Arne Schroder

Numerical Design and Analysis of Conical Blackbody Targets With Advanced Shape

Advanced shapes for conical blackbody targets, as applied in millimeter wave remote sensing instruments, are designed and analyzed for frequencies between 20 and 600 GHz. We propose exponential shaped targets and show that exponential cones are superior to commonly used linear cones. Design and scattering analyses are carried out using the body of revolution method of moments and the finite-element method. Furthermore, a highly efficient ray-tracing approach is introduced and applied. Numerical studies regarding absorbing materials, beam waists, potential manufacturing artifacts, as well as several types of beam misalignment are performed to study practical challenges. Finally, starting from an exponential profile, the blackbody shape is further improved using numerical optimization techniques.

Fast Evaluation of Electromagnetic Fields Using a Parallelized Adaptive Cross Approximation

This communication shows a novel application of the adaptive cross approximation (ACA). A hierarchical ACA is presented for accelerating the evaluation of electromagnetic fields from a known current distribution, as it is required in the post-processing stage of the method of moments. Furthermore, a parallelization which employs a master-worker scheme is outlined, resulting in a highly efficient parallel code. Numerical examples validate the accuracy and efficiency of the method for various electromagnetic problems such as field coupling and radiation problems. It is demonstrated that the proposed approach is applicable in a broad frequency range, where it provides a definable error bound. Moreover, an acceleration factor of more than 200 is achievable, making an extensive field analysis of electrically large objects feasible.

Analysis of High Intensity Radiated Field Coupling into Aircraft Using the Method of Moments

In this paper, electromagnetic effects arising from high intensity radiated fields (HIRF) within realistic aircraft structures are investigated using the method of moments (MoM) and experimental tests. This study focuses on simulation-to-measurement correlation, where two potential error sources are investigated: Accuracy of the numerical techniques and the generation of numerical models. It is shown that the conventional mixed potential electric field integral equation may lead to inaccurate results regarding the field penetration through apertures. An alternative integral equation is introduced which splits the computational domain into an interior and an exterior domain, improving the results for aperture problems. To analyze the accuracy and the range of applicability for these integral equations, a generic aircraft structure is investigated, both numerically and experimentally. Thereby, various modeling aspects required for a meaningful simulation of aircraft are discussed. Following these observations, a real aircraft is analyzed in a broad frequency range from 10 kHz to 1 GHz. It is demonstrated that accurate numerical techniques are as important as modeling and appropriate simplification of the considered structures.

HIRF Transfer Functions of a Fuselage Model: Measurements and Simulations

An entire set of high-intensity radiated field transfer functions including the main types of contemporary test methods is presented. Consequently, the applied frequency range for this task expands over many decades, from the kilohertz range up to 40 GHz. A major aim is to demonstrate the application of numerical computer modeling for such a task. Results of measurements and various solvers are compared to each other. As the activity serves also for the validation of such applications, the scenario is investigated by the use of a fuselage model with limited complexity.

Numerical RCS and micro-Doppler investigations of a consumer UAV

This contribution gives an overview of recent investigations regarding the detection of a consumer market unmanned aerial vehicles (UAV). The steadily increasing number of such drones gives rise to the threat of UAVs interfering civil air traffic. Technologies for monitoring UAVs which are flying in restricted air space, i. e. close to airports or even over airports, are desperately needed. One promising way for tracking drones is to employ radar systems. For the detection and classification of UAVs, the knowledge about their radar cross section (RCS) and micro-Doppler signature is of particular importance. We have carried out numerical and experimental studies of the RCS and the micro-Doppler of an example commercial drone in order to study its detectability with radar systems.

