S-band wideband bandpass filter (BPF) with improved upper-stopband performance for satellite communication systems

A wideband bandpass filter (BPF) using microstrip parallel-coupled line structure for s-band applications is presented in this paper. The filter is constructed of two sections of three coupled lines separated by stub-loaded resonator. The stub-loaded resonator is formed by attaching three open-ended stubs with the two high-impedance microstrip lines in center. The middle open-ended stub is implemented to move the second resonant mode inside the desired passband. The other symmetrical open-ended stubs are introduced to suppress the second harmonic. One of the outer coupled lines of each section is shorted to the ground in order to introduce a finite transmission zero at each edge of the desired passband. Those transmission zeros can be located at any desired frequency. The filter is designed to have a wideband passband to cover the whole s-band frequency range with improved upper-stopband performance.