkedIn will rank higher than one posted elsewhere, because LinkedIn is such an authority site. So this can give your course considerable exposure. You probably have written articles or have other content relevant to the course. Pick something that is 750-1500 words. To publish it, go to your LinkedIn home page, and click on the link that says “Publish a post.” The interface is very simple – easier than using Microsoft Word. Include an image if you can. You probably have something in your training materials that will be perfect. At the end of the post, add a sentence that says: “To learn more, attend my course on [title].” Link the title to the course description on the ATI website. For more tips about blogging, you are welcome to join ProResource’s online training website. The How to Write Blog Posts for LinkedIn course is free. Take the first step The most important version of your bio in the digital world is your LinkedIn summary. If you only make one change as a result of reading this blog post, it should be to add a strong summary to your LinkedIn profile. Write the summary promoting yourself as an expert in your field, not as a job seeker. Here are some resources that can help: Write the first draft of your profile in a word processing program to spell-check and ensure you are within the required character counts. Then copy/paste it into the appropriate sections of your LinkedIn profile. You will have a stronger profile that tells your story effectively with just an hour or two of work! Contributed by guest blogger Judy Schramm. Schramm is the CEO of ProResource, a marketing agency that works with thought leaders to help them create a powerful and effective presence in social media. ProResource offers done-for-you services as well as social media executive coaching. Contact Judy Schramm at jschramm@proresource.com or 703-824-8482.  

Computational Electromagnetics (CEM): New Course from ATI

Video Clip: Click to Watch With this course you will become more of an electromagnetic expert This three-day course teaches the basics of Computational Electromagnetics (CEM) with application examples. Fundamental concepts in the solution of EM radiation and scattering problems are presented. Emphasis is on applying computational methods to practical applications. Students will be able to […]
Maxwell’s Equations in Vector Form
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With this course you will become more of an electromagnetic expert
This three-day course teaches the basics of Computational Electromagnetics (CEM) with application examples. Fundamental concepts in the solution of EM radiation and scattering problems are presented. Emphasis is on applying computational methods to practical applications. Students will be able to identify the most relevant CEM method for various applications, avoid common user pitfalls, understand model validation and correctly interpret results. Students are encouraged to bring their laptop to work examples using the provided FEKO Lite code. You will also learn the importance of model development and meshing, post- processing for scientific visualization and presentation of results. COMPUTATIONAL ELECTROMAGNETICS What You Will Learn: • A review of electromagnetics and antennas with modern applications. • An overview of popular CEM methods with commercial codes as examples • Hands-on experience with FEKO Lite to demonstrate modeling guidelines and common pitfalls. • An understanding of the latest developments in CEM methods and High Performance Computing. Course Outline, Samplers, and Notes Determine for yourself the value of this course before you sign up. See Slide Samples. Participants will receive a complete set of notes, a copy of FEKO and textbook for future reference. You can add notes and more detail based on the in-class interaction. After completion, all students receive a certificate of completion. Please visit our website for more valuable information. About ATI and the Instructors Our mission here at ATI is to provide expert training and the highest quality professional development in space, communications, defense, sonar, radar, and signal processing. We are not a one-size-fits-all educational facility. Our short classes include both introductory and advanced courses. ATI’s instructors are world-class experts who are the best in the business. They are carefully selected for their ability to clearly explain advanced technology. Dr. Keefe Coburn is a senior design engineer with the U.S. Army Research Laboratory in Adelphi MD. He has a Bachelor’s degree in Physics from the VA Polytechnic Institute with Masters and Doctoral Degrees from the George Washington University. In his job at the Army Research Lab, he applies CEM tools for antenna design, system integration and system performance analysis. He teaches graduate courses at the Catholic University of America in antenna and remote sensing. He is a member of the IEEE, the Applied Computational Electromagnetics Society, the Union of Radio Scientists and Sigma Xi. He serves on the Configuration Control Board for the Army developed GEMACS code and the ACES Board of Directors. Dates and Locations For the dates and locations of this short course, please see below: May 16-18, 2012 in Columbia, MD Sincerely, The ATI Courses Team P.S Call today for registration at 410-956-8805 or 888-501-2100 or access our website at www.ATIcourses.com. For general questions please email us at ATI@ATIcourses.com or Join, Link, Follow or Share with us at: Join us on Facebook Link to us on LinkedIn Follow us on Twitter Share with us on Slideshare P.P.S. What Happens at ATI does NOT Stay at ATI because our training helps you and your organization remain competitive in this changing world. Please feel free to call Mr. Jenkins personally to discuss your requirements and objectives. He will be glad to explain in detail what ATI can do for you, what it will cost, and what you can expect in results and future performance.

