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In this letter, a compact wideband bandpass filter with a wide stopband is proposed. The filter is composed of three parts: a half-wavelength (λ/2) microstrip resonator with a loaded broadside-coupled microstrip/CPW (BCMC) stub, two λ/4 I/O feeding-lines, and two microstrip short-stubs. The loaded BCMC stub can not only introduce the perturbation to affect the λ/2 microstrip resonator acting as a dual-mode resonator, but also provide two transmission zeros to improve the upper passband selectivity and suppress the first odd-mode spurious. Then, to avoid the first even-mode spurious, two microstrip short-stubs are employed to obtain another transmission zero. Meanwhile, two λ/4 I/O feeding-lines are employed to obtain strong passband enhancement around the dual-resonances. To verify the mechanism mentioned above, a bandpass filter is designed. The proposed filter has the merits of low insertion loss, good passband selectivity, wide stopband, flat group delay, and a compact size.
Date of Publication: July 2011