Radar Cross Section Reduction of an Arbitrary Object Using Active Antenna Elements

Various methods exist for reducing the radar cross section (RCS) of an object. Using radar absorbent materials (RAM) or selective sculpting can reduce an object's RCS. Another method is active cancellation, where a source is put on the object to emit a countersignal that interferes with and therefore partially cancels the object-scattered signal (e.g., a radar signal). The study presented in this paper shows that a microstrip antenna put on the surface of an object can minimize its radar cross section (RCS). To make an object invisible to a monostatic radar operating in a specified frequency range, the radiation of the defending antenna can be changed in real-time to cancel the scattering from the object. In the proposed scheme an analog sensor on the object measures the time-domain field, which is then linked to the antenna through an amplifier and phase shifter to regulate the radiation from the patch antenna. As a result, no digitizing or signal processing is required. Thus, a wide range of incident signals within the bandwidth of the system can be mitigated in real time. Using two sensors and two feed ports on the patch antenna, this method is expanded to achieve RCS reduction for an arbitrary polarization of the incident signal. An amplifier and phase shifter links each sensor to an orthogonal feed port on the patch. With correct calibration of the amplifiers and phase shifters, the monostatic RCS may be eliminated for both potential polarizations of the incoming signal (and consequently for any polarization). The RCS reduction technique discussed here works well for time-varying incident signals like chirped radar signals. A Figure of Merit (FoM) compares the energy in the scattered signal with and without the RCS reduction technique. The energy in the scattered signal can be reduced greatly if the bandwidth of the patch antenna is larger than the bandwidth of the incoming signal and the time delay of the system (from amplification and phase shifting) is not too large.