Design of compact wideband combline filters in Substrate Integrated Waveguide (SIW)

A compact wideband filter based on combline structure in Substrate Integrated Waveguide (SIW) technology is presented in this paper. The combline structure contains a grounded post connected to a floating metallic disk and the disk is isolated from the top plate of the SIW cavity through an annular gap. This enables an important reduction of the resonate frequency (f0) of the resonator thus the filter's size is significantly reduced and the f0 can be tuned through the radius of the disk (r), the gap's with (wg). The coplanar waveguide line (CPWL) etched at the top of cavities is used to realize the direct coupling between cavities so we got a wideband filter. To achieve sharp skirt at the upper stopband, a couple of open stubs are used to obtain a transmission zero (Tz) located at the upper stopband and the location of the Tz can be changed through the length of the stubs. A four-pole Chebyshev filter has been designed, fabricated and measured. The fabricated device shows an excellent agreement with simulated results. These structures have the characteristics of compact, miniaturization, wideband and high stopband rejection.