Mauro A. Alves

Reduction of the radar cross section of a wind turbine using a microwave absorbing material

Wind turbines are devices which usually have a large surface area. The combination of effects related to the large surface area and properties of the materials used in their construction can make a wind turbine an important reflector of radar waves, which may interfere with the proper operation of civilian and military radars. There are several possible methods to reduce the radar cross section (RCS) of a wind turbine; here we simulated the effects of a composite microwave absorbent material that can be used to coat or as structural elements of the wind turbine. This material can absorb up to 95% of the energy of the incident wave. Simulations were carried out at 10 GHz (X-band). The use of the absorbent material can significantly reduce the RCS of the wind turbine. The simulations also indicated which parts of the wind turbine contribute more to the reflection of radar waves.

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

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.

Simulations of the radar cross section of a stealth aircraft

The radar cross section (RCS) of a CAD model of the stealth bomber B-2 Spirit was simulated with the CADRCS software. Results from simulations with the aircraft model having a perfectly conducting surface and rotating about the yaw, pitch and roll axes are presented and compared with results of simulations where the surface of the model was covered with a radar absorbing material (RAM). The objective of this study was to investigate how the shape can affect the RCS of an aircraft and how the use of RAM can further reduce its RCS.

Evaluation of a nanostructured microwave absorbent coating applied to a glass fiber/polyphenylene sulfide laminated composite

The rapid coating of composites with absorbing paints yields materials that can absorb microwave radiation and still have approximately the same specific mass of the original composites. The use of paints with specific electromagnetic properties together with carbon- nanotube-based materials allows the production of structural materials of interest to the aeronautical industry. Thus, the objective of this study was to produce and characterize the electromagnetic properties of a material consisting of a microwave absorbing coating (carbon nanotubes and polyurethane) applied to a laminated composite made with polyphenylene sulfide and glass fiber. The attenuation of microwaves (8 to 12 GHz) incident on this material was evaluated using the waveguide technique to determine whether this material can be used as an absorbing structural material. The results show that the material absorbs up to 90% of the energy of the incident microwave, indicating that the material is an efficient absorber of microwave radiation.

Electromagnetic radiation absorbing paints based on carbonyl iron and polyaniline

In this paper are presented the processing and characterization of electromagnetic radiation absorbing paints based on magnetic and dielectric materials. Two different paint formulations containing carbonyl iron and/or polyaniline, and using polyurethane as matrix were prepared. The paints were applied to a metallic surface and the absorption of electromagnetic radiation was measured using the Naval Research Laboratory (NRL) arch method. Measurements of the electric permittivity and magnetic permeability of the paint were also carried out. The paints absorbed 60%–80% of the incident electromagnetic radiation, indicating their potential as radiation absorbing materials.

A Medium Open Range Radar Cross Section Facility in Brazil

In this paper, we report the establishment of a new radar measuring facility in Brazil. This facility has a radar operating in the X-, Cand S-bands. To the best of our knowledge, this facility is the first of its kind in Brazil and Latin America. Some of the first RCS measurements carried out in this facility are presented.

Orientation of a support pylon used in radar cross section measurements

Simulations of the radar cross section (RCS) of a four-column square-based support pylon were performed in order to find the orientation between a radar antenna and the pylon in which the radar return from the pylon is minimal. From RCS simulations at 2, 6 and 10 GHz it was found that the optimal positioning of pylon occurs when the side of the pylon is at an angle of about 20deg with respect to the line-of-sight of the radar antenna.

Dynamics of Environmental Ionizing Radiation between May to September 2016 in the Region of São José dos Campos, SP, Brazil

Measurements of gamma radiation (200 keV to 10 MeV) were performed between May 25 to September 3

Comparison of the spatial distribution of precipitation estimated by an S-band Doppler radar and by a rain gauge network in São Paulo, Brazil

Isohyetal maps of daily accumulated precipitation were made using data collected in January, 2015, by a rain gauge network and an S-band Doppler weather radar. The maps were compared to determine the quality of the precipitation estimated using the radar data. The results indicate that within the study area, the S-band Doppler radar and the rain gauge network produced similar results, suggesting that within certain conditions the weather radar can perform as well as a rain gauge network.

The electromagnetic spectrum from 1 Hz to 9.4 GHz near ground level in the region of São José dos Campos, SP, Brazil

In the period from June 2012 to May 2013 measurements of the electromagnetic spectrum from 1 Hz to 9.4 GHz were collected in São José dos Campos, SP, Brazil. At this site, the electromagnetic spectrum is produced by both natural and artificial sources. The intensities of the electric and magnetic fields were measured in two frequency ranges (1 Hz to 1 MHz, and 1 MHz to 9.4 GHz) with hand-held detectors and compact antennas. Measurements were performed in sweep-time mode and changing precision in the resolution bandwidth (RBW). Main peaks in the spectrum correspond to Schumann resonances at 7.8, 14, 20 and 33 Hz, emissions by power lines, radio frequencies, navigational radio beacons, mobile phone and Wi-Fi systems, C- and X-band radars (ground stations and on board aircraft).