Multifunctional Switchable Filter Using Shorted Coupled-Line Sections

This paper presents a novel multifunctional RF filter based on RF-switched parallel-coupled line sections. It demonstrates three different reconfigurable responses namely a bandpass filter (BPF) response, a bandstop filter (BSF) response and a dual-band (DBPF) response. Reconfigurability is realized by turning on and off four p-i-n diodes that are placed at specific locations and either connect or disconnect a uniform transmission line and shorted parallel coupled-line sections to the main RF signal path. To verify the validity of the proposed design, a switchable filter prototype is fabricated and measured. For the BPF response, the measured 3-dB fractional bandwidth (FBW) is 43.48 % (1.75-2.75 GHz) with a passband insertion loss of 0.8 dB. For the BSF response the measured 3-dB FBW is 36.52 % (1.90-2.74 GHz) with an in-band suppression level above 12 dB. Finally for the dual-band BPF response, the measured 3-dB FBWs of the two bands are 18.2% and 18.5% respectively.