Yu Zhan

This letter proposes a highly compact hybrid-mode diplexer based on the metal-integrated suspended line (MISL) technology. By embedding nonresonant nodes (NRNs) into suspended patch resonators, independently controllable transmission zeros (TZs) are generated to improve the interchannel isolation. A double-sided dual-mode metal-integrated waveguide (MIW) is employed as the common junction, which facilitates a seamless mode transition between the TE mode of the waveguide resonator and the TM mode of the patch resonator, synergizing the spatial compactness of suspended patch resonators with the high quality-factor of MIW resonators. Consequently, mode-conversion losses are effectively suppressed while preserving a miniaturized footprint. For validation, an X-band diplexer prototype was designed and fabricated. Experimental measurements reveal dual-channel operation at center frequencies of 10.36 and 12.28 GHz, with −15-dB reflection bandwidths of 9.31% and 8.91%, respectively. The realized minimum insertion losses of two channels are 0.85 and 0.77 dB, respectively, alongside an interchannel isolation exceeding 39 dB. This work provides an effective solution for the design of low-loss, high-isolation, and miniaturized diplexers.

In modern RF and microwave systems, the electromagnetic environment is increasingly congested. Demand for massive data throughput and ultra-high-resolution sensing has driven systems to higher frequency bands. Beyond 30 GHz (subterahertz and above), dielectric loss becomes the primary bottleneck limiting system noise figure improvement and power efficiency. At these frequencies, traditional planar transmission lines, such as microstrip lines and substrate-integrated waveguides, degrade significantly due to increased dielectric loss and radiation leakage. Traditional metal waveguides offer excellent power-handling capability and near-zero dielectric loss. However, they are highly dependent on high-precision computer numerical control milling, resulting in bulky, heavy, high-cost structures that are incompatible with miniaturization of modern satellite payloads and mobile terminals.

This article presents a systematic electromagnetic (EM)-mechanical co-design methodology based on metal-integrated suspended line (MISL) technology. The method is demonstrated through the design, fabrication, and experimental validation of an F-band mixer. Due to the absence of a supporting substrate in MISL, incorporating the specific mechanical support design is indispensable to ensure mechanical stability. To address this challenge, the innovative approach in this article fully leverages the dual functionality of the short-circuit structures within filters in the mixer for both filtering and support. This eliminates the dependency on additional support structures, thereby reducing redundant circuit area usage and associated insertion loss. By establishing an EM-mechanical bi-objective evaluation function, both the intermediate frequency (IF) and local oscillator (LO) filter structures were designed and optimized. For the first time in terahertz circuit design, mechanical reliability is incorporated from the initial design stage. Experimental results demonstrate that the mixer exhibits conversion losses ranging from 5.48 to 7.72dB across 113–120 GHz, which aligns well with simulation curves, demonstrating competitive radio frequency (RF) performance and verified mechanical fabrication reliability. This approach provides a new solution for terahertz circuit packaging and MISL circuit design, achieving high performance and miniaturization.

This article presents a novel quasi-planar TM₁₀ singlet based on the metal-integrated suspended line (MISL) technology. Compared with the conventional TE₂₀₁ waveguide singlet, the proposed structure achieves an 87% reduction in planar area, demonstrating significant potential for circuit miniaturization. A systematic design approach is developed by exploiting independent control over the transmission pole and zero, thus providing a general framework for the rapid design of MISL singlet. For pole placement, accurate analytical expressions for the TM₁₀ mode are derived using the method of images. Subsequently, zero placement is accomplished by formulating a slope equation that relates the pole-zero ratio to key parameters of the source–load coupling, supplemented by an univariate single-objective parameter fitting process. In contrast to the multivariate multiobjective parameter fitting process typically required for the TE₂₀₁ waveguide singlet, the proposed approach substantially simplifies both the circuit design and modeling procedures for the TM₁₀ MISL singlet. To validate the proposed structure and design approach, two representative examples are provided. The implemented third-order bandpass filter exhibits an insertion loss (IL) of 0.62 dB, and the fourth-order filtering antenna array attains the maximum radiation efficiency of 96.8%. Both designs attest to distinct advantages in circuit miniaturization and low loss, highlighting the promise of the proposed TM₁₀ MISL singlet for millimeter-wave RF filtering circuits.

