The MM-Wave Group have developed a range of free-space ferrite devices for use at frequencies from 10-20GHz up to 300GHz. These consist of a thin layer of a self-magnitised ferrite material, sandwiched between two dielectric layers which act as anti-reflection coatings.
Our W-band (80-110 GHz) devices look a bit like a “bathroom tile” but they can provide a level of performance superior to conventional waveguide isolators and circulators. (Click the small picture if you want a better view.)
Typical mm-wave free-space isolators offer wideband loss values of around 0.5dB and isolations of 30dB across most of W-band. Spot performance can reach 0.25dB loss and over 50dB isolation. The free-space form of the isolators/circulators means that they can also pass much higher power levels than conventional waveguide devices.
As the devices are self-magnetised they do not require external bias coils or magnets. The basic device acts as a 45 degree Faraday rotator, but we also know how to produce devices which contain integral polarisation-dependent signal dumps. This makes it possible to make a sheet device which acts as a “one way” window - it only passes radiation through in one direction with one polarisation. All other waves are either absorbed or reflected.
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University of St. Andrews, St Andrews, Fife KY16 9SS, Scotland.