Design and simulation of wide band input matching circuit for RF power transistor in VHF range

Abstract

This paper demonstrates the design and simulation of input matching circuit for BLF578XR power transistor working at center frequency of 225 MHZ with bandwidth of more than 50 MHZ. Based on the calculated Q-factor and when using the transistor in push pull mode, the input matching circuit is designed in two stages, the first stage is a balun to match 50 ohm to 12.5 ohm and the other stage is to match 12.5 ohm to the input impedance of BLF578XR. Each stage is designed and simulated separately then both stages are integrated and simulated together. Simulation is done using Microwave office AWR software. From simulation results, the balun has a phase difference between the two output ports that is approximately 180 degree with good amplitude balance and has −20dB bandwidth larger than 150MHZ. The intermediate matching network has a small insertion loss and very good return loss that is less than −30 dB with −20 dB bandwidth about 110 MHZ. By integration of the balun circuit with the intermediate matching circuit, the resultant input matching circuit has a return loss better than −23dB with −20dB bandwidth about 100 MHZ.