Electromagnetic analysis of active radar absorbers

The details of an experimental active radar absorber have been presented. The absorber is based on the topology of a Salisbury screen but uses an active impedance layer to provide reflectivity tuning. The active impedance layer is a FSS controlled by semiconductor pin diodes. Measured reflectivity characteristics have been presented and compared to predictions obtained from a simple equivalent circuit transmission line model. The structure has also been analysed using the Ansoft HFSS electromagnetic simulator software in which the diode has been modelled by a small planar slab of material with variable surface impedance. This model provides superior result to the transmission line model in predicting the resonance frequencies of the FSS.