Ultrasonic simulation of antenna radiation



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Fullscale experimental work on location as well as determination of the type of antenna on aircrafts to obtain "essentially isotropic" coverage (within [plus-minus]10 db for 93% points) is expensive. Therefore, an ultrasonic simulation of antenna radiation pattern in a laboratory controlled environment becomes very desirable. This topic of radiation coverage of antennas on airframes is covered in this thesis. The University of Houston Wave Propagation Laboratory has extensively used ultrasonic radiation sources to study the propagation, scattering and diffraction of horizontally polarized electromagnetic radiation. In this work, the antenna radiation is ultrasonically simulated for the case of antennas mounted on a flat ground plane as well as on airframes and ultrasonic simulation results are shown to very well match the fullscale antenna radiation patterns. The aircraft F 102 and drone 34A were modeled using special composition material (0.80 A1 F[subscript 3]) so that the Fresnel reflection coefficient for a plane surface for horizontally polarized electromagnetic waves was quite similar to that for longitudinal ultrasonic waves for normal to grazing incidence. A 12.7 mm spherical transducer, composed of two hemispheres epoxied together, was used to simulate a cavity-backed slot antenna which has essentially hemispherical pattern. In order to obtain "essentially isotropic" radiation, the transducer was provided with vertical and horizontal skirt and ground plane cylindrical base wrap of synthetic adhesive called Miracle Seal. The transducers with essentially same isotropic levels are mounted on the 22.6 to 1 scaled down models of F 102 aircraft and 34A drone at the antenna locations on them. The fullscale experiments on the aircrafts were conducted at RAT-SCAT facility. White Sands Missile Range, Nevz Mexico, while the ultrasonic simulation experiments were performed at the Wave Propagation Laboratory of the University of Houston for different antenna excitations and roll angles from 0° to 180° at 0° pitch. The results obtained at the two facilities are compared with a view to the isotropicity of radiation pattern, spatial location of maximas and minimas as well as the percentage of points lying between [plus-minus]5 db and [plus-minus]10 db levels with reference to isotropic levels. The comparison in case of F 102 aircraft shows that the two radiation patterns are of "essentially isotropic" (within [plus-minus]10 db for 93% points) in coverage and have similar spatial location of maximas and minimas (82%). The worst deviations between two radiation patterns so far as to the percentage of points for F 102 are [plus-minus]9% at 40° roll angle for all four, [plus-minus]18% at 40° roll angle the front two and [plus-minus]13% at 0° roll angle for the rear two antennas excitations. In case of 34A drone radiation patterns, the deviations are [plus-minus]16% at 90° roll angle for left wing and [plus-minus]15% at 0° roll angle for right wing antenna excitation. This comparison of experimental fullscale and simulated results show that horizontally polarized electromagnetic antenna and their radiation patterns can be fairly well simulated by ultrasonic radiation sources with, or without either simple or complex ground planes.