Comparison of full scale (RAT-SCAT) and ultrasonically simulated F-102 radiation patterns

The radiation pattern at 1775 megahertz of a F-102 airplane with four cavity backed slot antennas at given locations measured by U.S.A.F. RAT-SCAT, New Mexico, is compared with its ultrasonically simulated radiation pattern taken at the Radar Simulation facility of the Wave Propagation Laboratory, University of Houston, using a 22.6 to 1.0 scaled down model, at 0.2 megahertz utilizing spherical transducers to simulate isotropic antennas. The exact simulation of horizontally polarized electromagnetic waves in air by longitudinal ultrasonic waves in water was further supplemented by a reasonable match of the Fresnel reflection coefficient by the aircraft fuselage material in both cases. The comparison shows that overall radiation patterns are indeed well simulated, as to their general variation around their isotropic level, including the location of major maxima and minima. Furthermore, there are no nulls deeper than 10 db and wider than at their +3 db points in both patterns. This comparison verifies the utility of ultrasonic simulation of electromagnetic radiation of antennas mounted on complex aerodynamic bodies. It is believed to be the first time that antenna radiation has been successfully ultrasonically simulated for a flat ground plane as well as a large aerodynamic Ground plane such as the F 102.