Research On Pattern Reconfigurable Antenna And Array

The main beam scaning range of the traditional phased arrays is relatively narrow due to the existing of the mutual coupling between elements and limited distribution range of the energy of the isolated antenna element, which highly dissatisfies the development of modern science and technology. Pattern reconfigurable antenna is favored by many domestic and foreign researchers for its adjustable radiation beam characteristics and becomes one of the most effective methods to widen the main beam scanning range of the phased arrays. The pattern reconfigurable antenna and array are investigated in this thesis. The content of this thesis includes six chapters as follows.Chapter I introduces the background, the significance, the history and the current status of the pattern reconfigurable antenna and array at home and abroad. The main task of this thesis is also briefly summarized.Chapter II briefly introduces some basic concepts and theories related to the pattern reconfigurable antenna and array, including microwave switches, microstrip antennas, Yagi antennas and antenna arrays. How to use the active element pattern method to synthesize the pattern of a linear phased array is also introduced.Chapter III proposes a kind of pattern reconfigurable microstrip Yagi antenna loaded with varactor diodes. Each of the two lateral parasitic dipoles is loaded with two varactors and acts as either a reflector or a director by tuning the capacitances of corresponding varactors, thus the microstrip Yagi antenna can achieve reconfigurable radiation pattern. Through analyzing the reactance characteristics of an isolated loaded-dipole element, the range of the capacitances of the varactors which makes each of the two lateral parasitic strips act either a reflector or a director is obtained. The relationship between the pattern in H plane of the microstip Yagi antenna and the loaded capacitances of varactors are extensively discussed by large numbers of simulation.In Chapter IV, an improved phased array using pattern reconfigurable antenna elements proposed in chapter III is developed to realize wide-angle scanning performance. The effects of several key parameter variations, including the spacing between adjacent elements and the capacitances of the loaded varactors, on the reflection coefficient and the active element pattern of each array element are provided. A five-element linear phased array is fabricated and experimentally verified. It is seen from the measured results that the main beam of the array can scan from-70° to 70° in the H-plane with a gain fluctuation less than 2 dB, which validates our design exhibiting a good performance of wide-angle scanning compared to the traditional phased array.In Chapter V, a prilimilary study on the pattern reconfigurable slot array is performed. The main beam scanning range of the proposed slot array is from-60° to +60°, which exibits wide angle scanning performance with vertical polarization in the horizontal plane. Compared with the phased array with horizontal polarization, the studied pattern reconfigurable slot array suffers smaller attenuation loss when propagating along the ground plane of the earth.Chapter VI concludes all the work in this thesis and proposes the possible improvement approaches.