Improvement of spurious property of waveguide bandpass filter based on artificial dielectrics

An improvement of spurious property of a miniaturized waveguide bandpass filter based on the artificial dielectric rectangular resonators is reported. The resonators which are realized by lamination of rectangular metal strips etched on a printed circuit board for obtaining the anisotropic effect are intended to excite TE₁₀₈-mode selectively, aligning the rectangular metal patterns along the direction of the mode electric field line. To obtain a better spurious property for the filter application, the resonators are improved to have a different density of permittivity. The resonant frequencies of an improved artificial dielectric rectangular resonator are analyzed using HFSS simulation and compared with the measurement results. To demonstrate the feasibility of improvement, a miniaturized two-stage waveguide bandpass fiter made of the artificial dielectric rectangular resonators with the center frequency of 1.665 GHz, bandwidth of 140 MHz, and insertion loss of 0.81 dB is successfully created.