Ultra-wideband spurii-free quasi-elliptic function filter

This paper describes the implementation of a high-rejection wideband microstrip bandpass filter. The proposed filter employs open-loop ring resonators which are loaded with triangular shaped patches at both open-ends of the resonator in order to enhance its out-of-band harmonic rejection across an ultra-broadband frequency range. Furthermore, by including L-shaped slots within the patches and open-end stubs in the resonator structure itself an even wider upper band rejection is realized which is in excess of 6f_o without compromising the filter´s insertion-loss and return-loss characteristics. The filter design was fabricated to verify its viability for commercial applications.