A miniaturized bandpass filter implemented with substrate integrated coaxial line

This article proposed a miniaturized bandpass filter implemented with the substrate integrated coaxial line (SICL).A four‐pole quasi‐elliptic SICL bandpass filter with two symmetric transmission zeros is designed, fabricated, and measured with a minimal size of 0.168 λ0 by 0.088 λ0, where λ0 is the wavelength of free space at the central operating frequency.