Active Radar Absorbers Research Articles

Signature management of radar returns from wind turbine generators

The large radar cross section of wind turbine generator (WTG) blades combined with hightip speeds can produce significant Doppler returns when illuminated by a radar. Normally,an air traffic control radar system will filter out large returns from stationary targets, butthe Doppler shifts introduced by the WTG blades are interpreted as moving aircraftthat can confuse radar operators and compromise safety. A possible solution tothis problem is to incorporate an active layer into the structure of the WTGblades that can be used to dynamically modulate the radar cross section (RCS) ofthe blade return. The active blade can operate in one of two modes: first theblade RCS can be modulated to provide a Doppler return that is outside thedetectable range of the radar receiver system so that it is rejected; a second mode ofoperation is to introduce specific coding onto the Doppler returns so that theymay be uniquely identified and rejected. The active layer used in the systemconsists of a frequency selective surface controlled by semiconductor diodes and is adevelopment of techniques developed for active radar absorbers. Results of theoreticaland experimental work using a 10 GHz Doppler radar and scale-model WTG arepresented.

Measured performance of active radar absorber with either DC or modulated current control

An active radar absorber based on a pin diode controlled impedance surface is described. Measured data are presented to show that the absorber can be operated in two distinct modes: first, it can be controlled by varying the DC bias applied to the pin diodes; second, the absorber can be modulated by a time varying signal to operate as a phased-switched screen absorber.

Reflectivity null tuning in multi-layer phase-switched active radar absorbers

An ‘array’ polynomial approach is used to predict the positions of the reflectivity nulls for an ideal phase-switched screen (PSS) having many active layers. Several layer-switching schemes are examined and it is found that the resulting null position diagrams exhibit bifurcation behaviour similar to that found in many dynamical systems. The chaotic state is never achieved, however, since the ideal PSS is a linear system.

A smart radar absorber based on the phase-switched screen

Although conventional (i.e., passive) radar absorbers are widely used for modifying the radar cross-section (RCS) of current military platforms, such absorbers may not have adequate performance to satisfy future requirements. Active absorbers, however, offer the potential to overcome the so-called Rozanov performance limit and to enable additional smart functionality such as monitoring damage, adaptive control of RCS or target appearance, identification-friend-or-foe, and absorb-while-scan. This paper outlines the concept and basic properties of a novel type of active radar absorber, the so-called phase-switched screen (PSS). The basic PSS topology is then modified so as to enable it to operate as a smart radar absorber when used together with an external sensor and feedback control loop. System implementation issues and the optimum choice of design parameters for a range of operational scenarios are discussed, and theoretical predictions are supported by measured performance data.