Miniaturized UWB Microstrip Bandpass Filter with Notched Band

This paper introduces a pioneering approach to the design of an ultra-wideband (UWB) microstrip bandpass filter featuring a narrow notch. The proposed filter incorporates two identical high-impedance short-circuited stubs, one low-impedance short-circuited stub, and two identical sections with three parallel-coupled lines. The electrical length of both the short-circuited stubs and the parallel-coupled lines is meticulously set to a quarter-wavelength at the center frequency of the desired passband. Additionally, a very short-length open-circuited stub is strategically placed at the end of one of the outer lines in a parallel-coupled line section. This configuration enables the filter to exhibit a narrow notched band within the passband, effectively attenuating unwanted WLAN signals. The filter is designed utilizing a RT/Duriod 6010 microstrip substrate characterized by a relative dielectric constant of 10.8 and a thickness of 1.27 mm. The design of the proposed filter is successfully realized in theory and verified by full-wave electromagnetic simulation and the experiment. The filter shows an UWB passband from 2.1 to 11.9 GHz. An excellent agreement between the expected and measured results is obtained.