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How to choice gps antenna

GPS is related to our daily life, some classification, this paper introduces the GPS antenna structure, performance should be grasped, and the need to pay attention in the choice of GPS antenna in the process, to the need to purchase some suggestions.


One, overview of GPS


GPS is to receive signals from the satellites, the terminal positioning or navigation. And accept the signal must be used in antenna. The GPS satellite signal is divided into L1 and L2, frequency is 1575.42MHZ and 1228MHZ, where L1 is the civil signal open, circular polarization signal. Signal strength is about 166-DBM, which belongs to the weak signal. These characteristics decided to GPS signal to accept prepare special antenna.


Classification of two, GPS antenna


1, from the polarization mode of GPS antenna is divided into vertical polarization and circular polarization. With today's technology, vertical polarization effect than the circular polarization. Therefore, except in special circumstances, GPS will use circular polarization antenna.


2, from the position GPS antenna consists of a built-in antenna and external antenna. The assembly location of the antenna is very important. Early GPS handset with eversion antenna, the internal antenna and the basic isolation, EMI almost no impact, the star effect is very good. Now with the miniaturization trend, GPS antenna with built-in. The antenna must in all metal parts must be above, shell plating and well grounded, EMI away from the interference source, such as CPU, SDRAM, SD card, crystal, DC/DC.


The application of vehicle GPS will become more and more popular. But the automobile shell, especially car explosion-proof membrane GPS signal generating serious obstacles. A magnet (can be adsorbed onto the roof) of the external antenna is very necessary for vehicle GPS.


Three, the GPS antenna structure


At present, most of the GPS antenna for the right-hand circularly polarized ceramic dielectric, its components: ceramic antenna, low noise signal module, cable, connector.


The ceramic antenna is also called passive antenna, dielectric antenna, PATCH, which is the core technology of GPS antenna. A signal of GPS antenna reception, most ingredients depends on how its ceramic parts.


Low noise signal module, also known as LNA, is the signal amplification and filtering part. The selection of components is also very important, otherwise it will increase the reflection loss of GPS signals, as well as the cause of the noise is too large.


Cable selection to reduce reflection as the standard, ensure the impedance matching.


Four, the performance of GPS antenna


Effects of GPS antenna performance is mainly the following aspects:


1, ceramic piece: quality of ceramic powder and sintering process directly affects its performance. Ceramic is the market is mainly used in the 25 x 25, 18 x 18, 15 x 15, 12 x 12. Ceramic chip area is greater, larger dielectric constant, the resonance frequency is higher, the better the effect of acceptance. Ceramics are mostly square design, in order to ensure the basic coherence resonance in the XY direction, so as to achieve the effect of uniform star.


2, a layer of silver: ceramic antenna surface silver layer can affect the antenna resonance frequency. GPS ceramic frequency ideal accurately fall in 1575.42MHz, but the antenna frequency is very vulnerable to the surrounding environment, especially in the assembly, must by adjusting the silver surface coating profile, to adjust the frequency point to keep in 1575.42MHz. So the GPS machine manufacturers in the procurement of the antenna must be combined with antenna, provide the samples for testing.


3, the feed point: ceramic antenna through the feed point collection resonance signal and sent to the back-end. Due to the impedance matching of antenna, the feed point is generally not in the antenna is the central?


But do minor adjustments in the direction of XY. The impedance matching method is simple and does not increase the cost. Only move in a single direction is called a single partial antenna, in the two are doing mobile called dual polarization.


4, amplifying circuit: PCB shape and area bearing ceramic antenna. Because GPS has the characteristics of a rebound, when the background is 7cm * 7cm continuous earth, patch antenna efficiency can play to the extreme. Although restricted by the appearance of the structure and other factors, but try to keep a considerable area and uniform shape. Amplifier gain selection must be with the back-end LNA gain. Sirf GSC3F requirements shall not exceed the total gain of 29dB signal input, otherwise the signal supersaturation can generate self.


The GPS antenna has four important parameters: gain (Gain), standing wave (VSWR), noise figure (Noise Figure), axial ratio (Axial ratio). With particular emphasis on the axial ratio, it is an important index to measure the signal gain of different direction difference. Because the satellite is randomly distributed in the hemisphere sky, so ensure the antenna are similar in every direction sensitivity is very important. Axial ratio by the antenna performance, appearance and structure, the internal circuit and EMI effect.


Five, GPS antenna selection


GPS, can produce the ceramic antenna manufacturers mainly jiashan  jinchang


Taiwan also has Leadtek and other manufacturers.


Buy from domestic and foreign manufacturers are most ceramic parts, with the amplification circuit design. Procurement can choose ouqiao electronics.


Super intelligent terminal become represent the general trend, put forward a very high request size small space for accessories.


The current domestic technology only in the 15 x 15 or more mature, 10 x 10 or more mature. Smaller antennas need to import.


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