A New Approach to Design High Directivity, Compact Omnidirectional CP Antenna Arrays

A new approach to design high directivty, compact omnidirectional circularly polarized (OCP) antenna arrays is presented in this paper. An array of collinear electric (E-) and magnetic (M-) radiators is realized by simply cascading copper loops and vertical strips to form an electrically long antenna structure. This array has two identical half sections that is excited in its center. The circumference of each loop and the length of each vertical strip are about a half-wavelength. The configuration facilitates the currents on all of the loop and the strip radiators to achieve the same phase and, hence, the array is a set of in-phase E- and M-radiators. Due to the fact that the phases of the magnetic radiator currents are 90 degrees ahead of the electric ones, the 90 degrees phase difference between the two subsets of radiators required to achieve OCP radiation is realized. An optimized prototype was fabricated and measured. The whole structure is compact and easily fabricated. It covers a 130 MHz bandwidth from 2.34 to 2.47 GHz and produces OCP radiation. The peak measured LHCP realized gain for the four-stage version is 5.1 dBic.