ATI’s Top 5 Engineering Course Samplers of 2011

Video Clip: Click to Watch ATI specializes in short course technical training Our mission here at the Applied Technology Institute (ATI) is to provide expert training and the highest quality professional development in space, communications, defense, sonar, radar, and signal processing. We are not a one-size-fits-all educational facility. Our short classes include both introductory and advanced […]
What Are the Tools of Your Trade?
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ATI specializes in short course technical training
Our mission here at the Applied Technology Institute (ATI) is to provide expert training and the highest quality professional development in space, communications, defense, sonar, radar, and signal processing. We are not a one-size-fits-all educational facility. Our short classes include both introductory and advanced courses. ATI’s Top Five Engineering Courses for 2011 The five engineering courses for 2011 are highlighted below: #1 Practical Statistical Signal Processing – using MATLAB This 4-day course covers signal processing systems for radar, sonar, communications, speech, imaging and other applications based on state-of-the-art computer algorithms. These algorithms include important tasks such as data simulation, parameter estimation, filtering, interpolation, detection, spectral analysis, beamforming, classification, and tracking. Until now these algorithms could only be learned by reading the latest technical journals. This course will take the mystery out of these designs by introducing the algorithms with a minimum of mathematics and illustrating the key ideas via numerous examples using MATLAB. Designed for engineers, scientists, and other professionals who wish to study the practice of statistical signal processing without the headaches, this course will make extensive use of hands-on MATLAB implementations and demonstrations. Attendees will receive a suite of software source code and are encouraged to bring their own laptops to follow along with the demonstrations. Click here for the tutorial #2 Advanced Topics in Digital Signal Processing This four-day course is designed for communication systems engineers, programmers, implementers and managers who need to understand current practice and next generation DSP techniques for upcoming communication systems. DSP is more than mapping legacy analog designs to a DSP implementation. To avoid compromise solution appropriate for an earlier time period, we return to first principles to learn how to apply new technology capabilities to the design of next generation communication systems. Click here for the tutorial #3 Engineering Systems Modeling WithExcel/VBA This two-day course is for engineers, scientists, and others interested in developing custom engineering system models. Principles and practices are established for creating integrated models using Excel and its built-in programming environment, Visual Basic for Applications (VBA). Real-world techniques and tips not found in any other course, book, or other resource are revealed. Step-bystep implementation, instructor-led interactive examples, and integrated participant exercises solidify the concepts introduced. Application examples are demonstrated from the instructor’s experience in unmanned underwater vehicles, LEO spacecraft, cryogenic propulsion systems, aerospace & military power systems, avionics thermal management, and other projects. Click here for the tutorial #4 Wavelets: A Conceptual, Practical Approach Fast Fourier Transforms (FFT) are in wide use and work very well if your signal stays at a constant frequency (“stationary”). But if the signal could vary, have pulses, “blips” or any other kind of interesting behavior then you need Wavelets. Wavelets are remarkable tools that can stretch and move like an amoeba to find the hidden “events” and then simultaneously give you their location, frequency, and shape. Wavelet Transforms allow this and many other capabilities not possible with conventional methods like the FFT. This course is vastly different from traditional math-oriented Wavelet courses or books in that we use examples, figures, and computer demonstrations to show how to understand and work with Wavelets. This is a comprehensive, in-depth, up-to-date treatment of the subject, but from an intuitive, conceptual point of view. We do look at a few key equations from the traditional literature but only AFTER the concepts are demonstrated and understood. If desired, further study from scholarly texts and papers is then made much easier and more palatable when you already understand the fundamental equations and how they relate to the real world. Click here for the tutorial #5 Computational Electromagnetics This 3-day course teaches the basics of CEM with application examples. Fundamental concepts in the solution of EM radiation and scattering problems are presented. Emphasis is on applying computational methods to practical applications. You will develop a working knowledge of popular methods such as the FEM, MOM, FDTD, FIT, and TLM including asymptotic and hybrid methods. Students will then be able to identify the most relevant CEM method for various applications, avoid common user pitfalls, understand model validation and correctly interpret results. Students are encouraged to bring their laptop to work examples using the provided FEKO Lite code. You will learn the importance of model development and meshing, post- processing for scientific visualization and presentation of results. Click here for the tutorial Course Outline, Samplers, and Notes Determine for yourself the value of these or our other courses before you sign up. See our samples (See Slide Samples) on some of our courses. Or check out the new ATI channel on YouTube. After attending the course you will receive a full set of detailed notes from the class for future reference, as well as a certificate of completion. To see the complete course listing from ATI, click on the links at the bottom of the page. Please visit our website for more valuable information. About ATI and the Instructors Since 1984, ATI has provided leading-edge public courses and onsite technical training to DoD and NASA personnel, as well as contractors. ATI short courses are designed to help you keep your professional knowledge up-to-date. Our courses provide you a practical overview of space and defense technologies which provide a strong foundation for understanding the issues that must be confronted in the use, regulation and development such complex systems. Our short courses are designed for individuals involved in planning, designing, building, launching, and operating space and defense systems. Whether you are a busy engineer, a technical expert or a project manager, you can enhance your understanding of complex systems in a short time. You will also become aware of the basic vocabulary essential to interact meaningfully with your colleagues. ATI’s instructors are world-class experts who are the best in the business. They are carefully selected for their ability to clearly explain advanced technology.


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ATI’s Practical Statistical Signal Processing — using MATLAB, January 9-12, 2012 (Laurel, MD)

Could you use a toolbox of Digital Signal Processing algorithms written by the well-known professor Dr. Stephan Kay, as well as his personal instruction on how to use these algorithms to solve practical problems in your area of work? At his January class you will receive his two textbooks, a set of printed notes, and […]
Could you use a toolbox of Digital Signal Processing algorithms written by the well-known professor Dr. Stephan Kay, as well as his personal instruction on how to use these algorithms to solve practical problems in your area of work? At his January class you will receive his two textbooks, a set of printed notes, and a disk with MATLAB code implementing his algorithms.   ATI’s Practical Statistical Signal Processing — using MATLAB course will be presented on January 9-12, 2012 in Laurel, MD.   This 4-day course covers signal processing systems for radar, sonar, communications, speech, imaging and other applications based on state-of-the-art computer algorithms. These algorithms include important tasks such as data simulation, parameter estimation, filtering, interpolation, detection, spectral analysis, beamforming, classification, and tracking. Until now these algorithms could only be learned by reading the latest technical journals. This course will take the mystery out of these designs by introducing the algorithms with a minimum of mathematics and illustrating the key ideas via numerous examples using MATLAB. Designed for engineers, scientists, and other professionals who wish to study the practice of statistical signal processing without the headaches, this course will make extensive use of hands-on MATLAB implementations and demonstrations. Attendees will receive a suite of software source code and are encouraged to bring their own laptops to follow along with the demonstrations. Each participant will receive two books, Fundamentals of Statistical Signal Processing: Vol. I and Vol. 2 by instructor Dr. Kay. A complete set of notes and a suite of MATLAB m-files will be distributed in source format for direct use or modification by the user. See selected samples of the course materials. View course sampler Instructor: Dr. Steven Kay is a Professor of Electrical Engineering at the University of Rhode Island and the President of Signal Processing Systems, a consulting firm to industry and the government. He has over 25 years of research and development experience in designing optimal statistical signal processing algorithms for radar, sonar, speech, image, communications, vibration, and financial data analysis. Much of his work has been published in over 100 technical papers and the three textbooks, Modern Spectral Estimation: Theory and Application, Fundamentals of Statistical Signal Processing: Estimation Theory,, and Fundamentals of Statistical Signal Processing: Detection Theory. Dr. Kay is a Fellow of the IEEE. Tuition: Original: $2,095 Special blog price if you register before January 1, 2012: $1,995 ( We are testing how many people read the ATI blog and will register based on the blog information)   Start your New Year with proper training! Register here.   This link shows you the current SCHEDULE of all courses.   Please circulate the information to any and all you think will be interested courses as well.


