Single-Layer Broadband Reflectarray Antenna using Quasi-Spiral Phase Delay Lines

A single-layer broadband reflectarray (RA) antenna using the quasi-spiral phase delay lines (PDLs) is proposed in this paper. The unit-cell structure is composed of three gapped rings attached with two identical PDLs, which can exhibit about 960° phase variation by adjusting the length of PDLs. An offset-fed RA antenna composed of 278 unit-cells forming a circular-shape aperture is designed and simulated. Since large phase swing can be obtained by the proposed unit-cell, the effects of selected phase range on gain bandwidth is studied and the optimized results are used for the final RA design. Simulation results show that 33.2 % of 1-dB gain bandwidth is realized. Moreover, the maximum gain at 10 GHz is 27.85 dBi, which is equivalent to an aperture efficiency of 52.5%. The sidelobe level and cross polarization are below -21.6 dB and -40 dB at 10 GHz, respectively.