A novel compact ultra-wideband bandpass filter using hourglass stub

A novel compact microstrip line ultra-wideband (UWB) bandpass filter (BPF) using the proposed stub-loaded multiple-mode resonator (MMR) is presented. This MMR is formed by loading three hourglass stubs in shunt to a high impedance microstrip line in center and two symmetrical locations, respectively. By properly adjusting the dimensions of the stubs, the first four resonant modes of this MMR can be roughly allocated within the 3.1-to-10.6 GHz UWB band while the fifth resonant frequency is raised to above 16.6 GHz. Thus, a novel UWB BPF with compact-size, sharpened upper rejection skirt is finally constituted, designed. Results show the UWB bandpass behaviors own good performance with the insertion loss lower than 0.5 dB, return loss at the center frequency of UWB band (6.85GHz) up to 45.0 dB and higher than 28.0 dB in the upper-stopband (13.0 to 20.0 GHz), while the group delay variation in the passband is less than 0.3 ns.