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What You Really Need to Know About Remote Sensing Technology

Can You Do a Hyperspectral Cube? Video Clip: Click to Watch ATI’s Hyperspectral and Multispectral Imaging course This three-day class is designed for engineers, scientists and other remote sensing professionals who wish to become familiar with multispectral and hyperspectral remote sensing technology. Students in this course will learn the basic physics of spectroscopy, the types of […]
Can You Do a Hyperspectral Cube?
Can You Do a Hyperspectral Cube?
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ATI’s Hyperspectral and Multispectral Imaging course
This three-day class is designed for engineers, scientists and other remote sensing professionals who wish to become familiar with multispectral and hyperspectral remote sensing technology. Students in this course will learn the basic physics of spectroscopy, the types of spectral sensors currently used by government and industry, and the types of data processing used for various applications. Case studies of applications will be used throughout the course
After taking this course, students should be able to communicate and work productively with other professionals in this field. Each student will receive a complete set of notes and the textbook, Remote Sensing of the Environment, an Earth Resource Perspective. What You Will Learn: • The limitations on passive optical remote sensing • The properties of current sensors • Component modeling for sensor performance • How to calibrate remote sensors • The types of data processing used for applications such as spectral angle mapping, multisensor fusion, and pixel mixture analysis • How to evaluate the performance of different hyperspectral systems Course Outline, Samplers, and Notes Still not convince of the value of this course? See actual slide samples before you sign up (See Slide Sample). Or check out the new ATI channel on YouTube for our other short courses. Please visit our website for more valuable information. About ATI and the Instructors Our mission here at ATI is to provide expert training and the highest quality professional development in space, communications, defense, sonar, radar, and signal processing. We are not a one-size-fits-all educational facility. Our short classes include both introductory and advanced courses. ATI’s instructors are world-class experts who are the best in the business. They are carefully selected for their ability to clearly explain advanced technology. William Roper, P.E. holds a PhD in Environmental Engineering, Mich. State University and BS and MS in Engineering, University of Wisconsin. He is currently serving as: Research Professor, Geography and GeoInformation Science Dept. George Mason University, a Visiting Professor, Johns Hopkins University, Senior Advisor, Dawson & Associates and President & Founding Board Member, Rivers of the World Foundation and leading a number of consulting efforts with the private sector. His research interests include remote sensing and geospatial applications, sustainable development, environmental assessment, water resource stewardship, and infrastructure energy efficiency. He teaches graduate courses in the science and technology of remote sensing and GIS applications which include the application of multispectral, hyperspectral, utraspectral and high spatial resolution imagery. Dr. Roper is also the author of four books, over 150 technical papers and scientific journal articles as well as presenting at numerous national and international forums. Times, Dates, and Locations ATI’s Hyperspectral and Multispectral Imaging course will next be offered on: September 20-22, 2011 in Albuquerque, NM Onsite pricing is also available.


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ATI Features World Class Instructors for Our Short Courses

Washington, DC Tuesday, November 30, 2010 “Even I Could Learn a Thing or Two from ATI” Video Clip: Click to Watch Since 1984 ATI has provided leading-edge public courses and onsite technical training The short technical courses from the Applied Technology Institute (ATI) are designed to help you keep your professional knowledge up-to-date. Our courses provide […]
Washington, DC
Tuesday, November 30, 2010
“Even I Could Learn a Thing or Two from ATI”
“Even I Could Learn a Thing or Two from ATI”
Video Clip: Click to Watch
Since 1984 ATI has provided leading-edge public courses and onsite technical training
The short technical courses from the Applied Technology Institute (ATI) are designed to help you keep your professional knowledge up-to-date. Our courses provide a practical overview of space and defense technologies which provide a strong foundation for understanding the issues that must be confronted in the use, regulation and development such complex systems. The classes are designed for individuals involved in planning, designing, building, launching, and operating space and defense systems. Whether you are a busy engineer, a technical expert or a project manager, you can enhance your understanding of complex systems in a short time. ABOUT ATI AND THE INSTRUCTORS Our mission here at the ATI is to provide expert training and the highest quality professional development in space, communications, defense, sonar, radar, and signal processing. We are not a one-size-fits-all educational facility. Our short classes include both introductory and advanced courses. ATI’s instructors are world-class experts who are the best in the business. They are carefully selected for their ability to clearly explain advanced technology. For example: Robert Fry worked from 1979 to 2007 at The Johns Hopkins University Applied Physics Laboratory where he was a member of the Principal Professional Staff. He is now working at System Engineering Group (SEG) where he is Corporate Senior Staff and also serves as the company-wide technical advisor. Throughout his career he has been involved in the development of new combat weapon system concepts, development of system requirements, and balancing allocations within the fire control loop between sensing and weapon kinematic capabilities. He has worked on many aspects of the AEGIS combat system including AAW, BMD, AN/SPY-1, and multi-mission requirements development. Missile system development experience includes SM-2, SM-3, SM-6, Patriot, THAAD, HARPOON, AMRAAM, TOMAHAWK, and other missile systems. Robert teaches ATI’s Combat Systems Engineering course Wayne Tustin has been president of Equipment Reliability Institute (ERI), a specialized engineering school and consultancy he founded in Santa Barbara, CA, since 1995. His BSEE degree is from the University of Washington, Seattle. He is a licensed Professional Engineer in the State of California. Wayne’s first encounter with vibration was at Boeing/Seattle, performing what later came to be called modal tests, on the XB-52 prototype of that highly reliable platform. Subsequently he headed field service and technical training for a manufacturer of electrodynamic shakers, before establishing another specialized school on which he left his name. Based on over 50 years of professional experience, Wayne has written several books and literally hundreds of articles dealing with practical aspects of vibration and shock measurement and testing. Wayne teaches ATI’s Fundamentals of Random Vibration & Shock Testing course. Thomas S. Logsdon, M.S For more than 30 years, Thomas S. Logsdon, M. S., has worked on the Navstar GPS and other related technologies at the Naval Ordinance Laboratory, McDonnell Douglas, Lockheed Martin, Boeing Aerospace, and Rockwell International. His research projects and consulting assignments have included the Transit Navigation Satellites, The Tartar and Talos shipboard missiles, and the Navstar GPS. In addition, he has helped put astronauts on the moon and guide their colleagues on rendezvous missions headed toward the Skylab capsule. Some of his more challenging assignments have centered around constellation coverage studies, GPS performance enhancement, military applications, spacecraft survivability, differential navigation, booster rocket guidance using the GPS signals and shipboard attitude determination. Tom Logsdon has taught short courses and lectured in thirty one different countries. He has written and published forty technical papers and journal articles, a dozen of which have dealt with military and civilian radionavigation techniques. He is also the author of twenty nine technical books on various engineering and scientific subjects. These include Understanding the Navstar, Orbital Mechanics: Theory and Applications, Mobile Communication Satellites, and The Navstar Global Positioning System. Courses Mr. Logsdon teaches through ATI include: Understanding Space Fundamentals of Orbital & Launch Mechanics GPS Technology – Solutions for Earth & Space and Strapdown Inertial Navigation Systems COURSE OUTLINE, SAMPLERS, AND NOTES Determine for yourself the value of our courses before you sign up. See our samples (See Slide Samples) on some of our courses. Or check out the new ATI channel on YouTube. After attending the course you will receive a full set of detailed notes from the class for future reference, as well as a certificate of completion. Please visit our website for more valuable information. DATES, TIMES AND LOCATIONS For the dates and locations of all of our short courses, please access the links below. Sincerely, The ATI Courses Team P.S. Call today for registration at 410-956-8805 or 888-501-2100 or access our website at www.ATIcourses.com. For general questions please email us at ATI@ATIcourses.com.
Mark N. Lewellen
Consultant/Instructor
Washington, DC
240-882-1234

