FDTD modelling of active radar absorbers

An active absorber, such as the phase-switched screen (PSS), achieves an apparent reduction in the level of the electromagnetic energy reflected from its surface by using binary phase modulation to redistribute it over a bandwidth which is much wider than that of the receiver [Chambers B. and Tennant A., 2004]. Previous analyses of the PSS have been based on either transmission-line theory [Chambers B. and Tennant A., 2004] or the Fourier series [Chambers B. and Tennant A., 2006]. The former enables the PSS reflectivity bandwidth to be estimated, whereas the latter reveals the frequency spectra of signals reflected from the PSS when different switching strategies are employed. Both these previous analyses assumed ideal switching behaviour (i.e. active layer either perfectly transparent or perfectly reflecting) and ideal binary switching waveforms (i.e. zero rise and fall times). Practical PSSs, however, use active layers consisting of arrays of PIN diode loaded resonant elements [Chambers B. and Tennant A., 2004]. Hence a more general analysis of the PSS based on Finite Difference Time Domain (FDTD) techniques is currently being investigated and initial progress is described below.