A Novel Magnetic Coupling for Miniaturized Bandpass Filters in Embedded Coaxial SIW

Abstract

In this paper, embedded coaxial substrate integrated waveguide (CSIW) filters with innovative magnetic couplings are presented and studied. By creating the loading capacitance of a combline topology using inner layers of a low-temperature co-fired ceramic (LTCC) stack-up, it is possible to achieve resonator miniaturization while improving the spurious-free band and providing full-packaged solutions. Moreover, a new magnetic coupling scheme consisting of short-ended stripline probes is proposed and analyzed in detail, both for direct and external couplings. An in-line three-pole filter at L-band is designed, manufactured, and measured proving how the proposed approach can be used for designing wideband bandpass filter (BPF) with extremely compact size. The designed BPF is centered at 1.5 GHz with 10 % fractional bandwidth (FBW), while the layout size is just 35 × 9.5 mm 2 . The experimental results validate the coaxial SIW technology that allows for, at the same time, easy integration, compact size, flexible design, and enhanced stop-band performance.