Vehicle-mounted antenna refers to a mobile communication antenna designed to be installed on a vehicle, and the most common one is the suction cup antenna. Since the suction cup antenna is easy to install and place, it is often used instead of the base antenna in some simple settings. The vehicle-mounted antenna structure includes shortened, quarter-wavelength, middle-loaded, five-eighths-wavelength, double half-wavelength and other forms of antennas. In theory, their efficiency increases in turn, and the length of the antenna in the same working frequency band also increases in turn. Due to the limited height of the vehicle itself, and the wind resistance formed by the overly long antenna when the vehicle is traveling at high speed, it is a problem to pass through the bridge hole and enter the underground garage. Therefore, the longer the vehicle-mounted antenna is, the better. Generally, the antenna of a car is required to be no more than 70 cm, and the antenna of a van is required to be shorter. The shortened antenna is small in size. Although the gain is not high, it is suitable for use in occasions where a concealed antenna is required. It is recommended to install a high-gain antenna for general police vehicles, especially for vehicles with a relatively large activity area. The 350MHZ high-gain antenna is mostly divided into a five-eighths-wavelength load-in form, and there is an inductor coil at a half-wavelength distance from the top of the antenna. The 400MHZ frequency band dual half-wave antenna has a high gain. Its appearance feature is that there are two loading coils on the antenna vibrator. The five-eighths wavelength antenna and the middle loading antenna also have high gain and are relatively cheap, so they are widely used. When used as a temporary fixed antenna, you can consider using a high-gain suction cup antenna, and the length of the antenna does not have to be too limited. Since the suction cup antenna is designed according to the use environment of the car, it will have a better effect if a metal plate (such as iron sheet) with a radius greater than 1 meter is sucked under it when it is used as a fixed antenna. Since the price of imported original car antennas is very expensive and the advantages are not prominent, domestic car antennas are generally used. In the antenna selection stage, the appearance and gain of the antenna are mainly referred to.

The most ideal installation position for the car antenna is the center of the roof. The antenna is adsorbed on the roof with a magnetic suction cup. Although it is usually insulated from the metal roof, there is a large capacitance between the two, forming a path in the high-frequency state. The roof is used as the ground network of the antenna feed system, and together with the antenna, it constitutes the antenna system of the car radio. However, in real life, due to various external conditions, such as the long antenna affecting the entry into the garage, in order to prevent the paint from being scratched, bumped and falling off, or when using a larger and heavier antenna with high gain, the vehicle antenna is often not installed in this position, but is installed on the car's luggage rack, spare tire rack, front and rear bumper, side frame, trunk lid or even exhaust pipe using a stainless steel base. Some are even placed directly in the car. Changing the position of the antenna actually changes the ground grid of the antenna system, and the standing wave ratio will naturally change. In addition to the center of the roof, can the antenna be adjusted to the ideal working state in other positions? The answer is yes, as long as you use a standing wave ratio power meter (SWR meter) during installation, or directly use an antenna tester, measure and adjust the selected position, and ensure that the antenna standing wave ratio is less than 1.5, it can be placed anywhere other than the roof.