News Release from: Sarantel
Edited by the Electronicstalk Editorial Team on 8 November 2002
Report puts helical antennas to the test
Sarantel has issued an applications note that compares the performance of patch and miniature helical antennas in GPS environments.
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Sarantel has issued an applications note that compares the performance of patch and miniature helical antennas in GPS environments. The information, which will be of particular interest to engineers designing mobile GPS handsets and equipment, shows that although the patch antennas generally have a higher gain at the zenith angle (ie pointing vertically), the helical antennas typically have a wider beamwidth. The application note is available as a PDF download from Sarantel's website.
Both gain and beamwidth are important in the design of GPS systems.
However, the application note confirms that because the miniature helical antenna is isolated from its surroundings, the effects of a plastic case and human tissue on the tuning are reduced.
Originally developed for navigational and guidance purposes, particularly in military equipment, GPS is now becoming widely used in everyday life.
It is based on a series of satellites owned by the US Government and can give positional information anywhere on earth to an accuracy of about 10m.
It is now common to find the systems fitted in vehicles where, in conjunction with mapping systems, they offer passenger information or routing instructions.
The next major market is to incorporate GPS in US cellphones to meet the E-911 mandate.
It is also used for asset tracking.
Sarantel compared the performance of patch antennas, with both 1in square and 2in square ground planes, against miniature helical antennas based on its own PowerHelix technology at the GPS frequency of 1575.42MHz.
On average, the gain of the antennas at the zenith angle was found to be about 2.0dBi greater in the case of the patch antenna, but the helical antenna had a greater 3dB beamwidth (125 versus 100 degrees).
A large beamwidth is critical for GPS antennas as it enables more satellite signals to be acquired and a more accurate positional fix to be made.
In general, lack of gain can be easily compensated for by the use of low-noise front-end amplifiers.
The helical antennas also performed better than patch antennas as far as the effect of human tissue on the receiver performance is concerned.
The report suggests that portable receivers using patch antennas are more likely to be detuned when used in handheld mode than those using helical antennas.
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