Design of hexagonal filter with source-load coupling

A method for synthesising a novel hexagonal filter with source-load coupling is presented. The equivalent circuit of the lowpass prototype of a general lossless coupled resonator filter is proposed, and the corresponding transfer function t(s) is derived. A novel quasi-elliptic function microstrip hexagonal filter is designed and fabricated. Simulated and measured results are presented. Compared with the conventional cross-coupling filter, the proposed hexagonal filter acquires more than 27.5 size reduction and provides improved selectivity by a relatively small bandwidth.