Analysis and Design of Two-Dimensional Resonant-Type Composite Right/Left-Handed Transmission Lines With Compact Gain-Enhanced Resonant Antennas

A two-dimensional (2-D) resonant-type composite right/left-handed transmission line (CRLH TL) is proposed consisting of complementary split-ring resonators (CSRRs) and series capacitive gaps. For characterization and design, the circuit parameters extraction procedure for the TL element is derived, and the unique 2-D dispersion characteristics (CRLH nature) are analytically investigated and further verified by eigenmode analysis performed in HFSS and phase analysis in ADS. A good agreement of dispersion diagram is obtained between full-wave simulation and theory. To demonstrate potential applications, two types of microstrip antennas have been designed, fabricated, and measured following the design procedures that are established. In the first design, a multifrequency antenna operating at three resonant modes of n = -1, n = 0, and n = + 1 is designed by arranging a 2×2 CRLH array in a conventional patch. The frequency ratios between these modes are 1.98 and 1.15, respectively, which can be arbitrarily modulated by controlling the proportion between the CRLH section and the patch. In the second design, zeroth-order resonant antennas are researched. These antennas exhibit simultaneously a leaky-wave characteristic and an omnidirectional radiation behavior, distinguishing them significantly from any previous designs. In both cases, the antenna gain is comparable, and the cell structure is uniplanar and electrically small.