Microstrip dual I-band bandpass filter with symmetrical twin-inductor resonators

A novel compact microstrip dual-mode dual-band bandpass filter using two symmetrical twin-inductor resonators for I-band application is proposed.Double twin symmetrical rectangular-shaped inductors are connected with the stepped-impedance resonator terminals for matching 50 Omega impedance. The two twin-inductor ends are connected to ground with via connections. The two opposite inductors are joined and become twin-inductor structure that also behaves as an inductor-interdigital coupling. The combination of the two those twin-inductor interdigital structures give strong inductive couplings between the two ports and develop a fixed resonance frequency. This filter is designed to operate at 8.1 GHz and 10.7 GHz resonant frequency with a 20.98 and 13.08% effective bandwidth, respectively, at the 3-dB passband. More than 20 dB spurious suppression was measured in between two distinct bands. The measured insertion loss (S-21) was less than 1 dB recorded for both bands and return loss (S-11) was more than 21 dB measured at center operating frequencies of both bands. (C) 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:638-641, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26617