2-turn helical antenna with extremely small pitch angle

A 2-turn helical antenna with small pitch angle between 0.60 and 30 has been studied as a radiation element of circular polarization waves in this paper. The antenna with pitch angle 20 exhibits a 3-dB axial ration bandwidth of 9.8%, and the optimal axial ratio of 0.1dB. When the pitch angle decreases to 0.60, the 3-dB axial ration bandwidth and the best axial ratio are 5% and 0.15dB respectively. Variation of on-axis axial ratio as a function of the straight wire height h has been computed. Experimental verification of the antenna performance is presented. The antenna with low profile and high polarization purity characteristics is suitable for application of array antenna.