Research On Miniaturized Multi-mode Substrate Integrated Waveguide (SIW) Filters

The rapid developments of modern mobile communication,radar system and spaceborne electronics have proposed a higher requirement on the microwave cir-cuits.As an important component of microwave system,microwave filters with ad-vantages of compact size and high performance are in large demand.Substrate inte-grated waveguide(SIW)has been widely utilized in microwave filter designs for its advantages of low-profile,low-weight,easy fabrication and integration with other planar circuits.This dissertation mainly discusses on the design of SIW filters by making full use of the multi-mode characteristics.By employing the methods such as adjustment to multi-mode,capacitive loading and folding operation,single-and dual-band bandpass SIW filters with small circuit occupation area and compact size have been proposed and fabricated.The current researches on multi-mode SIW filters are still mainly concentrated on the degenerate modes and single passband.To address this,the electric field dis-tribution of resonant modes in SIW or half-mode SIW(HMSIW)has been studied.Metallized via-holes are introduced in these structures to serve as the perturbation to different resonant modes.The perturbation causes mode shifting of certain resonant modes near to the other resonant modes which are not affected in order to form the passband.Triple-and quadruple-mode bandpass filters using triangular HMSIW have been designed.Besides,we also propose a novel dual-band bandpass filter based on four resonant modes in a single perturbed SIW cavity.Capacitive loading is an effective way to miniaturize the SIW cavity resonator and it is usually applied on the dominant mode.In this dissertation,two conductive posts are embedded in the SIW cavity to achieve a dual-capacitive loading on both dominant mode and high order mode.A miniaturized dual-band filter with two pass-bands independently-controlled has been realized using the proposed SIW cavity resonator.Besides,combining the perturbation to the dominant mode and capacitive loading on the high order mode,resonant frequencies of several resonant modes could be allocated closer to form a passband.Through multilayer printed circuit board(PCB)process and low temperature co-fire ceramic(LTCC)process,two tri-ple-mode bandpass filters with controllable bandwidth using quarter-mode SIW(QMSIW)are designed and fabricated.Furthermore,three dumb-bell-shaped de-fected ground structures(DGS)are etched under the two feedlines respectively to widen the stopband and strengthen out-band rejection.Folding the SIW cavity is another effective method to reduce the circuit occu-pation area.Through folding a rectangular SIW cavity three times,a triple-folded SIW(TFSIW)cavity resonator is proposed and the first two resonant modes in the TFSIW are utilized to achieve a dual resonance response.The designed filter using the TFSIW has up to 86%size reduction compared to the conventional dual-band filter using the unfolded square SIW resonator.Besides,it breaks through the innate limitation of the double-folded SIW(DFSIW)that the DFSIW structure cannot achieve a small frequency ratio in dual-band filter design.The center frequencies of two passbands are located at 1.91 GHz and 2.32 GHz while the frequency ratio is only 1.21.