Research On Reconfigurable Planar Reflectarray Antennas

Planar microstrip reflectarray antennas, combining the main advantages of both parabolic reflectors and conventional phased arrays, are rapidly becoming an attractive alternative in satellite communication. The reflectarrays present many features, such as low profile, low cost, easy to be intergrated, high gain and implementing accurate beam direction, and the direction is always fixed when the reflectarray is fabricated. However, by adding some electronically tunable elements to reflectarrays, reconfigurable reflectarray antennas are able to form dynamically-controllable radiation patterns for beam- forming applications without changing the structure of reflectarrays. Thus reconfigurable reflectarray antennas have widespread applications in radars and long distance communication systems.The thesis begins with some research backgrounds of microstrip reflectarrays, focusing on backgrounds and current researches of reconfigurable reflectarrays, followed by detailed introductions of theory and method of reflectarrays design. All the study lays a foundation for the following work.A frequency agility reflectarray element, which is based on two split-rings, is proposed in the thesis. By controlling the states of the PIN diodes on the spit-rings, the reflectarray element can achieve frequency agility between 4.6GHz and 5.8 GHz. Moreover, through tuning the capacitances on the 225 elements arranged in a 15?15 layout, the reflectarray can scan the beams in two dimensions, and the scanning angle can reach to 60°. Then, based on the former design, we proposed a dual-band and dual-polarized reflectarray element, the frequency is different in the orthogonal polarization direction, which are 4.2GHz and 6.5GHz. Besides, the reflectarrays, containing 225 elements, can also scan the beams in two dimensions with the range from-60°to 60°.Finally, one scan angle of the second design is fabricated and measured, and the measured results almost agree with the simulations, which verify the availability of the designs.Furthermore, a 1-bit digital reconfigurable reflectarray antenna loaded with varactor diodes is proposed. The principle is that the phases compensated by the elements are quantized into two phase, which differ 180 degrees from each other. The technique not only decreases the requirement of the element to phase range, which simplifies the design of the reflective element, but also expands the bandwidth of reflectarray. A 20 ?20 reflectarray with working frequency of 3.5GHz is designed, by controlling the varactor diodes, the 20?20 reflectarray can also scan the beams in two dimensions and the array can scan from-60°to 60°.What's more, the fabricated model with fixed capacitors on is measured, and the results almost agree with the simulations, which verify the availability of the designs.As the aforementioned two designs replace the varactor diodes with fixed capacitors, the third one is the reconfigurable reflectarray designing with DC bias circuit. The influences of the DC bias circuit on reflectarray are studied. And the 9 ?7 reconfigurable reflectarray with the bias lines also scan the beams in two dimensions.The reconfigurable reflectarra y antennas proposed in this thesis can control the direction of the main beam through tuning the bias voltage on the varactor diodes, without var ying the structure of the reflectarrays. It makes the reconfigurable reflectarray potentially applicable in radars, long distance communication and other wireless communication systems.