Substrate Integrated Waveguide Bandpass Filtering With Fourier-Varying Via-Hole Walling

Abstract

In this paper, an optimization-driven methodology is proposed for the design of substrate integrated waveguide (SIW) bandpass filters (BPFs) with predefined passbands. The width between the metallic walls of via-holes is governed by a truncated Fourier series to achieve the desired filtering performance. The theory of rectangular waveguide is used to establish the optimization framework and obtain the series coefficients under predefined physical constraints. Two types of end-terminations are studied; specifically, with and without SIW-to-microstrip transitions. To validate the proposed methodology, two Ku-band BPF prototypes with 2.5% and 5.8% 15-dB fractional bandwidth (FBW) are designed, simulated, and measured. Furthermore, the half-mode SIW (HMSIW) concept is incorporated in one prototype to facilitate a miniaturized physical structure. Simulations and measurements are in close proximity with passband matching and transmission losses better than-15 dB and-2.5 dB, respectively. The proposed methodology allows for designing BPFs with predefined wideband or narrowband FBW by modifying the underlying physical constraints and optimization parameters. The resulting filters are planar, compact, and have wide stopband rejection. In addition, a derivation for the characteristic impedance of the SIW line is provided, which can be used to find the optimum SIW-to-microstrip transition without performing a parametric study. INDEX TERMS Bandpass filter (BPF), half-mode substrate integrated waveguide (HMSIW), SIW-tomicrostrip transition, narrowband, rectangular waveguide, substrate integrated waveguide (SIW), wideband.

A half‐mode substrate integrated waveguide filtering power divider with Fourier‐varying via holes

“…The even‐mode equivalent circuit of the proposed design is shown in Figure 2(A). The width, w ( x ), between the metallic walls and symmetry plane is varied to obtain specified electrical characteristics considering physical constraints including machining limitations 17 . The HM‐SIW has a length l with varying characteristic impedance Z 0 ( x ) and matches source impedance, Z s , to load impedance, Z l .…”

“…Then, w eff ( x ) is modeled with a truncated Fourier series 19 : where w r is reference effective width and N is the number of the series coefficients. To find ABCD parameters of each uniform segment, the phase constant, β , and the characteristic impedance, Z 0 , are calculated first as elaborated in Reference 17, section II.A. Once Z 0 is calculated for all M segments, the ABCD parameters of the m th segment are found as follows 20 : where Δ x m = ( m − 0.5)Δ x ( m = 1, 2, …, M ) is the center of each segment.…”

“…The source impedance Z s = 2 Z 0 ( x = 0), where Z 0 ( x = 0) is found as given in Reference 17, section II. On the other hand, Z l = Z 0 ( x = l ) for SIW, which is approximately doubled in the counterpart HM‐SIW 17,21 .…”

Narrowband and Wideband Bandpass Filters Based on Empty Substrate Integrated Waveguide Loaded With Dielectric Elements

“…Moreover, they are low cost, low profile and can be easily manufactured. Except for higher losses and smaller quality factor, SIW and HMSIW bandpass filters preserve the advantages of the rectangular waveguide filters and, in addition, allow easy integration with planar circuits, antennas, and passive and active devices on the same substrate [16]- [21].…”

Analysis, Design, and Actual Fabrication of a Hybrid Microstrip-SIW Bandpass Filter Based on Cascaded Hardware Integration at X-Band

“…SIW structures, which act as highpass filters, are used in filter design due to their mentioned properties [5]. Different structures are used to obtain a bandpass filter in Manuscript received 11 August, 2020; accepted 23 December, 2020. some of the previous studies, such as microstrip structure [5], air-filled structure [6], symmetric inductive post structure [7], resonator structure [8], bent structure [9], Low Temperature Co-fired Ceramics (LTCC) structure [10], Through-Silicon Via (TSV) structure [11], cross-coupled structure [12], perturbed circular cavity structure [13], Fourier-varying via-vole walling structure [14], and GaAsbased chip filter structure [15], [16]. As the microstrip structure is easier, cheaper, and more comprehensible, it is preferred for the lowpass filter section of the bandpass filter [17].…”