ZERO-POLE APPROACH TO COMPUTER AIDED DESIGN OF IN-LINE SIW FILTERS WITH TRANSMISSION ZEROS

This paper presents a fast technique for the automated design of pseudo-elliptic lters in in-line topology implemented in substrate integrated waveguide (SIW) technology. The proposed method is based on an optimization routine with cost function involving zeros and poles of scattering parameters. To realize transmission zeros in in-line topology, frequency-dependent couplings were used. Such dispersive couplings were implemented as shorted stubs. The design process starts with the generation of a suitable starting point. To this end, an approximation of SIW as a rectangular waveguide is used and a fast electromagnetic solver based on mode-matching technique is utilized (μWave Wizard). The next step is the optimization process of a lter in a full-wave 3D EM simulator Ansoft HFSS. To increase the speed of convergence, a built-in derivative calculation feature was used and zeros and poles and their derivatives with respect to design parameters were extracted using the vector fitting algorithm. Experimental validation of the method is demonstrated by a third-order filter with asymmetric response and a fifth-order filter with two transmission zeros in addition to an asymmetric response. The experimental results show good agreement between the simulated and measured data.