Super-Directional Arrays Study

Since HF over-the horizontal radar works at short wave band, in order to maintain the performance of its antenna array, the size of receiving antenna array is always very large. With the development of radar technique, the inherent weak point of conventional antenna array has become a bottleneck limiting the performance of entire system. Over large size not only makes the radar easier to be detected, but also increases engineering costs. Meanwhile, large size also brings serious troubles in the antenna setting-field choosing, installation and maintenance. Besides in order to equip the antenna array onto the board of military naval vessel, the minimization of antenna array is a key technique, and thereby it becomes increasingly urgent for the research work on minimized array on in HF radar.Superdirectivity array can reach much higher array directivity, its pattern synthesis method is the key point of this research. The external noise is much greater than internal ones in HF band, making it possible to employ superdirective antennas in HF band. Assuming the value of REIN ensures the dominance of external noise and the other parameters in radar system are constant, the system SNR will just be proportional to the array directivity, which provides the principles in HF compact array design. Since the existing pattern synthesis method can't give attention to both directivity and REIN, as well as the sidelobe problem, it is not suitable for superdirective arrays synthesis.A new pattern synthesis method which can be applied to superdirective arrays is presented in this dissertation. In this method the dominance of external noise is ensured by constraining the array REIN, and the desired sidelobe level is achieved by implementing linear constraints through iteration. By optimizing the array directivity subject to array REIN and sidelobe constraints, the highest possible directivity with controlled REIN and desired sidelobe level is achieved. the method proposed in this thesis completely satisfies the requirement of superdirective arrays synthesis.Basing on the above mentioned superdirective array synthesis approaches, a 3-element superdirective endfire array and5-element superdirective circular array is designed. By considering the requirement of external noise dominance at 3~15MHz, we obtain a directivity of morethan 15dB at entire working band. On the condition of the same directivity, two array size both are greatly less than the array size designed by general approaches.