We know that GPS is a terminal that uses satellite signals for positioning or navigation (what is GPS). And in the process of receiving signals, an antenna must be used, so we call the antenna that receives signals a GPS antenna. GPS satellite signals are divided into L1 and L2, with frequencies of 1575.42 MHz and 1228 MHz, respectively. L1 is an open civilian signal with circular polarization (GPS principle). The signal strength is around 166-DBM, which is a relatively weak signal. These characteristics determine the need to prepare specialized antennas for GPS signal reception. Below, the editor will introduce knowledge about the performance and usage precautions of GPS antennas (GPS positioning).
　　
　　The main factors affecting the performance of GPS antennas are as follows
　　
1. Ceramic chips: The quality of ceramic powder and sintering process directly affect its performance. The ceramic tiles currently used in the market are mainly 25 × 25, 18 × 18, 15 × 15, and 12 × 12. The larger the area of the ceramic plate, the higher the dielectric constant, the higher the resonance frequency, and the better the acceptance effect. Most ceramic tiles are designed in a square shape to ensure consistent resonance in the XY direction, thereby achieving uniform star collection.
　　
2. Silver layer: The silver layer on the surface of ceramic antennas can affect the resonant frequency of the antenna. The ideal GPS ceramic chip frequency point accurately falls at 1575.42MHz, but the antenna frequency point is very susceptible to the influence of the surrounding environment, especially when assembled in the whole machine. It is necessary to adjust the silver coating shape to re maintain the frequency point at 1575.42MHz. Therefore, GPS manufacturers must cooperate with antenna manufacturers when purchasing antennas and provide complete machine samples for testing.
　　
3. Feed point: The ceramic antenna collects resonance signals through the feed point and sends them to the backend. Due to impedance matching of the antenna, the feed point is generally not located in the center of the antenna, but is adjusted slightly in the XY direction. This impedance matching method is simple and does not increase costs. Moving only in a single axis direction is called a single offset antenna, while moving in both axes is called a double offset antenna.
　　
4. Amplification circuit: The shape and area of the PCB carrying the ceramic antenna. Due to the ground bounce characteristic of GPS, when the background is a 7cm × 7cm uninterrupted ground, the effectiveness of the patch antenna can be maximized. Although constrained by factors such as appearance and structure, try to maintain a considerable area and uniform shape as much as possible. The selection of amplification circuit gain must be coordinated with the backend LNA gain. Sirf's GSC3F requires that the total gain before signal input should not exceed 29dB, otherwise signal supersaturation will result in self excitation.
　　
The GPS antenna has four important parameters: gain, standing wave ratio (VSWR), noise figure, and axial ratio. Special emphasis is placed on the axial ratio, which is an important indicator for measuring the difference in signal gain of the whole machine in different directions. Due to the random distribution of satellites in the hemisphere sky, it is crucial to ensure that the antenna has similar sensitivity in all directions. The axial ratio is affected by antenna performance, appearance structure, internal circuit of the whole machine, and EMI.
　　
　　Precautions for using GPS antenna
　　
1. GPS cannot provide 100% positioning, let alone believe the nonsense of indoor positioning. GPS is not like mobile broadcasting, where signals can be received anywhere. Many things can affect GPS reception, including the distribution of sky stars, buildings, elevated bridges, radio waves, leaves, thermal paper, etc. There are too many things that can be affected. Generally speaking, the area of the sky that can be seen from the GPS position is the area where the GPS can receive signals.
　　
2. Don't use it once or twice, or for a day or two, to determine the quality of GPS - because the satellite status in the sky is different every day, perhaps in the same place, the morning signal is full, but at night it cannot be located. It is possible that the positioning situation is not good for several days in a row.
　　
3. To compare the quality of GPS, it is necessary to compare it at the same time and in the same location - many people who buy a new GPS will say things like 'the one I used before was better', but this statement is incorrect because the results are much different due to different usage times and locations. It is necessary to use it for a long time or at the same time and place to feel the differences between the two types of GPS.
　　
4. The GPS signal intensity meter is no longer sufficient as a reference for purchasing GPS - when buying GPS, people only look at the signal meter in the electronic map. In the past, it may have been quite accurate, but now GPS has fake signals or simulated signals to make the signal meter look good. The signal meter is indeed beautiful, but it may not be accurately located or even displayed correctly.
　　
5. There is no GPS for indoor positioning - basically, if there is no signal indoors, there is no signal. True indoor positioning starts from Coldstart indoors, but if it can still be located, it is true indoor positioning. However, indoor positioning is basically meaningless because I cannot navigate at home.
　　
6. When purchasing GPS, there is no need to choose the manufacturer as the purchasing option, but internal chips can be selected - basically, there are many GPS manufacturers, and choosing a manufacturer only considers after-sales service. It is not necessarily the case for large manufacturers to receive messages. Generally speaking, GPS with the same chip will not have significant differences in effect when made by different manufacturers. Therefore, when choosing GPS, you can choose GPS receiving chips instead of choosing a manufacturer.
　　
7. Do I really need to use Bluetooth, CFgps, Or gpsmose? -Generally speaking, this is a matter of personal opinion. When using Bluetooth or CF, one must worry about the problem of GPSORPDA running out of power at any time, and the cost is relatively high. However, navigation can be done anytime and anywhere, and using GPSMouse is economical and good for receiving messages. There is no need to worry about power issues, but there are problems with wired communication.
　　
8. Inaccurate positioning may not necessarily be due to GPS errors - basically, a positioning error of less than 20 meters is considered a good GPS. In addition, the GPS position may not be very accurate on the road due to various reasons, such as poor reception, errors, map data problems, or wide roads. Therefore, it seems that the GPS is stably offset from the road surface. After using it for a long time, you will know whether it is a problem with the GPS or the map.
　　
9. When purchasing GPS, the specification sheet is for reference only. The GPS specifications include how many seconds to complete positioning, how many meters of error, sensitivity, and other information. These are all well written and need to be truly used to know. To be honest, comparing the specification sheet is a waste of time.
　　
10. Using GPS, there is no need to charge communication fees - although everyone knows about it, some people still think that there is an additional monthly rental fee.