One-dimensional low-profile slot-loaded epsilon-negative zeroth-order antenna with improved radiation efficiency
A novel low-profile slot-loaded epsilon-negative (ENG) transmission line (TL) is proposed for efficiency-improved zeroth-order resonant antennas. It is demonstrated that the quality factor of the ENG TL-based zeroth-order resonator can be remarkably reduced by enlarging the slot size, therefore, a highly efficient radiating resonator can be designed with higher gain at the zeroth-order frequency. Two one-dimensional zeroth-order resonant antennas with identical unit cell size but different unit cell number are fabricated and measured, each of which can realize a monopole-like radiation pattern at nearly the same frequency. A maximum gain of 1.96 dBi is generated for the electrically small two-unit-cell configuration together with an improved efficiency from 57.0% to 69.1%, while the compact four-unit-cell antenna can realize a maximum gain of 3.86 dBi with an improved efficiency from 71.0% to 82.4%.  2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.
slot-loaded improved radiation efficiency zeroth-order resonant antenna epsilon-negative transmission line