Nonuniformly Folded Waveguide Resonators and Their Filter Applications

Nonuniformly folded substrate integrated waveguide (SIW) resonator is proposed to design compact cavity filters with narrow to wide bandwidths. By taking advantages of the generated stepped impedance resonator (SIR), the harmonic resonance frequencies of the proposed resonator may be controlled by properly adjusting the length and impedance ratio of the resonator. With the first harmonic moved away from the fundamental, a compact filter of 5% bandwidth may be realized with better stopband performance than the conventionally unfolded one. Alternatively, by moving the first harmonic toward the fundamental, one may utilize the first two resonances of two cavities to realize a four-pole filter with a wide bandwidth of 38.5%.