Research On Limited Electronically Scanning Antenna On Board

To meet the demand for the development of military satellite communication, satellite antennas are required not only to produce spot beams with high quality, but also to have the flexible ability of beam scanning in their service region. Related tightly to a "the Tenth Five-Year Plan" National Defense Pre-research project, this dissertation presents a systematic investigation on the analysis and design of the wide-angle scanning antenna on board, and the Side-Fed Offset Cassegrain (SFOC) dual-reflector antenna suitable for mounting on satellites is discussed emphatically. The author's major contributions on the subject can be summarized as follows:1. The method for synthesizing composite beams is investigated and a pattern synthesis method suitable for array-fed reflector antennas is presented to overcome the disadvantage of conjugate field matching (CFM) and optimum directivity (OD) method.2. A hybrid approach combining physical optics (PO) with geometrical optics (GO) is investigated for analyzing the pattern of dual-reflector antennas, which avoids the problem of low accuracy (GO/GO) or large calculation quantity (PO/PO) when only a single method (PO or GO) is adopted. In the analysis process, the current on the main reflector is first obtained by applying GO to the sub-reflector analysis. Then, by using PO, an integration of the obtained current over the main reflector yields the radiation fields of the antenna.3. The structures and the scanning mechanism of the confocal reflector antenna and the bicollimated reflector antenna are discussed and emphases are laid on the analysis and design of the bicollimated reflector antenna. The results show that the bicollimated configuration has a scanning range over 40 percent greater than the equivalent confical configuration when the maximal aperture error is given. These results provide the foundation for the reflector shaping of dual-reflector antennas.4. The side-fed offset Cassegrain (SFOC) antenna that has an outstanding scanning performance and suits to be mounted on satellites is studied, and its structural parameters are designed in detail. Firstly, some mathematical expressions under the condition of zero cross-polarization component and minimum leaking energy are derived by using the idea of equivalent paraboloid, and some basic structural parameters independent of the scanning are calculated by adopting these developed expressions. Secondly, to meet the demand of beam scanning, other parameters dependent on the scanning, such as the feed position and direction to the sub-reflector during the scanning process, as well as the dimension and shape of the sub-reflector, are also designed.5. To improve the scanning properties of the satellite antenna, the method of ray tracing and the idea of optimization are used to shape the reflector(s) of the single reflector antenna and the SFOC dual-reflector antenna. In the shaping design, in order to enhance the flexibility of the expressions for the reflector, a two-dimensional cubic B-spline is used to approach the reflector surface according to the initial data. Then, taking the rays'path to be equal from every feed to the corresponding apertures as the optimization objective, the interpolation data points for the spline function are adjusted through a new global optimization algorithm named particle swarm optimization. Finally, the shaped reflector surface is obtained by the iteration.6. The average power pattern of the SFOC dual-reflector antenna is calculated, and the effect of the random surface error on radiation characteristics of the antenna is addressed. Firstly, utilizing Ruze's theory about the surface error, the random surface error is defined as the error of the standard reflector in its normal direction and the error in a small zone of the reflector is considered as equal. Secondly, on the assumption that the phase error on the aperture led by the random surface error obeys the Gaussian distribution with zero mean, the expression of the average power pattern is deduced. Finally, the data related to the radiation characteristics of the antenna are calculated and the corresponding curves are presented. The obtained results will be useful for determining the manufacturing accuracy of the antenna's reflectors.