Photonic Control Of Phased Array Antennas System

Phased array antennas have many merits, such as veering without physics movements, highly scan agility, accurate beam pointing direction, precision phase and amplitude distribution control corresponding to low sidelobe and shaped beam, and so on. So phased array antennas play a significant role in high performance radar and communication system. Because of the characteristics of the speediness and agility of the phased array antenna beam scanning, it makes phased array radar has performance of multiformity and agility which a machine scan radar can't achieve. Furthermore phased array radars possess higher self-adaptability than others'. Conventionally, phased array antennas steer the beam using phase shifters. Due to the restriction of the aperture effect and the aperture traverse delay, it is difficult to get a wide instantaneous bandwidth under wide scan scope for conventional phased array radars. In order to get a wide instantaneous bandwidth, the true-time delay technology must be applied to phased array antennas.In recent years, with the development of the photonic technology, photonic control phased-array technique attracts more and more attention. Photonic control phased array antennas realize the functions of beamforming and beamsteering by using the true-time delay method based on the fiber and photonic techniques, with which a wide instantaneous signal ability achieved.In this paper, the theories and practical methods of phased array antennas areintroduced in detail. An exact measure method for the delay time of a fiber delay line's is presented. A photonic control phased array antennas system is designed and fabricated. Wideband and wide scan scope characteristics of the photonic control phased array antennas are demonstrated. The author's major contributions are as follows.1. True-time delay methods in phased array antenna application are analyzed. With the desired performances (the radiation pattern of an antenna, the range of scanning angel and the instantaneous bandwidth)given, a most simple and feasible switched fiber delay line is chosen. In addition, its characteristics of temperature, amplitude, phase, and consistency are tested. The measured results indicate that this kind of optical delay line works stably, has wide bandwidth and meets the demands of the system, simultaneously.2. Because of rough results that the vector network analyzer measured directly, a new method for the delay time measurement of a fiber delay line is presented in which the frequency domain method are improved by using the least-square method. The measured transmitted phase curve versus frequency is dealt with by fold-line firstly. Then linear fitting is accomplished by use of the least-square method. Finally, with the slope of fitting line figured out and divided by 360, the delay time can be achieved. The measure precision obtains 0.01ns.3. Quasi-Yagi microstrip antenna is designed in order to satisfy the system bandwidth. For the purpose of reducing the design difficulty of a power divider, the antenna array in horizontal surface is divided into severalsubarrays with taylor distribution, while the subarrays and vertical surface of the array are of the uniform distribution. A broadband corporate power divider is designed for the wide bandwidth antennas.4. The radiation pattern was measured in an indoor far field lab. A comparison of the measured patterns of the array controlled by phase shifters to steer the beam scan only with that of the array with the fiber delay lines used additionally, shows that there is an obvious squint in the beam pointing direction in the first system, while the disadvantage is overcome in the system with the fiber delay lines used. Furthermore, the performances of a broadband and wide-angle scan are obtained.