Packaged Low-Loss MISL Bandpass Filters With General Mixed-Coupling Circuit Model

In this article, we demonstrate low-loss bandpass filters (BPFs) using two types of coupled-line structures with multilayer metal-integrated suspended line (MISL) technology. In addition, we introduce a novel circuit model that offers a straightforward and general explanation for the occurrence of transmission zeros (TZs) in mixed electric and magnetic (mixed-EM) coupling BPFs. The structure of this article is as follows. First, we introduce a new equivalent circuit model that accurately explains how multiple TZs are generated through mixed-coupling structures. At the same time, the proposed model is used to theoretically explain the cause of flat group delay. Second, we provide two specific design examples that demonstrate the flexibility in placing TZs. These examples show that TZs can be located on the right or both sides of the passband. Finally, we implement all the proposed BPFs with MISL. We conduct simulations and measurements to validate the effectiveness of the proposed theory and design techniques on the implemented BPFs. The results from both the simulations and tests confirm that filters designed based on MISL technology not only offer ease of fabrication but also possess very compact sizes with low losses.