Radar Cross Section Measurements and Simulations of a Model Airplane in the X-band

Abstract

The objective of this study was to illustrate how difierent methods of obtaining the Radar Cross Section (RCS) of an object may produce difierent results. RCS diagrams of a metallic airplane model (length, 0.64m) were obtained in an anechoic chamber, with a Lab- Volt RCS system, and simulated with a simulation software. The measurements and simulations were carried out at the radar frequency of 9.4GHz. The resulting RCS diagrams show that although there was a good correspondence between the main features in the RCS diagrams, some difierences can still be observed, highlighting the need for difierent techniques to fully represent the RCS of an object. Radar cross section (RCS) diagrams are usually di-cult to interpret due to the fact that they are two-dimensional representations of three-dimensional objects. Moreover, the di-culty in interpret- ing RCS diagrams is dependent upon the geometry of the object and, sometimes, on the techniques used to measure or calculate the RCS. Measurements are also afiected by many external factors, such as instrumental errors, spurious re∞ections and interferences, which can degrade the quality of the experimental data. In this study, we measured the RCS of an airplane model with a conduct- ing surface using two difierent experimental set-ups, and also simulated its RCS using commercial electromagnetic simulation software. The comparison of the data obtained shows that difierences will arise regardless of the care taken while performing an experiment or carrying out simulations and that these difierences should be taken into consideration when interpreting the data. 2. EXPERIMENTAL MEASUREMENTS The experimental data were collected using two difierent experimental setups: One inside an ane- choic chamber and another in a laboratory room using the Lab-Volt Radar Training System. The anechoic chamber, is located in the Instituto de Fomento Industrial (IFI/CTA, Brazil). Figure 1 shows the radar antennas used in the measurements. These X-band horn antennas were manufactured by M2SAT (Brazil); each antenna has a gain of 10dBi, and symmetric radiation patterns with low level of secondary lobes. The radar operated at 9.4GHz, in a quasi-monostatic conflguration and vertical polarization. A HP8360B (HP, USA) synthesized CW generator was use to generate the microwave radiation and the re∞ected signal was analyzed by a HP8593E (HP, USA) spectrum analyzer. It is estimated that the deviation of the RCS measurements was within 0.7dB. The model used in the measurements is also shown in Figure 1; it is a scale model of a Boeing 777 with total length of 0.64m (» 20‚). The body of the model is composed of an epoxy resin and its surface is coated with aluminum (the thickness of the coating is about 10 times larger than the skin depth of the aluminum at this frequency). The distance between the radar antennas and the model was about 6m. Electronic Warfare Laboratory (LGE/CTA, Brazil), consisting of interconnected subsystems that allow detailed studies of RCS in a laboratory environment. Measurements were carried out with inverse synthetic aperture radar, operating also at 9.4GHz at short range, in the presence of noise and clutter. The efiects of noise and clutter were removed using time-gating and subtraction techniques during the measurements. For the measurements, the distance between antenna and model was the same one used for the measurements in the anechoic chamber. Figure 2 shows the arrangement of the radar antenna and the model in the laboratory. The model was placed on a Styrofoam pedestal, invisible to radar waves.