What is GPS antenna

Do you know about the GPS antennas? The following NiceRF will science the relevant knowledge for you. The GPS antenna is divided into vertical polarization and circular polarization, built-in and external antennas from the way of placement, and active and passive antennas from the power supply.

What is GPS antenna

GPS is a terminal that receives satellite signals for positioning or navigation. The antenna is necessary for receiving signals. The GPS satellite signal is divided into L1 and L2, with frequency of 1575.42MHz and 1228MHz, of which L1 is an open civil signal with a circular polarization. The signal strength is about -166dBM, which is a weak signal. These characteristics determine the special antenna for receiving the GPS signal.

GPS antenna function

1. The GPS antenna is used to capture satellites and receive satellite positioning information, that is, radiation and receiving electromagnetic waves. Any high -frequency circuit, as long as it is not completely shielded, can radiate electromagnetic waves to the surrounding space more or less, or receive electromagnetic waves more or less from the surrounding space. Depending on the GPS antenna, it can be divided into flat antennas and spiral antennas. The spiral antenna has a stronger star search capability.

2. Transform the electromagnetic wave energy of the radio signal from the satellite into the current of the electronic devices of the receiver, that is, the energy conversion. For dedicated equipment or vehicle equipment, because the device is often a certain distance before the equipment and the GPS receiving module, more than 1 meter of collapse may be used in the real environment. In this case, GPS active antenna is better because of the signal loss of feed line.

(GPS Active antenna AGPS25A-60C)

GPS antenna structure

At present, most of the GPS antennas are right –rotating polarized ceramic media, and their components are: ceramic antenna, low noise signal module, RF cable, and radio frequency connector.

Among them, ceramic antennas are passive antennas, which is the core technology of the GPS antenna. The signal acceptance capacity of a GPS antenna is mostly determined by the ingredients of the ceramic part.

Low noise signal blocks, also known as LNA low noise amplifiers, are part of amplification and filtering signals. The selection of components is also very important, otherwise the reflection loss of the GPS signal will be increased and the noise will be excessive.

The selection of RF microwave cables should also be used to reduce reflection as the standard to ensure the matching of impedance.

GPS antenna performance

The main aspects that affect the performance of GPS antenna:

1. Ceramics: The quality of ceramic powder and the sintering process directly affect its performance. The current ceramics in the market are mainly 25X25, 18X18, 15X15, 12X12. The larger the ceramic area, the larger the dielectric constant, the higher the resonance frequency, and the better the acceptance effect. Most of the ceramic sheets are square design, to ensure that the resonance in the XY direction is basically the same, so as to achieve the effect of uniform star collection.

2. Silver layer: Silver layer on the ceramic antenna surface can affect the antenna resonance frequency. The ideal GPS ceramic frequency point is accurate to 1575.42MHz, but the antenna frequency point is very vulnerable to the surrounding environment. Especially assembled in the whole machine, it must be adjusted by adjusting the shape of the silver surface coating to adjust the frequency points to 1575.42MHz again. Essence Therefore, when purchasing antenna, the GPS entire machine must cooperate with the antenna manufacturer to provide the whole machine sample for testing.

3. Ceramic antennas to discuss the resonance signals and send them to the back end. Due to the matching of the antenna yang resistance, the point is generally not in the center of the antenna, but a tiny adjustment in the XY direction. Such impedance matching methods are simple and do not increase costs. Move only in a single -axis direction is called a single bias antenna, and the movement of both axes is called dual bias.

4. Amplification circuit: PCB shape and area of the ceramic antenna. Because GPS has the characteristics of a touch of ground, when the background is 7cmx7cm non-intermittent land, the effectiveness of the Patch antenna can be exerted to the extreme. Although it is restricted by factors such as appearance structure, try to maintain a fairly uniform shape. The choice of amplifying circuit gain must be matched with the back -end LNA gain. SIRF's GSC3F requires that the total gain before the signal input must not exceed 29dB, otherwise the signal is full saturation.

There are four important parameters of the GPS antenna: Gain, VSWR, Noise Fiaure and Axial ratio. Among them, a axial ratio is particularly emphasized, which is an important indicator to measure the difference in signal gain in different directions. Because satellites are randomly distributed on the hemisphere sky, it is very important to ensure that the antenna is similar in all directions. The axial ratio is affected by antenna performance, appearance structure, internal circuit of the whole machine, and EMI, etc.

GPS antenna recommendation