An adaptive impedance matching system and its application to mobile antennas

Abstract

An adaptive antenna impedance matching system for mobile communication terminals is proposed. The system adaptively controls two varactors of the pi-network matching circuit detecting the change in the reflection coefficient between the antenna combined with the matching circuit and the RF front end of a transceiver. This system consists mainly of analog circuits and employs only a simple algorithm for convergence, therefore does not need any complicated mathematical formulation for modeling of the system itself as well as its nonlinear control elements. Also the proposed system utilizes only simple digital circuits for timing generation. In this paper, the performance of the adaptive impedance matching system is investigated by simulation. The input impedance of three antennas is alternated assuming the change of the environment due to a human head or a hand and the performance of the impedance matching is compared with fixed capacitance matching systems. As a result, it is found that the input power to the antenna for transmission can be increased by about 2-3 dB per second compared with the fixed capacitance matching system.