Strictly Inline Filter With Planar-Coaxial Hybrid Integration for Compact Package

This article proposes a novel planar-coaxial hybrid-integrated (PCHI) structure enabling strictly inline nonresonant node (NRN) filter design for a compact package. The proposed PCHI filter has a strictly inline configuration and can introduce arbitrarily placed transmission zeros (TZs) to enhance band-edge selectivity and rejection level. Moreover, the physical dimension of the strictly inline NRN filter can be derived deterministically without the time-consuming full electromagnetic (EM) simulation. For verification, a four-pole filter design example is implemented where the measured result agrees well with the theory.