Impedance Adjustment for Constant Efficiency Power Amplifier Applying Stage Bypass Method

Maintaining high efficiency at high power level while improving efficiency at low power of a power amplifier is an important design criterion to be considered in two way radio systems. In this paper, a stage bypass scheme demonstrated constant efficiency of about 45 % and 41 % for low power (1 W) and high power (5 W), respectively. The work is extended by a novel idea of impedance adjustment incorporated into the stage bypass method. This idea allows constant efficiency over a wide range of power levels (1 to 5 W). We have demonstrated efficiency values of 37 to 52 % for the 1 to 2 W power range at frequency range from 430 to 450 MHz. Simulated and measured results show a good agreement.