Innovation: GNSS Antennas -- An Introduction to Bandwidth, Gain Pattern, Polarization, and All That
- From: Sam Wormley <swormley1@xxxxxxxxx>
- Date: Wed, 25 Feb 2009 22:27:08 GMT
Innovation: GNSS Antennas
http://sidt.gpsworld.com/gpssidt/content/printContentPopup.jsp?id=580982
An Introduction to Bandwidth, Gain Pattern, Polarization, and All That
Feb 1, 2009
By: Daniel Orban, Gerald J.K. Moernaut
GPS World
INNOVATION INSIGHTS with Richard Langley
The antenna is a critical component of a GNSS receiver setup. An antenna's job is to capture some of the power in the electromagnetic waves it receives and to convert it into an electrical current that can be processed by the receiver. With very strong signals at lower frequencies, almost any kind of antenna will do. Those of us of a certain age will remember using a coat hanger as an emergency replacement for a broken AM-car-radio antenna. Or using a random length of wire to receive shortwave radio broadcasts over a wide range of frequencies. Yes, the higher and longer the wire was the better, but the length and even the orientation weren't usually critical for getting a decent signal.
Not so at higher frequencies, and not so for weak signals. In general, an antenna must be designed for the particular signals to be intercepted, with the center frequency, bandwidth, and polarization of the signals being important parameters in the design. This is no truer than in the design of an antenna for a GNSS receiver.
The signals received from GNSS satellites are notoriously weak. And they can arrive from virtually any direction with signals from different satellites arriving simultaneously. So we don't have the luxury of using a high-gain dish antenna to collect the weak signals as we do with direct-to-home satellite TV.
Of course, we get away with weak GNSS signals (most of the time) by replacing antenna gain with receiver-processing gain, thanks to our knowledge of the pseudorandom noise spreading codes used to transmit the signals. Nevertheless, a well-designed antenna is still important for reliable GNSS signal reception (as is a low-noise receiver front end). And as the required receiver position fix accuracy approaches centimeter and even sub-centimeter levels, the demands on the antenna increase, with multipath suppression and phase-center stability becoming important characteristics.
See: http://sidt.gpsworld.com/gpssidt/content/printContentPopup.jsp?id=580982
.
- Prev by Date: Re: BBC - Sat-nav to aid disabled motorists
- Next by Date: Re: BBC - Sat-nav to aid disabled motorists
- Previous by thread: coord transformation with Proj4
- Next by thread: Kalman filter for PVT computation using pseudoranges and pseudorange rates
- Index(es):
Relevant Pages
|
