SIW bandpass filters in modified box‐section scheme with bypass/constant/frequency‐dependent coupling in diagonal cross‐coupling path

Abstract

Here, three fourth‐order bandpass filters (BPFs) in modified box‐section schemes using substrate integrated waveguide (SIW) are proposed and researched. The proposed filters are based on a conventional box‐section structure with considering bypass/constant/frequency‐dependent coupling (FDC) in the diagonal cross‐coupling path to construct new filtering responses. Based on the different type of the cross‐coupling path, the frequency response of each proposed structure is analysed and presented, which indicates that the proposed filters have flexible response in terms of finite transmission zeros (FTZs). The proposed filters can realise generalised Chebyshev responses with one/two/three FTZs at arbitrary positions. Moreover, one FTZ may be produced by using bypass coupling and direct inductive coupling window to improve lower stopband performance, which is verified by a coupling matrix. For the demonstration, three quasi‐elliptic response filters were designed, fabricated, and measured. Good agreement is achieved between simulated and measured results.

Multi‐layered dual‐mode substrate integrated waveguide bandpass filter with input and output ports located on same substrate layer

“…Based on the proposed structure and equivalent coupling scheme, single-and dual-band responses with four controllable FTZs can be achieved only by changing its the structure parameters, which will be analysed in detail below. It should be noted that the presence of the dominant mode TE 101 deteriorates the lower stopband performance of the proposed filter, and the presences of high modes TE 103 , TE 301 and TE 202 deteriorate the upper stopband performance [21,22]. Then, compared with two coupled TE 101 -mode-based SIW cavities with resonances of 10 GHz, the overall size of the dual-mode SIW cavity with operating frequencies of 10 GHz increases 13.5%.…”

“…The filter can realise two FTZs at any locations. In [22], we propose three SIW filters in box-section coupling scheme based on four single-mode cavities, and the filters also can realise flexible responses. However, the proposed SIW filters in [21,22] have larger sizes because the single substrate layer and the single-mode SIW cavities are employed.…”

Balanced substrate integrated waveguide filters with controllable finite transmission zeros

“…where, [18][19][20]. It means that the FTZ is produced by the two coupling paths R 1 -R 2 -R 4 and R 1 -R 3 -R 4 as well the resonances R 2 and R 3 .…”

“…Similarly, the balanced SIW filter under DM operation can be equivalent to the coupling scheme in Figure 11c. A cross-coupling path between two single-mode SIW cavities is realized, and thus the balanced SIW filter in Figure 11a can produced two FTZs [18][19][20]. Because the crosscoupling strength in the box-section coupling scheme can be controlled well by D 3 , locations of the two FTZs can also be controlled well [19,20].…”

“…In this part, a quasi-elliptic response is demonstrated. Because all the coupling coefficients based on the proposed balanced SIW filters can be controlled well, flexible responses with two controllable FTZs can be realized [18][19][20]. Other type responses with two FTZs at lower or upper DM stopband are not presented here.…”