A Compact Reconfigurable NRI-TL Metamaterial Phase Shifter for Antenna Applications

This communication presents a compact reconfigurable phase shifter based on negative-refractive-index transmission-line (NRI-TL) metamaterial unit cells. Two interswitchable NRI-TL metamaterial unit cells are collocated within the same board area, and can be reconfigured based on the biasing polarity of embedded p-i-n diodes to provide two discrete phase states. The p-i-n diodes are located on the shunt branches of the metamaterial line in order to reduce losses in the direct signal path. Design limitations in terms of return loss and insertion loss are discussed in relation to the two phase states. A proof-of-concept module with a size of 17.8 x 21.6 mm(2) is designed at 1 GHz, with measured insertion phases of -14.5 degrees and +58.5 degrees in the two phase states leading to a differential phase shift of 73 degrees, while exhibiting insertion losses of 1.43 and 0.89 dB, respectively. The combined bandwidth for which the reflection coefficient in both states remains simultaneously below -10 dB is 0.46 GHz (46%), from 0.83 to 1.29 GHz.