Research On Substrate Integrated Waveguide Balanced Filtering Circuilts

With the rapid development of modern communication technology,the balanced filtering circuits play an irreplaceable role in communication systems because of their high immunity to environment noise and interference.The study and application on the balanced filtering circuits have been drawn much attention with the demand of integration,miniaturization,modularization and high reliability in radio frequency/microwave circuit systems.In this dissertation,the design principles and methods of the balanced filtering circuits based on the substrate integrated waveguide technology are studied,the advantages of low loss,low cost,high quality factor and easy integration of the substrate integrated waveguide are utilized to construct novel balanced microwave filtering circuits with high selectivity,high common-mode suppression,low insertion loss,small size and high integration.The innovative work of this dissertation includes the following aspects:(1)Novel substrate integrated waveguide balanced bandpass filters with high selectivity and high common-mode suppression are proposed.Two orthogonal degenerate modes in a SIW resonator are used to realize the novel balanced feeding structure and high common-mode suppression.The coupling topology and coupling matrix with quasi-elliptic filtering response are constructed.The equivalent models for extracting the external quality factor and internal coupling coefficients of the balanced filter are built.A single-layer dual-mode balanced filter with single coupling aperture and a double-layer dual-mode balanced filter with a pair of coupling apertures are designed.The two filters are designed to exhibit high-frequency selectivity while achieving common-mode suppression of 3 7dB and 48dB,respectively.(2)The method of utilizing balanced resonant modes of the substrate integrated waveguide resonator to design balanced dual-band bandpass filter is proposed.The TE102 TE201 modes in a rectangular resonator are used to construct the dual passbands of the balanced filter.The coupling between source and load is introduced by the novel internal coupling structure,resulting in two additional transmission zeros and improved out-of-band suppression performance.A balanced filter based on the diagonal TE102 and TE302 modes in the square waveguide integrated cavity is proposed.By adjusting the position of the perturbation vias,the frequency ratio of the two passbands can be changed.Surface-etched slots are adopted to improve common-mode suppression,high common-mode suppression of 55dB and 50dB in the two passbands are realized.(3)Methods for designing novel miniaturized filters based on eighth-mode substrate integrated waveguide(EMSIW)resonators are proposed.The coupling between source and load is introduced to construct a new type of feeding and coupling structure.A single passband and a dual passband miniaturization filters both with four transmission zeros are designed.On this basis,a balanced feed resonator based on EMSIW is proposed.A single-layer balanced third-order Chebyshev bandpass filter based on QMSIW and EMSIW resonators,and a double-layer balanced fourth-order quasi-elliptic bandpass filter based on EMSIW resonators are designed,respectively.Both exhibit compact structures,high common-mode suppression and harmonic suppression.(4)A series of novel substrate integrated waveguide balanced filtering multi-functional circuits are proposed.Firstly,a balanced filtering power divider with high selectively is designed,a coupling topology with quasi-elliptic filtering response is constructed,and coupling matrix synthesis method is presented.The power divider displays high selective filtering response under differential-mode operation and high suppression under common-mode operation.Then,a filtering magic-T based on a circular substrate integrated waveguide resonator is designed.Two orthogonal modes are used to realize in-phase and out-of-phase outputs and the isolations between sum and difference ports,and two power-dividing ports.Finally,a unbalanced-to-balanced diplexer is proposed.The SIW resonant cavity working in dual-resonant modes is utilized to construct the common connection part of the transmitting and receiving channels,filtering response and isolation are achieved.