3-D Printing Dual-Band Cavity Filter With Capacitive Stubs Producing Transmission Zeros

This paper presents a dual-band cavity bandpass filter based on basic modes and high-order modes. By adjusting the sizes of the coupling irises between the waveguide ports and cavity resonators, the TE
101
mode and TM
120
mode are excited simultaneously at different frequencies. Therefore, the dual-band filter is designed with two modes. Since the isolation of two passbands is not good, the capacitive stubs are introduced to produce transmission zeros (TZs). Three TZs can be controlled by the sizes of the capacitive stubs, respectively. Owing to the six small capacitive stubs, Three TZs are generated to improve the frequency selectivity. Moreover, the first spurious mode is suppressed. The central frequencies of the two passbands are at 4.55 GHz with a fractional bandwidth of 1.11% and 5.00 GHz with a fractional bandwidth of 0.72%. Finally, a 2
^nd
-order dual-band cavity bandpass filter is fabricated by 3-D printing technology.