Why Not Give Yourself the Gift of a Short Course this Holiday Season?

Washington, DC Monday, November 29, 2010 Is One of These Yours? Video Clip: Click to Watch When Did You Last do Something for Your Career? Since 1984, the Applied Technology Institute (ATI) has provided leading-edge public courses and onsite technical training to DoD and NASA personnel, as well as contractors. Our courses provide a practical overview of space […]
Washington, DC
Monday, November 29, 2010
Is One of These Yours?
Is One of These Yours?
Video Clip: Click to Watch
When Did You Last do Something for Your Career?
Since 1984, the Applied Technology Institute (ATI) has provided leading-edge public courses and onsite technical training to DoD and NASA personnel, as well as contractors. Our courses provide a practical overview of space and defense technologies which provide a strong foundation for understanding the issues that must be confronted in the use, regulation and development such complex systems. ATI short courses are designed to help you keep your professional knowledge up-to-date. Our short courses are designed for individuals involved in planning, designing, building, launching, and operating space and defense systems. Whether you are a busy engineer, a technical expert or a project manager, you can enhance your understanding of complex systems in a short time. You will become aware of the basic vocabulary essential to interact meaningfully with your colleagues. Course Outline, Samplers, and Notes Determine for yourself the value of our courses before you sign up. See our samples (See Slide Samples) on some of our courses. Or check out the new ATI channel on YouTube. After attending the course you will receive a full set of detailed notes from the class for future reference, as well as a certificate of completion. Please visit our website for more valuable information. About ATI and the Instructors Our mission here at the Applied Technology Institute (ATI) is to provide expert training and the highest quality professional development in space, communications, defense, sonar, radar, and signal processing. We are not a one-size-fits-all educational facility. Our short classes include both introductory and advanced courses. ATI’s instructors are world-class experts who are the best in the business. They are carefully selected for their ability to clearly explain advanced technology. Dates, Times and Locations For the dates and locations of all of our short courses, please access the links below. Sincerely, The ATI Courses Team P.S Call today for registration at 410-956-8805 or 888-501-2100 or access our website at www.ATIcourses.com. For general questions please email us at ATI@ATIcourses.com.
Mark N. Lewellen
Consultant/Instructor
Washington, DC
240-882-1234

Submarine Damages Towed Array Sonar

This is of interest to ATIcourses sonar group. It is clear that the towed sonar array would have detected the nearby submarine. There was not that much surface ship could do to maneuver to prevent the submarine from hitting the towed array. Conversely the submarine should have known that this class of surface ship was […]
This is of interest to ATIcourses sonar group. It is clear that the towed sonar array would have detected the nearby submarine. There was not that much surface ship could do to maneuver to prevent the submarine from hitting the towed array. Conversely the submarine should have known that this class of surface ship was towing an array. I personally doubt that this was inadvertently.
A Chinese submarine hit an underwater towed array sonar being towed by the destroyer USS John McCain on Thursday. The array was damaged, but the sub and the ship did not collide, the official said. A sonar array is a device towed behind a ship that listens and locates underwater sounds. The incident occurred near Subic Bay off the coast of the Philippines. The official, who declined to be named because the incident had not been made public, would not say whether the U.S. ship knew the submarine was that close to it. But of course the sonar knew the submarine was close, but could not maneuver to get out of the way. However, the Navy does not believe this was a deliberate incident of Chinese harassment, as it would have been extremely dangerous had the array gotten caught in the submarine’s propellers. The Navy has complained in the past that Chinese vessels, including fishing boats, have deliberately tried to disrupt U.S. naval activities in international waters near China. In one widely publicized incident in March, five Chinese vessels maneuvered close enough to the USNS Impeccable to warrant the use of a fire hose by the unarmed American vessel to avoid a collision. The Navy later released video of that incident.
http://www.cnn.com/2009/US/06/12/china.submarine/index.html

Antennas: The Interface with Space

Antennas: The Interface with Space by Robert A. Nelson The antenna is the most visible part of the satellite communication system. The antenna transmits and receives the modulated carrier signal at the radio frequency (RF) portion of the electromagnetic spectrum. For satellite communication, the frequencies range from about 0.3 GHz (VHF) to 30 GHz (Ka-band) […]

Antennas: The Interface with Space

by Robert A. Nelson

The antenna is the most visible part of the satellite communication system. The antenna transmits and receives the modulated carrier signal at the radio frequency (RF) portion of the electromagnetic spectrum. For satellite communication, the frequencies range from about 0.3 GHz (VHF) to 30 GHz (Ka-band) and beyond. These frequencies represent microwaves, with wavelengths on the order of one meter down to below one centimeter. High frequencies, and the corresponding small wavelengths, permit the use of antennas having practical dimensions for commercial use. This article summarizes the basic properties of antennas used in satellite communication and derives several fundamental relations used in antenna design and RF link analysis.

