A dual mode substrate integrated waveguide filter with capacitive I/O coupling structure

The basic perturbation theory is discussed in this paper to excite a dual mode rectangular resonator cavity. A two order dual mode filter is designed with the center frequency at 35 GHz. An I/O coupling structure is proposed to improve the skirt performance of the filter. Using the I/O coupling greatly increase the out-of-band rejection by introducing transmission zeros on each side of the passband located at 32.1GHz, 38.5GHz and 43GHz while keep the passband characteristic is almost unchanged.