Balanced substrate integrated waveguide bandpass filter with high selectivity and common‐mode suppression

Abstract

A new method of designing balanced (differential) bandpass filters (BPFs) with high selectivity and common-mode suppression is proposed and implemented by taking advantage of the existence of multiple substrate integrated waveguide cavity modes. The major design concept is by properly choosing, feeding and coupling dual-mode cavities operating at TE 102 and TE 201 modes so as to not only provide capabilities to realise the desired differential-mode passband associated with two transmission zeros, but also generate high common-mode suppression over a wide range. Two X-band BPFs with different internal coupling mechanisms are then proposed and designed. The two design examples having the same centre frequency of 10 Hz and respective passband width of 300 and 270 Hz are fabricated for demonstration. High selectivity is observed for both filters. Meanwhile, c is ∼37 dB for the first design example, whereas it is improved to 48.5 dB for the second one with multi-layered structure. Good agreement can be observed between simulated and measured performances in the authors' study.

High selectivity and common‐mode suppression balanced bandpass filter with TM dual‐mode SIW cavity

“…The substrate integrated waveguide (SIW) has been widely used in microwave circuits due to its high Q-factor, low loss, and easy fabrication etc. In recent years, SIW balanced BPFs have been extensively investigated and various design approaches with respect to CM suppression have been proposed [4][5][6][7][8][9][10]. In [4,5], the CM suppression is realised by arranging the TE 102 mode cavities on the symmetrical plane.…”

“…The microstrip-slotline feed is adopted to achieve an excellent CM signal rejection in both the in-band and out-band [6,7]. By properly choosing, feeding, and coupling dual-mode cavities [8] or QMSIW and EMSIW cavities [9], desired DM passband with TZs and CM suppression are realised. In [10], an aperture is etched in the middle common ground of the vertically stacked cavities, which results in a good CM suppression.…”

“…The dual-mode cavity resonators have attracted much attention because the number of resonators required for a given degree of filter can be reduced by half, resulting in a compact filter structure. The classical dual-mode cavity utilises two mutually orthogonal TE degenerate modes [7,8] in a single physical cavity. Recently, the compact waveguide bandpass filters (BPFs) excited by two orthogonal feeding waveguides in [11,12] have been proposed by using two TM degenerate modes, namely TM 120 and TM 210 .…”

Compact Single-Layer Balanced Eighth-Mode Substrate Integrated Waveguide Bandpass Filter With High Selectivity

“…Recently, balanced/differential filtering circuits have attracted substantial attention because of their excellent performances in terms of the immunity of environmental noises and interferences compared with single-end counterparts [1][2][3][4]. Furthermore, balanced bandpass filters (BPFs) using substrate integrated waveguide (SIW) technique have been studied due to their advantages of low loss, high power-handling capability, and low cost [5][6][7]. In [5,6], balanced SIW filters are proposed and designed by using traditional full-mode SIW cavities, but their sizes are large.…”

“…Balanced SIW filters with compact size and high selectivity are required in modern wireless communications. To reduce the size, dual-mode SIW and half-mode SIW (HMSIW) cavities are exploited to design balanced filters [7][8][9][10]. However, their sizes are still large.…”