HISTORY OF ELECTROMAGNETIC WAVES

The quantitative study of electricity and magnetism began with the scientific research of the French physicist Charles Augustin Coulomb. In 1787 Coulomb proposed a law of force for charges that, like Sir Isaac Newton’s law of gravitation, varied inversely as the square of the distance. Using a sensitive torsion balance, he demonstrated its validity experimentally for forces of both repulsion and attraction. Like the law of gravitation, Coulomb’s law was based on the notion of “action at a distance,” wherein bodies can interact instantaneously and directly with one another without the intervention of any intermediary. At the beginning of the nineteenth century, the electrochemical cell was invented by Alessandro Volta, professor of natural philosophy at the University of Pavia in Italy. The cell created an electromotive force, which made the production of continuous currents possible. Then in 1820 at the University of Copenhagen, Hans Christian Oersted made the momentous discovery that an electric current in a wire could deflect a magnetic needle. News of this discovery was communicated to the French Academy of Sciences two months later. The laws of force between current bearing wires were at once investigated by Andre-Marie Ampere and by Jean-Baptiste Biot and Felix Savart. Within six years the theory of steady currents was complete. These laws were also “action at a distance” laws, that is, expressed directly in terms of the distances between the current elements. Subsequently, in 1831, the British scientist Michael Faraday demonstrated the reciprocal effect, in which a moving magnet in the vicinity of a coil of wire produced an electric current. This phenomenon, together with Oersted’s experiment with the magnetic needle, led Faraday to conceive the notion of a magnetic field. A field produced by a current in a wire interacted with a magnet. Also, according to his law of induction, a time varying magnetic field incident on a wire would induce a voltage, thereby creating a current. Electric forces could similarly be expressed in terms of an electric field created by the presence of a charge. Faraday’s field concept implied that charges and currents interacted directly and locally with the electromagnetic field, which although produced by charges and currents, had an identity of its own. This view was in contrast to the concept of “action at a distance,” which assumed bodies interacted directly with one another. Faraday, however, was a self-taught experimentalist and did not formulate his laws mathematically. It was left to the Scottish physicist James Clerk Maxwell to establish the mathematical theory of electromagnetism based on the physical concepts of Faraday. In a series of papers published between 1856 and 1865, Maxwell restated the laws of Coulomb, Ampere, and Faraday in terms of Faraday’s electric and magnetic fields. Maxwell thus unified the theories of electricity and magnetism, in the same sense that two hundred years earlier Newton had unified terrestrial and celestial mechanics through his theory of universal gravitation. As is typical of abstract mathematical reasoning, Maxwell saw in his equations a certain symmetry that suggested the need for an additional term, involving the time rate of change of the electric field. With this generalization, Maxwell’s equations also became consistent with the principle of conservation of charge. Furthermore, Maxwell made the profound observation that his set of equations, thus modified, predicted the existence of electromagnetic waves. Therefore, disturbances in the electromagnetic field could propagate through space. Using the values of known experimental constants obtained solely from measurements of charges and currents, Maxwell deduced that the speed of propagation was equal to speed of light. This quantity had been measured astronomically by Olaf Romer in 1676 from the eclipses of Jupiter’s satellites and determined experimentally from terrestrial measurements by H.L. Fizeau in 1849. He then asserted that light itself was an electromagnetic wave, thereby unifying optics with electromagnetism as well. Maxwell was aided by his superior knowledge of dimensional analysis and units of measure. He was a member of the British Association committee formed in 1861 that eventually established the centimeter-gram-second (CGS) system of absolute electrical units. Maxwell’s theory was not accepted by scientists immediately, in part because it had been derived from a bewildering collection of mechanical analogies and difficult mathematical concepts. The form of Maxwell’s equations as they are known today is due to the German physicist Heinrich Hertz. Hertz simplified them and eliminated unnecessary assumptions. Hertz’s interest in Maxwell’s theory was occasioned by a prize offered by the Berlin Academy of Sciences in 1879 for research on the relation between polarization in insulators and electromagnetic induction. By means of his experiments, Hertz discovered how to generate high frequency electrical oscillations. He was surprised to find that these oscillations could be detected at large distances from the apparatus. Up to that time, it had been generally assumed that electrical forces decreased rapidly with distance according to the Newtonian law. He therefore sought to test Maxwell’s prediction of the existence of electromagnetic waves. In 1888, Hertz set up standing electromagnetic waves using an oscillator and spark detector of his own design and made independent measurements of their wavelength and frequency. He found that their product was indeed the speed of light. He also verified that these waves behaved according to all the laws of reflection, refraction, and polarization that applied to visible light, thus demonstrating that they differed from light only in wavelength and frequency. “Certainly it is a fascinating idea,” Hertz wrote, “that the processes in air that we have been investigating represent to us on a million-fold larger scale the same processes which go on in the neighborhood of a Fresnel mirror or between the glass plates used in exhibiting Newton’s rings.” It was not long until the discovery of electromagnetic waves was transformed from pure physics to engineering. After learning of Hertz’s experiments through a magazine article, the young Italian engineer Guglielmo Marconi constructed the first transmitter for wireless telegraphy in 1895. Within two years he used this new invention to communicate with ships at sea. Marconi’s transmission system was improved by Karl F. Braun, who increased the power, and hence the range, by coupling the transmitter to the antenna through a transformer instead of having the antenna in the power circuit directly. Transmission over long distances was made possible by the reflection of radio waves by the ionosphere. For their contributions to wireless telegraphy, Marconi and Braun were awarded the Nobel Prize in physics in 1909. Marconi created the American Marconi Wireless Telegraphy Company in 1899, which competed directly with the transatlantic undersea cable operators. On the early morning of April 15, 1912, a 21-year old Marconi telegrapher in New York City by the name of David Sarnoff received a wireless message from the Marconi station in Newfoundland, which had picked up faint SOS distress signals from the steamship Titanic. Sarnoff relayed the report of the ship’s sinking to the world. This singular event dramatized the importance of the new means of communication. Initially, wireless communication was synonymous with telegraphy. For communication over long distances the wavelengths were greater than 200 meters. The antennas were typically dipoles formed by long wires cut to a submultiple of the wavelength. Commercial radio emerged during the 1920s and 1930s. The American Marconi Company evolved into the Radio Corporation of America (RCA) with David Sarnoff as its director. Technical developments included the invention of the triode for amplification by Lee de Forest and the perfection of AM and FM receivers through the work of Edwin Howard Armstrong and others. In his book Empire of the Air: The Men Who Made Radio, Tom Lewis credits de Forest, Armstrong, and Sarnoff as the three visionary pioneers most responsible for the birth of the modern communications age. Stimulated by the invention of radar during World War II, considerable research and development in radio communication at microwave frequencies and centimeter wavelengths was conducted in the decade of the 1940s. The MIT Radiation Laboratory was a leading center for research on microwave antenna theory and design. The basic formulation of the radio transmission formula was developed by Harald T. Friis at the Bell Telephone Laboratories and published in 1946. This equation expressed the radiation from an antenna in terms of the power flow per unit area, instead of giving the field strength in volts per meter, and is the foundation of the RF link equation used by satellite communication engineers today.

