Comparisons of via-coupling and gap-coupling for end-coupled bandpass filters

This paper investigates and compares the via-coupling and gap-coupling mechanisms in end-coupled structures, in which the former is realized by the shared metallic via between two resonators. Comparisons show that the via-coupling provides more design flexibility, owns better tolerance to fabrication errors and requires more ordinary substrate than the traditional gap-coupling. These merits have been validated by comparison of two end-coupled Chebyshev response bandpass filters (BPFs) using the via- and gap-couplings, respectively. The filters are fabricated and measured for the purpose of verification. For the via-coupling BPF, satisfactory performance was obtained and good agreements have been observed between the measured and simulated results. However, the gap-coupling BPF owns poor performance in measured results. It verifies that the via-coupling merits better fabrication tolerance than the gap-coupling.