A MINIATURIZED TRIPLE-BAND METAMATERIAL ANTENNA WITH RADIATION PATTERN SELECTIVITY AND POLARIZATION DIVERSITY

A novel triple-band single-fed compact microstrip antenna with varied polarization states and radiation patterns is proposed based on two-dimensional artificial metamaterial transmission line (TL). The TL element is composed of complementary split ring resonators (CSRRs) etched in the ground plane and a capacitive gap embedded in the stepped-impedance conductor line. By inserting a 2 x 2 array of the original element in conventional patch and feeding the resultant structure with an annular-ring slot along the diagonal, an antenna working in three resonant modes (n = -1, n = 0, and n = +2) is engineered at three specific well-separated frequencies [f.sub.-1] = 1.5, [f.sub.0] = 2.4 and [f.sub.+2] = 3.5 GHz, respectively. As a result, both the numerical and experimental results illustrate that the antenna exhibits a patch-like radiation with pure linear polarization in the n = -1 mode, a monopolar radiation with circular polarization in the n = 0 and also an asymmetric quasi monopolar radiation with a hybrid linear polarization in the n = +2 mode. The antenna features compact whose patch occupying only an area of 0.246[λ.sub.0] x 0.246[λ.sub.0] x 0.03[λ.sub.0] at [f.sub.-1] and exhibits groups of advantages such as high radiation efficiency. Moreover, the proposed prescription, free of any metallic via, perturbation structure and complicated feeding network, is of practical value and opens an alternative avenue toward new types of antenna with agile polarization capability and versatile radiation patterns.