| High frequency surface-wave radar works on the short-wave band. As the working frequency is relatively low, the wavelength is long. In order to maintain the performance of radar system, the size of receiving antenna array is always very large. Superdirective arrays can be utilized to reduce the size. However the extremely small efficiencies and impractical tolerances make the superdirective array impractical. When the element spacing is small, the mutual coupling between array elements can't be ignored anymore. After mutual coupling compensation, the efficiency changes with the current. Formal studies didn't consider this aspect, so the conclusion about superdirective arrays was not precise. Investigating the change may improve the synthesis method.Firstly, the basis of superdirective arrays is presented. We analyses the Schelkunoff unit-circle method and the Chebyshev-Dolph super-directive synthesis method of the line arrays in detail. As the Schelkunoff method can not control the sidelobe and Chebyshev-Dolph super-directive synthesis method can only be applied to array with odd number elements. A simple algorithm which achieves the maximum directivity while meeting the sidelobe specification is presented. A distribution of array elements which can achieve more directivity and efficiency than the uniform distribution is given.On the base of the study on method of moments, this dissertation analyses the problem of the mutual coupling of the thin dipole antenna array and discusses the effect of mutual coupling to the pattern and the amplitude-phase consistency.Finally, a method to compensate the coupling to approach the ideal pattern is presented. The mutual coupling effect in the efficiency and gain is investigated. The range of the efficiency change is given. The relationship between the efficiency change and height of the dipole array is proposed. Computer simulation results show that the efficiency is improved in the presence of mutual coupling. |
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