Research on circularly polarized conical-beam antennas

This antenna is intended for communication between a stationary satellite and mobile stations, and is designed to possess circularly polarized conical beams. It generates a beam in the desired direction, by means of changing the inclination angle of the linear-antenna elements, and the spacing between the antenna elements, without phase shifters. The antenna inclination angle (α), the antenna length (e), the distance between antenna elements (d), and the radius of the circular reflector (R), are adopted as parameters, and optimum values for the directivity of the research objective are obtained by calculation. Four elements of the antenna are fed by in-phase signals, the distances between elements are set to appropriate lengths, and by providing spatial phase differences of 90°, circularly polarized waves are obtained. The antenna elements are fundamentally monopole radiators. Ultimately, the antenna parameters were determined as follows: ℒ=0.64λ (120 mm), R=0.43λ (80 mm), α=45°, and d=0.48λ (90 mm). In the calculation, the frequency was set to 1.6 GHz. It was seen that the beam radiation intensity took the maximum value in the angular range of &thetas;=30° to 60°, and that the &thetas; and φ components of the electric field were approximately equal. In other words, the radiated waves were circularly polarized. An experiment for measuring the directivity of the circularly polarized conical-beam antenna was carried out by using four monopole antennas, and the effectiveness of the theoretical analysis was confirmed. Experiments were carried out for the impedance and directivity