LAUSR

A high selectivity microstrip dual-mode diplexer with a stepped-impedance opened-end structure is implemented to reduce the size of a dual-mode resonator and suppress the harmonics. The proposed dual-mode resonator structure consists of a microstrip half-wavelength resonator and an opencircuited stepped-impedance stub. The stepped-impedance opened-end structure can control an even mode in the upper and lower desired bands to improve the cutoff responses. The sharp cutoff selectivity of the filter is created to enhance the diplexer performance and wide suppress harmonics. The dualmode diplexer prototype is analyzed, fabricated, and measured. The measured result agrees well with the analyzed result. The simulated and measured dual-mode diplexers are designed at the operational frequency of Tx/Rx at 1.95 GHz and 2.14 GHz, respectively. It is shown that the dual-mode filter has a wide stopband due to the stepped-impedance stub.