TYPES OF ANTENNAS

A variety of antenna types are used in satellite communications. The most widely used narrow beam antennas are reflector antennas. The shape is generally a paraboloid of revolution. For full earth coverage from a geostationary satellite, a horn antenna is used. Horns are also used as feeds for reflector antennas. In a direct feed reflector, such as on a satellite or a small earth terminal, the feed horn is located at the focus or may be offset to one side of the focus. Large earth station antennas have a subreflector at the focus. In the Cassegrain design, the subreflector is convex with an hyperboloidal surface, while in the Gregorian design it is concave with an ellipsoidal surface. The subreflector permits the antenna optics to be located near the base of the antenna. This configuration reduces losses because the length of the waveguide between the transmitter or receiver and the antenna feed is reduced. The system noise temperature is also reduced because the receiver looks at the cold sky instead of the warm earth. In addition, the mechanical stability is improved, resulting in higher pointing accuracy. Phased array antennas may be used to produce multiple beams or for electronic steering. Phased arrays are found on many nongeostationary satellites, such as the Iridium, Globalstar, and ICO satellites for mobile telephony.

GAIN AND HALF POWER BEAMWIDTH

The fundamental characteristics of an antenna are its gain and half power beamwidth. According to the reciprocity theorem, the transmitting and receiving patterns of an antenna are identical at a given wavelength The gain is a measure of how much of the input power is concentrated in a particular direction. It is expressed with respect to a hypothetical isotropic antenna, which radiates equally in all directions. Thus in the direction (q , f ), the gain is

G(q , f ) = (dP/dW)/(Pin /4p )

where Pin is the total input power and dP is the increment of radiated output power in solid angle dW. The gain is maximum along the boresight direction. The input power is Pin = Ea2 A / h Z0 where Ea is the average electric field over the area A of the aperture, Z0 is the impedance of free space, and h is the net antenna efficiency. The output power over solid angle dWis dP = E2 r2 dW/ Z0, where E is the electric field at distance r. But by the Fraunhofer theory of diffraction, E = Ea A / r l along the boresight direction, where l is the wavelength. Thus the boresight gain is given in terms of the size of the antenna by the important relation

G = h (4 p / l2) A

This equation determines the required antenna area for the specified gain at a given wavelength. The net efficiency h is the product of the aperture taper efficiency ha , which depends on the electric field distribution over the antenna aperture (it is the square of the average divided by the average of the square), and the total radiation efficiency h * = P/Pin associated with various losses. These losses include spillover, ohmic heating, phase non-uniformity, blockage, surface roughness, and cross polarization. Thus h = ha h *. For a typical antenna, h = 0.55. For a reflector antenna, the area is simply the projected area. Thus for a circular reflector of diameter D, the area is A = p D2/4 and the gain is

G = h (p D / l )2

which can also be written

G = h (p D f / c)2

since c = l f, where c is the speed of light (3 ´ 108 m/s), l is the wavelength, and f is the frequency. Consequently, the gain increases as the wavelength decreases or the frequency increases. For example, an antenna with a diameter of 2 m and an efficiency of 0.55 would have a gain of 8685 at the C-band uplink frequency of 6 GHz and wavelength of 0.050 m. The gain expressed in decibels (dB) is

10 log(8685) = 39.4 dB.

Thus the power radiated by the antenna is 8685 times more concentrated along the boresight direction than for an isotropic antenna, which by definition has a gain of 1 (0 dB). At Ku-band, with an uplink frequency of 14 GHz and wavelength 0.021 m, the gain is 49,236 or 46.9 dB. Thus at the higher frequency, the gain is higher for the same size antenna. The boresight gain G can be expressed in terms of the antenna beam solid angle WA that contains the total radiated power as

G = h * (4p / WA )

which takes into account the antenna losses through the radiation efficiency h *. The antenna beam solid angle is the solid angle through which all the power would be concentrated if the gain were constant and equal to its maximum value. The directivity does not include radiation losses and is equal to G / h *. The half power beamwidth is the angular separation between the half power points on the antenna radiation pattern, where the gain is one half the maximum value. For a reflector antenna it may be expressed

HPBW = a = k l / D

where k is a factor that depends on the shape of the reflector and the method of illumination. For a typical antenna, k = 70° (1.22 if a is in radians). Thus the half power beamwidth decreases with decreasing wavelength and increasing diameter. For example, in the case of the 2 meter antenna, the half power beamwidth at 6 GHz is approximately 1.75° . At 14 GHz, the half power beamwidth is approximately 0.75° . As an extreme example, the half power beamwidth of the Deep Space Network 64 meter antenna in Goldstone, California is only 0.04 ° at X-band (8.4 GHz). The gain may be expressed directly in terms of the half power beamwidth by eliminating the factor D/l . Thus,

