Compact and wideband planar loop antenna with microstrip to parallel strip balun feed using metamaterials

Abstract

In this paper, a small size, wideband and high gain planar loop antenna with a new feed is presented. The antenna consists of a printed rectangular loop with two gaps, a corrugated reflector in order to reduce the antenna size and a dipole. In addition, a parasitic strip and metamaterials are also used in the antenna structure. Corrugating the reflector will extend the current path, it means the effective electrical length increases and resonance frequency decreases and therefore, the current on the reflector flows over a longer path which results in a size reduction. Compared to the originally printed loop antennas, the size of the proposed antenna is reduced by 50.1%. The parasitic strip and metamaterials act as a director for a quasi-Yagi-Uda in high frequency, and also improve the main directivity. In addition, using the metamaterials improve the antenna gain and impedance matching. To demonstrate the capability of the proposed design method, the antenna has been fabricated and its parameters measured. Measured results show that the fabricated antenna has a wide fractional bandwidth of 53% from 2.01 to 3.478 GHz with return loss of better than 10 dB and a measured peak gain of 5.4 dBi.