GPS is the terminal that USES satellite signals to locate or navigate. The receiving signal must use the antenna. The GPS satellite signals are divided into L1 and L2 respectively, and the frequency is 1575.42MHZ and 1228MHZ respectively, where L1 is the open civil signal and the signal is circular polarization. The signal strength is -166dbm, which is a weak signal. These features determine the preparation of specialized antennas for GPS signals.
The performance of GPS antenna is mainly influenced by the following aspects
1. Ceramic tablets: the quality of ceramic powders and sintering process directly affect its performance. The existing ceramic tablets are 25 x 25, 18 x 18, 15 x 15, 12 x 12. The larger the area of ceramic slice, the greater the dielectric constant, the higher the resonance frequency, the better the acceptance. Most of the ceramic tiles are square design to ensure that the resonance is basically consistent in the x and y direction, thus achieving the effect of uniform harvesting of stars.
2. Silver layer: the surface silver layer of ceramic antenna can affect the antenna resonant frequency. Ideal GPS ceramic chip frequency point accurately on 1575.42 MHz, but antenna frequency point very easily affected by surrounding environment, especially the assembly in the machine, must by adjusting the silver coating appearance, to adjust the frequency points to keep in the 1575.42 MHz. Therefore, the GPS unit must cooperate with the antenna manufacturer when purchasing the antenna, and provide the complete machine sample for testing.
3. Feeding point: the ceramic antenna collects the resonant signal through the feed point and sends it to the back end. Because of the antenna impedance matching, the feed point is generally not in the center of the antenna, but in the XY direction. This impedance matching method is simple and does not increase the cost. It is only in the single axial direction that it is called a single eccentric antenna, and both of the two axes are moving as bipartial.
4. Amplifier circuit: the shape and area of the PCB bearing ceramic antenna. Due to the characteristics of the gps-hit bounce, the performance of patch antennas can be extremely effective when the background is 7cm x 7 cm. Although the appearance structure and other factors restrict, but try to maintain a considerable area and uniform shape. The selection of amplifying circuit gain must match the back-end LNA gain. Sirf’s GSC3F requires a total gain of no more than 29dB before the signal is entered, otherwise the saturation of the signal will be self-excited.
The GPS antenna has four important parameters: Gain, VSWR, Noise figure, Axial ratio. Especially the axial ratio, which is an important index to measure the difference of signal gain in different directions. Since satellites are randomly distributed across hemispheres, it is important to ensure that antennas are similar in all directions. The axial ratio is influenced by the antenna performance, the appearance structure, the internal circuit of the machine and EMI.
Structure: most GPS antennas are right-handed polarizable ceramic media, and its components are: ceramic antennas, low-noise signal modules, cables, joints.
The ceramic antenna is also called passive antenna, dielectric antenna and PATCH, which is the core technology of GPS antenna. A GPS antenna’s reception capacity, most of which depends on the ingredients of its ceramic part.
The low-noise signal module, also known as LNA, is the part of amplifying and filtering the signal. Its component selection is also important, otherwise it will increase the reflection loss of the GPS signal, and make the noise too loud. The selection of cables should also be used to reduce reflection and ensure impedance matching.
Post time: Sep-25-2018