Design of a compact multi-mode UWB band pass filter with flexible notch band employing interdigital coupled lines

Abstract

A novel ultra-wideband Microstrip bandpass filter using Radial Stub Loaded Resonator (RSLR) and interdigital coupled Lines is presented in this paper. The RSLR and decagonal patch form a resonator named M to create tuneable multiple notches in the passband for the suppression of Wireless Local Area Network systems’ interference. To realize sharp roll-off, two adjustable transmission nulls are located at the lower and upper frequencies out of the passband. Even and odd-mode analysis is presented to calculate modal resonance frequencies contributing to create the ultra-wide passband. Bessel function is employed to estimate the input impedance of the radial stub which is used in formulation of even and odd mode admittances. Simulated and measured results show a passband from 3.4 to 12 GHz (135% bandwidth around 6.39 GHz) with a rejection notch at 4.99 GHz is achieved with return losses better than 14 and 12 dB in the first and second passbands, respectively. The insertion loss is lower than 0.9 dB in the 90% of passband and rejection level is greater than 19 dB from 12.25 to 17.45 GHz.