Design of substrate integrated waveguide based bandpass filters and power dividers

A microwave system is, in general, designed by using fundamental components such as filters, couplers, dividers, etc. Due to the fact that wavelength becomes comparable with lumped element dimensions, at microwave frequencies distributed elements are used for building these components. Microstrip based devices can be used up to certain frequencies. However, when radiation loss increases, waveguide based devices are used which are bulky and costly. Recently, substrate integrated waveguide (SIW) based devices have attracted the attention of many researchers due to low cost, lightweight and efficient high frequency characteristics. SIW is the printed circuit realization of a waveguide. SIW is fabricated on a dielectric material with top and bottom sides are conductors, and two linear arrays of metallic vias form the side walls. In this thesis, by using SIW structure, iris type bandpass filters are designed, analyzed and fabricated for verification. After that, complementary split ring resonator (CSRR) and dumbbell type defected ground structure (DGS) etched filters that are available in the literature are investigated and verified with simulations. Having investigated different filter topologies in the literature, a novel SIW based bandpass filter is proposed, where its second harmonic is suppressed using a dumbbell type DGS underneath the microstrip feed line. The filter is demonstrated with a fabricated prototype, where the simulated and measured results agree well. Furthermore, SIW based power dividers available in the literature and the corrugated SIW (CSIW) architecture which uses open-circuit ended quarter-wavelength stubs instead of vias as the sidewalls, are investigated. CSIW architecture is implemented to a power divider structure available in the literature and a novel CSIW based high isolation power divider is designed and demonstrated with a fabricated prototype. Good agreement between simulated and fabricated results are observed.