Circularly polarized crossed-dipole turnstile antenna for satellites

In this work, a crossed-dipole turnstile of single or double bays is designed to operate as a circularly polarized antenna for low-orbit satellites. It is shown that a single-bay turnstile in free space gives a near-isotropic radiation pattern whereas a double-bay turnstile can be designed to give a quite-isotropic radiation pattern. It is also shown that when a single-bay turnstile is placed above a square conducting plate, it gives an omni-directional radiation pattern of either balloon-like or conical shape according to its height above the square plate. An integral equation method employing a Galerkin's technique is applied to get the input impedance and power gain and to investigate the polarization characteristics of the antenna. A wire-grid model is used to represent the square conducting plate above which the antenna is placed. The validity of the wire-grid model is investigated and the accuracy of the obtained results regarding the current distribution on the square plate is realized when compared with other published results based on a real surface model of the square plate. The frequency response of the input impedance and the VSWR of the antenna in free space as well as mat when it is placed above a square conducting plate are presented, and the bandwidth of the antenna is investigated.