Anisotropic Microwave/Terahertz Metamaterials for Satellite Applications (ANISAT)

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There is growing interest in the UK space sector for communications, imaging and earth observation. Key to this is sending and receiving electromagnetic waves. To enable higher communication rates and get greater accuracy in imaging often higher frequencies are used. This project will develop new structures using microfabrication techniques to develop novel antennas and polarizers for satellites and the earth segment over frequencies from 28 GHz up to 1 THz. This frequency range overlaps and extends the currently used frequencies.ANISAT will address these five technical challenges:1) Designing anisotropic metamaterials;2) Exploiting these properties to design novel antennas, polarizers and RF devices;3) Developing novel methods of measuring these properties;4) Microfabricating heterogeneous anisotropic structures;5) Combining these elements into a series of demonstrators.The above five points are addressed in more detail below:i) When an electromagnetic wave moves through a material it is slowed down by the dielectric properties. If an artificial dielectric can be composed of small (compared to a wavelength) rectangular or elliptical inclusions, then this composite material will behave differently when the incident electromagnetic wave has different polarizations. This can be exploited to create circularly polarized antennas where the electric field traces a circle in time. This is an advantageous property for space communications. ii) Currently, dielectric measurements only consider the dielectric properties for one polarization and effectively assume the materials are isotropic. ANISAT will develop a novel measurement system using resonant metasurfaces that can measure the properties along all three axes. This will open a new degree of freedom for antenna and radiofrequency engineers. iii) These anisotropic artificial dielectrics will be used to design novel circularly polarized antennas. It is currently challenging to feed antennas to create circular polarization at frequencies above 50 GHz due to the small scale of the feed structure. High gain multi beam cavity antennas and polarizers will be designed at a range of frequencies up to 1 THz. iv) Initial anisotropic artificial dielectrics will be fabricated using 3D-printing. This provides a simple and readily exploitable fabrication process. However, the upper frequency range is limited to approximately 40 GHz by the size of the small-scale air/metal inclusions inside the composite. Above this frequency the inclusions approach the scale of a wavelength and they become resonant. To extend the frequency range, novel microfabrication processes in clean rooms will be developed and exploited. These include fully metallised SU8 photoresist polymers and/or silicon layers with a high dimensional accuracy of the scale of a few microns. v) The learning process will be multidisciplinary and iterative as each stage innovates further advances. The close geographical proximity of the two universities will be highly beneficial in this regard. The plan is to create laboratory demonstrators that can be showcased to industry. These provisionally include: a novel dielectric measurement system; a high gain circularly polarized antenna at Ka band (26 - 40 GHz); a circularly polarized Fabry-Perot antennas at frequencies up to 110 GHz; and linear to circular polarizers and beam splitters from 220 - 300 GHz and at a central frequency of 640 GHz.