Design of High-Power Harmonic Rejection Filter for SDR Applications

This paper presents a design of lumped elements based low pass elliptic filter for UHF frequency band. Elliptic filter is preferred to provide higher roll off. The filter is designed with power handling capability of 50 watts in continuous wave mode operation. The design is simulated and it is further validated by the measurement results. The experimental results show close agreement with the simulation results. The filter has a pass band cutoff frequency of 400 MHz, insertion loss better than 1.13 dB and return loss better than 14 dB. The rejection achieved is greater than 55 dB at stop-band to pass-band transition ratio greater than 1.125:1. The designed filter can be integrated with a 225 MHz-400 MHz power amplifier for software defined radio (SDR). The filter is implemented in 52 mm × 23 mm circuit area.