Design of Tunable Substrate Integrated Waveguide Cavity Resonator under Slow-wave and Fast-wave Loading Conditions

In this paper, a series of fixed-size substrate integrated waveguide (SIW) resonators with continuously varying TE110 mode resonating frequencies are proposed. The microstrip polyline network replaced the top metallic surface of SIW and an up to 40% size-reduction of the effective resonating area has been achieved with reference to the conventional SIW counterpart at the same resonating frequency. By adjusting the area of loading polyline network and the polyline parameters lp2, a tuning frequency range of 5.6-7.65 GHz (similar to 28%) with fixed SIW resonator size is obtained. In particular, when lp2 is less than a certain value, the slow-wave factor (SWF) of the loading region will be smaller than the substrate material, so that the loading region as a whole exhibits a fast-wave effect, which results the resonating frequency higher than the conventional SIW. Six prototypes of the proposed SIW cavity were designed, fabricated and measured. The experimental results are in good agreement with the simulation. Its wide resonating frequency tuning range and convenient design process can serve as a good frequency-selection component for high-quality and low profile oscillator design.