A Simple Method to Suppress the Radiation of the Feeding Cable for Small Circularly-Polarized Antennas

In order to obtain accurate radiation patterns of an antenna, it is necessary to reduce the unbalanced current on the surface of the feeding cable. The common method is to place a balun on the feeding cable close to the antenna under the test (AUT) to suppress the common-mode current on the outer surface of the coaxial cable. In this paper, an improved feeding structure is developed to suppress the parasitic radiation without using an additional balun. The coaxial cable feeds a small circularly-polarized (CP) antenna vertically and it connects to the center of the antenna ground. The simulated results show that the proposed feeding scheme has the least perturbation on the CP radiation of the antenna, and its performance is better as compared with the traditional balun.