Ultra-wide stopband waveguide bandpass filter based on out-of-band staggered tuning coupling technology

ABSTRACT A design method of greatly widening the stopband of waveguide bandpass filter is proposed in this paper. The parasitic passband of the filter mainly comes from the high-order oscillation mode of the resonant unit. Based on the theory of capacitance loading shortening of the transmission line and the transmission characteristics of each mode in the resonant cavity, a pair of transverse one-dimensional uniform capacitive diaphragms are placed in the center of the resonant cavity to shorten the resonant cavity and suppress the high-order modes. By changing the width of the waveguide and the height of the waveguide on the distribution of out-of-band transmission poles, the out-of-band transmission poles of each resonator can be staggered, which destroys or weakens the high-order oscillation coupling transmission conditions between the resonant units of the filter and further expands the stopband width of the filter. The results show that the length of the X-band waveguide bandpass filter (center frequency 9.5 GHz, bandwidth 400 MHz) is reduced by 54%, and the 40 dB stopband rejection bandwidth is 5.7 times the cutoff frequency of the transmission waveguide, compared with the prototype half-wavelength direct-coupled filter of the conventional Chebyshev filter.