Study On Beamforming In Multi-Target Digital Phased Array Antenna And Array Calibration Technology

With the development of aerospace technology and the demand of national defense construction, multi-target digital phased array antenna technology has been developed gradually. Its application has been extended to the airborne satellite communication, data link communications and other fields.In the multiple beams antenna, the whole frequency band is much larger than that in the single traditional array antenna, because there are multiple sub-band signals. Generally,the traditional frequency down-conversion technology can only deal with a single beam instead of the broadband signal that contains multiple targets. So it is required to take new methodology to realize the channeling.The channel mismatch is a serious issue in the phased array antenna, which means the amplitude and phase responses between different channels do not keep consistent perfectly. This mismatch could results in unacceptable performance degradation. Obviously, it is demanded to calibrate these error of array channels before implementing the beamforming.Considering these problems mentioned above, this thesis studies the solutions from a few facets as follows:(1) According to the planar array, the basic principle of phased array is introduced firstly. Then the pattern and array gain of phased array is derived.(2) The broadband digital frequency down-conversion technology is investigated. We concentrate primarily on two structures that are mixer postpositional structure and least common multiple structure. At the same time, all these actions are used on the condition of real signal, such as orthogonal transform and digital down conversion. So that the complexity of the system and required FPGA resource are both reduced.(3) One multiple targets digital phased array antenna design is finished. In the design, some advanced signal processing methods are employed, for instance, polyphase filter, mixer postpositional structure and so on. In details, the phased array consists of 8×8 elements. And three times decimation is applied in polyphase structure for the low pass filter, which is followed by mixer to transfer the intermediate frequency into zero intermediate frequency. Then we generate three weight vectors to play the role of beamforming for baseband signal. At last, the array generates three isolated beams and outputs three signals with higher signal to noise ratio. On the other hand, the program design with VHDL in Xilinx Vivado is also completed. The simulation proves that our algorithm and program are accurate.(4) For the channel mismatch calibration, we firstly introduce the traditional equalization method based on least square filtering in frequency domain, where the complex coefficients are utilized. The proposed strategy only considers about the mismatch in the frequency band where the interested signal exists, so that a more ideal filter with real coefficients could be derived. However, a pre-bandpass filter is required to avoid the noise outside the frequency band to be amplified due to the calibration filter. Some simulations are taken to prove the feasibility of the proposed methodology.