A High Selectivity Tunable Bandpass Filter for V/UHF

A high selectivity tunable 2nd order coupled resonator bandpass filter designed for operation in the V/UHF Band at frequencies from 30 to 88 MHz, 88 to 188 MHz, and 188 to 512 MHz is presented. The tunable filter with two symmetrical resonators is tuned separately by PIN diode-switched capacitor banks. The filter has an insertion loss of less than 10 dB in VHF, less than 25 dB in UHF and a return loss of better than 15 dB in V/UHF. The 3-dB fractional bandwidth of the filter is less than 4.4% and the shape factor (BW30 dB/BW3 dB) is less than 9.7 over the entire tuning range. The tunable BPF shows >6 dB rejection at f<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> ± 3% and the measured results show good agreement with the simulated results.