G = h (p k / a )2

Inserting the typical values h = 0.55 and k = 70° , one obtains

G = 27,000/ (a° )2

where a° is expressed in degrees. This is a well known engineering approximation for the gain (expressed as a numeric). It shows directly how the size of the beam automatically determines the gain. Although this relation was derived specifically for a reflector antenna with a circular beam, similar relations can be obtained for other antenna types and beam shapes. The value of the numerator will be somewhat different in each case. For example, for a satellite antenna with a circular spot beam of diameter 1° , the gain is 27,000 or 44.3 dB. For a Ku-band downlink at 12 GHz, the required antenna diameter determined from either the gain or the half power beamwidth is 1.75 m. A horn antenna would be used to provide full earth coverage from geostationary orbit, where the angular diameter of the earth is 17.4° . Thus, the required gain is 89.2 or 19.5 dB. Assuming an efficiency of 0.70, the horn diameter for a C-band downlink frequency of 4 GHz would be 27 cm.

EIRP AND G/T

For the RF link budget, the two required antenna properties are the equivalent isotropic radiated power (EIRP) and the “figure of merit” G/T. These quantities are the properties of the transmit antenna and receive antenna that appear in the RF link equation and are calculated at the transmit and receive frequencies, respectively. The equivalent isotropic radiated power (EIRP) is the power radiated equally in all directions that would produce a power flux density equivalent to the power flux density of the actual antenna. The power flux density F is defined as the radiated power P per unit area S, or F = P/S. But P = h * Pin , where Pin is the input power and h * is the radiation efficiency, and S = d2 WA ,where d is the slant range to the center of coverage and WA is the solid angle containing the total power. Thus with some algebraic manipulation,

F = h * (4p / WA )( Pin / 4p d2) = G Pin / 4p d2

Since the surface area of a sphere of radius d is 4p d2, the flux density in terms of the EIRP is

F = EIRP / 4p d2

Equating these two expressions, one obtains

EIRP = G Pin

Therefore, the equivalent isotropic radiated power is the product of the antenna gain of the transmitter and the power applied to the input terminals of the antenna. The antenna efficiency is absorbed in the definition of gain. The “figure of merit” is the ratio of the antenna gain of the receiver G and the system temperature T. The system temperature is a measure of the total noise power and includes contributions from the antenna and the receiver. Both the gain and the system temperature must be referenced to the same point in the chain of components in the receiver system. The ratio G/T is important because it is an invariant that is independent of the reference point where it is calculated, even though the gain and the system temperature individually are different at different points.

ANTENNA PATTERN

Since electromagnetic energy propagates in the form of waves, it spreads out through space due to the phenomenon of diffraction. Individual waves combine both constructively and destructively to form a diffraction pattern that manifests itself in the main lobe and side lobes of the antenna. The antenna pattern is analogous to the “Airy rings” produced by visible light when passing through a circular aperture. These diffraction patterns were studied by Sir George Biddell Airy, Astronomer Royal of England during the nineteenth century, to investigate the resolving power of a telescope. The diffraction pattern consists of a central bright spot surrounded by concentric bright rings with decreasing intensity. The central spot is produced by waves that combine constructively and is analogous to the main lobe of the antenna. The spot is bordered by a dark ring, where waves combine destructively, that is analogous to the first null. The surrounding bright rings are analogous to the side lobes of the antenna pattern. As noted by Hertz, the only difference in this behavior is the size of the pattern and the difference in wavelength. Within the main lobe of an axisymmetric antenna, the gain G(q ) in a direction q with respect to the boresight direction may be approximated by the expression

G(q ) = G – 12 (q / a )2

where G is the boresight gain. Here the gains are expressed in dB. Thus at the half power points to either side of the boresight direction, where q = a /2, the gain is reduced by a factor of 2, or 3 dB. The details of the antenna, including its shape and illumination, are contained in the value of the half power beamwidth a . This equation would typically be used to estimate the antenna loss due to a small pointing error. The gain of the side lobes can be approximated by an envelope. For new earth station antennas with D/l > 100, the side lobes must fall within the envelope 29 – 25 log q by international regulation. This envelope is determined by the requirement of minimizing interference between neighboring satellites in the geostationary arc with a nominal 2° spacing.

TAPER

The gain pattern of a reflector antenna depends on how the antenna is illuminated by the feed. The variation in electric field across the antenna diameter is called the antenna taper. The total antenna solid angle containing all of the radiated power, including side lobes, is

WA = h * (4p / G) = (1/ha) (l2 / A)

where ha is the aperture taper efficiency and h * is the radiation efficiency associated with losses. The beam efficiency is defined as

e = WM / WA

where WM is thesolid angle for the main lobe. The values of ha and are e calculated from the electric field distribution in the aperture plane and the antenna radiation pattern, respectively. For a theoretically uniform illumination, the electric field is constant and the aperture taper efficiency is 1. If the feed is designed to cause the electric field to decrease with distance from the center, then the aperture taper efficiency decreases but the proportion of power in the main lobe increases. In general, maximum aperture taper efficiency occurs for a uniform distribution, but maximum beam efficiency occurs for a highly tapered distribution. For uniform illumination, the half power beamwidth is 58.4° l /D and the first side lobe is 17.6 dB below the peak intensity in the boresight direction. In this case, the main lobe contains about 84 percent of the total radiated power and the first side lobe contains about 7 percent. If the electric field amplitude has a simple parabolic distribution, falling to zero at the reflector edge, then the aperture taper efficiency becomes 0.75 but the fraction of power in the main lobe increases to 98 percent. The half power beamwidth is now 72.8° l /D and the first side lobe is 24.6 dB below peak intensity. Thus, although the aperture taper efficiency is less, more power is contained in the main lobe, as indicated by the larger half power beamwidth and lower side lobe intensity. If the electric field decreases to a fraction C of its maximum value, called the edge taper, the reflector will not intercept all the radiation from the feed. There will be energy spillover with a corresponding efficiency of approximately 1 – C2. However, as the spillover efficiency decreases, the aperture taper efficiency increases. The taper is chosen to maximize the illumination efficiency, defined as the product of aperture taper efficiency and spillover efficiency. The illumination efficiency reaches a maximum value for an optimum combination of taper and spillover. For a typical antenna, the optimum edge taper C is about 0.316, or – 10 dB (20 log C). With this edge taper and a parabolic illumination, the aperture taper efficiency is 0.92, the spillover efficiency is 0.90, the half power beamwidth is 65.3° l /D, and the first side lobe is 22.3 dB below peak. Thus the overall illumination efficiency is 0.83 instead of 0.75. The beam efficiency is about 95 percent.

