How much do you know about GPS? Let's give you a minute to introduce the performance of GPS

Performance of GPS antenna

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

1. Ceramic sheet: the quality of ceramic powder and sintering process directly affect its performance. The ceramic chips used in the market are mainly 25x25, 18x18, 15x15 and 12x12. The larger the area of ceramic sheet, the greater the dielectric constant, the higher the resonance frequency and the better the acceptance effect. Most of the ceramic plates are square in design, which is to ensure that the resonance in the XY direction is basically consistent, so as to achieve the effect of uniform star reception.

2. Silver Exhibition: the silver Exhibition on the surface of ceramic antenna can affect the resonance frequency of antenna. It is very easy to adjust the shape of the whole machine at the 425.5 MHz, but it must be adjusted in the ideal environment through the coating of the whole machine, especially at the 425.5 MHz. Therefore, when purchasing antennas, GPS manufacturers must cooperate with antenna manufacturers to provide complete machine samples for testing.

3. Point: the ceramic antenna receives the resonance signal through the feed point and sends it to the back end. Due to the positive reactance matching of the antenna, the 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 antenna

4. Amplification circuit: the shape and area of PCB carrying ceramic antenna. Because GPS has the characteristics of ground bounce, when the background is 7cmx7cm continuous ground, the efficiency of patch antenna can be brought into full play. Although restricted by factors such as appearance and structure, try to keep a considerable area and uniform shape. The gain of the amplifier circuit must be selected according to the gain of the back-end LNA. The gsc3f of SiRF requires that the total gain before signal input shall not exceed 29dB, otherwise the signal over saturation will produce self excitation

GPS antenna has four important parameters: gain, standing wave (VSWR), noise figure and axial ratio. Special emphasis is placed on the shaft 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 hemispheric sky, it is very important to ensure that the antenna has similar sensitivity in all directions. The axial ratio is affected by antenna performance, appearance structure, internal circuit of the whole machine and EMI.

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