What impact the performance of the GPS antenna？

Affect GPS antenna performance is mainly the following aspects
1, the ceramic sheet: good or bad, and sintering of ceramic powder directly affect its performance. Ceramic chip market is now mainly used in 25 × 25,18 × 18,15 × 15,12 × 12. Ceramic chip area, the greater the dielectric constant, the higher the resonance frequency, the better the acceptance. Most ceramic pieces are square design, in order to ensure consistent direction in the XY resonance, so as to achieve a uniform income star effect.
2, silver layer: the surface of the silver layer ceramic antenna may affect the antenna resonance frequency. Ideal accurate GPS ceramic chip frequency falls 1575.42MHz, but the antenna frequency is very vulnerable to impact the surrounding environment, particularly in the assembly of the machine, you must adjust the shape of the silver surface coating to re-adjust the frequency is maintained at 1575.42MHz ʱ?? Therefore, machine manufacturers in the procurement of GPS antenna with antenna manufacturers must provide the whole sample to be tested.
3, the feed point: ceramic antenna resonance signals collected and sent to the back-end through the feed point. Due to the antenna impedance matching, antenna feed point is generally not in the middle, but make minor adjustments in the XY direction. Such impedance matching is simple and does not increase costs. Only in a uniaxial direction it is called a single partial antennas were done in two axes move known as a double side.
4, the amplifier circuit: bearing ceramic antenna of PCB shape and size. Since GPS has ground bounce characteristics, when the background is 7cm × 7cm earth without interruption, performance patch antenna can play to the extreme. While the appearance of the structure and other factors that, but try to maintain a considerable area and uniform shape. Amplifier gain must be selected with the back-end LNA gain. Sirf before the GSC3F request signal input may not exceed the total gain 29dB, otherwise signal saturation will produce self-excited.
GPS antenna has four important parameters: Gain (Gain), a standing wave (VSWR), noise figure (Noise figure), the axial ratio (Axial ratio). With particular emphasis on the axial ratio, which is a measure of an important indicator of overall signal gain for different directions of difference. Since the satellite was randomly distributed on the hemisphere sky, so to ensure that sensitive antenna are similar in all directions is very important. Axial ratio by the antenna performance, appearance of the structure, the whole internal circuit and EMI and other effects.