Low-Profile and Wideband Circularly Polarized Magneto-Electric Dipole Antenna Excited by a Cross Slot

Abstract

In this article, we present the design of a low-profile circularly polarized (CP) magneto-electric (ME) dipole antenna with enhanced CP bandwidth properties. The ME dipole antenna is excited by a simple microstrip line aperture-coupled feeding structure. The coupling aperture is composed of two crossed slots of unequal lengths to realize CP operation. Four identical inverted $L$ -shaped parasitic elements, each consisting of a horizontal patch and a vertical metallic plate, are vertically positioned around the ME dipole. It was found that such parasitic elements can remarkably improve the 3 dB axial ratio (AR) bandwidth while retaining the wide impedance bandwidth. A prototype with a low profile of only $0.134\lambda _{L}$ ( $\lambda _{L}$ is the wavelength in free space at the lowest operating frequency) is fabricated and tested to verify the proposed design. The experimental results show that the prototype has an overlapping impedance bandwidth ( $|S_{11}| \leq -10$ dB) and a 3 dB AR bandwidth of 3.16–5.36 GHz (51.35%) with a maximum broadside left-handed CP gain of 9.75 dBic. Additionally, nearly identical radiation patterns on two principle cutting planes are obtained over the operating band.