Compact $X$ -Band Filter Based on Substrate Integrated Coaxial Line Stubs Using Advanced Multilayer PCB Technology

In this paper, a compact filter based on substrate integrated coaxial line (SICL) stubs was designed using an advanced multilayer printed circuit board (PCB) substrate. This technology is convenient to implement high-density interconnect (HDI) devices, which are dedicated to mass market and require to be compact and low cost. In addition, in order to avoid parasitic effects, HDI devices need to be shielded. The laser-drilled microvias used in the low-loss advanced multilayer PCB are the assets that allow the fabrication of compacted and shielded microwave filters. Using this technology, a third-order <inline-formula> <tex-math notation="LaTeX">${X}$ </tex-math></inline-formula>-band filter based on SICL stubs was designed. The SICL topology is convenient to be used for shielded devices thanks to the outer-grounded metallization. The filter was implemented in an advanced PCB substrate composed of seven layers of Megtron 6+. The via-holes fabricated with plated through-holes or laser-drilled microvias allow implementing SICL stubs throughout the thickness of the substrate. Measurements of the <inline-formula> <tex-math notation="LaTeX">${X}$ </tex-math></inline-formula>-band filter are in a good agreement with the simulation. In comparison with other compact filters, the <inline-formula> <tex-math notation="LaTeX">${X}$ </tex-math></inline-formula>-band filter based on SICL stubs has a good footprint reduction while maintaining good electrical performances.