Frank Gumbmann

Millimeter-Wave Imaging With Optimized Sparse Periodic Array for Short-Range Applications

This paper presents a multiple-input-multiple-output imaging system on the basis of a hybrid concept with synthetic aperture radar and digital beam forming. By moving a multistatic linear array perpendicularly to the array dimension, a 2-D aperture is sampled. The scope of application is concealed weapon detection in conjunction with the imaging of humans and, alternatively, nondestructive testing (NDT). The frequency range of 75-90 GHz was chosen because of the inherent high lateral resolution. For NDT, it seems to be a good compromise between lateral resolution and penetration depth as well. A moderate number of transmit and receive channels are achieved by a sparse periodic array (SPA) design. Since this is a far-field approach, ambiguities are not well suppressed in the near-field point spread function of the sparse array. An extension of the SPA concept for short-range applications on the basis of an optimized array design and an optimized beamforming algorithm is presented in this paper.

A Fast Scanning W-Band System for Advanced Millimetre-Wave Short Range Imaging Applications

The paper presents the development of a fast scanning W-Band (75-100 GHz) system and a suitable antenna concept for advanced imaging applications. The goal is to obtain a broadband frequency response from a large target area within a short time period. Two typical approaches for the design of a free space millimetre-wave imaging setup will be discussed. The first approach consists of a focused bistatic measurement setup that includes a combination of a conical horn and a dielectric lens in order to focus the beam. The basic idea of the second approach is to use an unfocused measurement setup employing synthetic aperture radar (SAR) algorithms in order to focus the image numerically. Both measurement setups will be discussed with respect to the capability for fast scanning mm-wave imaging systems. Experimental results on planar test objects demonstrate the performance of the developed W-Band system compared to a commercial vector network analyzer (VNA)

Optimization of a fast scanning millimetre-wave short range SAR imaging system

This paper presents the development of a W-band short range imaging system for security and non-destructive testing applications, which uses an unfocused measurement setup employing SAR algorithms in order to focus the image numerically. The active imaging system offers the possibility to get a broadband frequency response from each pixel in the measurement plane. For real-time applications a fast scanning, monostatic virtual antenna concept has been developed and optimized. The monostatic setup is demonstrated in two different configurations, on the one hand using a quasioptical, broadband diplexer with high decoupling between transmitter and receiver channel and on the other hand a very compact setup using a commercially available high directivity waveguide coupler. The measurement setups are compared with special respect to their RF-performance. Experimental results on specific test objects are presented to prove the performance of the fast short range SAR imaging system.

Multistatic Short Range Ka-Band Imaging System

This paper presents the concept of a Ka-Band (26.5 - 40 GHz) multistatic active short range imaging system. The motivation for this work was the development of a fast scanning imaging system for non destructive testing (NDT) or security scenarios. The goal was to derive a 3D reconstruction of the device under test (DUT). The imaging system consists of a linear receive array and spatially distributed transmitters with non focussing antenna elements. This transmit/receive array is moved perpendicular to the array dimension. By switching between each transmitter and simultaneous reception of the scattered field by each receiver, a fast sampling of the 2D aperture plane is achieved. Due to unfocussed antenna elements numerical reconstruction algorithms have to be applied for a highT lateral resolution. An aperture synthesis concept is presented to reconstruct the raw data. It is based on the separation of the reconstruction kernel into a horizontal and a vertical part. Range resolution is achieved by a broadband stepped frequency continuous wave (SFCW) radar. In order demonstrate the efficiency of the new reconstruction kernel first results are demonstrated with simulated and measured data.

Inherent resolution limit analysis for millimeter-wave indirect holographic imaging

Abstract In the classical indirect holographic setup, a wave emitted by the measurement object is superimposed with a reference wave at the aperture of the imaging system. The resulting interference pattern can be recorded with a simple intensity detection. However, the complex object field can be obtained from the plane wave spectrum (PWS) of the interference pattern. Dedicated methods can be used to calculate the field distribution at the object position, which is equivalent to the object properties and to an image of the object, respectively. This paper shows that the resolution of the created image is constricted due to the fact that the bandwidth of the extracted field is limited by the extraction process. A relation between the maximum possible bandwidth and the geometrical dimensions of the imager setup is deduced. Furthermore, a formula for the minimum achievable resolution is derived. Experimental results are presented to illustrate the issue.

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