Design and Optimization of a Nonuniform Multilayer Nonfocal Lens With Improved Phase Error at Ka-Band

In this letter, we present a nonuniform multilayer lens based on the nonfocal lens design methodology to improve phase error at the K
_a
-band frequency. The lens consists of five cascade layers with different refractive indices, and nonuniform contours are defined using Fourier series expansion within the parallel plates region. By utilizing Fourier series coefficients, along with other parameters, such as layer position, refractive index, and maximum subtended angle, as new optimization parameters, the average phase error is significantly improved compared with the multilayer Rotman lens structure. The proposed lens features five beam ports and seven array ports, with an overall size of 140 × 94 × 10 mm
³
. It achieves an average phase error of 1.07 × 10
⁻³
over the array aperture. Furthermore, the lens exhibits beam scanning capability of ±22° with a step size of 11° and a sidelobe level better than 10 dB for all beam ports within the 24–30 GHz frequency range. To validate the design, a waveguide-based five-layer structure was implemented, utilizing periodic cubic metallic posts with varying heights to achieve the refractive index of the layers. Measurement results of the fabricated lens confirm good agreement with the simulated outcomes.