Design of a Switchable Microstrip Dual-Band Lowpass-Bandpass Filter

This study proposes a filter with four switching modes (dual-band lowpass-bandpass filter mode, lowpass filter (LPF) mode, bandpass filter (BPF) mode, and both-bands-turned-off mode). In the dual-band lowpass-bandpass mode, the measured lowpass channel in-band insertion loss and cutoff frequency were less than 0.37 dB, and approximately 1.5 GHz, respectively; the measured center frequency, measured minimal insertion loss, and 3 dB fractional bandwidth of the bandpass response were approximately 2.4 GHz, 3.3 dB, and 9%, respectively. The measured suppression levels of the turned-off lowpass band and bandpass band responses were better than 26 and 33 dB, respectively.