A Miniaturized Wide-Beamwidth Circularly Polarized Planar Antenna via Two Pairs of Folded Dipoles in a Square Contour

Abstract

A circularly polarized (CP) antenna with a wide axial-ratio (AR) beamwidth is presented by placing the two pairs of folded dipoles in a square contour. First, our study demonstrates that the CP radiation can be achieved at the broadside by setting a 90° phase difference between the vertical- and horizontal-paired folded dipole radiators. Second, a radiation pattern subtraction approach is presented to explain how the radiation beamwidth of the paired folded dipoles could be appropriately widened or narrowed according to the radiation pattern subtraction of two opposite electric current densities in the folded dipoles. Using this approach, the E-plane beamwidth of a pair of folded dipoles is made certainly widened, whereas its H-plane counterpart becomes narrowed. On this basis, the E- and H-plane radiation patterns can still be made approximately identical with each other over a wide range of polar angle, even though the distance between dipoles is deliberately shortened. As such, the desired CP antenna with shortened dipole-to-dipole distance and unaffected wide AR beamwidth can be achieved using two pairs of parallel folded dipoles with shortened distance between them instead of linear dipoles in [24] . Finally, a CP printed antenna is designed and fabricated on a single dielectric substrate. Experimental results are found in good agreement with the simulated ones in terms of radiation patterns, gain, AR, efficiency, and reflection coefficient. In particular, the 3-dB AR beamwidth at the central frequency of 1.6 GHz is extended to 135° at $XZ$ -plane and 142° at $YZ$ -plane. Moreover, the overall size of the constituted CP antenna with folded dipoles is decreased to $\mathbf{0}.\mathbf{43}\;{\boldsymbol{\lambda }_\mathbf{0}} \times 0.43\;{\boldsymbol{\lambda }_\mathbf{0}}$ ( ${\mathbf{\lambda }_\mathbf{0}}$ is the wavelength in free space).