Sebastian Methfessel

Advanced Microwave Imaging

Due to the enormous advances made in semiconductor technology over the last few years, high integration densities with moderate costs are achievable even in the millimeter-wave (mm-wave) range and beyond, which encourage the development of imaging systems with a high number of channels. The mm-wave range lies between 30 and 300 GHz, with corresponding wavelengths between 10 and 1 mm. While imaging objects with signals of a few millimeters in wavelength, many optically opaque objects appear transparent, making mm-wave imaging attractive for a wide variety of commercial and scientific applications like nondestructive testing (NDT), material characterization, security scanning, and medical screening. The spatial resolution in lateral and range directions as well as the image dynamic range offered by an imaging system are considered the main measures of performance. With the availability of more channels combined with the powerful digital signal processing (DSP) capabilities of modern computers, the performance of mm-wave imaging systems is advancing rapidly.

Millimeter-wave imaging concepts: Synthetic Aperture Radar (SAR) and Digital Beam Forming (DBF)

Short range radar imaging systems for various security and non-destructive testing (NDT) applications are mainly based on synthetic aperture radar (SAR) or digital beam forming (DBF) techniques. In this article the development of a real-time SAR and a real-time DBF system is presented. The goal is to achieve a 3D image of a large measurement area with a high lateral and range resolution in order to detect suspicious items or material approach. This can be realized with a SAR system which is based on a new rotating virtual antenna concept. Another approach is a digital beam forming concept consisting of spatially distributed transmitters and receivers. Experimental results on specific test objects are presented to prove the performance of both concepts. Index Terms – Millimeter-wave imaging, Synthetic Aperture Radar, Digital Beam Forming

Size-reduction and suppression of cavity-resonances in hybrid mm-wave antennas for polarimetric measurements

Size and feed structure are some of the important constraints for using antenna-elements in multi-element two-dimensional arrays, where easy planar integration with transceiver chips is essential. This applies especially when differential signaling and adaptable polarization is required. Based on a balanced-fed patch-excited cavity-backed horn antenna (hybrid antenna), feeding concepts and approaches to reduce size are discussed and evaluated in this paper. The influence of the substrate integrated cavity is analyzed and methods to overcome the restrictions are presented, together with simulated and measured results. The optimized antennas achieve a relative bandwidth of more than 17% for 10 dB return loss, a gain of more than 5 dBi as well as symmetric and homogeneous radiation patterns in amplitude and phase with low cross-polarization.