Optimum switching of a phase-switched active radar absorber

In conventional radar absorbent materials, the incident electromagnetic energy is absorbed and converted into heat. Several recent papers (Tennant A., 1997; Chambers, B. and Tennant, A., 2002), however, have considered an alternative technique for achieving an apparent reduction in the level of the electromagnetic energy reflected from a surface, using the so-called "phase-switched screen" (PSS). At resonance, the ideal single layer PSS presents a periodic reflection coefficient, ρ(t) = ±1, to an electromagnetic wave incident on its surface in such a way that the time-averaged value of ρ(t) is zero. This is achieved by applying binary phase modulation to the reflected wave with the result that the energy is redistributed into sidebands with, ideally, none remaining at the original carrier frequency f_c. Hence, by adjusting the frequency of the waveform that controls the surface reflection coefficient, these sidebands may be positioned so that they lie outside the pass-band of a receiver tuned to f_c. However, the amplitude of some of the sideband components is still high enough that they could aid detection of a PSS-coated target; hence, the paper aims to formulate the optimum switching strategies for the PSS so as to prevent this.