Performance Characteristics of a Dual-sense Helical-beam Antenna

Several years ago, Coleman and Wright [1], experimentally demonstrated the feasibility of exciting a dual-sense circularly polarized field, using a single-element helical antenna. The results obtained and described by [1] suggest that good on-axis axial ratios then become available, and that the off-axis axial ratios may be rated 'reasonable'. It was discovered [1], in particular, that the off-axis axial ratio for the added port of the antenna's feed arrangement was significantly worse on account of an imbalance in the feed as well as currents excited along the axially located outer coaxial conductor. This paper, using a moment-method analytical approach earlier developed for elliptical cylindrical thin-wire helical antenna [2], investigates the possibility of improving off-axis ratios for the dual-sense helical antenna through an informed location of the added port and choice of amplitude and relative phase of feed point excitation voltage. Computational results obtained suggest that both choice of location and magnitude and relative phase of feed point excitation voltage can lead to significant improvements in both on-axis and off-axis axial ratios for the dual-sense helical antenna. In addition to offering possibilities for compensating for the imbalance in the feed and effects of currents excited in the outer coaxial conductor alluded to in [1], the proposals described in this paper indicate such other antenna parameters as polarization sense of radiated field, of interest to optimum energy transfer can be controlled through the use of the dual-feed arrangement of the type proposed in [1].