Experiments on evanescent-wave amplification and transmission using metamaterial structures

We present a theoretical and experimental study on the evanescent-wave amplification (EWA) and evanescent-wave transmission (EWT) using a waveguide structure. The evanescent waves (or cutoff waves) can be easily generated in a planar substrate integrated waveguide (SIW), which behaves quite similarly to a conventional rectangular waveguide. We insert a structured left-handed material (LHM) that is composed of distributed series capacitors and shunt inductors into a SIW to verify the EWA and EWT phenomena. From both simulation and experimental results on transmission coefficients, we observe that evanescent waves are amplified and transmitted through the structured LHM metamaterial within the frequency band that exhibits negative refraction. We also show that evanescent waves cannot be transmitted if we insert a right-handed microstrip line or distributed capacitor circuit inside the SIW. Such experiments directly confirm the EWA and EWT phenomena in the LHM metamaterial. We notice that there is a discrepancy in internal electric field distributions between theoretical predictions in the ideally homogeneous LHM and experimental observations in the structured metamaterial. We give an explanation for this discrepancy.