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What are the aspects that affect the performance of GPS antennas?

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1. Ceramic sheet affects the performance of gps antenna

1. Ceramic sheet affects the performance of gps antenna

The quality of the ceramic powder and the sintering process directly affect the performance of the gps antenna. The ceramic sheets currently used in the market are mainly 25×25, 18×18, 15×15, and 12×12. The larger the area of ​​the ceramic sheet, the greater the dielectric constant, the higher the resonant frequency, and the better the GPS antenna reception effect.

2. The silver layer affects the performance of the GPS antenna

The silver layer on the surface of the ceramic antenna can affect the resonant frequency of the antenna. The ideal GPS ceramic chip frequency is exactly 1575.42MHz, but the antenna frequency is very easily affected by the surrounding environment. Especially when it is installed in the whole machine, it is necessary to adjust the shape of the silver surface coating to adjust the frequency of the GPS navigation antenna and keep it at 1575.42MHz. Therefore, the GPS machine manufacturer must cooperate with the antenna manufacturer when purchasing the antenna, and provide the whole machine sample for testing.

3. Feeding point affects the performance of gps antenna

The ceramic antenna collects the resonant signal through the feed point and sends it to the back end. Due to the factor of antenna impedance matching, the feed point is generally not in the center of the antenna, but slightly adjusted in the XY direction. Such an impedance matching method is simple and does not increase the cost. Only moving in a single axis direction is called a single-biased antenna, and moving in both axes is called a double-biased antenna.

4. The amplifier circuit affects the performance of the GPS antenna

Due to the shape and area of ​​the PCB carrying the ceramic antenna, due to the characteristics of GPS rebound, when the background is 7cm × 7cm uninterrupted ground, the performance of the patch antenna can be maximized.

Although it is restricted by factors such as appearance and structure, try to keep a considerable area and a uniform shape.

The selection of the gain of the amplifier circuit must match the gain of the back-end LNA. Sirf’s GSC 3F requires that the total gain before signal input must not exceed 29dB, otherwise the GPS navigation antenna signal will be oversaturated and self-excited.

The GPS antenna has four important parameters: Gain, Standing Wave (VSWR), Noise Figure, and Axial Ratio, Among them, the axial ratio is particularly emphasized, which is an important indicator to measure the difference of the signal gain of the whole machine in different directions.

Since the satellites are randomly distributed in the hemisphere sky, it is very important to ensure that the antenna has similar sensitivity in all directions. The axial ratio is affected by the performance of the GPS antenna, the appearance and structure, the internal circuit of the whole machine and EMI.

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