The basic principle of radio frequency technology refers to the circuit whose electromagnetic wavelength is the same order of magnitude as the size of the circuit or device. At this time, due to the relationship between the device size and the wire size, the circuit needs to be processed by the theory of distributed parameters.

This kind of circuit can be regarded as radio frequency circuit, and there is no strict requirement on its frequency. For example, the long-distance transmission of AC power lines (50 or 60Hz) sometimes needs to be dealt with by radio frequency theory.

A system model of a wireless communication transceiver includes a transmitting circuit, a receiving circuit and a communication antenna. The transceiver can be used for personal communication and wireless local area network.

In this system, the digital processing part mainly deals with digital signals, including sampling, compression, coding and so on. Then it is converted into analog form by A/D converter and enters the analog signal circuit unit.

Analog signal circuit is divided into two parts: transmitting part and receiving part. The main function of the transmitting part is: the low-frequency analog signal output by digital-to-analog conversion and the high-frequency carrier provided by the local oscillator are up-converted into RF modulation signals through the mixer, and the RF signals are radiated into space through the antenna.

The main function of the receiving part is: the space radiation signal is coupled into the receiving circuit through the antenna, and the received weak signal is amplified by the low noise amplifier, and then down-converted into a signal containing the intermediate frequency signal component together with the local oscillator signal through the mixer.

The function of the filter is to filter out useful intermediate frequency signals, and then input them into an analog-to-digital converter to convert them into digital signals, and then enter the digital processing part for processing.