Design Approach for Quasi-Planar TM 10 MISL Singlet Toward Circuit Miniaturization

This article presents a novel quasi-planar TM10singlet based on the metal-integrated suspended line (MISL) technology. Compared with the conventional TE201waveguide 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 TM10mode 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 TE201waveguide singlet, the proposed approach substantially simplifies both the circuit design and modeling procedures for the TM10MISL 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 TM10MISL singlet for millimeter-wave RF filtering circuits.