Research On Microstrip Reflectarray Antennas

By combining some of the advantages of reflector and of microstrip array antennas, such as low cost, light weight, easy integrated with active control circuit, microstrip reflectarrays have received more and more attention. However, the traditional microstrip reflectarray unit has a narrow phase shift bandwidth that is the main factor hindering their development and practical applications.By using basic theories of microstrip reflectarray antennas, the thesis proposes two ways, the dual-resonant method and the non-resonant one, to increase the phase shift bandwidth of the array elements. Both the center-fed and offset-fed reflectarrays of these two methods are designed in the form of fixed beam direction. Dual-resonant method is based on the single layer double ring structure. The 1dB gain bandwidth increases to 36%. The non-resonant method is based on the rectangular patch that the unit spacing is much smaller than the resonant wavelength. This method shows 16% bandwidth. Simulation results show that both of the design methods are effective in increasing the bandwidth of microstrip reflectarrays when compared with the traditional microstrip reflectarrays.Finally, the varactor-diode-loaded "mushroom" structrual artificial impedence surface is researched to construct an electronically controlled phase shift element. Then one-dimensional beam scanning reflector is constructed. By using different bias voltage the reflector can control the beam direction. In order to improve the beam pointing accuracy, an improved electronic control phase shift element is designed. The above study paves the way for the design of high accuracy and efficiency electronically controlled beam scanning microstrip reflectarrays.