What aspects affect the performance of GPS antenna?

1、 Ceramic chip affects the performance of GPS antenna

The quality of ceramic powder and sintering process directly affect the performance of GPS antenna. At present, 25 ceramic chips are mainly used in the market × 25、18 × 18、15 × 15、12 × 12。

The larger the area of the ceramic sheet, the greater the dielectric constant, the higher the resonance frequency, and the better the receiving effect of the GPS antenna. Most of the ceramic sheets are square, and the design is to ensure that the resonance is basically consistent in the XY direction, so as to achieve the effect of uniform star receiving.

2、 The silver layer affects the performance of GPS antenna

The silver layer on the surface of the ceramic antenna can affect the resonant frequency of the antenna. The ideal frequency point of the GPS ceramic chip accurately falls at 1575.42MHz, but the antenna frequency point is very vulnerable to the surrounding environment.

Especially when it is assembled in the whole machine, the frequency point of GPS navigation antenna must be adjusted and maintained at 1575.42MHz again by adjusting the shape of silver coating. Therefore, GPS whole machine manufacturers must cooperate with antenna manufacturers when purchasing antennas and provide complete machine samples for testing.

3、 The feed point affects the performance of GPS antenna

The ceramic antenna collects the resonance 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.

This impedance matching method is simple and does not increase the cost. Moving only in the single axis direction is called single polarization antenna, and moving in both axes is called double polarization.

4、 The amplifier circuit affects the performance of GPS antenna

The shape and area of the PCB carrying the ceramic antenna, because the GPS has the characteristics of ground bounce, when the background is 7cm × When the ground is 7cm without interruption, the efficiency of patch antenna can be brought into full play.

Although restricted by the appearance structure and other factors, it is necessary to keep a considerable area and uniform shape as far as possible, and the selection of amplification circuit gain must match the back-end LNA gain.

The GSC 3F of SiRF requires that the total gain before signal input shall not exceed 29dB, otherwise the over saturation of GPS navigation antenna signal will produce self excitation.

GPS antenna has four important parameters: gain, standing wave (VSWR), noise figure and axial ratio, with special emphasis on axial ratio, which is an important index to measure the signal gain difference of the whole machine in different directions.

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

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