Metamaterials intrigue researchers for their potential to fabricate tunable and wideband passive components. Because of line parasitics, the reactive elements responsible for the left-handed (LH) band exhibit a forward or right-handed (RH) transmission band at higher frequencies. Usually, they are separated from the LH band by a stop band. Due to the composite behavior of LC loaded lines, these structures were called composite right/left-handed (CRLH) transmission lines. At Spain’s Universitat Autonoma de Barcelona, Marta Gil, Jordi Bonache, and Ferran Martin implemented a CRLH transmission line by means of complementary-splitring- resonators (CSRRs) and interdigital capacitors. In doing so, they provided a transmission band for Ultra Wideband (UWB) applications in the interval of 3.1 to 10.6 GHz.

To obtain this large bandwidth, the researchers merged the LH and RF bands that are typical of these structures. To eliminate possible interfering signals, these UWB bandpass filters could use an attenuation pole within the band. In their work, the researchers designed several UWB bandpass filters that exhibited attenuation poles at different frequencies. Those frequencies have been located at the CRLH passband at 5.5 and 4.5 GHz.

The structure was designed to exhibit a transmission zero at f_Z = 2.4 GHz and a characteristic impedance of about 50 O. According to measured and simulated filter responses, the measured 3-dB filter bandwidth extends from 3.08 to 11.09 GHz. Insertion loss is 1.3 to 2.5 dB or better above and/ or below the notch. Lower stop-band rejection is 45 dB or more. See “Metamaterial Filters with Attenuation Poles in the Pass Band for Ultra Wide Band Applications,” Microwave And Optical Technology Letters, December 2007, p. 2909.