Brightness Temperature Computation of Microwave Calibration Targets

A rigorous numerical technique to compute the brightness temperature of arbitrarily shaped microwave calibration targets is presented. The proposed method allows the brightness temperature of calibration targets to be investigated depending on frequency, absorber material, geometry, antenna pattern, field incidence, and temperature environment. We have validated the accuracy and studied the numerical complexity of the approach by means of analytical reference solutions. Fundamental brightness temperature investigations of pyramid absorbers are shown for various thermal environments in different frequency bands between 20 and 450 GHz. Based on these analyses, a novel pyramid geometry was designed, which features a superior electromagnetic and thermal performance compared with conventional pyramid designs. Using the theoretical findings, we have developed reduced-order models of pyramid targets for rapid brightness temperature studies.

Numerical Shielding Analysis of Anisotropic Multilayer Materials by the Method of Moments

In this contribution, an efficient method is developed to calculate the shielding effectiveness of anisotropic conducting multilayer materials by the method of moments. An analytical solution is used to approximate the wave propagation inside the multilayer material. This solution is coupled with a method of moments implementation, allowing to numerically calculate the electromagnetic fields in exterior and interior regions of a shield. Obtained results are compared to those of alternative numerical techniques and form the basis to validate the modeling of anisotropic multilayer materials by a homogeneous material of equivalent conductivity.

Design and Characterization of the ALMA Band 5 Vacuum Window

This paper summarizes the electromagnetic design process of the vacuum window for the Atacama Large Millimeter/sub-millimeter Array (ALMA) Band 5 (163-211 GHz). We have carried out investigations by means of numerical simulations as well as reflection and transmission measurements. Simulations were performed using the finite element method, an efficient quasi-analytical technique, and rigorous coupled-wave analysis. We used an injection-molded vacuum window prototype as a starting point of the design process and investigated deterioration in the electromagnetic performance caused by different types of manufacturing artifacts. Following these analyses, an optimization of the window has been performed based on simulations. We measured the reflectivity and transmittance of the newly designed window and this paper demonstrates that the optimized window exhibits a return loss better than -20 dB, as required by the ALMA specifications.

HIRF Transfer Function Observations: Notes on Results Versus Requirements and Certification Approach

HIRF transfer functions results are rarely available to the public. Generally, the data provided in applicable guidance material are used for estimation of internal HIRF environment in an air vehicle. An exemplary set of HIRF transfer functions for a small aircraft is presented here. Results for the aircraft (10.4-m wingspan and 8.3 m of length) are compared with regard to state of the art approaches applied for aircraft HIRF certification campaigns. This is done in appropriate frequency ranges and by the use of applicable test methods with regard to requirements in place. For all major types of contemporary test methods, results are generated by measurement and numerical computer modeling. Principles of outcomes are discussed and compared to current practice in place. This concerns the shapes of the transfer functions on one hand and the order of magnitudes of obtained levels on the other hand. The obtained results show significant deviations from generic transfer functions currently applied in aircraft industry. The coupling to the interior of the aircraft observed here was higher than indicated by the applicable generic transfer functions. Numerical computer modeling is used here to verify the obtained outcomes by principle.

Electromagnetic Design of Calibration Targets for MetOp-SG Microwave Instruments

We describe the electromagnetic development of microwave calibration units for the second generation of meteorological operational satellites. In particular, we focus on the electromagnetic and thermal design of on-board calibration targets (OBCT) for the microwave sounder (MWS) and the ice cloud imager (ICI), respectively. The OBCTs act as temperature reference for calibration. Therefore, they are required to exhibit a low electromagnetic reflectivity and a uniform temperature. This paper discusses the numerical design of pyramid absorbers for MWS and ICI. Based on theoretical studies, we have developed a novel pyramid design, which exhibits superior electromagnetic and thermal properties compared with conventionally used layouts. A comprehensive numerical study on the impact of common types of manufacturing tolerances has been carried out, and the most critical types were identified. This work presents remedies that reduce the susceptibility to manufacturing tolerances. All numerical results have been verified experimentally, and the manufactured OBCT prototypes have been shown to fulfill the specific requirements in all frequency bands.