Effective Epsilon-Near-Zero (ENZ) Antenna Based on Transverse Cutoff Mode

In this paper, inspired by the homogeneous field configuration and the exotic flexibility of the epsilon-near-zero (ENZ) metamaterial, an effective ENZ antenna is proposed with length-irrelevant operating frequency and controllable radiation pattern. In our approach, the ENZ response is achieved by using the substrate-integrated waveguide at its cutoff frequency, with two open ends for radiation. Interestingly, this transverse cutoff mode decouples the operating frequency and the spacing distance between the radiating apertures, such that the radiation pattern can readily be adjusted by stretching or even bending the structure without changing the operating frequency. The prototypes with straight and planar-curved styles are designed and experimentally tested, both working on transverse cutoff mode at 3.5 GHz while offering the difference pattern and the broadside fan-shape pattern, respectively. The measured radiation patterns are in a good agreement with the simulation, with the peak total efficiencies higher than 63%. In addition, the high quality factor with narrow bandwidth (similar to 0.5%) is observed and discussed. With devisable radiation pattern and extremely low profile (similar to 0.02 lambda(0)), the proposed ENZ antenna exhibits promising potentials for sensing, conformal, and reconfigurable applications.