David Escot-Bocanegra

The workshop “Radar Signatures & EM Benchmarks” has been established by the European Defence Agency (EDA) in 2017, with the aim of bringing together scientific experts in the field of electromagnetic scattering simulations, specifically in the context of radar signatures. The 3^rd workshop was held in 2023, and a few months prior to the workshop, several test cases were published on the workshop’s webpage, which served as benchmarks to compare results obtained by different simulation codes. It turned out that such activities are extremely important for the community, both for the comparison of simulation results and evaluation of tools as well as for the interesting discussions among the leading experts in the field. This paper will provide insights into the workshop by presenting some of the recent test cases and showing some exemplary evaluation of the data computed by the participants.

A method, hereinafter referred to as Discrete Chaff Cloud Model (DCCM), for the electromagnetic modeling of general chaff clouds is presented, with which harmonic or wideband impulse scattering responses can be evaluated. The model applies to a wide range of scenarios, for any combination of illumination and observation angles and polarizations. The technique considers the geometry of the cloud and the statistical distributions of the elements, both in density and orientation. After a one-dimension (1D) discretization of the cloud, the complete statistical response or single-experiment observations can be evaluated. The model is formulated in a very general form to extend its applicability as much as possible. Its limitations have been identified and assessed in relevant scenarios. Validation cases have been included, comparing results obtained with DCCM, other published formulations, and full-wave simulations.

We provide a model able to predict the shielding effectiveness (SE) of carbon fiber composite (CFC) panels made of stacked layers of conducting fibers. This model permits us to obtain simple formulas in which the only parameters needed are the sheet square resistance and the effective panel thickness. These tools let us predict a minimum SE, which always increases with the frequency and therefore constituting the worst case, from an electromagnetic shielding perspective. Consequently, the measurement of minimum SE requirements can be simply measured with a micro-ohmmeter using an specific experimental setup which is also described here. Additionally, this method allows to measure very high SE falling far beyond the dynamic range of the values measurable with the most commonly used standard, the ASTM D4935. After describing the modeling technique and the different test setups used, across-validation between theoretical and experimental results is made for four different samples of CFC; two designed to test the modeling assumptions and two which are representative of the ones nowadays used in a real aircraft.

Along the years, RADAR absorbing materials (RAM's) have been widely introduced in aeronautic applications and platforms. However, this kind of materials presents three main problems for certain applications when they are intended to be used in real operations. First, they must be scalable from a laboratory sample to actual size, at a reasonable cost. Second, they must be able to work without metal backing for applications in non‐metallic vehicles or other objects which surface might not be flat. Indeed, they should also be flexible and surface adaptable. Finally, their absorbing properties against electromagnetic fields should be preferably characterised under real conditions, that is, in free space (FS), in order to design and fabricate an appropriate material for the intended application. In this study, a self‐developed, low‐cost, bilayer, X‐band RAM, composed of a lower layer of polyaniline silicon rubber and a top layer of silicon rubber with graphite was characterised in a bistatic anechoic chamber called BIANCHA, and the results are presented, analysed and compared with software simulation and with the typical single polarisation waveguide measurement method, showing the adequacy of FS measurements for the development of this type of RAM.

Open area test sites (OATS) have been traditionally employed for aircraft electromagnetic compatibility certification tests because of the large size of these items. In this regard, unmanned aerial vehicles (UAVs) have emerged in the last years and, albeit being sometimes notably smaller, yet they have to accomplish for the same certification process. This paper investigates into the possibility of using a reverberation chamber for performing two aircraft low-level coupling tests, namely, low-level direct drive and low-level swept fields, and compares the results with those obtained in an OATS, in both cases using a representative part of a UAV.

Electrical and electronic systems on board air vehicles are susceptible to electromagnetic interference (EMI). This has made the topic of electromagnetic compatibility (EMC), a major concern for aircraft safety. The use of composite materials worsens this situation, for their poor shielding and low conductive capabilities. Some of the main experimental E3 certification scenarios used in aeronautics are revisited in this chapter. Guidelines to achieve simple, yet accurate, numerical models of them are provided, with appropriate tradeoffs between computational simplicity and accuracy. The numerical method, endowed with extended capabilities, has been chosen for this task for its ability and efficiency to deal with complex problems of arbitrary materials. The feature selective validation (FSV) IEEE standard procedure, commonly used to quantify the comparison of data in electromagnetic problems, is also revisited. The simulation of three different air vehicles in several certification scenarios is finally described and the numerical results compared to experimental data.

The increased use of carbon-fiber composites in unmanned aerial vehicles is a challenge for their EMC assessment by numerical solvers. For accurate and reliable simulations, numerical procedures should be tested not only for individual components, but also within the framework of complete systems. With this aim, this paper presents a benchmark test case based on experimental measurements coming from direct-current injection tests in the SIVA unmanned air vehicle, reproduced by a numerical finite-difference-time-domain solver that employs a new subgridding scheme to treat lossy composite thin panels. Validation was undertaken by applying the feature selective validation method, which quantifies the agreement between experimental and numerical data.

BIANCHA (BIstatic ANechoic CHAmber) is a singular facility located at the premises of the National Institute for Aerospace Technology (INTA), Spain. It was devised to enable both monostatic and bistatic automatic positioning and, therefore, permits to perform a wide variety of electromagnetic tests. In this regard, it is worth noting that in the last years, a renewed interest has arisen in bistatic radar. Some of the main reasons behind this renaissance are the recent advances in passive radar systems added to the advantages that bistatic radar can offer to detect stealth platforms. On the other hand, with the aim of developing new aeronautic materials with desired specifications, research on the electromagnetic properties of materials has also attracted much attention, demanding engineers and scientists to assess how these materials behave in the presence of electromagnetic fields. Consequently, this paper introduces BIANCHA and demonstrates its applicability for these purposes by presenting results of tests for two different applications: a bistatic scattering analysis of scaled aircraft targets and the extraction of the electromagnetic properties of composite materials utilized in an actual aeronautical platform.