How to choose the right GPS antenna

GPS relation to all aspects of our daily lives , this paper introduces GPS antenna classification, structure, performance should grasp the points , as well as issues in the selection process needs to pay attention to the GPS antenna , and give some suggestions need to purchase .

One , GPS Overview

Is accepted by the GPS satellite signals for positioning or navigation terminal. And you must use an antenna to receive the signal . GPS satellite signal and the divided L1 L2, respectively 1575.42MHZ frequency and 1228MHZ, wherein L1 is open to civil signals , the signal is circularly polarized . The signal strength is about 166-DBM, a relatively weak signal. These characteristics determine the need to prepare for the GPS signal receiving antenna specialist .

Second, the classification GPS antenna, how to choose the right GPS antenna

1 , from the GPS antenna polarization into vertical polarization and circular polarization . With today's technology , vertical polarization effects compare circular polarization . Therefore, except in special cases , GPS antenna will adopt circular polarization.

2 , from the placement of the GPS antenna into the built-in antenna and external antenna. The position of the antenna assembly is also very important. Early use more valgus handheld GPS antenna , then the whole internal antenna and basic isolation , EMI almost no impact on its closing Star works well. Now, with the miniaturization trend , GPS antenna multi-use built-in. At this point the antenna must be on top of all metal components, and the shell plating shall be 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 of the shell, particularly in the automotive GPS signal proof film may be a serious obstacle . External antenna with a magnet ( can be adsorbed to the roof ) for the car GPS is very necessary .

Third, the structure of the GPS antenna

Currently most of the GPS antenna is right-hand polarized ceramic dielectric , its components are: ceramic antenna , low noise signal modules , RF cables, RF connectors.

Ceramic antenna which is also called passive antenna , dielectric antenna , PATCH, which is the core technology of the GPS antenna is located . A GPS signal receiving antenna capabilities , most dependent part of the component ingredients with how the ceramic .

Low -noise signal is also called the module low-noise amplifier LNA is to amplify and filter the signal portion . Its Component selection is also very important , otherwise it will increase the return loss of the GPS signal , as well as causing excessive noise .

RF and microwave cables should choose to reduce the reflection of standards to ensure impedance matching .

Fourth, the performance of the GPS antenna

Affect GPS antenna performance is mainly the following aspects :

A ceramic piece : good or bad , and sintering of ceramic powders directly affect its performance. Now commercially used ceramic mainly 25 × 25,18 × 18,15 × 15,12 × 12. Ceramic sheet size , the greater the dielectric constant , the higher the resonance frequency , the better the acceptance . Most ceramic square design , to ensure consistency in the XY direction substantially resonant , so as to achieve a uniform closing star effect.

2, the silver layer : a layer of silver ceramic antenna surface can affect the antenna resonance frequency. Ceramic ideal GPS frequency accuracy falls 1575.42MHz, the antenna is very susceptible to the surrounding frequency environmental effects , particularly in the assembly of the machine must be adjusted by the shape of the silver surface coatings to adjust the frequency again held at 1575.42MHz . Therefore GPS antenna machine manufacturers in the procurement must meet antenna manufacturers, providing the whole sample for testing.

3, the feed point : ceramic antenna resonance signals collected and sent to the back-end through the feed point . Due to the antenna impedance , the antenna feed point at the center of generally not , but to make minor adjustments in the XY directions . Such simple impedance matching without increasing the cost . Only in a uniaxial direction called single partial antennas are made ​​in the two-axis movement is called double side.

4, the amplifier circuit : carrying a ceramic PCB antenna shape and size . Since the GPS has a touchdown rebound characteristics , when the background is 7cm × 7cm ground without interruption , performance patch antenna can play to the extreme . Although the exterior of the structure and other factors, but try to maintain a considerable area and uniform shape . Amplifier gain must be selected to match the back-end LNA gain. Sirf before the GSC3F request signal input shall not exceed the total gain 29dB, otherwise the signal will produce oversaturated self-excited .

GPS antenna has four important parameters : Gain (Gain), VSWR (VSWR), noise figure (Noise figure), axial ratio (Axial ratio). With particular emphasis on the axial ratio , which is an important indicator of overall signal gain for different directions of difference . Because the satellites are randomly distributed in the sky hemisphere , so the sensitivity of the antenna in all directions to ensure both are very important to close . Receive antenna axial ratio performance, appearance of the structure , the whole internal circuits and EMI and other effects .