A low cost electrically tunable bandpass filter with constant absolute bandwidth

Abstract

This paper presents an electrically tunable bandpass filter which provides nearly constant absolute bandwidth (CABW) within the center frequency tuning range. The proposed tunable band pass filter (BPF) is designed on a low cost FR4 substrate with mixed coupled 3rd order open loop ring resonators, high frequency varactor diodes, chip capacitors and some RF chokes. The center frequency of the BPF is tunable from 1.9GHz to 2.52GHz with 3dB absolute bandwidth of 201.5±1.5MHz. The measured insertion loss of the proposed BPF is found less than 3dB within the tuning range. There is a good agreement found between the simulated and measured results of the proposed BPF.