RF Power Amplifier Efficiency Improvement under Antenna Impedance Variation Using a Tunable Matching Network

Abstract

The antenna input impedance is commonly assumed to be constant but in a real scenario, the impedance value is affected by the environment. This impedance variation affects the performance of the RF power amplifier and its parameters: stability, output power, linearity and efficiency. Among the methods that can mitigate the effects of impedance variation to impedance performance, the tunable matching network (TMN) was used because this technique provides the direct compensation by re-matching the mismatched impedance. A power amplifier was designed first in order to observe the variation of its performance with respect to load impedances which have a VSWR value of less than or equal to four and resulted a PAE variation from 35% to 68%. There was a reduction of 10 percent to the highest achievable PAE mainly due to the loss contributed by the varactors use in the TMN. An improvement up to 10 percent is also seen in various loads especially those near the edge of the VSWR = 4 after integrating the TMN. In addition, the lowest possible output power due to impedance variation was increased from 36 dBm to 38 dBm after integrating the TMN. Another set of simulations was done using ideal varactors in the TMN and resulted to a variation in PAE from 65% to 69% with the lowest output power level of 39.4 dBm recorded.