In this article, a polarimetric millimeter-wave FMCW radar operating in the 222-228 GHz frequency range is proposed for mapping applications in indoor environments. Equipped with a mechanically scanning fan-beam reflector antenna with 360° field of view, the radar can generate 2D images of its scene, offering LiDAR-like azimuthal resolution of 0.3°. The system’s performance for indoor mapping as well as Line-of-Sight (LOS) and None-Line-of-Sight (NLOS) obstacle detection tasks is demonstrated in building corridors. The measurement scenarios include various wall types and wooden doors with metallic frames. The overall corridor map is created by taking multiple radar images and combining them through post-processing. Given the strong presence of ghost targets in the radar images, an algorithm is developed for NLOS target detection and localization. As a foundation for this investigation, the wave reflection coefficients of painted drywall for both vertical and horizontal polarizations, ΓVVand ΓHH, are measured. Based on these results, a novel technique for NLOS target identification using polarization discrimination is proposed and experimentally verified. This technique is further tested in a realistic scene, where an L-shaped corridor is mapped using the polarimetric radar measurement, and NLOS targets are detected and localized using a mirroring transformation.

Mapping the electromagnetic permittivities and thicknesses of underground layers is a vital step for proper focusing and image formation in subsurface imaging radars. Compared to traditional ground penetrating radar (GPR) that samples the scattered field along straight lines, detailed spatial information can be obtained using the concept of a newly developed subsurface multistatic synthetic aperture radar (SAR). For such system the scattered field samples are acquired along arbitrary multistatic paths. In this paper, an inversion algorithm for mapping underground layers using a multistatic subsurface SAR system is proposed. The algorithm forms a forward scattering model (FM) for the underground layers based on image theory and the generalized reflection coefficient of the layers. Subsequently, the misfit between the FM and the radar response is minimized with stochastic hill-climbing (SHC) algorithm to achieve inversion. The algorithm is tested on several full-wave simulation scenarios under noisy conditions demonstrating its potential effectiveness for mapping underground layers.

This paper presents a thorough phenomenological study of the responses of human subjects to millimeter-wave radars operating at J-band (220-325 GHz). In highly automated vehicles, identifying vulnerable road users such as pedestrians and bicyclist on the road and its vicinity is crucial. This paper presents various characteristics of the human body response to J-band radars and possible detection and identification techniques.

Detection and localization of buried pipelines is an important problem for oil and water distribution industries as well as for excavation and construction companies. The unique scattering mechanism exhibited by pipelines under multi-static radar configuration makes their detection and localization a challenging task. This is because the scattering phase centers (SPCs) along the pipelines change depending on the relative position between the transmitter and receiver which makes point-target based focusing algorithms such as back projection (BP) rather ineffective. To address this issue, this paper uses a special technique for determining the pipelines’ SPCs to construct a first order forward scattering model of multiple buried pipelines that considers the propagation phase and amplitude attenuation. After that, a cost function representing the misfit between the forward model and the radar response is defined. Minimization of such cost function leads to the simultaneous detection and localization of the buried pipelines. Comparison results with a basic focusing algorithm relying solely on the scattered field phase shows the superior ability of the cost function approach to resolve closely spaced buried pipelines.

A mechanically scanned high-resolution 2-D imaging radar system with full 360° Field-of-View (FoV) is presented. The system is composed of a multi-function 222-228 GHz frequency modulated continuous wave (FMCW) radar and a moment of inertia optimized 3-D printed offset reflector antenna. The reflector geometry is made from anElliptic Toroidalsurface which is shown to produce a high-gain fan-beam with an 11:1 aspect ratio. The reflector is rotated at speeds up to 10 Hz for high throughput imaging. The wobble generated by the high speed rotation is suppressed by optimizing the mass distribution of the reflector body. It is fabricated in-house using a low-cost table-top Fused Deposition Modelling (FDM) 3-D printer. The reflecting surface is metallized with a silver coated copper paint and processed using simple steps to ensure smoothness and accuracy. The reflector achieves beamwidths of 4.6° in elevation and 0.42° in azimuth, with a peak gain of 38.7 dBi. The 3 dB azimuthal resolution of the radar two-way beam is measured to be 0.3°. The system is tested in real-world scenarios and the resulting images and videos are of unprecedented quality due to the large area of coverage, high resolution, high speed and excellent dynamic range. To the best of our knowledge, this is the first demonstration of a compact radar system that is comparable in resolution, speed and angular coverage to lidars, while offering higher dynamic range and immunity to severe weather and lighting conditions.

Radars operating at the higher region of the millimeter-wave frequencies are proposed to applications in new generation of automotive radars. This work is conducted to provide the base knowledge required to optimize the design and operation of such radars. Scattered signals by road surfaces provide useful information in recognizing the road condition and assessing the navigation. The radar polarimetric responses at near-grazing incidence angles of various road surfaces are characterized experimentally. Asphalt and concrete, being the most popular surfaces, are carefully measured and characterized in dry conditions. Road surface that are wet, ice-covered, or snow-covered are also examined.

A high resolution 3-D images of underground objects might be achieved using bistatic subsurface synthetic aperture radar (SAR) due the bistatic configuration's ability to view the objects from multiple angles. However, a major obstacle preventing the imaging is the dominance of the direct and ground reflection signals over the scattered signals from the buried objects. This paper presents a technique to mitigate such obstacle. By utilizing the multiple sampling points SAR provides, each adjacent sampling points are processed together as two-element array that has a null along the direction of the direct and ground reflection signals leading to significant enhancement for the scattered signals from the buried objects. The technique is explained and both simulation and measurement results for buried metallic objects are presented as a test of performance.

