An Equivalent Circuit/System by Design Approach to the Design of Reflection-Type Dual-Band Circular Polarizers

A dual-band reflection-mode wide-bandwidth and wide-angle scanning circular polarizer is designed. The proposed polarizer can convert linearly polarized waves into right- and left-hand circularly polarized (RHCP and LHCP) waves in the two separate nonadjacent receiving and transmitting K/Ka frequency bands. The polarizer is based on dual-layer dipole arrays printed on both sides of a dielectric substrate separated by a second substrate from the ground plane. An analytic model based on transmission line equivalent circuits is developed. Closed-form expressions are derived to demonstrate the operating principle providing a simple design procedure. The proposed model can be used to optimize the converter for a specific propagation angle of the incident wave. Finally, a system-by-design (SbD) strategy is proposed to improve the performance of analytically synthesized devices. Toward this goal, a computationally efficient “digital twin” of the accurate full-wave model is built to speed up the solution space exploration and efficiently reach the global optimum. A prototype is designed for the incident angle θ0 = 30◦ and it is shown that the axial ratio lower than 3 dB is maintained for a wide-angle field of view of Δθ = 60◦ (θmin = 0◦, θmax = 60◦) in both frequency bands.