| With the technique developments of phased arrays, the phased array antennas have been widely applied in the military and civilian areas of radars, communications, electronical wars, and navigations. By adjusting the phase difference in adjacent array elements, the radiation patterns (RP) of phased array antennas can be controlled. Presently, most researches pay attentions only to the characteristics of amplitude RP, such as gains, beamwidthes, and sidelobe levels (SLL). However, with the advancements and extensions of applications on phased array, in certain fields, some new array performances are demanded, such as the phase radiation patterns and phase centers (PC) of array antennas.Additionally, in satellite communications and navigations, circularly polarized (CP) antennas are widely used for their prevention from depolarization effects of rain and fog and their anti-multipath reflection effects on the propagations of electromagnetic wave. In present years, along with the developments of new techniques on satellite communications, further requirements for CP antennas are put forward, such as wide beamwidthes, wide bandwidthes, high gains, compact configurations, etc.In the above background, being associated with the research projects tightly, this dissertation makes deeply insight to the phase center techniques of array antennas and the CP antenna techniques on satellite communications. The author's major contributions are as follows:1. The relationship and expression between the phase RP function of array and its PC offset is built. Basing on the radiation far-field expressions and by adopting the practical models, the variation of phase RP functions is built. The before-mentioned relationship is derived accordingly. The expression displays the array antennas can be analyzed as a whole. However, its phase RP functions will be changed with the variation of the array parameters, and the PC will be affected correspondingly.2. The solutions of 2D and 3D apparent phase center (APC) of phased array antennas are provided. According to the definition of array APC, the expressions of APC offset are derived through Method of Least Squares (LSM). Then the softwares for calculation and simulation array PC are developed, and they include the parameters on the cases of different operating modes and states.3. The variations of PC are studied on the cases of different operating modes and states, which include scanning beam, transmitting and receiving states, the existence of amplitude and phase errors, the presence of quantization errors of phase shifter, frequency variation, and array elements effects. The experiment results indicate the change of array parameters will cause PC offset. Especially amplitude and phase errors and quantization errors of phase shifter both will cause larger offsets at z-axis direction (longitudinal direction) than x- and y-axis directions (transverse direction). Moreover, the larger the errors are, the more the offset is.4. The effect of measured errors on PC calculation accuracy is analyzed. A mathematic model is built to study the difference on PC calculation accuracy at longitudinal and transverse directions, as well as the effect of half power beamwidth (HPBW) on calculation accuracy. Finally, it proves, under the condition of finite measurement accuracy and measurement errors existence, that PC is difficult to decide uniquely. If we want to enhance the calculation accuracy, the measurement accuracy has to be improved.5. A CP widebeam self-phase crossed-dipoles antenna is analyzed and studied. The antenna applies self-phase structure to realize CP operation, and adopts reflected ground and drooping dipole techniques to achieve widebeam characteristic. The co-polarized RP beamwidth can achieve more than 150°, and 3dB axial ratio (AR) bandwidth can get 8.47% in theory. The proposed antenna can be used in satellite navigation mobile terminals.6. A wideband CP yagi antenna is designed for UHF band satellite communication. The antenna applies 3dB branch coupler to feed double orthogonal yagi antennas. The minimization of 3dB coupler is carried out for compact antenna structure, and co-design of antenna and feeding network is adopted. The proposed antenna has 24.3% of 3dB-AR bandwidth, and 17% bandwidth for the gains more than 6dBic. The performances of the prototype can meet the engineering demands very well, and the antenna has been used in link communication experiment presently.7. A novel TM11-mode CP annular-ring microstrip antenna (CP-ARMSA) is proposed. The co-design method is adopted to construct annular ring and feeding network, which is used to provide two-point feeding but not increase the external sizes of the antenna. The feeding network with the shape of Archimedes gradual-change line is designed at the inner of the annular ring. In the relative chapter, the AR character of the CP-ARMSA is studied firstly, and the rules of parasitic patch parameters impacting on AR are obtained. The measurement results confirmed the design methodology. The measured 3dB-AR bandwidth can get 6%. The methodology of arranging feeding network at inner of antenna could be applied in other CP-ARMSA.8. Two realizations of narrow-band TM21-mode CP annular ring microstrip antenna (TM21-CP-ARMSA) are studied. They include impedance matching and CP realization. Two kinds of prototypes working at L-band are designed, which separately adopts the feeding network and the perturbation segments to get circular polarization. Both antennas can obtain well radiation at low elevation, and they can be applied in the terrestrial mobile terminals for local and global navigation satellite system. In addition, the wide-band TM21-CP-ARMSA is designed. Adding parasitic patch above annular ring can enlarge the bandwidth obviously. The impedance bandwidth for S11?-10dB gets 10.2%. Its advanced configuration, adopting "radiation bowl" structure, can enhance the gains at low elevation. It is a good candidate for wide-band satellite communication and navigation systems. |
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