Two switchable microstrip bandpass circuits are investigated. Owing to the low loading effect from the distributed coupling technique, many channels are obtained without a complicated matching network. Each passband can be turned on and off independently. Both the bandpass single-pole quadruple-throw switch and the switchable quadruplexer consisting of asymmetrical quarter-wavelength resonators, shunt open stubs and p-i-n diodes feature compactness, high isolation and wide stopband. The isolation is better than 35dB, and the 20-dB stopband extends up to 13 times of the lowest operation centre frequency. To validate this design concept, theory as well as experiment are presented and compared.