Erich Kemptner

An autonomous, non-cooperative, wide-area traffic monitoring system using space-based radar (TRAMRAD)

To meet the challenges of ever increasing road traffic and the associated economic and sociological impacts, new techniques and technologies for better traffic management are needed. The TRAMRAD project (Traffic Monitoring with space-based Radar) aims to profit from research and development in earth observation and advances in radar remote sensing techniques to define a future space-based sensor system for the wide-area monitoring of road traffic. The paper describes the requirements for the system and the concepts being investigated. In particular, it discusses the complex detection conditions, the requirements on the radar instrument and the methods for processing the data. Possible system concepts are described and their capabilities are discussed.

Experimental Characterization of a Broadband Transmission-Line Cloak in Free Space

The cloaking efficiency of a finite-size cylindrical transmission-line cloak operating in the X-band is verified with bistatic free space measurements. The cloak is designed and optimized with numerical full-wave simulations. The reduction of the total scattering width of a metal object, enabled by the cloak, is clearly observed from the bistatic free space measurements. The numerical and experimental results are compared resulting in good agreement with each other.

Bistatic scattering characterization of a three-dimensional broadband cloaking structure

Here we present the results of full experimental characterization of broadband cloaking of a finite-sized metallic cylinder at X-band. The cloaking effect is characterized by measuring the bistatic scattering patterns of uncloaked and cloaked objects in free space and then comparing these with each other. The results of the measurements demonstrate a broadband cloaking effect and are in good agreement with numerical predictions.

A free space measurement approach for dielectric material characterization

The free space method allows nondestructive dielectric characterization of materials in a wide range of frequencies and temperatures, which is basic to several applications, as the development of radomes for aerospace proposals. This paper comprises the free space method from an initial procedure, the TRL calibration, to the permittivity calculation by the NRW method, including the software implemented and its practical validation with specific materials.

Determination of lines of constant phase in the near-field of a metallic cube and an airplane

A method is presented which enables one to calculate the scattered field very close to the surface of a perfectly conducting body as well as at the surface itself. The method is based on the representation of the scattered field by an integral over the surface current distribution. The integrand is treated by identity transformations that the singular terms can be integrated analytically, while the remaining nonsingular terms are integrated numerically. The surface current distribution is determined by the magnetic field integral equation. The theory is validated by experiments with the scattered field of a metallic cube with an edge length of a wavelength. The current distribution and the normal as well as the tangential electric field at the surface of the cube are measured by small probes, and the results are compared to those of the theory. The theoretical results of the current distributions are presented as gray value graphics-those of the near-field distribution of a cube and an airplane with the help of lines of constant phase. >

Computation and validation of bistatic RCS in the upper-middle and high frequency region

Two computer codep have been developed at DLR in order to calculate bistatic RCSs. The first code treats the high frequency case and is based on the physical optics (PO) method. The second one is suited for objects with dimensions comparable to the wavelength and is based on the finite-difference time-domain (FDTD) method. For test objects with perfectly conducting surfaces (a sphere and an elliptical cylinder) numerical results of the codes are compared and validated with those of the IEM-code NEC-2, analytical solutions and experimental results achieved by measurements at 94 GHz.

Impedance modeling of electromagnetic scattering from canonical bodies with metamaterial absorbers and chessboard-patterned deflectors

This paper summarizes the studies on impedance modeling of electromagnetic scattering from electrically large structures with metamaterial absorbers and chessboard-patterned deflectors performed at the DLR in the recent years. In particular, analytical, numerical and experimental results for mono- and bistatic scattering from metal plates, cubes and cylinders coated with periodic arrays of subwavelength-sized metal inclusions printed on top of a thin dielectric layer are presented.

An approximation for bistatic scattering matrix of a target above a ground plane

The paper derives a high-frequency approximation for the scattering matrix of a target placed above an infinite ground plane which can be either perfectly electrically conducting (p.e.c.) or non-metallic. The approximation accounts for electromagnetic interactions between the target and the ground plane, which involves a single reflection from the target and up to two reflections from the ground. It provides the correction for amplitude, phase, and polarization of the scattered signal for both mono- and bistatic configurations. The approximation is validated by application to a test configuration (a p.e.c. sphere over a dielectric half space), for which independent results obtained with the Method of Moments are available.

Ka-Band Transmission Measurements of Dielectric Coplanar Plates at High Temperatures Using Solar Energy

If one is looking for dielectric properties of natural or synthetic materials, it is easy to find lots of references and tables, most of them even covering a broad bandwidth of frequencies. Unfortunately these values are only valid at room temperature, and the dielectric properties are not generally supposed to stay constant with temperature. In order to measure dielectric properties at high temperatures, a new method has been developed and tested for the first time. The material can be heated at the same time as measuring the transmission coefficient by electromagnetic wave propagation (in Ka-band) through the medium, without having to remove the sample from the measurement setup. The Solar Furnace at the German Aerospace Center (DLR) in Koln-Porz made this possible, using concentrated solar radiation to heat the sample non-invasively.

Bistatic RCS Computations by FDTD and Comparison with other Rigorous Methods and Experiments

Der bistatische Streuquerschnitt von Testobjekten wird mit Hilfe von Rechenprogrammen basierend auf der Methode der Finiten Differenzen im Zeitbereich (FDTD) und der Integralgleichungsmethode (IEM) berechnet und experimentell validiert.