| It's an important development tendency for phased array radar to operate in wideband and wide-angle condition. However, for the phase shifters based phase array radar, it is hard to achieve desired beam forming and steering due to the transition time and aperture effect.In order to realize wideband beam steering and beam forming, two effective methods for wideband beam steering and beam forming can be used to replace the phase shifter in traditional phased array radar. They are true time digital delay in baseband and optical true time delay (OTTD) in RF band.In optically controlled phased array radar (OCPAR), optical real delay and optical fiber transmission technology are introduced, where the aperture transition time and aperture effects are reduced at sub-array level via OTTD, thus realize the broadband and wide-angle scanning of phased array antennas. Meanwhile, the optical fiber transmission link is flexible, light, with small size and has super anti-electromagnetism interference capability. The wideband and weak attenuation of optical fiber are suitable for long time transmission of radar signals.Digital array radar (DAR), where the digital technique is used both in transmitting and receiving, is a fully digitized array antenna radar. It can realize beam forming and beam direction control via the use of amplitude-phase weighting and digital delay in baseband. Therefore, it's easy to fulfill low sidelobes, multi-beam and multi-target processing, adaptive anti-jamming, wideband and wide-angle scanning for DAR. When the wideband signal waveforms are used in DAR, it is called as Wideband digital array radar (WDAR).The beam steering technique of OCPAR and WDAR are deeply researched in this dissertation, including the structure of OCPAR, the design and realization of OTTD, digital T/R moudle, digital delay algorithm and channel digital equalization algorithm. The main work and results are as follows:1. The L band OCPAR technique is studied. A design scheme of L band OCPAR is given, and the mathematic model is built to analyze the improvement of aperture effect. An OTTD which is based on magneto-optic switches is designed and manufactured firstly, and the far-field test results verify the improvement of wideband and wide-angle performance for the first time in China.2. The millimeter wave OCPAR technique is studied. The methods of achieving millimeter wave OCPAR based on one tunable laser and Photonic Crystal Fiber are optimized. Furthermore, the millimeter wave OCPAR method based on intermediate frequency (IF) delay and shifter is proposed. The simulation results demonstrate the improvement of wideband and wide-angle performance.3. The serially fed OCPAR technique is studied. The method of achieving serially fed OCPAR is optimized, the mathematic model of serially fed OCPAR based on one tunable laser and one Bragg fiber-optic grating is built. The simulation results verify that it's easy to realize wideband and wide-angle scanning with serially fed OCPAR.4. The channel equalization theory and effective realize methods are studied. The frequency domain equalization algorithm is investigated to compensate channel mismatch. The effects of several important parameters to digital equalizer are discussed and analyzed with simulations. A simple structure which combines channel equalization and digital down conversion (DDC) in FPGA is proposed. It is proved to be valid, feasible and highly efficient with tests.5. The T/R module and waveform generation in WDAR are studied. The DDWS technology is used to generate wideband digital waveforms. And the effect of clock jitter error in digital-to-analog converter is analyzed. The filter based on Farrow structure is designed to achieve fractional delay. From the results on a test board, it can be seen that the fractional delay is accurate and the delay structure is efficient and simple. A digital T/R module in S band is designed and manufactured.The work in this dissertation covers the concerned theories and key technologies of wideband phased array radar beam steering in OCPAR and WDAR. The research results provide theoretical evidence and practical experience for the development of phased array radar in the future. |
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