The U-Shaped Structure in Dual-Band Circularly Polarized Slot Antenna Design

The U-shaped structure is presented for designing a dual-band circularly polarized (CP) slot antenna that has a single metallic layer and is fed by a coplanar waveguide (CPW). To evaluate the performance of the versatile structure, a U-slot and a U-strip slot antenna have been designed for 2.6/3.6 and 2.5/3.5 GHz bands application. By employing a Differential Evolution (DE) algorithm to optimize some primary parameters of the proposed antennas, the optimum impedance and axial-ratio bandwidths at the given operating frequency can be achieved without using the trial-and-error method. Prototypes of the two proposed designs were constructed and studied experimentally. The measured results show that the frequency ratio of the upper band to the lower band is 1.4 (3.6/2.6 GHz, 3.5/2.5 GHz) or less. Other characteristics such as impedance bandwidths, axial-ratio bandwidths, radiation patterns, and peak gains will also be presented for design validation.