Near-field uniformity analysis and compensation for finite-sized beam combiner with the asymmetric layout

In a hardware-in-the-loop simulation system, the insertion of an asymmetric layout beam combiner will seriously affect the near-field uniformity. In this study, the effects of the aperture shape, transverse distance and size of the beam combiner on the near-field uniformity were analysed. The square beam combiner with a transverse distance of 0.51 m and a size of 1.05 m × 1.05 m was regarded as the optimal design, but it still cannot meet the test requirements. In order to obtain excellent near-field uniformity, an asymmetric Uniform + Linear taper compensation method was proposed. The maximum values of the amplitude fluctuation (E_pv) and phase ripple (φ_pv) decreased dramatically from 2.62 dB and 16.79° to 0.78 dB and 7.42°, respectively. Asymmetric Uniform + Linear taper was achieved through serrating the edge of the beam combiner. When the number of serrations N was 22, E_pv and φ_pv were <0.83 dB and 7.50°, respectively, which indicated that the near-field uniformity can be significantly improved by asymmetric Uniform + Linear taper.