Controllable Waveguide Bandstop Filter Using S-Shaped Ring Resonators

Abstract

In a novel application a slab of S-shaped ring resonators is used to fill a rectangular waveguide for the construction of a band-rejection waveguide filter with adjustable bandwidth and cutoff frequency. Results obtained from theoretical analysis, simulation and measurement of a specific structure are presented. Then, by using finite element simulation, we show that the cutoff frequency and stopband bandwidth of the filter can be controlled by changing the slab substrate properties (permittivity and thickness) and its position inside the waveguide. Results also show that varying the real part of relative permittivity of the slab substrate from 1 to 6, while keeping its physical thickness fixed (0.508 mm), the cutoff frequency drops from 10.6 to 6.9 GHz. On the other hand, when the physical thickness of slab substrate changes from 0.508 mm to 4 mm while keeping its permittivity fixed (ε r = 2.2), the filter cutoff frequency decreases from 8.8 to 5.9 GHz. We show that the width of rejection band of the filter can be decreased from about 4.7 GHz to about a few MHz by increasing the distance of the slab from the central plane of the waveguide.