Design And Realization Of Adaptive Impedance Matching System

Microwave impedance matching means no reflection at the junction of transmissionline with different impedance. It determines the transmission efficiency, power capacityand working stability of system. Besides, Impedance matching can also affect systemaccuracy of test and the quality of microwave components.In a word, impedance matching plays an crucial role in microwave system. The mostpopular mothed to implement impedance matching is adding matching network betweenload and source. For this mothed, there is at least one disadvantages ie it is hard to changeafter integrated on PCB. While the environment around the antenna may deeply infect itsimpedance, under this conditions traditional matching network can do nothing to help.In this paper, a system that can adjust antenna impedance real time is proposed.Mismatching detector module, matching network, control unit and RF transmit modulebuild up the system. As an important part, Mismatching detector consist of directionalcoupler and RF power detector.At433MHz, once mismatching state detected by mismatching module, control unitwill add suitable voltage to varactor, and the capacitance of varactor will be changed due toits bias voltage. Test results show that when input power is0dBm, this system can adjustVSWR from maximum3to1.5, it matches well with design goals.