Smart phase switched screen

In general, both passive and active radar absorbers operate in one of two ways. They either rely on destructive interference effects, or else the incident energy is absorbed and converted into heat. During the last few years, however, a new type of active "absorber" has been proposed. In the phase switched screen (PSS), incident energy is not absorbed but is shifted in frequency using phase modulation so that any reflected energy falls outside the receiver bandwidth and is thus not detected. This may be achieved, for example, in a Salisbury screen configuration by replacing the normal resistive sheet by a layer whose conductance can be changed periodically with time in accordance with some externally applied electrical or optical stimulus. The PSS has a time-averaged reflection coefficient of zero and appears to act as a perfect absorber at a particular frequency. In order to exploit fully the properties of an active radar absorber, it would be advantageous to make it "smart". A smart absorber is defined as one which combines the attributes of incident field sensing, feedback and electromagnetic reconfiguration. We present a recently evolved smart PSS structure which is electromagnetically compact and which may be controlled digitally.