Ana Arboleya-Arboleya

Phaseless Synthetic Aperture Radar With Efficient Sampling for Broadband Near-Field Imaging: Theory and Validation

This paper presents a broadband and phaseless synthetic aperture radar (SAR) with efficient sampling. The design relies on a novel phaseless monostatic element comprising a transmitter and a receiver. This element, together with a computationally inexpensive algorithm, can retrieve the phase of the monostatic scattered field at all the working band except for two small safety margins at the lower and upper frequencies. Furthermore, the phase retrieval works independently of the transmitter/receiver position. Consequently, conventional approaches to reduce the number of monostatic acquisition points can be employed. Thus, the proposed strategy is suitable to implement either arrays that benefit from a reduced number of low-complexity elements or raster scan systems that benefit not only from the cost reduction of the scanning components but also from a remarkable speed-up due to the reduced number of acquisition points. Moreover, in contrast to other off-axis schemes, the proposed system does not require neither mechanical nor electrical phase shifting and, therefore, it can be directly adapted to a large number of frequency bands. The performance of the system is validated by simulation and measurement examples in the millimeter-wave band.

Millimeter Wave Imaging Architecture for On-The-Move Whole Body Imaging

This paper presents a novel interrogation system that combines multiple millimeter wave transmitters and receivers to create real-time high-resolution radar images for personnel security screening. The main novelty of the presented system is that the images can be created as the person being screened continuously moves across a corridor where the transmitters and receivers, working in a fully coherent architecture, are distributed. As the person moves, the transmitters and receivers are sequentially activated to collect data from different angles to inspect the whole body. Multiple images, similar to video frames, are created and examined to look for possible anomalies such as concealed threats. Two-dimensional (2-D) and three-dimensional (3-D) setups have been simulated to show the feasibility of the proposed system. The simulation results in 2-D have been validated using measurements.

Interferometric Technique With Nonredundant Sampling for Phaseless Inverse Scattering

A phaseless data acquisition applied on a reduced set of points is presented for inverse scattering problems. The setup is based on the Leith-Upatnieks holography with synthesized reference waves so that the phase of the reference wave can be adjusted to acquire the so-called “reduced field” instead of the regular field. Thus, nonregular sampling techniques can be applied resulting in strong reduction in the number of acquisition points. The technique is validated using simulation and measurement examples at microwave frequencies.

Phaseless Antenna Diagnostics Based on Off-Axis Holography With Synthetic Reference Wave

An antenna diagnostics method based on off-axis holography is presented in this letter. In this novel phaseless antenna measurement setup, the reference wave is synthesized by means of a mechanical phase shifting, and therefore the use of a phase shifter is avoided, yielding an accurate low-cost antenna diagnostics system. The technique is validated by means of simulation as well as measurement. Accurate results prove the system capability for antenna diagnostics tasks.

A Modified Phaseless Inverse Scattering Setup Based on Indirect Holography Implemented at Submillimeter-Wave Band

The aim of this communication is to present an enhanced phaseless inverse scattering setup and its implementation at the submillimeter-wave band. This setup is based on a modified indirect holography with synthesized reference signal so that a phase shifter is not required. Thus, a phaseless scanner can be built using a simple power detector resulting in a simplified measurement scheme very suitable to work in the millimeter-wave band and beyond. Mechanical phase shifting is used to bypass the use of electrical phase shifters. In addition, the reference signal is injected by coupling the transmitter and receiver antennas so that directional couplers and power combiners are avoided. New errors introduced by these techniques are analyzed and quantified. The method is validated with simulations as well as measurements at 300 GHz.

Multiview three-dimensional reconstruction by millimetre-wave portable camera

Millimetre-wave imaging is a powerful non-destructive inspection technique which has become widely used in areas such as through-the-wall imaging or concealed weapon detection. Nevertheless, current systems are usually limited to either a single view point providing a limited 3D millimeter-wave model or a multiview relying on the accurate movement of a robot arm through precise positions resulting in very bulky systems. In this paper, we present a set of techniques to achieve a multiview millimetre-wave scanner. The aperture of the scanner is kept below 16 cm so it can be portable and, consequently, multiview can be achieved by simple hand movements. In addition, optical images are also acquired with a two-fold purpose: i) building a complementary 3D-model by employing Structure from Movement (SfM) techniques; ii) estimating the scanner position and poses. The proposed technology is illustrated for people screening, proving the capacity of the system to detect hidden weapons.

Error characterization tool for planar near-field antenna measurement and diagnostics applications

An error characterization tool is presented in this contribution to study the effect of mechanical and positioning errors in the near-field to far-field transformation and the computation of the aperture field processes in different planar measurement setups. Validation of the error simulation tool is made by comparison of the results with a set of measurements in a planar near-field range.

Antenna Manufacturing at VHF Frequencies Applied to Weather-Satellite Data Reception [Education Column]

The aim of this paper is the description of experience in teaching a university extension course for manufacturing homemade antennas and receiving weather-satellite images with them. We thus introduce students to the field of antennas with a very entertaining application example that they can easily reproduce by themselves. The different topics covered by the course are described, with a special emphasis on the description of the antennas and how they are manufactured, which are the core topics of the course. Antenna reflection parameters and received weather images are shown to illustrate the good results achieved by the students.

Multistatic Millimeter-Wave Imaging by Multiview Portable Camera

The aim of this paper is to introduce the use of sparse multistatic arrays to reduce the number of elements in novel portable and muti-view millimiter-wave scanners. Thus, the complexity of these novel scanners is significantly reduced. Furthermore, sparsity is expected to enable embedding a conventional optical camera sensor inside the aperture of the scanner allowing a reduction of the scanner size. This camera sensor is used to build a complementary 3-D optical model as well as to estimate the millimeter-wave scanner position so that the imaging merging techniques can be applied. The approach is validated for concealed weapon detection by means of simulation as well as measurements, in which the scanner aperture is emulated by raster scan, showing a performance comparable to the case of dense arrays.

SVD-Based clutter removal technique for gpr

The main goal of this contribution is to present a clutter reduction technique for Ground Penetrating Radar (GPR) imaging. The proposed technique is based on a subspace projection method applied to the focused Synthetic Aperture Radar (SAR) image. It consists of decomposing the image in its different eigenimages and classifying them as belonging to clutter, target or noise subspaces. Several scenarios have been simulated in order to test this technique and its performance has been measured analyzing the variation in the Signal-to-Clutter Ratio (SCR). In addition, it has been compared with background subtraction and other subspace projection methods.