Reconfigurable and Tunable S-Shaped Split-Ring Resonators and Application in Band-Notched UWB Antennas

This paper proposes a compact reconfigurable (bandstop/bandpass) and frequency-tunable structure based on S-shaped split-ring resonators (S-SRRs). It is known that an S-SRR coupled to a coplanar waveguide (CPW) provides a stopband in the transmission characteristic of the line. It is shown here that this behavior of the S-SRR can be switched between fundamental resonance and second harmonic response by introduction of a p-i-n diode in the center segment of the S-SRR. Alternatively, if the S-SRR is loaded with a varactor diode instead of a switch, the frequency of the stopband can be continuously tuned from the S-SRRs fundamental resonance frequency to its second harmonic. Furthermore, it is shown that if a pair of shunt p-i-n diodes are introduced across the slots of the host CPW, the structure can be reconfigured from a bandstop to a bandpass structure. Thus, the proposed resonator structure can be used as the building block of reconfigurable (bandstop/bandpass) filters with tunable operating frequency. Finally, to demonstrate a practical application of the proposed structure, an ultrawideband antenna with a tunable band notch is designed and experimentally validated.