Wideband Circularly Polarized Antenna Using Single-Arm Coupled Asymmetric Dipoles

This article presents a novel design concept to realize a wideband circularly polarized (CP) antenna by using single-arm coupled asymmetric dipoles (SCADs). First, an impedance compensation method is developed to obtain flat antenna input impedance by designing different arm lengths of the asymmetric dipole. Then, a single-arm coupling method is introduced to improve the antenna bandwidth. Four asymmetric dipoles are bent and sequentially coupled to each other among the long arms of the dipoles. By elaborately adjusting the coupling among the long arms, improved bandwidth and compact radiator size are achieved simultaneously. In addition, to further enhance and optimize the operating bandwidth of the antenna implementation, impedance matching strip and interdigital structure are introduced into SCADs. To verify the design concept, a prototype of the SCAD antenna was designed, fabricated, and measured. Experimental results agree well with the simulations, showing a wide impedance bandwidth of 108% (1.53-5.12 GHz) and an axial ratio (AR) bandwidth of 96% (1.78-5.06 GHz). To the best of our knowledge, the proposed design concept of SCADs is first used to design a wideband CP antenna. Both the simulated and measured results prove that the proposed antenna is a promising candidate for modern broadband CP applications.