Thomas Dallmann

Discrimination of scattering mechanisms via polarimetric rcs imaging [measurements corner]

Radar cross section (RCS) images describe position and scattering brightness of scattering centers of a radar target, but lack information about the underlying scattering mechanisms. This information can be valuable help for the design of radar targets, as soon as it becomes available. The proposed method uses a polarimetric approach to detect and discriminate three different scattering mechanisms, independently of the orientation of the scatterers. These mechanisms can be separately visualized for easy interpretation of the physical processes occurring at the radar target. Measurement results recorded in a compact range demonstrated the practical applicability of this approach.

Theoretical Investigation of the Effects of a Linear Phase Center Shift Onto Antenna Impulse Responses

It is known that the phase center of some antennas can shift its position over frequency. The effects of such a phase center movement on the time-domain behavior of an antenna are studied throughout this letter. By linearizing the shift of the phase center, exact and approximate derivations of the time-domain impulse response are derived and discussed comprehensively. Contrary to expectations, the extent of the antenna impulse response increases with increasing antenna bandwidth under certain conditions. These theoretical findings are discussed in detail using examples .

A frequency steerable Substrate-Integrated Waveguide slot antenna for 77 GHz radar application

For a low cost radar system a serially fed, linear and equidistant waveguide slot antenna has been developed. A meander shaped waveguide path allows a frequency steerable main lobe without additional mechanical or electrical components. The antenna design focused on a maximum steering angle of ±60°. In order to further reduce the costs and simplify fabrication of the antenna a Substrate-Integrated Waveguide (SIW) structure was used. A new concept to reduce the parasitic coupling of these structures has been investigated. To fulfill the requirements on the radiation characteristics and matching of the antenna, a new slot shape and a cavity based waveguide-SIW transition were designed. Simulations and measurement results show that the antenna could be realized successfully.

Improving calibration of array antennas via Microwave Imaging

Complex array signal processing algorithms like Multiple Signal Classification often require a precise knowledge of the radiation characteristics of the array antenna in use. Calibration of group antennas by determination of antenna array radiation patterns is therefore a fundamental task for improving the performance of these algorithms. From a practical point of view this requirement is challenging, since the environment surrounding the antenna may alter over time or may even be completely unknown. This environment can have a severe influence on the group antenna radiation patterns. The approach proposed in this paper uses a Microwave Imaging technique to reconstruct position and shape of scatterers surrounding the array antenna. This information can further be used to calculate the field scattered by these objects as well as the total radiation pattern of group antenna and environment. The proposed algorithm only requires S-parameters of the antenna array measured in presence of the scatterers. The theoretical concept of this method is presented in this paper. Results obtained by numerical simulation show that this algorithm provides better radiation pattern estimates than other commonly known calibration methods.

Enhancing radar cross-section images of artificial targets using radar polarimetry

Nowadays polarimetric decompositions are common processing techniques for synthetic aperture radar images. However, some of the decomposition methods can also be applied to imagery obtained in radar cross-section measurement ranges. Since commonly artificial targets are measured in these ranges, coherent decompositions are of special interest for the analysis of these images. In this paper, a Kennaugh matrix decomposition is used to remove non-polarized clutter from fully polarized targets. Therefore two averaging techniques required for the decomposition will be compared. Also a variation of this decomposition which is related to a well-known image processing filter will be introduced. Finally it will be demonstrated that both methods can enhance the contrast of radar cross-section images.

Simulative investigation of the effects of a phase center shift onto a Log-Periodic Dipole Array

Recently the effects of a frequency-dependent phase center on the time domain behavior of an antenna were described with an analytical expression for the antenna impulse response. This relation will be compared to the characteristics of a Logarithmic-Periodic Dipole Array (LPDA) within this paper. Similarities between the impulse response of an LPDA and a moving phase center will be identified. The results indicate that the dispersive behavior of an LPDA is caused by this phase center movement.

A Boundary Criterion for the Effects of a Linear Phase Center Shift onto Antenna Impulse Responses

It is known that the phase center of some antennas can shift its position over frequency. The effects of such a phase center movement on the time domain behavior of an antenna were analyzed within an earlier publication. It could be shown that contrary to expectations the pulsewidth of the antenna impulse response increases with increasing antenna bandwidth under certain boundary conditions. These conditions are studied throughout this paper. A boundary will be derived which defines a range of validity for the aforementioned observations. These theoretical findings are discussed in detail using examples.