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In harmonic radar applications, images produced using algorithms of conventional radar applications experience some defocusing effects of the electronic targets’ impulse responses. This is typically explained by the dispersive transfer functions of the targets. In addition, it was experimentally observed that objects with a linear transfer behavior do not contribute to the received signal of a harmonic radar measurement. However, some signal contributions based on a multipath propagation can overlay the desired signal, which leads to an undesired and unusual interference caused by the nonlinear character of the electronic targets. Here, motivated by the analysis of measured harmonic radar data, the effects of both phenomena are investigated by theoretical derivations and simulation studies. By analyzing measurement data, we show that the dispersion effects are caused by the target and not by the measurement system or the measurement geometry. To this end, a signal model is developed, with which it is possible to describe both effects, dispersion and multipath propagation. In addition, the discrepancy between classic radar imaging and harmonic radar is analyzed.

Soil moisture and ocean salinity mapping by earth observation satellites has contributed significantly towards a better understanding of the earth’s climate and hydrosphere. Nevertheless, an increased spatial resolution of radiometric data could yield a more complete picture of global hydrological and climate processes. High-resolution radiometers, such as SMOS, have already approached prohibitive sizes for spacecraft due to the required large antenna apertures. Radiometer concepts based on satellites flying in close proximity have been proposed as a possible solution. Individual receivers placed on a large number of smaller satellites orbiting a central satellite would form a combined interferometric array. Recent technological progress in formation flying, satellite miniaturisation, inter-satellite links and data processing could make a future satellite swarm-based radiometer possible. The design of such a system requires a methodology which enables the determination of orbit parameters in a way that optimizes radiometer performance and ensures system feasibility. In the past, the optimization of interferometric array configurations has only aimed to optimize the image quality without taking into account system constraints, such as satellite collision risk, satellite fuel consumption and other feasibility considerations. This resulted in idealized array configurations that might put unrealistic constraints on the satellite system. A current research project of the DLR Microwaves and Radar Institute investigates methodologies for the orbit optimization of large satellite swarm-based interferometric radiometers regarding future earth observation radiometry missions. For this purpose a system simulator has been created for the study of radiometers based on a large number of spacecraft. First results have indicated that an approach based on statistical methods for the quantification of radiometer performance and the use of numeric optimization solvers can yield promising orbit configurations. This paper provides an overview of the optimization approach and first results in generating a feasible and performant satellite swarm configuration for interferometric radiometry purposes.

Erprobung und Entwicklung von Messverfahren, die dazu dienen sollen, in kurzer Zeit die bauwerksindividuellen geometrischen, physikalischen und strukturellen Eigenschaften eines Gebäudes zu erfassen. Auf diese Weise soll zu überschaubaren Kosten eine wesentlich besser auf das individuelle Bauwerk angepasste Sanierungsplanung durchgeführt werden können. Perspektivisch können dieselben Messverfahren auch zur Qualitätskontrolle nach Sanierungen und bei Neubauten eingesetzt werden.

Polarizer miter bends are used to alter the polarization in overmoded waveguides. For future space debris observation with broadband high power W-band radar sensors these are important transmission line components. A polarizer miter bend uses a grooved mirror as phase grid for polarization. The present paper addresses a suitable design of such a phase grid for broadband high power radar applications within the frequency range from 90GHz to 100GHz. An appropriate parameter combination is found by a parametric study. For reduction of the required amount of calculation a plane wave approximation and unit cell simulations are used. With a suitable parameter combination a cross polarization of Xpol B −26 dB can be achieved within the considered frequency range. This corresponds to a suitable value for radar applications.

The characterization of dielectric materials is of great importance for many applications. Remote sensing from stand-off position is often desirable, and the use of microwaves, millimeter-waves or THz waves offers useful interaction with matter, depending on its chemical and physical decomposition and of course frequency and polarization. In former investigations a linearly polarized Ka-band radiometer and an electronically steerable polarization rotator were used to extract permittivity from different linear polarization states. Now the radiometer is realized by a W-band fully-polarimetric receiver. In this paper the theoretical background of the new approach is briefly outlined and compared to first measurement results.

The characterization of dielectric materials is of great importance for many applications, being for instance quality control during product fabrication or status control of outside constructions over time. In many outside situations the objects of interest have limited accessibility, and the investigation has to be done without destruction of any part of the object and without any health risks for an operator. Hence remote sensing from stand-off position is desirable, and the use of microwaves, millimeter-waves or THz waves offers some penetration capability into matter, depending on its chemical and physical decomposition and of course frequency. Many objects of interest consist of a dielectric coating or enclosure, which can electromagnetically be treated as a dielectric layered structure or a dielectric slab surrounded by air. Radar as an active remote sensing technology has great potential with respect to precise range measurements and spatial resolution. However, its mostly mono-static implementation suffers from low or no back reflection of signals in case of plane and tilted surfaces, delivering hence no information. In contrast radiometric imaging as passive remote sensing technology uses naturally generated noise-like radiation of thermal origin, being available everywhere and from all directions. Quite often the sky can be used as large illumination source, providing rather low radiation power compared to objects on Earth, using frequencies up to few hundred GHz. Furthermore, thermal radiation originally is un-polarized, but becomes polarized when reflected partly on a dielectric surface. Hence, the use of polarimetric measurements at various incidence angles can provide information on the type and structure of the reflecting object. The approach and the measurement setup are described. Experimental results of polarimetric measurements are shown and discussed.