Research On Beamforming Technology On Wideband Optical Delay And Phase-shifting Network

Optically controlled phased array antenna(OCPAA) is one of research hotspots in the field of phased array antenna because of its high performance on wideband and large scanning angle. As the core components of phased array antenna beamforming,optical delay and phase-shifting network(ODPSN) has made the microwave signal phase shift and beam-form in the optical domain to overcome the classic limitations on bandwidth owing to the “aperture effect” and “aperture traverse delay”. Because technical specifications of ODPSN play very urgent role on the performance of phased array antenna beamforming, it is very necessary to research the ODPSN with wideband,high-precision and multi-beam to attain a high- performance OCPAA.By introducing magneto-optic switch(MOS), single-mode fiber(SMF), splitter wavelength division multiplexer(WDM) and other optical devices, this dissertation carries out a detailed analysis of various kinds of topologies in ODPSN for engineering applications of OCPAA and proposes an ODPSN to satisfy the demands on bandwidth,precision and multi-beam to realize the implementation design and technical parameters.Theoretical analysis is derived on this dissertation to describe relationship between the delay error, amplitude error and space beam parameters including phased array antenna beamforming theory and statistic theory. Also, the numerical relationship between the noise figure of RF-optical transceiver, output signal noise ratio, key parameters of optical link, and space beam parameters are discussed from optical link phase noise theory. According to the numerical simulation and theoretical analysis, it shows that: delay error of ODPSN plays a dominant role in deterioration of space beam parameters, amplitude error only has an obvious affect on side lobe level; in optical link, the standard deviation of phased array antenna beam pointing error is proportional to the square root of optical links noise figure and inverse proportional to the cubic square root of number of array elements; meanwhile, figure of Relative Intensity Noise(RIN) of laser, fiber links insertion loss and laser average power is the main cause of space beam deterioration. With the increase of the above three parameters, it reduces the main lobe gain and increase the side lobe level, and the impact of RIN on lobe levels is more obvious. When the RIN of laser less than-140dB/Hz, fiber linksinsertion loss less than 10 dB, the system performance can be improved.Adopting detection of the envelope vertex of coherent optical power, Null detection all-fiber length measuring system based on M-Z fiber optic interferometer is designed for high-precision measurement of ODPSN delay. The measurement accuracy of this system is on the level of sub-picosecond. Moreover, a highly precise fiber cleaver has been developed to achieve an accuracy of 10μm. On the basis of above self-developed measuring system and fiber cleaver, high-precision WDM fiber delay line and 5bit MOS fiber delay line has been developed in which standard deviation of delay error is less than 0.14 ps and 0.62 ps,standard deviation of amplitude error is less than 0.13 dB and 0.32 dB.ODPSN with wideband,high-precision and multi-beam is developed for phased array receiving antenna(2~6GHz) with 16 elements. The network includes 256 delay lines which forms 15 fixed beams and 1 configurable beam in the space, and the main technical specifications are: passive network’s standard deviation of delay error of fixed beams and configurable beam is less than 0.16 ps and 0.63 ps, standard deviation of amplitude error is less than 0.18 dB and 0.34dB; RF-optical transceiver’s standard deviation of amplitude error is less than 0.65 dB, standard deviation of phase error is less than 1.96°. All of these parameters realize a high-precision phase delay and amplitude profile to meet the application requirements of a phased array antenna system.