Study On Single-Layer Microstrip Reflectarray Based On Multipe-Resonance Behavior

Microstrip reflectarrays combine certain advantages of reflector antennas and planar phased arrays. Since introduced in 1978, microstrip reflectarrays have attracted so much attention and developed rapidly from 1990s. However, the advantage of narrow bandwidth is inherited from microstrip antennas. The purpose of this thesis is to develop a new broadband microstrip reflectarray element, which can increase the bandwidth of the array. The method of calculating the phase shift of the elements and the designing process of the reflectarray are presented.The target of designing an element is to achieve good phase shift characteristic in broadband. But enough phasing range should be achieved to reduce the lope of the phase shift characteristic. Based on the study of the principle of single-layer multiple-resonance structures, by analyzing the surface current distribution of dipoles and rectangle loops, a fourfold-resonance structure composed with dipoles and served rectangle loop is proposed, called as"double D"structure. By using the"double D"structure, not only the number of resonance elements are increased, which increases the bandwidth of the element, but also the size of the element is controlled to be smaller than the maximum element spacing that will lead to the grating lobe.Then, the Method of Moments combined with Generalized Scattering Matrix(GSM-MoM) is studied, and the detailed process to calculate the phase shift of the element is proposed.With enough phasing range, structure of the element should be optimized. Simply, with a"double C"structure instead of"double D"structure as reflectarray element, the affects on phase shift characteristic are studied when changing the ratios of resonant frequencies of the elements and behavior of the substrate. Then, on the basis of that, the"double D"structure is optimized, and method of structure optimizing and the optimized result are presented. It is shown that good phase shift characteristics of optimized structure are obtained from 7-10GHz. The phase shift of"double D"structure is calculated by the GSM-MoM and CST microwave studio, and similar results are achieved. With the advantages of briefer structure and lower cost, the bandwidth of"double D"structure is twice that of stacked patches presented in the paper, and about 65% more than that of aperture-coupled patches. Also, compared with other single-layer multiple-resonance structures, the distinct advantage of"double D"structure is that the resonant elements are increased while the size of element is compact.As validation of the structure, a reflectarray with 12×13 elements is fabricated, computed and tested. The measured result and the computed result are consistent. About 45% aperture efficiency is achieved from 7-10GHz.