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The main factors influencing the performance of GPS antennas are the following aspects
Apr 07, 2017

1, ceramic film: The good or bad of ceramic powder and sintering process directly affect its performance. The present market uses ceramic film mainly 25x25, 18x18, 15x15, 12x12. The larger the ceramic-sided product, the larger the dielectric constant, the higher the resonance frequency, the better the reception effect. The ceramic film is mostly square design, is to ensure that the resonance in the XY direction is basically consistent, so as to achieve the effect of homogeneous star.

2, Silver layer: Ceramic antenna surface silver layer can affect the antenna resonance frequency. The ideal GPS ceramic slice frequency points accurately falls in 1575.42MHz, but the antenna frequency point is very easy to be affected by the surrounding environment, especially the Assembly in the whole machine, must adjust the appearance of the silver surface coating, to regulate the frequency point to keep in 1575.42MHz. Therefore, GPS machine manufacturers in the procurement of antenna must be matched with antenna manufacturers, providing complete sample test.

3. Feed: The ceramic antenna collects the resonance signal through the feed point and sends it to the back end. Because of the antenna impedance matching, the feed point is not generally in the center of the antenna, but in the xy direction of minor adjustments. This impedance matching method is simple and does not increase the cost. Moving in single-axis direction is called a single-biased antenna, which is called double bias in both axes.

4. Amplifier circuit: PCB shape and area of bearing ceramic antenna. Because the GPS has the characteristic of the touchdown bounce, when the background is 7cmx7cm uninterrupted earth, the patch antenna efficiency can play to the Acme. Although the appearance of the structure and other factors, but as far as possible to maintain a considerable area and uniform shape. The gain of amplifying circuits must be matched with the back-end LNA gain. SIRF GSC3F requires that the total gain before input can not exceed 29dB, otherwise the signal saturation will generate self-excited.

GPS antennas have four important parameters: Gain (Gain), standing Wave (VSWR), noise coefficient (Noise figure), Axis ratio (Axial ratio). Especially emphasizing axle ratio, it is an important indicator to measure the difference of signal gain in different directions. Since 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 influenced by antenna performance, exterior structure, internal circuit and EMI.


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