Multi-static subsurface synthetic aperture radar (SAR) is a promising tool capable of providing 3-D high resolution images of targets buried underground. The high detection capability of the system stems from the fact that the multi-static configuration allows for viewing the targets from many directions. However, a primal limiting factor for such configuration is the dominance of the direct and ground reflection signals over the scattered target signal hindering the system sensitivity. This letter presents a simple technique to overcome such drawback. By an appropriate utilization of SAR data, each adjacent sampling points are co-processed together as a two-element array in such a way as to have a null along the direction of the direct and ground reflection signals suppressing such signals and making the target signals more discernible. The technique is described in details and the potential problems arising from array processing are discussed. Additionally, a modified version of back projection imaging algorithm suitable for the array is provided. The performance of the proposed technique is assessed by simulation data of buried metallic spheres as well as measurement data for a buried metallic pipeline. Both simulation and measurements show a significant improvement in target detection and image quality.

This paper presents novel detection and target identification techniques for a polarimetic J-band millimeter-wave automotive radars. Three major target categories are considered, and extensive experimental and numerical data have been generated to find unique features of different target types. The response of vehicles is experimentally studied to build scattering maps for different kinds of cars. The radar backscatter response level from road surfaces is investigated and possible applications such as lane detection and road condition recognition are discussed. Sample results for each target type is presented to illustrate the suggested detection techniques. A method for micro-Doppler spectrum measurements of a moving human body is suggested as a very useful and unique feature to detect pedestrians in traffic scenes.

This paper proposes radar sensors operating at J-band (220-320 GHz) for automotive applications. Operating at J-band, at about three times higher frequency than the currently available automotive radars operating at 77 GHz, will result in three-fold improvement in cross-range resolution for the same antenna size. Since the characterization of the radar backscatter from different objects on the traffic scenes is necessary for optimizing the design of automotive sensors, the work reported in this paper is the start of a broader study that attempts to fill the lack of knowledge on radar backscatter behavior of road environment at this frequency band. Considering vehicles as the most important object for automotive radars, this paper investigates the response of vehicles from different aspects. A combination of outdoor high-resolution synthetic aperture radar imaging experiments and real-aperture imaging measurements of vehicles are performed using a 222-GHz polarimetric instrumentation radar. The aim of these experiments is to identify the scattering centers on different vehicle bodies and to determine the statistics of the radar return. The results show that significant scattering is due to a limited number of fixtures on the vehicle's outer surfaces facing the radar. The strongest scattering phase-centers observed are due to specular reflections and, hence, have a strong dependence on the relative look angle. The statistics associated with backscatter from vehicles are found, in most cases, to best fit the Weibull distribution.

This paper summarizes the results of an extensive study to model the statistics of the polarimetric backscatter response of vehicles at 222 GHz. Radars operating at high millimeterwave frequencies provide the necessary high azimuth resolution envisioned for many advanced applications of automotive radars, including autonomous vehicles. The data of many polarimetric measurements of vehicles are used here to extract the statistical behavior of radar scattering from vehicles. It is found that the radar statistics for a given vehicle are different as the percentage of the illuminated area of the vehicle is changed. The Weibull distribution is found to be the best fit to all measured data, with its shape parameter adjusted for different types of vehicles, radar polarization, and percentage illumination area. The results reported in this paper should provide valuable information for developers of such radars to optimize the performance of their detection and classification algorithms.

A microstrip lowpass filter based on transmission line elements for UWB medical applications is proposed in this paper. The filter is constructed of two symmetric shunt open‐circuited stubs and three series unit elements. The filter is designed to exhibit an elliptic function response with equal ripple in the passband and the rejection band. A prototype is successfully designed, fabricated, and measured, where a good agreement is attained. The filter shows a high filtering selectivity and an ultra‐wide stopband up to 20 GHz with an attenuation level of more than 20‐dB. The filter is compact and has a low insertion loss and an ultra‐wideband (UWB) rejection which makes it attractive for many technologies such as UWB medical applications.

The paper reports on an extensive set of outdoor measurements aimed at characterizing the polarimetric radar backscatter response of vehicles at 222 GHz. This effort supports the future application of high frequency radars operating around 230 GHz in autonomous vehicle navigation and collision avoidance. It is observed that radar backscatter is primarily from the outer surfaces of the vehicle and that few strong scattering centers dominate the radar return. Derived radar statistics from reported data may be used by researchers in optimizing detection.

This paper reports on a set of radar experiments conducted at 222 GHz in support of envisioned application of radars to autonomous vehicles. The measured radar backscatter data of road surfaces at incident angles between 80 and 88oare presented. The polarimetric radar response level from different surfaces encountered in roads and highway environments and the angular dependency are discussed. The results are helpful in developing models for different surfaces and in the design process and assessment of autonomous vehicles sensors.

A compact millimeter-wave bandpass filter for automotive radar systems is developed and proposed in this paper. The filter is designed to select the UWB spectrum (2229GHz) to meet the FCC specifications. The filter consists of two of parallel-coupled line sections that are quarter-wavelength long at a center frequency of about 25.5 GHz. In order to improve the filter performance and to allow the filter to exhibit a new transmission zero at each side of the passband, a shunt ring resonator and a shunt stepped-impedance open-circuited stub are loaded at the center between the coupled line sections. As a result, the filter can exhibit a high selectivity filtering characteristic. The filter design is realized using RT/duroid 6002 substrate and the design is verified by the EM simulation and the experiment. The filter design is successfully fabricated and measured and a very good agreement between the simulated and measured results is attained. The fabricated filter is compact in size and has low insertion loss, high selectivity and excellent out-of-band performance.