Microstrip diplexer for GSM and WLAN bands using common shorted stubs

A novel microstrip diplexer for global system of mobile (GSM) and wireless local area network (WLAN) bands using common shorted stubs is proposed. Two transmission zeros on both sides of the passband response can be easily realised for each passband. Additional transmission zeros created by the shorted stubs are introduced to suppress the harmonic of the microstrip diplexer. A microstrip diplexer with high isolation and selectivity can be achieved by locating the transmission zeros of each channel. A microstrip diplexer prototype with 30 dB isolation from 0.1 to 6.0 GHz has been designed and fabricated.