Electronically Reconfigurable Reflectarray Antennas Using 2-bit Phase Shift Unit Cells Embedded With Reflecting Circuits

We present an electronically reconfigurable reflectarray capable of performing 2-D beam-scanning. This reflectarray uses an electronically reconfigurable unit cell, consisting of an antenna and a reflecting circuit that provides a 2-bit reflection phase shift. A general method for designing this unit cell is presented that can be adapted for use with different antenna types and reflecting circuit designs according to the user’s requirements. The unit cell used to verify this approach consists of an E-shaped patch located above a ground plane and a reflecting circuit located underneath it. The reflecting circuit uses three p-i-n diodes to provide four phase shift states. Each unit cell uses three dc bias lines to switch the p-i-n diodes on and off. The p-i-n diodes are the only lumped element components used in each unit cell, which reduces the design and assembly complexity when constructing large-scale reflectarrays. Simulation results demonstrate that the unit cells can achieve less than 2.2-dB loss and a phase error under 35° in the frequency range of 5.6–6.2 GHz. This unit cell was used to design a 208-element reconfigurable reflectarray prototype with a circular aperture diameter of 40 cm (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\lambda $ </tex-math></inline-formula> at 6.0 GHz). The reflectarray prototype along with its digital control circuit was designed, fabricated, integrated, and experimentally characterized. The system is capable of controlling the state of each individual p-i-n diode to perform electronic beam steering. Measurements of the reconfigurable reflectarray reveal its capability to perform 2-D beam scanning within a scan range of up to ±60° across the operational bandwidth of 5.6 to 6.2 GHz. The aperture efficiency was measured to be 34.2%.