The aim of this paper is to present a freehand scanning system with a compact mm-wave radar. In order to achieve high-resolution images, the system exploits the free movements of the radar to create a synthetic aperture. However, in contrast to conventional synthetic aperture radar (SAR), in which canonical acquisition surfaces (e.g., planes or cylinders) are used, the system allows for a given tolerance compatible with real handmade trajectories. Moreover, different techniques are studied to compensate for the impact of irregular sampling to reduce the artifacts in the image. As a result, real-time scanning can be readily performed even by inexperienced users. The scanning system, comprising a commercial motion capture system and an mm-wave module, can be easily deployed and calibrated. Several results involving different objects are shown to illustrate the performance of the system. INDEX TERMS SAR imaging, mm-wave imaging, FMCW radar, real-time imaging, freehand scanner.
In recent years, Unmanned Aerial Vehicles (UAV)-based Ground Penetrating Radar (GPR) systems have been developed due to their advantages for safe and fast detection of Improvised Explosive Devices (IEDs) and landmines. The complexity of these systems requires performing extensive measurement campaigns in order to test their performance and detection capabilities. However, UAV flights are limited by weather conditions and battery autonomy. To overcome these problems, this contribution presents a portable and easily-deployable measurement setup which can be used as a testbed for the assessment of the capabilities of the airborne system. In particular, the proposed portable measurement setup replicates fairly well the conditions faced by the airborne system, which can hardly be reproduced in indoor GPR measurement facilities. Three validation examples are presented: the first two analyze the capability of the measurement setup to conduct experiments in different scenarios (loamy and sandy soils). The third example focuses on the problem of antenna phase center displacement with frequency and its impact on GPR imaging, proposing a simple technique to correct it.
Airborne-based Ground Penetrating Radar (GPR) systems have proved to be an efficient solution for safe and accurate detection of buried threats such as Improvised Explosive Devices (IEDs) and anti-personnel and anti-tank landmines. The design of these prototypes is influenced by several parameters such as the working frequency band or the maximum weight and size of the payload to be placed on board the Unmanned Aerial Vehicle (UAV). In this sense, one of the main bottlenecks found in the design of these systems is the proper selection of the GPR antenna. This contribution focuses on the analysis of different Ultra Wideband (UWB) Vivaldi antennas and their performance in the context of an airborne-based GPR system. First, the Vivaldi antennas are characterized in terms of S 11 , radiation pattern, directivity, and phase center. Next, they are placed on board the implemented airborne-based GPR prototype to assess their impact on the detection capabilities of the system. In addition, other criteria such as the weight and size of the antennas are considered to make the final selection. Finally, the selected UWB Vivaldi antennas are tested in a realistic scenario.INDEX TERMS Ground Penetrating Radar (GPR), Ultra Wideband (UWB) antenna, Vivaldi antenna. Unmanned Aerial Vehicle (UAV), Synthetic Aperture Radar (SAR), antenna measurement.
This paper presents a freehand imaging system, which takes full-advantage of a compact multiple-input multipleoutput (MIMO) radar to provide real-time results by means of freehand movements. The system is based on a commercial radar-on-chip, equipped with four receivers and two transmitters, and an optical tracking system (i.e., motion capture system) for retrieving its position and attitude. The reduced size of the radar enables its handheld operation, making possible to create a synthetic aperture by moving the scanner over the area of interest. Due to the new degrees of freedom with respect to previous implementations based on quasi-monostatic topologies, a novel calibration strategy for the system is required in order to mitigate positioning errors. After calibration, simulations and measurements are accomplished revealing that the novel freehand multistatic setup significantly outperforms the monostatic setup in terms of scanning speed and image quality. Multimedia material is provided to illustrate this performance.
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