Gregory Hislop

Spatial smoothing for 2D direction finding with passive RFID tags

This work presents a novel method of using spatial smoothing techniques for finding the azimuth and elevation of correlated signals. The method is the first to solve this problem using the array interpolation technique for a given 2D array. A fast iterative method progressively obtains higher accuracy as it reduces the solution space. Synthetic examples are given which show the algorithm accurately positioning multiple correlated signals. A practical system for locating RFID (Radio Frequency Identification) tags is also described.

Microwave radar for detection of resin defects in Pinus elliottii Engelm var elliottii

Abstract Surface penetrating microwave radar is identified as a low-cost, reliable, portable, and safe means of detecting resin defects in plantation-grown pine logs. This new method of non-destructively testing logs has the potential to be applied at several intervention points in the value chain, including on standing trees, fallen stems, and merchandised logs either in the forest or in the mill. Results clearly distinguish resin-affected logs from unaffected logs, even in logs of high moisture content.

Direction Finding With MUSIC and CLEAN

The well known MUSIC algorithm for direction-finding is improved by applying the CLEAN post-processing method. A mathematical explanation for the performance improvement, is presented along with both synthetic and experimental validations.

On the Mathematical Link Between the MUSIC Algorithm and Interferometric Imaging

Radio astronomy and direction finding are closely related fields. However, there is almost no overlap between the two sets of literature. Interferometric imaging and the MUSIC algorithm are perhaps the most popular algorithms in the respective domains. This paper presents the exact mathematical link between them.

Modeling of an Ultra-Wideband antenna array devoted to near-field imaging

This paper presents the mutual coupling analysis in Ultra-Wideband (UWB) antenna arrays devoted to near-field imaging from 1 to 4 GHz. Vivaldi antennas have been designed to build the antenna array. The Method of Moments (MoM) in iterative form is used to find the array impedance matrix and the different near-field patterns. Very strong agreement between the simulated and the measured coupling coefficients, testifies the validity of the modelling of the antenna array. The localization of isolated targets with an accuracy of the order of 2 mm is also demonstrated.

Antenna Calibration for Near-Field Material Characterization

A novel antenna calibration method is presented for near-field problems, such as material characterization or inverse scattering. The procedure accurately accounts for differences between simulations of objects close to antennas and the equivalent experimental measurements. It is based on the method of moments (MoM) solution to surface integral scattering equations. An efficient choice of macrobasis functions (MBFs) is applied to the antenna, which reduces the computational costs by several orders of magnitude. The calibration involves scanning a target of known constitution through the antenna near field, assigning a tuning parameter to each MBF and optimizing said parameters, so as to reduce the error between antenna simulations and measurements. This adjusts the antennas simulated surface currents, so as to more accurately represent the currents on the experimental apparatus. Thus, an efficient antenna model is obtained, which more accurately represents the real-world antenna. The calibration technique is verified by applying it to the characterization of dielectric objects of known but arbitrary shape.

Low-rank approximation for fast image acquisition

We propose a scanning procedure for fast image acquisition, based on low-rank image representations. An initial image is predicted from a low resolution scan and a smooth interpolation of the singular triplets. This is followed by an adaptive cross correlation scan, following the maximum error in the difference image. Our approach aims at reducing the scanning time for image acquisition devices that are in the single-pixel camera category. We exemplify with results from our experimental microwave, mm-wave and terahertz imaging systems.