Bandpass filters with resistive attenuators being located at 2(nd) and 4(nd) spurious pass-bands

Abstract

In this paper, a novel resonator consisting of one half-wave transmission line and the resistive attenuator is proposed to build BPF (bandpass filter) with good stop-band suppression. The resonance characteristics of this type of resonator are intuitive through the ABCD matrix analysis. By means of utilizing the conventional design methodology for parallel coupled-line based BPF, the newly proposed filters can be easily realized by inserting attenuator in coupled-line filter. To confirm the validity of the technique, filters of orders-2 BPF centered at 2.25 GHz with a 5% FBW (Fractional Bandwidth) and orders-3 BPF centered at 2.05 GHz with a 12% FBW were used. Successfully, filters in this paper revealed the 2(nd) spurious response of at least 30 dB insertion loss.