Compact Fractal Left-Handed Structures for Improved Cross-Polarization Radiation Pattern

A set of two-dimensional (2-D) left handed (LH) transmission line (TL) structures are proposed based on the single-layered and double-layered fractal-perturbed mushrooms. The effects of the Koch Island on the LH characteristics have been investigated physically by examining the dispersion diagram of the LH structure with and without fractal perturbations, showing that the parasitic transverse electric mode has been considerably suppressed without any deteriorative penalty on the dominant transverse magnetic mode. Therefore, the interaction of the degenerated parasitic mode with the operation modes has been considerably weakened. The concept has been employed to suppress the cross-polarization (XP) radiation of a microstrip antenna which incorporates a 2 × 2 array of the LH structure into a conventional microstrip patch. Numerical and experimental results indicate that the XP radiation (<; -30dB) has been notably reduced at three working frequencies (f_-1 = 1.5, f₀ = 2.96 and f₊₁ = 3.7 GHz) while the antenna performances such as gain, co-polarization radiation and impedance matching are without any deterioration.