Beam Steering Transmitarray Using Tunable Frequency Selective Surface With Integrated Ferroelectric Varactors

A tunable frequency selective surface (FSS) with beam steering capability is presented. The FSS is used as a transmitarray with a bandpass characteristic in Ku-band. The periodic sub-wavelength (λ
₀
/25) unit-cells are composed of capacitive and inductive structures creating a bandpass for an incident wave. By patterning the capacitive elements on a screen-printed barium-strontium-titanate (BST) thick-film ceramic, the resonant frequency of the FSS can be tuned. This technology offers a simple and cost effective way for integrating varactors into the FSS and is particularly attractive for microwave circuits with a high varactor density. A prototype is fabricated including two capacitive layers with an overall size of 40 mm × 40 mm. Each layer includes a total of 1600 integrated BST varactors that are fabricated by using a patterning and metallization process. A transmitted wave passing through the FSS will experience a phase shift, which can be tuned by tuning the passband. This allows steering the transmitted wave to a certain direction by applying a phase gradient along the FSS interface. A phase shift range of 360° can be covered by cascading several FSS panels. The prototyped tunable FSS demonstrates the feasibility of the proposed technology and its potential for beam steering.