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In this article, a general and effective method for designing compact bandpass filters (BPFs) with extensible orders and channels on a modified patch resonator is presented, for the first time. A comprehensive demonstration and validation of the proposed method are conducted, employing a circular patch resonator. First, the electric-field distributions under different mode resonances of a circular patch resonator are investigated. The TM00 modes can be efficiently excited by loading a metal via at the center of the circular patch resonator. Interestingly, when dividing the modified circular patch resonator by magnetic walls along the radii, the resonant frequencies of the TM00 mode in the resulting subresonators, are almost identical. These subresonators effectively suppress the excitation of higher order modes. Building upon this principle, second-, third-, and fourth-order BPFs with compact size and good stopband rejection are presented. Furthermore, by introducing multiple perturbed metal vias, BPFs with extensible channel numbers are developed. Dual-, tri-, and quad-channel BPFs with constant and compact size, wideband, and wide frequency range isolation are designed for verification. All measured results are in good agreements with the simulated ones, providing compelling evidence for the feasibility of the proposed design method.

In this work, a new 45-GHz millimeter-wave (mm-wave) on-chip bandpass filter (BPF) for IEEE 802.11aj standard application is presented. The BPF is designed using a hybrid structure of shield half-mode substrate integrated waveguide (SHMSIW) and microstrip in 0.25- $\mu $ m gallium arsenide (GaAs) pHEMT technology. First, a second-order SHMSIW on-chip BPF is developed. The metal layer forms electric walls when connected to discrete vias, whereas it forms magnetic walls when they are not connected. Ulteriorly, to enhance frequency selectivity, two coupled microstrip resonators are embed into the coupling window of the two coupled SHMSIW cavities. The cross couplings between these hybrid resonators introduce two transmission zeros (TZs), achieving high-frequency selectivity without increasing the original circuit size. For verification, a quasi-elliptic on-chip BPF prototype is designed, fabricated, and measured. The measured results show good consistency with the simulated ones.

In this article, novel packaged wideband highly selective filtering power dividers (FPDs) with arbitrary phase shifts and power dividing ratios using multilayer stacked stripline are presented, for the first time. In the proposal, the arbitrary phase shift $\Delta \Phi $ and power dividing ratio $k^{2}$ are mainly attained by developing a novel topology consisting of a looped double-coupled line (LDCL)-based power dividing section, a pair of shorted stubs and a delay line. And, it requires no additional output transformers to terminals under arbitrary power dividing ratios. In addition, a co-shared structure composed of a transmission line and an open-circuit stepped impendence stub is inserted in front of the proposed LDCL, which can enhance the flexibility of overall impedance requirement and bring more transmission poles (TPs) and a pair of transmission zeros (TZs), realizing a wide and high-selective filtering bandwidth and enhanced isolation. A comprehensive analysis is carried out to guide the proposed FPDs design in detail. For verification, two design prototypes are implemented in self-packaged forms using the multilayer stacked stripline printed circuit board (PCB) technology. Prototype I is a FPD with 84% 3-dB FBW, phase shift $\Delta \Phi $ = 45°, and power dividing ratio $k^{2}$ = 1, while prototype II is an FPD with 72% 3-dB FBW, phase shift $\Delta \Phi $ = 90°, and power dividing ratio $k^{2}$ = 6. Simulated and measured results are provided with satisfying agreement among them.

This article proposes a novel microwave displacement sensor based on a filtering phase shifter (FPS), which can provide displacement sensing and intrinsic filtering functions simultaneously. The FPS comprises a third-order Chebyshev bandpass filter (BPF) network and a pair of transmission lines. With the derived closed-form formula of magnitude and phase response of the proposed FPS structure, variable insertion phase and constant filtering response characteristics are applied to design the linear displacement sensors for the first time. The displacement sensor mainly consists of double layers, where a pair of fixed transmission lines connect two ports in the first layer as a stator and an FPS structure in the second layer as a movable contact slider. The insertion phase drifts linearly along the displacement, while the bandpass filtering response remains unchanged. A proof-of-concept microstrip sensor prototype operating at 2.98 GHz is implemented and tested to validate the proposed method experimentally. The measured results are in good agreement with the simulated ones, which shows that the proposed sensors can achieve an average phase sensitivity of about 12.8°/mm with a constant bandpass filtering response of 29.5% 3-dB fractional bandwidth (FBW).

This article presents a design method for multilayer packaged single- and dual-band dual-channel bandpass filters (DCBPFs) based on square substrate integrated waveguide (SIW) cavities. By exploiting one or multiple pairs of orthogonal degenerate modes in square SIW resonators, two single-band and one dual-band DCBPFs with high channel isolations are implemented. By arranging feeding ports and coupling apertures, a highly selective single-band DCBPF with multiple types of operating states is demonstrated. In order to construct a dual-band DCBPF design, balanced feeding ports are introduced to excite the operating modes and suppress unwanted spurious modes between the dual passbands, thus realizing a satisfactory dual-band frequency response. To validate the design method, two single-band and one dual-band prototypes are designed, fabricated, and measured. The results exhibit excellent filtering performance and high channel-to-channel isolations.