Wideband Circularly Polarized UHF Crossed Monopole Antenna With Unequal Power Feed for Handheld Terminals

Abstract

A wideband circularly polarized crossed monopole antenna for handheld terminals operating at UHF band is presented. Two quasi-orthogonal monopoles loaded with meandering lines of unequal end-length are employed for compact low-profile design. A feeding network composed of an unequal power divider and ${\text{90}}^{\circ}$ phase shifter is meant for achieving wide operating band and circularly polarized radiation. Moreover, the ground for the feeding networks also serves as half ground for the radiating part. With proper arrangement of the size of meandering lines and feeding network accordingly, the proposed antenna was finally designed as compact as 0.24 $\lambda$ $\times$ 0.20 $\lambda$ $\times$ 0.005 $\lambda$ . Our measurements of a fabricated prototype confirm that the proposed antenna has an impedance bandwidth ( $\boldsymbol {|S_{11}|}$ $-$ 10 dB) of 30% and a 3 dB axial-ratio bandwidth of 17% around the center frequency 380 MHz, with stable radiation patterns and realized gain. Moreover, the antenna can be folded along the ground edge for potential space saving when it is unused.