A Circularly Polarized Spaceborne Antenna With Shaped Beam for Earth Coverage Applications

Since the earth is spherical in shape, the paths from the satellite to various points on the earth are different in both the distance and atmospheric attenuation. In order to maintain approximately uniform effective signal strength on the surface of the earth, the radiation pattern of the antenna should be formed according to the shape of the earth. Former antennas for earth coverage purpose are either bulky or hard to realize the desired beam pattern within a wide angle range, making them unsuitable for small satellite applications. To solve this problem, this paper presents a novel circularly polarized earth coverage antenna for spaceborne applications. The proposed antenna consists of a specially designed dielectric cylinder, in which a cavity backed patch antenna is embedded. With the help of the concave structure at the top of the dielectric cylinder, the refraction of electromagnetic wave can be controlled, and then the radiation pattern is shaped. A sequentially feeding network is designed to drive the antenna. To verify our concept, a prototype is fabricated and experiments are carried out. The simulation agrees well with the measurement. The earth coverage radiation pattern is obtained within the beamwidth of θ in the range of ±50° with the measured space axial ratio is better than 3 dB from 4.9 to 5.2 GHz. The measured peak gain is about 3.45 dBic at the elevation angle of ±50°.