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Application of terminal antenna

With the intelligent popularization of mobile phones, Global Positioned System (referred to as GPS) has become an essential function for smart terminals to support navigation, positioning and other services. Because GPS uses satellite communication technology, the downlink power signal through the atmosphere and other environmental factors (for example, in the city area due to multipath effects) have a loss, the actual arrival signal of the mobile terminal receiver is very weak, which requires the receiver has more excellent performance.
The testing of the radiation performance of the whole machine has been paid more and more attention in the radio frequency performance test of mobile phone. This radiation performance test reflects the ability of the final transmitting and receiving of the mobile phone. At present, there are mainly two kinds of methods of radiation performance of the mobile phone: one is on antenna radiation performance are directly determined, namely passive testing; the other is in particular full anechoic chamber, the test mobile phone radiation power and receiving sensitivity, called active test. OTA (Over, The, Air) test belongs to active test. Compared with the traditional passive testing, OTA testing focuses on measuring the radiation performance in the three-dimensional space of the whole machine, so it has gradually become a testing project that has been recognized and recognized by the mobile phone industry. At present, the darkroom environment for OTA testing in the industry mainly consists of two types: single antenna measurement and multi probe measurement.

The main factors that affect the performance of GPS antenna are the following aspects:
1, ceramic film: the quality of ceramic powder and sintering process directly affect its performance. The ceramics used in the market are mainly 25 x 25 and 18 * 18,
15 x 15, 12 * 12. The larger the area of ceramics, the greater the dielectric constant, the higher the resonance frequency, the better the acceptance. Ceramic plates are mostly square designs,
In order to ensure that the resonance in the XY direction is basically the same, so as to achieve the effect of uniform star.
2. Silver layer: the surface layer of the ceramic antenna can affect the resonance frequency of the antenna. The ideal GPS ceramic chip frequency point falls accurately on the 1575.42MHz, but the antenna
Frequency points are very easy to be affected by the surrounding environment, especially when assembled in a machine, the frequency of the silver surface coating must be adjusted to keep it in place
1575.42MHz. Therefore, GPS manufacturers in the purchase of antennas, must cooperate with the antenna manufacturers, to provide the whole machine samples for testing.
3 、 feeding point: ceramic antenna collects resonance signals through feed point and transmits to back end. Because of the impedance matching of the antenna, the feed point is not usually in the antenna
In the middle, but in the XY direction to make minor adjustments. The impedance matching method is simple and does not increase the cost. Move only in single axis direction
For single biased antennas, both axes are moved, called double deflection.
4. Amplifier circuit: PCB shape and area of ceramic antenna. Because GPS has the characteristic of touchdown rebound, when the background is 7cm * 7cm, it is uninterrupted
The effectiveness of the patch antenna can be reached to the limit. Although the appearance, structure and other factors, but as far as possible to maintain a considerable area and uniform shape. enlarge
The choice of circuit gain must match the gain of the back-end LNA. The GSC3F of Sirf requires that the total gain before signal input must not exceed 29dB, otherwise the signal will be saturated
Self excitation.
The GPS antenna has four important parameters: gain (Gain), standing wave (VSWR), noise factor (Noise, figure), and axial ratio (Axial, ratio).
In particular, the axis ratio is emphasized, which is an important index to measure the signal gain difference of the whole machine in different directions.
Since satellites are randomly distributed over the hemispherical sky, it is important to ensure that antennas have similar sensitivities in all directions. Axial ratio is affected by day
Linear energy, appearance structure, whole machine internal circuit and EMI influence.
Edit the selection of the GPS antenna in this section
Most manufacturers buy Ceramic parts from home and abroad, and cooperate with the designed amplifier circuit. Super smart terminal is becoming more and more popular and a small space
High requirements for the size of the fittings. At present, the domestic technology is only mature at 15 * 15 or above, 10 * 10 or more basically mature. Smaller antennas are needed

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