Design and characterization of single- and multiple-beam MM-wave circularly polarized substrate lens antennas for wireless communications

Single- and multiple-beam circularly polarized ellipsoidal substrate lenses suitable for millimeter-wave wireless communications have been designed, i mplemented, and experimentally characterized at 30 GHz, The lenses are made out of low-cost low-permittivity Rexolite material. The single-beam lens a chieves a directivity of 25.9 dB, a front-to-back ratio of 30 dB, and an ax ial ratio of 0.5 dB is maintained within the main lobe, The measured impeda nce bandwidth is 12.5% within a SWR less than or equal to 1.8:1. The single -beam antenna is well suited for broad-band wireless point-to-point links. On the other hand, the multiple-beam lens launches 31 beams with a minimum 3-dB overlapping level among adjacent beams. The coverage of the lens anten na system has been optimized through the utilization of a hexagonal patch a rrangement leading to a scan coverage of 45.40,vith a maximum loss in direc tivity of 1.8 dB due to multiple reflections. The multiple-beam lens antenn a is suitable for indoor point-to-multipoint wireless communications such a s a broad-band local area network or as a switched beam smart antenna. Duri ng the proposed design process, some fundamental issues pertaining to subst rate lens antennas are discussed and clarified. This includes the depolariz ation properties of the lenses, the effect of multiple internal reflections on the far-field patterns and the directivity, the nature of the far-field patterns, the estimation of the lens system F/B ratio, and the off-axis ch aracteristics of ellipsoidal lenses.