Reflectarray Antennas

Reflectarray Antennas

Prof. Dr.-Ing. Rolf Jakoby

Dipl.-Ing. Carsten Fritzsch

M.Sc. Saygin Bildik

Reflectarrays are, as the name already suggests a class of antennas combining features of reflectors and phased arrays. They consist of an array of elementary antennas illuminated by a feed. The elementary antennas reradiate the electromagnetic energy, while adjusting the phase so that the main beam points to a desired direction. Due to their low profile and low weight, microstrip elements have established themselves as array elements in reflectarrays.

Among the advantages that arise from the combination of two antenna classes are:

  • the planar(conformal) shape of the reflector – in contrast with the bulky metallic reflectors, where the phase is adjusted by the reflector shape
  • the absence of a feeding network – in contrast with phased arrays – which significantly reduces losses and improves the overall efficiency
  • the weight, low cost and ease of fabrication associated with microstrip technology
  • the possibility of integrating phase shifters with each microstrip element, thus achieving electronic beam scanning (reconfiguration)

Research

Our group’s research interest lies in the integration of a thin liquid crystal film in the reflectarray substrate to act as a phase shifter for the reflectarray elements. The function is based on the dielectric anisotropy of the liquid crystal.

With a suitably chosen DC voltage the relative permittivity of liquid crystal can be tuned in a certain range, allowing a phase adjustment across the reflector aperture. This phase adjustment further enables electronic beam reconfiguration or beam scanning.

The challenges in the design and realisation of liquid crystal reflectarrays lie in:

  • reduction of the losses, either by reducing intrinsic losses of the liquid crystal, or by specially designed elements
  • the absence of a feeding network – in contrast with phased arrays – which significantly reduces losses and improves the overall efficiency
  • improvement of switching times of the unit cells
  • measurement of characteristics (phase/magnitude of the reflection coefficient) of each unit cell on the reflectarray, in order to allow for efficient beam reconfiguration/ calibration algorithms

Veröffentlichung / Recent Publication

Mössinger, A.; Marin, R.; Müller, S.; Freese, J.; Manabe, A. & Jakoby, R. : „Electronically reconfigurable reflectarrays with nematic liquid crystals“ , IEE Electronics Letters , European Conference on Antennas & Propagation , 2006 , vol. 42 , pp. 899-900
Mössinger, A.; Marin, R.; Freese, J.; Müller, S.; Manabe, A. & Jakoby, R. : „Investigations on 77 GHz Tunable Reflectarray Unit Cells with Liquid Crystal“ , European Conference on Antennas and Propagation , 2006
Mössinger, A.; Marin, R.; Eicher, D.; Jakoby, R. & Schlaak, H. : „Liquid Crystal Reflectarray with Electronic 2D-Reconfiguration Capability“ , 29th ESA Antenna Workshop on Multiple Beams and Reconfigurable Antennas , 2007 , April
Marin, R.; Mössinger, A.; Gölden, F.; Müller, S. & Jakoby, R. : „77 GHz Reconfigurable Reflectarray with Nematic Liquid Crystal“ , 2nd European Conference on Antennas and Propagation , 2007
Marin, R.; Mössinger, A.; Freese, J.; Müller, S. & Jakoby, R. : „Basic Investigations of 35GHz Reflectarrays and Tunable Unit-Cells for Beamsteering Applications“ , Proc. 35th European Microwave Conf. , 2005 , October , pp. 2015-2018
Marin, R.; Mössinger, A.; Freese, J.; Manabe, A. & Jakoby, R. : „Realization of 35 GHz Steerable Reflectarray Using Highly Anisotropic Liquid Crystal.pdf“ , Eingereicht in European Conference on Antennas and Propagation , 2006 , November , pp. 1-4