Performance of GPS antenna

The main factors affecting the performance of GPS antenna are as follows

①Ceramic chip: the guality of ceramic powder and sinterina process directlv affect its performance. The ceramic chips used onthe market are mainlv 25 x 2518  18.15 x 15. 12  12 The laroer the area of the ceramic plate. the areater the dielectriconstant, the higher the resonance frequency and the better the acceptance effect, The ceramic chips are mostly square indesign to ensure that the resonance in the XY direction is basically consistent, so as to achieve the effect of uniform starcollection.

②Silver layer: the silver layer on the surface of the ceramic antenna can affect the resonance frequency of the antenna. The idealGPS ceramic chip frequency point accurately falls at 1575.42MHz, but the antenna freguency point is very vulnerable to theimpact of the surrounding environment, especially when it is installed in the whole machine. The frequency point must beadiusted to keep at 157542MHz again by adjusting the shape of the silver coating. Therefore, when purchasing antennas, the GPS manufacturer must cooperate with the antenna manufacturer to provide the complete machine samples for testing.

③Feed point: the ceramic antenna collects resonance sianals through the feed point and sends them to the rear end. Due toantenna impedance matching, the feed point is generally not in the center of the antenna, but slightly adiusted in the Xydirection. This impedance matching method is simple and does not increase the cost. Moving only in the direction of a singleaxis is called a monophasic antenna, and moving on both axes is called a biphasic antenna.

GPS antenna has four important parameters: Gain, VSWR, Noise figure and Axial ratio. The shaft ratio is particularly emphasized,which is an important indicator to measure the difference of signal gain of the whole machine in diferent directions. Sincesatellites are randomly distributed in the hemisphere sky, it is very important to ensure that the antenna has similar sensitivity inall directions.The axial ratio is affected by antenna performance, external structure, internal circuit of the whole machine andEMI.