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A reconfigurable aperture-coupled reflectarray element offering a continuous tuning of the reflection phase is presented. A single varactor load is demonstrated to be sufficient for a full tuning range. Experimental validations are reported for the measured reflection phase of an X-band reflectarray element.Introduction: Reflectarray antennas are very appealing for applications requiring beam scanning capabilities or pattern reconfigurability. They offer many advantages over conventional phased arrays such as reduced cost and volume, a simpler architecture owing to the absence of complicated beamforming networks, and increased efficiencies thanks to the use of spatial feeding. Many efforts have been spent in the design of reconfigurable reflectarray elements, resulting in different solutions such as mechanically tunable radiators [1] or microstrip elements with an integrated electronic control, such as MEMs-based structures [2] or varactor loaded patches [3 -5]. Very interesting results have been obtained in the case of varactor tuned reflectarray elements, which are able to offer a continuous phase tuning over a range of about 3608. However, all existing solutions present some drawbacks related to the undesired discontinuity reflections on the reflectarray surface [3,4] and the necessity to employ at least two varactors for each radiating element [4,5].In this Letter, a reconfigurable aperture-coupled reflectarray element is considered, which uses a transmission line loaded with a single varactor diode. This configuration offers a uniform reflecting surface, as the tuning element and the biasing circuitry are located below the ground plane. In this Letter, a phase tuning range of about 3208 is demonstrated by properly sizing the varactor loaded line, so exhibiting a mixed inductive/capacitive behaviour when the diode bias voltage is changed. Although a similar structure has been proposed in [6], a limited phase range of only 1208 has been demonstrated. The experimental validation performed on an X-band prototype shows a variation range close enough to that obtained from simulations.

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