Frequency switching of electrically small patch antenna using metamaterial loading

Abstract

A frequency switchable planar metamaterial loaded electrically small microstrip patch antenna, capable of resonating at different frequencies by varying the loading distance, has been presented in this paper. The rectangular microstrip patch antenna is loaded with planar metamaterial square spilt ring resonators (SRRs) in three different configurations at a distance of 0.25, 0.50 and 0.75 mm, respectively to get the switchable resonant frequency performance. The square SRRs reveals negative permeability (<img src='/image/spc_char/micro.gif' border=0>) presenting the single negative metamaterial (SNG) characteristics. The unloaded rectangular microstrip patch antenna resonates at 23 GHz. In loading condition at different distances, the rectangular microstrip patch antenna resonates at 9.61, 9.51 and 9.41 GHz, respectively. Using Chu limit, size of the antenna, that is <i>ka</i>, reaches 0.766, 0.775 and 0.787 in respective configurations, thus, satisfies the condition <i>ka</i> <1 for electrically small antenna. The resonant frequency of rectangular microstrip patch antenna decreases with respect to the loading distance due to magnetic coupling. As the loading distance gets reduced, the mutual inductance increases resulting in enhancement of the bandwidth of the antenna. In these three loading conditions, the radiation quality factor (<i>Q_rad</i>)is larger than the minimum <i>Q</i> that is <i>Q_chu</i>. The directivity is more than 7.50 dBi in the presented configurations of electrically small rectangular microstrip patch antenna.