An Effective Approach to Suppressing the Spurious Mode in Rectangular Waveguide Filters

In this letter, a new method for rectangular waveguides bandpass filters with improved stopband performance is presented. By setting the position of the coupling window, the coupling of the high-order mode can be attenuated, which makes it difficult to form parasitic passbands. It can significantly improve the stopband rejection of the filter without introducing additional elements. Furthermore, the whole structure can be fabricated using the conventional computer numerical control (CNC) milling technology. A
Ka
-band waveguide filter is designed and tested. The stopband rejection of the design is increased from 1.4 times to 1.94 times the center frequency of the filter with the insertion loss of 0.5 dB. Finally, the measurement results validated the proposed design.