The long string as a field probe

We show how a long string can be used to probe the incident field across the target zone of a radar cross section (RCS) test range. The string may be stretched horizontally from wall to wall, or vertically from floor to ceiling. One end of the string is fixed and the other end is moved by an actuator mounted in the wall or ceiling. The resulting motion changes the angle of the string with respect to the incident-field direction, during which time the coherent radar echo is recorded as a function of the string angle. The coherent signal-as-a-function-of-angle data are then transformed to the cross-range domain using the fast Fourier transform (FFT), whence we obtain a chart of the incident field amplitude as a function of cross-range distance. Numerical examples are presented that show how variations in the incident field influence the string echo. A sample of experimental data shows that the processed data are readily interpreted