Research On Retrodirective Array Antenna

With the development of wireless communication these years, there is a serious need for novel antennas with the features of low cost, high link gain and the capability of adaptive beam tracking. Retrodirective array antenna has the characteristic of retransmitting a wave toward the source without any prior knowledge of the source location and the complex digital signal processing. Compared with traditional antenna technique and adaptive antenna technique, it has the advantages of quickly tracking and low cost. Therefore, it can be widely used in the communication field for both military and commercial applications.The concept and feature of retrodirective array are theoretically studied based on the current research status both at home and abroad. The advantages and disadvantages of various kinds of realization methods and the structure characteristics of retrodirective arrays are summarized. The tracking characteristic used for judging the performance of a retrodirective array is evaluated by the analysis of beam pointing error in theory. Then the system performance under multi-path circumstance is analyzed.The phase-conjugation technique using mixers is the main approach of realizing a retrodirective arrays. By discussing the various structures of mixers used for phase-conjugation circuits, two kinds of phase-conjugation mixers are designed. In the single sideband mixer design, the sideband suppression influenced by the amplitude and phase error is analyzed and the condition for best outputs is deduced. Simultaneously, a mixer with a shared port for input and output signal using FET is accomplished. These two mixers are fabricated and measured. The measured results show that the mixers have good performance for phase-conjugating circuits.Broadband retrodirective array with frequency offset characteristic can be used for different-frenquency communication. In order to realize phased filtering for a broadband signal in the phase-conjugating circuits with frequency offset characteristic, a Van Atta array combined a single sideband mixer is proposed and the array operating at S band is practically designed and manufactured. The measurement results show good coincidence with theoretically results. This array achieves excellent frequency offset and broadband characteristics.Two broadband heterodyne retrodirective arrays operating at C band are designed for the communication application. In the array designs, frequency offset technique and frequency autonomous structure are used for more flexible performance, which can assure the array automatically retransmit a wave toward the source direction without any prior information of the source frequency. The design results of heterodyne technique using IF for restraining spurious signals in the phase-conjugation circuit show that this array obtain pure spectrum which can satisfies the communication system requirements.Compared with a single frequency retrodirective array, dual-frequency arrays have more widely applications in communication systems. Current researches of retrodirective array focus on single frequency. A bidirectional dual-frequency heterodyne retrodirective array is designed which can make a response signal at a high frequency to a low frequency interrogating signal, and be responsible for the reciprocal process. The phase-conjugation unit with only one mixer to realize bidirectional transceiver not only reduces system cost but also results in high transceiver isolation of the system. The bidirectional dual-frequency retrodirective array using IF mixing allows the system to easily add demodulation, receive and transmit information and can be well applied to the full-duplex communication systems.A heterodyne retrodirective array operating at C band for RFID application is designed and fabricated, in which a FET mixer is used in phase-conjugation cell. A90°coupler is introduced to increasing the isolation between receiving and retransmitting signals.Finally, for the system application requirements, several arrays with low sidelobe level are optimized by using DEGL algorithm. A16-element broadband unequally spaced array with a sidelobe level less than-20dB is designed. At the same time, a16-element dual-polarized retrodirective array with low sidelobe level characteristic is designed which can achieve±20°beam scanning, and the corresponding phase-conjugation circuit is also designed. The design results show that the low sidelobe retrodirective array can be more effectively applied to modern communication systems in the electronic interference environment.