Phase Analysis of a Variable Gain Amplifier Controlled Through Matching Networks

The phase is an important characteristic for the majority of communications circuits. In this paper a study of the effects in the phase of a type of variable gain amplifier (VGA) is presented. The VGA is controlled through the change in the reactance of the elements in impedance matching networks. Two control parameters are defined to change the gain and phase. Expressions are presented to predict such variations. Design examples of variable gain amplifiers are carried out and graphics for the properties of gain and phase are shown. Although control of these characteristics is not independent, the advantage is that it can be done by a single circuit. Its application in beamforming networks for antenna arrays is discussed.