Ana Arboleya

Millimeter and submillimeter planar measurement setup

A three-axes planar measurement setup for antenna characterization and inverse scattering applications is described. The need for a new measurement facility capable of working at millimeter and sub millimeter frequency bands is the main motivation of this work. The system can be divided into two main blocks devoted to mechanical and radiofrequency control respectively. Frequency band is extended up to 330 GHz by means of mixing heads, and a working surface of 1450×1500×1100 mm, with 0.01 mm positioning accuracy is achieved. Measurement setup is provided with an easy-to-use graphical user interface allowing configuration of mechanical and radiofrequency devices, as well as graphical representation of the results and post processing tasks.

Submillimeter-Wave Frequency Scanning System for Imaging Applications

A new submillimeter-wave imaging system based on the frequency scanning concept is presented. Using significantly less information than beam-steering techniques, frequency scanning-based imaging systems are able to provide angular information in range-based radar systems which do not allow mechanical or electronic beam steering. Several strategies have been adopted to overcome the low dynamic range due to the propagation losses and non-specular reflection on the object-under-test. Moreover, the system is not only capable of detecting the placement of the objects, but also their profile. In this sense, an imaging application showing the system capabilities for the detection of objects concealed under clothes is presented. Results using 1-D FSAA allowing profile imaging are shown, proving the validity of the proposed system.

Phaseless Characterization of Broadband Antennas

A new efficient method for broadband antenna characterization from phaseless acquisitions in the frequency-domain (FD) is presented. The phase-retrieval technique is based on an extrapolation of the off-axis indirect holography. In common with the conventional approach, the power of the interferometric field of the antenna under test (AUT) and a reference antenna, whose field is known in advance, as well as the power of the AUT alone, is measured at the desired frequencies. Nevertheless, the phase retrieval is accomplished independently at each spatial point by filtering in the time-domain (TD) rather than in the k-space. Thus, the dependency of the phase retrieval on the position accuracy is reduced and it can be accomplished simultaneously at all frequencies without resorting to iterative schemes. Moreover, it yields a less dense sampling and a phase-retrieval algorithm not dependent on the geometry of the acquisition. The method is illustrated with a numerical example in the W-band as well as with two near-field (NF) measurement examples in the Ka- and W-bands.

Broadband Synthetic Aperture Scanning System for Three-Dimensional Through-the-Wall Inspection

This letter presents a cost-effective technique for through-the-wall imaging of objects beyond a wall. The approach relies on an amplitude-only multimonostatic radar that operates as a synthetic aperture radar. In contrast to conventional approaches, the system employs recent broadband techniques for phase retrieval. Thus, the complexity of the scanner is reduced, whereas it preserves the capacities of a conventional broadband system to retrieve the 3-D profile of objects. Moreover, the system is compatible with state-of-the art techniques that require full (i.e., amplitude and phase) acquisitions. Results at different frequency bands are shown to illustrate how the system can provide accurate estimation of the profile of metallic objects behind building materials such as plywood, plasterboard, or hollow bricks and mortar.

SAR-based technique for soil permittivity estimation

ABSTRACT A conventional synthetic aperture radar (SAR)-based technique for soil permittivity estimation is presented in this contribution. Ground penetrating radar imaging techniques are mainly based on SAR imaging algorithms that take into account the wave velocity in the soil for accurate imaging of buried objects. Reflectometers, datasheets, and indirect observation methods are commonly considered for soil characterization. However, factors such as humidity and temperature may cause some variations in the soil constitutive parameters. This contribution proposes a methodology for in situ characterization of soil permittivity, using the known position of a reference object and the application of conventional SAR imaging to recover the reflectivity image, from which the required information to calculate the complex permittivity can be extracted. Experimental validation in both controlled and realistic scenarios proves the capability of the proposed technique to recover the permittivity of different types of soil and to improve the quality of the Underground-SAR image.

Measurement setup for profile reconstruction in the 90 GHz frequency band

A measurement setup for profile reconstruction of metallic targets in the 90 GHz frequency band is proposed and tested. Inverse Synthetic Aperture Radar (iSAR) formulation is used to calculate the radar reflectivity from the measured scattered field. This reflectivity gives a spatial image of the Objet Under Test (OUT) which provides information about the profile of the OUT. Measurements are done using a planar measurement setup for mm- and sub-mm frequency bands. Aiming to test the system resolution, a metallic plate with four different size holes has been chosen as OUT. Profile reconstruction results using this measurement setup are shown.

Multiview techniques for mm-wave imaging

An analysis of different strategies for an efficient implementation of multiview millimeter-wave imaging systems is presented. The goal is to show the impact on Synthetic Aperture Radar (SAR) image quality of different strategies to combine multiple SAR images obtained with a portable mm-wave scanner in order to obtain a full image of the area-under-scan. Simulation results for a 15 cm linear array working in the 75–79 GHz frequency band are presented.

Indirect Off-Axis Holography for Antenna Metrology

Phase acquisition in antenna measurement, especially at millimeterand submillimeterwave frequencies, is an expensive and challenging task. The need of a steady phase reference demands not only a very stable source but unvarying temperature conditions and strong positioning accuracy requirements. Indirect off-axis holography is an interferometric technique that allows for characterization of an unknown field by means of a simple filtering process of the hologram or intensity interference pattern in the spectral domain, provided that the reference field, employed to interfere with the unknown field, is known in amplitude and phase. This technique can be used to avoid the effect of the errors related to the phase acquisition and to further develop new efficient and robust techniques capable of phase retrieval from amplitude-only acquisitions allowing for cost and complexity reduction of the measurement setup. A short review of the state-of-theart in antenna metrology is presented in this chapter, as well as a description of conventional indirect off-axis techniques applied to this field. Last sections are devoted to the description of novel measurement techniques developed by the authors in order to overcome the main limitations of the conventional methods.

An Ultrathin 2-bit Near-Field Transmitarray Lens

A novel ultrathin near-field (NF) 2-bit 24

Improving independent learning and communication skills of students in last year of Engineering degrees through the use of Project-Based Learning methodologies

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