Triple-Mode Substrate Integrated Coaxial Resonator Based Bandpass Filter Featuring Flexible Transmission Zeros and Adjustable Bandwidth

This communication presents substrate integrated coaxial resonator (SICR) based triple-mode bandpass filters designed for K
_u
-band. A self-shielded SICR based third-order filter is realized using two planar coaxial resonators (SICR) embedded in a substrate integrated waveguide cavity (SIW). Merging the TEM based mode of two SICR's with TE
₁₀₁
mode of SIW significantly enhances the bandwidth in a compact size. A novel topology realized using short circuited metallic via connecting to the top conducting plane through a metal strip demonstrates high degree of flexibility in positioning the transmission zeros to improve the selectivity as well as extend the out-of-band rejection of proposed filter. The three experimental prototypes devised for K
_u
-band with fractional bandwidth more than 23% demonstrate multiple transmission zeros for good selectivity and out-of-band rejection with low insertion loss in a compact form factor.