High-isolation switchable bandpass filter using connected-coupling line

A new switchable bandpass filter using switchable connected-coupling lines (SCCLs) is presented. The SCCL is embedded in a bandpass filter and treated as an admittance inverter to provide adequate coupling coefficient to form a bandpass response in an on state. The passband of the bandpass filter is centerd at 1.5 GHz with 12.8% 3-dB fractional bandwidth. In the off state, the switchable line acts as a travelling-wave switch to cut off the coupling path to achieve a high isolation. The measured isolation of the circuit is greater than 48 dB over the operating bandwidth.