GPS antenna is through the acceptance of satellite signals, positioning or navigation of the terminal. And the antenna must be used to receive the signal. GPS satellite signals are divided into L1 and L2, the frequency is 1575.42MHZ and 1228MHZ, where L1 is an open civilian signal, the signal is circular polarization. Signal strength of -166DBM or so, are relatively weak signal. These features dictate the preparation of a dedicated antenna for the acceptance of GPS signals.
⒈ from the polarization of the GPS antenna is divided into vertical polarization and circular polarization.
With the present technology, the effect of vertical polarization is less than circular polarization. So in addition to special circumstances, GPS antenna will use circular polarization and linear polarization.
⒉ from the place on the GPS antenna is divided into built-in antenna and external antenna.
The location of the antenna is also very important. Early use of GPS mobile phone overturned antenna, antenna and the machine at this time the basic isolation, EMI almost no impact on it, the star effect is very good. Now with the miniaturization of the trend, GPS antenna built-in use. At this point the antenna must be above all metal devices, the shell must be plated and well grounded, away from EMI interference sources, such as CPU, SDRAM, SD card, crystal, DC / DC.
Car GPS applications will become increasingly common. The car’s shell, especially the car explosion-proof membrane will be a serious obstacle to the GPS signal. An external antenna with a magnet (which can be attached to the roof) is very necessary for car GPS.
3. From the power supply is divided into active and passive.
External GPS for the active antenna, compared to the gamma-gamma GPS external antenna is basically an active antenna. That passive antenna is not containing LNA amplifier, but the antenna body.
The impact of GPS antenna performance is mainly the following aspects
1, ceramic pieces: ceramic powder is good or bad and sintering process directly affect its performance. The ceramic tile used in the market is mainly 25 × 25, 18 × 18, 15 × 15, 12 × 12. The larger the ceramic sheet area, the greater the dielectric constant, the higher the resonant frequency, the better the acceptance effect. Ceramic pieces are mostly square design, is to ensure that the resonance in the XY direction is basically the same, so as to achieve the effect of uniform convergence.
2, silver layer: ceramic antenna surface silver layer can affect the antenna resonance frequency. The ideal GPS ceramic chip frequency accurately falls at 1575.42MHz, but the antenna frequency is very susceptible to the surrounding environment, especially in the machine, must be adjusted by adjusting the appearance of the silver coating to adjust the frequency to maintain at 1575.42MHz The So the GPS machine manufacturers in the purchase of the antenna must be with the antenna manufacturers to provide the whole sample for testing.
3, the feed point: ceramic antenna through the feedback point to collect the resonance signal and sent to the back-end. As the antenna impedance matching reasons, the feed point is generally not in the center of the antenna, but in the XY direction to do minor adjustments. This impedance matching method is simple and does not increase the cost. Only the movement in the uniaxial direction is called a single biased antenna, both of which are called two biases.
4, amplification circuit: carrying ceramic antenna PCB shape and area. As the GPS has a touch to the characteristics of the rebound, when the background is 7cm × 7cm without the earth, patch antenna performance can be played to the extreme. Although subject to the appearance of structural constraints, but try to maintain a considerable area and shape uniform. The gain of the amplifier circuit must be selected in conjunction with the back-end LNA gain. Sirf GSC3F requires that the total gain before signal input should not exceed 29dB, otherwise the signal over-saturation will produce self-excited.
GPS antenna has four important parameters: Gain, VSWR, Noise figure, Axial ratio. Which emphasizes the shaft ratio, which is a measure of the machine in different directions of the signal gain difference between the important indicators. As the satellites are randomly distributed in the hemisphere sky, it is important to ensure that the antenna has similar sensitivity in all directions. The shaft is affected by the antenna performance, the appearance of the structure, the machine internal circuit and EMI and so on.
Most GPS antennas are right-handed polarized ceramic media, whose components are: ceramic antenna, low noise signal module, cable, connector.
One ceramic antenna, also known as passive antenna, dielectric antenna, PATCH, it is the core technology of GPS antenna. A GPS antenna’s signal acceptance capability, most depending on the ingredients of its ceramic parts ingredients.
The low noise signal module, also known as LNA, is part of the signal that is amplified and filtered. Its component selection is also very important, otherwise it will increase the GPS signal reflection loss, and cause excessive noise.
The choice of cable should also reduce the reflection as a standard to ensure that the impedance of the match.
Post time: Sep-25-2018