An antenna is a device that converts electrical signals into magnetic field signals. Antennas allow only one frequency band to pass through, and generally the impedance of an antenna is 50Ω.
Antennas are directional, and the gain and transmission distance of an antenna are related to the directionality. Directional antennas have long transmission distance and high gain, but poor directionality. Antennas with good directionality do not have high gain, and you can't have both. Generally, a circuit (consisting of an inductor and two capacitors) is added between the antenna and the module for debugging the S11 parameters and antenna matching. Antenna matching has strict environmental requirements. When debugging the customer, it is necessary to recover the customer's use environment, such as the case and PCB copper on the antenna matching.
1, antenna matching parameters, principle
Directionality
The antenna has different radiation or reception ability for different directions. On the horizontal, the antenna that radiates and receives without maximum direction is called omnidirectional antenna, and the antenna with one or more maximum directions is called directional antenna.
Gain
The longer the propagation distance, the higher the gain.
Matching Principle
Impedance matching is a common operating condition in radio technology that reflects the power transfer relationship between an input circuit and an output circuit. When a circuit achieves impedance matching, maximum power transfer will be obtained. Conversely, when the circuit impedance is mismatched, not only will maximum power transfer not be obtained, but the circuit may also be damaged. It is important to note that antenna matching is not the only way to solve RF communication distance. Many problems are not caused by the antenna. Specific problems should be analyzed.
2, antenna matching process
Antenna matching steps:
1, S11 (self-reflection coefficient).
2, coupling power;
3, pull distance.
2-1, S11 coefficient
Generally, S11 tuning is done by adjusting the number of antenna turns (for spring antennas), and cutting the antenna short will move the center frequency point to the high frequency.
The steps for S11 are as follows:
1. Set the start and end frequencies on the instrument;
2. select the channel to be used and calibrate the instrument using the three ports of the calibrator;
3. check the S11 curve of the antenna and calibrate the center frequency point of the antenna according to the actual situation;
4. if it has been solved, proceed to the next step, if not, solve the problem by multi-tuning the antenna π to solve the problem circuit.
2-2. Coupling power
The coupling power is generally used to compare the parameters of the pending prototype and the calibration prototype. In general, each time the coupling power increases by 6dB, the communication distance is doubled compared to the previous one.
3, pull distance
Pull distance can visualize the performance of the device. Usually choose a relatively open area for pull distance to eliminate obstacles and wireless signal interference. In the process of pulling distance, record the parameters used in pulling distance and the communication effect, usually 90% of the communication success rate as the threshold, record the distance between the terminal and the base station as the communication distance under the parameters.
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