Unit Cell for Frequency-Tunable Beamscanning Reflectarrays
A reflectarray cell able to dynamically control the reflection phase at a variable frequency is presented. This capability enables beam-scanning reflectarrays with frequency reconfigurability, which is a novel capability with applications in frequency-hopping systems, cognitive radio and satellite communications. The proposed cell combines switching and variable impedance loading techniques to maximize the frequency range over which a large dynamic phase range can be obtained. Analytical and numerical approaches are used to design and optimize the reflecting cell, which uses two semiconductor RF-switches and one varactor. An analog phase range above 270 degrees is achieved over a 50% frequency range, from 1.88 GHz to 3.07 GHz, with flat losses of 0.8 dB. For an analog phase range of 180 degrees the cell achieves a 1: 2 frequency reconfiguration range. It is also verified that the cell preserves good performance, and in particular low crosspolarization, under oblique incidence as well. A fully operational cell was fabricated and measured, demonstrating good agreement with simulation results.