Analysis and design of dual-feed circularly polarized U-slot microstrip antennas

The dual feed circularly polarized (CP) U-slot microstrip antenna (MSA) has recently been proposed to provide more than 20% bandwidth that VSWR ≤ 1.5 and AR ≤ 3 dB overlapped, even with very small size. However, the working principles of the antenna and the design rules for it have not been yet presented. In this paper, simple formulations to estimate the resonant frequencies of the dual feed antenna are derived, and an iterative design procedure to determine the initial geometric sizes of the antenna is also given. Compared to the final dimensions of the antenna obtained by numerical simulations, the accuracy of the proposed approximate computer-aided-design (CAD) formulas is within 5.3%.