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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.

In this article, a novel design methodology of a half‐mode substrate integrated waveguide (HM‐SIW) filtering Wilkinson power divider is proposed. The width between the two metallic rows of vias in the conventional HM‐SIW divider is governed by a truncated Fourier series expansion to obtain specific passband/stopband performance. The optimized varying width is obtained using the even‐mode analysis, whereas the odd‐mode analysis is used to find the optimum values of three isolation resistors that achieve acceptable isolation and output ports matching over specific frequency range. For validation, a HM‐SIW divider with a center frequency of 12.3 GHz and 3.7% 10‐dB fractional bandwidth is designed, simulated, and measured. Simulated and measured results show a good agreement with passband return loss and transmission losses better than −15 and −3.0 dB, respectively.

In this article, a general design methodology of a multi‐way compact equal split Wilkinson power divider (WPD) with bandwidth redefinition characteristics and planar structure is proposed. Quarter‐wave matching uniform transmission lines in the conventional design are replaced with non‐uniform transmission lines (NTLs) governed by a truncated Fourier series. Even mode analysis is adopted to obtain NTLs with predefined bandwidth functionalities; whereas several isolation resistors are optimized in the odd mode analysis to achieve proper isolation and output ports matching over the frequency range of interest. Compactness is achieved by incorporating only one quarter‐wave wideband NTL transformer, with a length computed at the center frequency, in each arm. Two 3‐way WPDs with different frequency bands (i. e., 5‐9 GHz and 4‐10 GHz) and one 5‐9 GHz 4‐way divider examples are designed and simulated. Furthermore, a wideband 3‐way WPD operating over 4‐10 GHz band is fabricated and measured. Results show input and output ports matching and isolation below −15 dB, and transmission parameters in the range of [–4.9,–6.2] dB and [–6,–7.5] dB across the operating band of the 3‐way and 4‐way WPDs, respectively.

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-We propose a compact wideband multi-way power divider/combiner with planar structure for applications to RF power amplifiers (PAs). Uniform transmission lines in the conventional divider are replaced with non-uniform transmission lines (NTLs), which are governed by a truncated Fourier series. An optimization-driven framework is employed in even-mode analysis to obtain the coefficients of the NTLs considering predefined operating bands, whereas three isolation resistors are optimized in the odd-mode analysis to achieve optimal isolation and output port matching over the design bandwidth. For verification purposes, a 4-10 GHz 3-way divider is simulated, and measured. Simulations and measurements are in close proximity and show input/output ports matching of better than -10 dB and transmission of -4.9 ±1 dB across the design bandwidth.Index Terms -multi-way power divider, non-uniform transmission lines (NTLs), power amplifiers (PAs), power combiner, wideband Wilkinson power divider (WPD).

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