High-selectivity microstrip bandpass filter with notch-band for wideband wireless applications

A planar microstrip bandpass filter with wideband passband is designed using parallel coupled microstrip line (PCML) and short-circuited stubs. The proposed filter is composed of two short-circuited stubs separated by one section of parallel coupled line which are quarter wavelength long at the center frequency. The proposed filter is designed to cover the Federal Communication Commission (FCC) bandwidth for ultra-wideband (UWB) applications (3.1-10.6 GHz). In order to avoid the interference from existing radio system that operates in the frequency band of an FCC-defined indoor limit, a stepped-impedance resonator (SIR) is coupled to the parallel-coupled line section to generate a narrow notch band. The design of the proposed filter is successfully realized in theory and verified by full-wave electromagnetic simulation and the experiment. An excellent agreement between the expected and measured results is obtained.