Optimizing RF Efficiency of a Vector-Modulator-Driven Antenna Array

Abstract

The feed vector of an antenna array determines the array pattern and the active input impedance of each element. On the other hand, the output impedance of a variable-gain power amplifier, such as that used in a vector-modulator, depends on the amplification level. The resulting impedance mismatch is typically neglected when designing and controlling antenna arrays at the cost of reduced gain, bandwidth, and beam-steering range. This letter presents a simple method to find the array feed vector that maximizes the realized gain in a given direction in a case when the power amplifier output impedance depends on its amplification level. We verify the method with simulations for a test case consisting of a 4×1 patch array fed with ideal phase-shifters and realistic amplifiers. The simulation results of the case study show that the method improves transmission efficiency by 3.5 dB on average compared to the traditional phase shift.