Experimental and parametric studies on ultra wide-band and low X-pol helical antenna

Abstract

An innovative design of Ultra Wide-band (over 55% fractional bandwidth) and Low X-pol (Axial Ratio (AR) ≤1dB) helical antenna is presented in this paper. Presented design is generic in nature and can be implemented in any frequency band. We have demonstrated the same in S-band (2.1-3.7 GHz) to meet our internal application. The effect of spacing between turns, number of turns and pitch angle of helical conductor over axial ratio is investigated and presented here. Peripheral feeding technique is used in the design and the off-axis AR within ±100 from the bore sight is ≤ 1 dB over the band. An ultra wide band impedance match between helical conductor and 50 ohm coaxial feed line is achieved by introducing a matching section in between. The matching section presented here is novel, since it is an integral part of the helical conductor section and thus made out of same conductor wire. A minimum of −10dB input reflection coefficient (S11) over the desired band 2.1 GHz to 3.7 GHz is achieved. Further, near band center (2.9 GHz) demonstrated S11 is better than -30 dB using this method. Details of design, modeling in CST (Computer Simulation Technique), and fabrication of the antenna along with the comparison of simulated and measured parameters are presented. An excellent match is observed between simulated and measured results.