New S-Band Bandpass Filter (BPF) With Wideband Passband for Wireless Communication Systems

In this letter, a new wideband bandpass filter (BPF) using microstrip parallel-coupled line structure for s-band applications is proposed. The filter is constructed of two sections of three coupled lines separated by a nonuniform line resonator. In order to introduce one transmission zero at each edge of the desired passband, one of the outer coupled lines of each section is shorted to the ground. The nonuniform resonator is constructed by attaching pair of capacitive open-ended stubs at its central location. This resonator is implemented to increase the filter degree by moving the resonant mode inside the desired passband. The transmission zeros can be located at any desired frequency and the desired bandwidth can be obtained where the bandwidth is reversely proportional to the gap between the coupled lines. The filter is designed to have a wideband passband to cover the whole s-band frequency range. The design is successfully realized and verified by full-wave electromagnetic simulation and the experiment. Excellent agreement between the expected and measured results is obtained.