Abstract
This thesis presents a series of antennas with specific beam radiation for satellite communication applications. The beamwidth of a satellite antenna is an important parameter owing to the coverage requirement. A cost-effective satellite is the mainstream of modern communication, and its use benefits small satellite applications. Therefore, novel techniques of controlling the radiation beam in small antennas are investigated in this thesis. This work studies unidirectional and isoflux radiation beam antennas and solves the challenges associated with reported satellite antennas during the design procedure, such as unsteady structure and large size.The study begins with the demonstration of a dual-polarized antenna for spaceborne applications. First, we propose a novel differentially fed dual-polarized magnetic dipole antenna with a wide beamwidth, robust structure, and platform independence for spaceborne applications. The antenna is formed by a dual-polarized magnetic dipole backed by a specially designed rectangular cavity. A cross-shaped conductor fed by two pairs of capacity-coupling feeding probes is utilized to drive the dual-polarized magnetic dipole antenna. The size of the conducting platform that the antenna is mounted on has a limited effect on the antenna’s electrical performances, particularly its radiation pattern. A stable radiation pattern with a 3 dB beamwidth of 70º±3º and a -4 dBi maximum beamwidth of 152º is observed. In addition, the measured cross-polarization is lower than -20 dB within ±65º.
Second, we propose a circularly polarized antenna with a specified beamwidth for spaceborne applications. An antenna with a rectangular structure is proposed to realize the specified gain and axial-ratio (AR) within a beamwidth of 130o. It is composed of a patch and two cavities. The gain and AR are considered simultaneously. On the basis of this proposal, a circularly polarized antenna with a circular structure is developed to achieve the same radiation pattern on all elevation planes. The focus is on the gain and AR within a beamwidth of 130º. The working mechanism is also presented. Measurement results show that within a beamwidth of 130º, the realized gain is larger than -0.7 dBic, and the spatial AR is better than 3.3 dB. The average boresight gain is 5.37 dBic. These results indicate that the proposed antenna is a good candidate for spaceborne applications.
Third, we develop a novel circularly polarized earth coverage beam antenna for satellite applications. The proposed antenna consists of a specially designed cylindrical dielectric, in which a cavity-backed patch antenna is embedded. The isoflux radiation pattern is obtained within a beamwidth of θ in the range of ±50º and the measured space AR is greater than 3 dB from 4.9 GHz to 5.2 GHz. The measured peak gain is approximately 3.45 dBic at elevation angles of ±50º. With the purpose of enhancing gain and improving the radiation stability, a new circularly polarized isoflux radiation antenna with a truncated hemisphere dielectric is developed. The measured broadside gain is larger than 2.8 dBic and the maximum gain is approximately 4.7 dBic at an elevation angle of 40º. The measured gain is greater than 0.9 dBic within a beamwidth of 130º.
Lastly, an end-fire antenna with enhanced gain and fan-beam is built by using a metamaterial-based lens and two parallel plates. The parallel plates contribute to the height reduction of the lens by exciting its TE1 mode. The metamaterial-based lens is composed of the core and impedance matching layers, both of which are based on the gradient refractive index unit cells with a large refractive index variation range. The lateral excitation of a unit cell is investigated to improve the flexibility of determining the lens thickness. The final lens has a height and thickness of only 0.44λ0 and 0.36λ0, where λ0 is the wavelength of the center frequency in free space. The E-plane 3-dB beamwidth is reduced from 76º to 25º, and the achieved gain of the metamaterial lens antenna is approximately 5.4 dB higher than that of the source antenna.
| Date of Award | 22 Jun 2020 |
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| Original language | English |
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| Supervisor | Hang WONG (Supervisor), Kwok Wa LEUNG (Supervisor) & Quan XUE (Supervisor) |