In this letter, a novel filtering crossover based on metal integrated suspended lines (MISLs) technology is proposed. This design features an all-metal structure, achieving low loss characteristic. Rectangular metal patch resonators working at hybrid TEM mode and TE₁₀₂/TE₂₀₁ mode are used for the design of filtering crossover. Slots as coupling windows between TEM and TE₁₀₂ are exploited, then bandwidth and isolation can be controlled flexibly. By adjusting the frequency ratio of TEM mode against harmonics, wide stopband can be achieved successfully. To validate the proposed filtering crossover, a two-channel prototype operating at 7.85 GHz is designed and fabricated with the minimum insertion loss (IL) of only 0.7 dB, and the measured results are in good agreement with simulated data.

In this paper, a novel low-profile wideband cavity-backed slot antenna (CBSA) based on the metal integrated suspended line (MISL) structure is proposed. To increase the bandwidth, three different resonant modes are investigated. Initially, an improved antenna based on the patch mode is developed from the MISL structure, and the characteristics of the patch mode are thoroughly studied. To enhance the bandwidth, the cavity mode inherent to the MISL structure is introduced, forming a simple hybrid mode antenna by combining the cavity mode with the patch mode. Moreover, to further extend the bandwidth, a slot is incorporated into the patch, achieving a quad-mode hybrid wideband antenna that integrates slot dual modes, cavity mode, and patch mode. Owing to the inherent all-metallic characteristics of the MISL structure, the antenna is capable of achieving high gain and low-profile while realizing wideband operation. Experimental results demonstrate that the proposed CBSA operates within a frequency range of 7.08-11.5 GHz, achieving a bandwidth of 47.6% and a maximum gain of 10.6 dBi with the size of $\boldsymbol 1.14\lambda \times 1.13\lambda \times 0.17\lambda \unboldmath$. This successfully realizes an excellent balance between wideband performance, high gain, and low-profile.

This article proposes a novel structure based on vertically folded cascade resonators for the design of multiband filtering antenna with arbitrary order and arbitrary number of operating bands. A generalized fully-coupled theoretical model and the associated systematic synthesis method are established, enabling quantitative analysis and deterministic design of the proposed antenna structure to satisfy the given specifications. By constructing and solving the corresponding multiband lowpass prototype, the theoretical coupling matrix can be derived, which in turn guides the physical parameter extraction process of the circuit prototype, greatly simplifying the design and optimization of multiband filtering antennas. The independently tunable cascade modes excited by the cascade resonators allow for precise control over the multiband filtering response, while the vertically folded integrated structure contributes to circuit miniaturization. With the use of substrate integrated waveguide (SIW) technology, two examples, including a second-order dual-band and a third-order tri-band filtering antenna, are designed and fabricated. Good consistency between the simulated and measured results verifies the proposed structure, theoretical model and synthesis method.

This letter reports a crossbar mixer based on the substrate-integrated suspended line (SISL) platform, with two contributions below. First, multistage stepped double-ridge waveguides are designed for the radio frequency (RF) signal coupling to the Schottky diode pair directly, with low-RF path loss as well as easier wideband matching. Furthermore, the surface roughness of the waveguide sidewall plating layer is measured to analyze the additional metal loss. Measurements show that the results are in reliable agreement with the simulation after considering the practical factors, including surface roughness and dielectric frequency properties. The conversion loss of this mixer is 6.16–9.84 dB within the RF range of 104–118.5 GHz, which is competitive with those in the similar frequency band that adopt advanced processing technology, yielding a good balance between the cost, weight, and performance of the circuits.

This article presents a multiband bandpass filter structure with an in-line topology based on substrate-integrated waveguide (SIW) technology. A multi-layer configuration is employed to achieve circuit miniaturization. By constructing the coupling matrix, the coupling relationships among all resonators are quantitatively characterized, enabling the extraction of the theoretical frequency response and guiding circuit modeling and optimization. We designed and fabricated a third-order tri-band SIW filter and a third-order quad-band SIW filter, achieving a return loss of nearly 20 dB across all passbands. The close agreement between simulated and measured results validates the proposed design model. Additionally, the high in-band isolation of over 40 dB is demonstrated between all adjacent bands, highlighting the potential applicability of this technology in multiband scenarios.