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Letters to the Editor: Antennas and the Human Body

March 1, 2012  - By

GPS0212_01_Cover_lowres  Cover: GPS WorldAntennas and the Human Body

We have been reading with much interest the Innovation column, “GNSS Antennas and Humans” (Innovation, February issue). As the interaction with the human body is something many companies designing GPS into their products do not consider, it is great to see this topic being given some recent attention. We do feel, however, that we should comment on some issues we see in the article, especially as one of our antennas has been used as part of the testing.

As rightly mentioned in the article, many of the products using GPS where performance close to the body is potentially an issue are consumer products. These typically are of small size or at very least have major space constraints placed on those designing them. As such it is very unlikely that they would use either a large active patch antenna or in fact an active antenna from Sarantel. In the vast majority of consumer applications, either smaller patch antennas (12 × 12 millimeters, maximum) will be used with smaller ground planes or even small chip or planar inverted-F antenna (PIFA) style antennas.

From a Sarantel perspective, we would recommend our smallest antenna, the passive SL1300, for these types of applications. In terms of how this would then affect the results of the test described in the article, our extensive testing of various antennas would suggest that with smaller patch antennas and linear antennas like chip and PIFA types, the impact of the body on antenna performance is greater than you would typically see with a large patch with a large ground plane. In addition, one of the reasons we would recommend our smaller antenna for this kind of application is because the ceramic material used has a much higher dielectric value than our larger products and as such is affected much less by the body or other interfering aspects of a product design.

As I mentioned, we have done extensive testing of various antennas, much of which is available through the Application Centre section of our website. Further information can be shared if it would be of interest to your readers.

— Chris Muir
Director of Sales, Sarantel Limited

Spectrum Swap

I read with interest your article today (Latest News, February 1) concerning LightSquared looking at a possible spectrum swap in the current Aeronautical Mobile Telemetry band, used heavily by both the DOD and commercial side, primarily for aircraft and missile testing. I found it more interesting that the DOD MIDLANT Area Frequency Coordinator had been contacted concerning the same.

First let me say that both the DOD and civil aviation and defense industries guard these bands quite strongly as individual users and via the Aerospace Flight Test Radio Coordinating Council (AFTRCC). AFTRCC is also the recognized non-government coordinator for these bands and resists any encroachment in these bands, while additionally allowing some temporary sharing when feasible.

Secondly, I would add the the DOD has seven total Area Frequency Coordinators geographically spread across the United States, so contacting one would serve little purpose. Additionally, the coordinators are members of the DOD Frequency Management Group who one would say is the DOD equivalent of AFTRCC and believe me, both organizations are on the same sheet of music when it comes to defending AMT for flight-test purposes and even meet jointly twice a year to do just that. Combined with the DOD and if one looks at the member companies of AFTRCC any attempt to wrest any portion ATM spectrum away from the aerospace industry and DOD would be an expensive and lengthy process.

This email does not constitute a response from either DOD or AFTRCC but that of a private citizen.

— Wayne Morris
Greenville, Texas

Privacy Matters

Good editorial (“When the Gavel Comes Down,” February issue). The three or four bases for the unanimous ruling in the instant case show a diversion of philosophy on this matter that is dangerous for resolution only through case and constitutional law.

You are dead right, legislation is needed at the federal level before a hodgepodge of states and other jurisdictions make up their own policies for a global utility with manifold applications affecting privacy and personal and intellectual property, for good and for evil; morally neutral technology, as always….not just GNSS but as in most instances, GNSS enhanced.

It would not be popular with the federal legislature, but I think some European Union deliberations on these subjects would be instructive for the U.S. Congress to heed in writing legislation. I wish that the White House and an interagency group like EXCOM could first take a non-political look at the trades and lead Congress, but that is unlikely to happen. Look at what nearly happened with the Software Owners Protection Act (SOPA) because of the lobbying power of media interests.

Truly we live in interesting times, also from the stress on our constitutional concepts which often use tortured analogies to keep the law inside the four corners of the constitution.

— James D. Litton
President/CEO, Litton Consulting Group, Inc.

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