Design of Wide Passband/Stopband Microstrip Bandpass Filters With the Stepped Coupled Line

Novel wide passband microstrip bandpass filters with broader stopbands are provided in this paper. The proposed bandpass filters are composed of the stepped coupled line and two short-circuited stubs. The electrical length of the stepped coupled line is a quarter of wavelength so that the proposed filter is compact size. Moreover, the stepped coupled line with weak-strong-weak coupling results in a wide stopband. Furthermore, with short-circuited stubs connected at the input/output port, there is a steeper passband skirt and broader passband. In addition, the agreement between theoretical prediction and measurement validates our proposed structure.