COVERAGE AREA

The gain of a satellite antenna is designed to provide a specified area of coverage on the earth. The area of coverage within the half power beamwidth is

S = d2 W

where d is the slant range to the center of the footprint and W is the solid angle of a cone that intercepts the half power points, which may be expressed in terms of the angular dimensions of the antenna beam. Thus

= K a b

where a and b are the principal plane half power beamwidths in radians and K is a factor that depends on the shape of the coverage area. For a square or rectangular area of coverage, K = 1, while for a circular or elliptical area of coverage, K = p /4. The boresight gain may be approximated in terms of this solid angle by the relation

G = h¢ (4p / W ) = (h¢ / K)(41,253 / a° b° )

where a° and b° are in degrees and h¢ is an efficiency factor that depends on the the half power beamwidth. Although h¢ is conceptually distinct from the net efficiency h , in practice these two efficiencies are roughly equal for a typical antenna taper. In particular, for a circular beam this equation is equivalent to the earlier expression in terms of a if h¢ = (p k / 4)2 h . If the area of the footprint S is specified, then the size of a satellite antenna increases in proportion to the altitude. For example, the altitude of Low Earth Orbit is about 1000 km and the altitude of Medium Earth Orbit is about 10,000 km. Thus to cover the same area on the earth, the antenna diameter of a MEO satellite must be about 10 times that of a LEO satellite and the gain must be 100 times, or 20 dB, as great. On the Iridium satellite there are three main mission L-band phased array antennas. Each antenna has 106 elements, distributed into 8 rows with element separations of 11.5 cm and row separations of 9.4 cm over an antenna area of 188 cm ´ 86 cm. The pattern produced by each antenna is divided into 16 cells by a two-dimensional Butler matrix power divider, resulting in a total of 48 cells over the satellite coverage area. The maximum gain for a cell at the perimeter of the coverage area is 24.3 dB. From geostationary orbit the antenna size for a small spot beam can be considerable. For example, the spacecraft for the Asia Cellular Satellite System (ACeS), being built by Lockheed Martin for mobile telephony in Southeast Asia, has two unfurlable mesh antenna reflectors at L-band that are 12 meters across and have an offset feed. Having different transmit and receive antennas minimizes passive intermodulation (PIM) interference that in the past has been a serious problem for high power L-band satellites using a single reflector. The antenna separation attenuates the PIM products by from 50 to 70 dB.

SHAPED BEAMS

Often the area of coverage has an irregular shape, such as one defined by a country or continent. Until recently, the usual practice has been to create the desired coverage pattern by means of a beam forming network. Each beam has its own feed and illuminates the full reflector area. The superposition of all the individual circular beams produces the specified shaped beam. For example, the C-band transmit hemi/zone antenna on the Intelsat 6 satellite is 3.2 meters in diameter. This is the largest diameter solid circular aperture that fits within an Ariane 4 launch vehicle fairing envelope. The antenna is illuminated by an array of 146 Potter horns. The beam diameter a for each feed is 1.6° at 3.7 GHz. By appropriately exciting the beam forming network, the specified areas of coverage are illuminated. For 27 dB spatial isolation between zones reusing the same spectrum, the minimum spacing s is given by the rule of thumb s ³ 1.4 a , so that s ³ 2.2° . This meets the specification of s = 2.5° for Intelsat 6. Another example is provided by the HS-376 dual-spin stabilized Galaxy 5 satellite, operated by PanAmSat. The reflector diameter is 1.80 m. There are two linear polarizations, horizontal and vertical. In a given polarization, the contiguous United States (CONUS) might be covered by four beams, each with a half power beamwidth of 3° at the C-band downlink frequency of 4 GHz. From geostationary orbit, the angular dimensions of CONUS are approximately 6° ´ 3° . For this rectangular beam pattern, the maximum gain is about 31 dB. At edge of coverage, the gain is 3 dB less. With a TWTA ouput power of 16 W (12 dBW), a waveguide loss of 1.5 dB, and an assumed beam-forming network loss of 1 dB, the maximum EIRP is 40.5 dBW. The shaped reflector represents a new technology. Instead of illuminating a conventional parabolic reflector with multiple feeds in a beam-forming network, there is a single feed that illuminates a reflector with an undulating shape that provides the required region of coverage. The advantages are lower spillover loss, a significant reduction in mass, lower signal losses, and lower cost. By using large antenna diameters, the rolloff along the perimeter of the coverage area can be made sharp. The practical application of shaped reflector technology has been made possible by the development of composite materials with extremely low coefficients of thermal distortion and by the availability of sophisticated computer software programs necessary to analyze the antenna. One widely used antenna software package is called GRASP, produced by TICRA of Copenhagen, Denmark. This program calculates the gain from first principles using the theory of physical optics.

SUMMARY

The gain of an antenna is determined by the intended area of coverage. The gain at a given wavelength is achieved by appropriately choosing the size of the antenna. The gain may also be expressed in terms of the half power beamwidth. Reflector antennas are generally used to produce narrow beams for geostationary satellites and earth stations. The efficiency of the antenna is optimized by the method of illumination and choice of edge taper. Phased array antennas are used on many LEO and MEO satellites. New technologies include large, unfurlable antennas for producing small spot beams from geostationary orbit and shaped reflectors for creating a shaped beam with only a single feed.

Author

Dr. Robert A. Nelson, P.E. is president of Satellite Engineering Research Corporation, a satellite engineering consulting firm in Bethesda, Maryland, a Lecturer in the Department of Aerospace Engineering at the University of Maryland and Technical Editor of Via Satellite magazine.