Research On Highly Selective Equilibrium Filter Based On Matrix Integrated Waveguide

Substrate Integrated Waveguide (SIW) balanced filter has been widely used in actual engineering in recent years and have a very high value of engineering application due to its various advantages, such as high quality factor, high power capacity, small size, light weight, high immunity to the environmental noise, easy to be integrated and so on. Cross coupling technology is a common design method to introduce transmission zeros on both sides of passband which improve selectivity of the filter significantly. By utilizing the cross coupling technology, several single band and dual band SIW balanced filters with high selectivity^ high common-mode suppression have been proposed in this paper.To begin with, the basic theory of SIW and several typical structures of the balanced filter are introduced in this paper. Then a K-band SIW balance filter with single band response is proposed. The filter has relatively good performance in the desired passband but suffers from poorly selectivity, thus the improvement is highly required. In this context, an improved SIW balance filter is presented by etching S-type slot line on both top and bottom layers. As for the improved filter, two transmission zeros are introduced on both side of the passband to realize the high selectivity based on the mixed electromagnetic coupling. As a result, the presented improved filter has a high CM suppression with sharp selectivity.Afterwards, based on the single band balanced filter discussed above, two ways to achieve the SIW balanced filter with dual-band response are introduced. Firstly, by adding an extra cavity a controlled virtual transmission zero can be introduced within the passband so as to achieve dual-band behaviors. Meanwhile, the suppression of the common mode is also improved due to the introduced TE102 mode cavity. Secondly, the other one employs higher order modes of the cavity to realize dual-band response, namely TE102-mode and TE104-mode of the cavity are used to build the second DM passband. Besides, by the means of etching symmetric slot line in the top layer, the common-mode suppression characteristic gets improved greatly. Finally, measured and simulated results of these two dual-band SIW balance filter are provided with great agreement.