We present and discuss the case for full waveform pixel and image acquisition and processing to enable LiDAR sensors to penetrate and reconstruct 3D surface maps through obscuring media. To that end, we review work on signal propagation, on scanning and arrayed sensors, on signal processing strategies for independent pixels and employing spatial context, on reducing complexity and accelerating processing by sensor design, algorithmic changes, compressed sensing, and parallel processing. We report several experimental studies on LiDAR imaging through complex media, and how these can inform the automotive LiDAR scenario. We conclude with a discussion of future development and potential for full waveform LiDAR (FWL).

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Full Waveform LiDAR for Adverse Weather Conditions

In this letter, we report initial experimental results which provide the foundation for low-terahertz (low-THz) radar imagery for outdoor unstructured scenarios as expected in automotive sensing. The requirements and specifications for a low-THz single imaging radar sensor are briefly outlined. The imaging capabilities of frequency-modulated continuous-wave (FMCW) radar operating at 150 GHz are discussed. A comparison of experimental images of on-road and off- road scenarios made by a 150-GHz FMCW radar and a reference 30-GHz stepped-frequency radar is implemented, and their performance is analyzed.

Experimental Low-Terahertz Radar Image Analysis for Automotive Terrain Sensing

A novel broadband and wide-angle 2-bit coding metasurface for radar cross section (RCS) reduction is proposed and characterized at terahertz (THz) frequencies. The ultrathin metasurface is composed of four digital elements based on a metallic double cross line structure. The reflection phase difference of neighboring elements is approximately 90° over a broadband THz frequency. The mechanism of RCS reduction is achieved by optimizing the coding element sequences, which redirects the electromagnetic energies to all directions in broad frequencies. An RCS reduction of less than −10 dB bandwidth from 0.7 THz to 1.3 THz is achieved in the experimental and numerical simulations. The simulation results also show that broadband RCS reduction can be achieved at an incident angle below 60° for TE and TM polarizations under flat and curve coding metasurfaces. These results open a new approach to flexibly control THz waves and may offer widespread applications for novel THz devices.

/pdf/broadband-and-wide-angle-rcs-reduction-using-a-2-bit-coding-4aqqzswamr.pdf

Broadband and wide-angle RCS reduction using a 2-bit coding ultrathin metasurface at terahertz frequencies

In this paper, we propose a forward scanning synthetic aperture radar methodology for a forward-looking automotive (low-terahertz) radar, which combines scene scanning with synthetic aperture processing, resulting in enhanced angular resolution and improved imaging. We propose two algorithms, first, a modified back-projection (BP) algorithm and, second, a compressed sensing-based BP algorithm. We suggest techniques to reduce computational complexity of the proposed algorithms. Results of simulation and real-data experiments corroborate the validity of our proposed methodology and algorithms.

/pdf/imaging-for-a-forward-scanning-automotive-synthetic-aperture-42i3vezydx.pdf

Imaging for a Forward Scanning Automotive Synthetic Aperture Radar

This paper reviews the state of emerging transistor technologies capable of terahertz amplification, as well as the state of transistor modeling as required in terahertz electronic circuit research. Commercial terahertz radar sensors of today are being built using bulky and expensive technologies such as Schottky diode detectors and lasers, as well as using some emerging detection methods. Meanwhile, a considerable amount of research effort has recently been invested in process development and modeling of transistor technologies capable of amplifying in the terahertz band. Indium phosphide (InP) transistors have been able to reach maximum oscillation frequency (fmax) values of over 1 THz for around a decade already, while silicon-germanium bipolar complementary metal-oxide semiconductor (BiCMOS) compatible heterojunction bipolar transistors have only recently crossed the fmax = 0.7 THz mark. While it seems that the InP technology could be the ultimate terahertz technology, according to the fmax and related metrics, the BiCMOS technology has the added advantage of lower cost and supporting a wider set of integrated component types. BiCMOS can thus be seen as an enabling factor for re-engineering of complete terahertz radar systems, for the first time fabricated as miniaturized monolithic integrated circuits. Rapid commercial deployment of monolithic terahertz radar chips, furthermore, depends on the accuracy of transistor modeling at these frequencies. Considerations such as fabrication and modeling of passives and antennas, as well as packaging of complete systems, are closely related to the two main contributions of this paper and are also reviewed here. Finally, this paper probes active terahertz circuits that have already been reported and that have the potential to be deployed in a re-engineered terahertz radar sensor system and attempts to predict future directions in re-engineering of monolithic radar sensors.

https://www.mdpi.com/1424-8220/19/11/2454/pdf

Emerging Transistor Technologies Capable of Terahertz Amplification: A Way to Re-Engineer Terahertz Radar Sensors.

Millimeter-wave (MMW) radar, which is used for road feature recognition, has performance that is superior to optical cameras in terms of robustness in different weather and lighting conditions, as well as providing ranging capabilities. However, the signatures of road features in MMW radar images are quite different from that of optical images, and even physically continuous features, such as road edges, will be presented as a set of bright points or spots distributed along the roadside. Therefore, discrimination of the radar features is of paramount importance in automotive imaging systems. To tackle this problem, an approach called the stripe Hough transform (HT) is introduced in this paper, allowing enhanced extraction of the geometry of the road path. The performance of the approach is demonstrated by comparison of extracted features from MMW images with the real geometry of the road and with the results of processing by classical HT.

Road Edge Recognition Using the Stripe Hough Transform From Millimeter-Wave Radar Images

In this paper low-THz FMCW radar is introduced for automotive applications. Ability to produce a short-range high resolution image of the road ahead of the vehicle under any weather or terrain conditions is a considerable advancement for the automotive use. The 150 GHz FMCW radar requirements and specifications are discussed in this paper. The imaging performance of the 150 GHz radar in a real road scenario is demonstrated; the experimental results of the 150 GHz FMCW and a 30 GHz stepped frequency radar are presented and compared to each other.

Low-THz imaging radar for outdoor applications

In this paper the requirements for low-THz automotive sensors are presented with the focus on THz imaging of the terrain in front of the vehicle. Initial imaging performance at 150 GHz radar is demonstrated and a planned extension using an advanced 300 GHz radar system is described. Antenna requirements for these systems are discussed.

Antenna range evaluations of low THz imagers for automotive applications

A decoupling network for improving the isolation between two highly coupled antennas is proposed. In this method the input signals are combined linearly so that the mutual coupling between the ports becomes zero. The scattering matrix of the network is found using a mathematical procedure and has been demonstrated in this paper for a previously developed integrated wide/narrow band antenna. For this antenna the network can be realised using a rat race coupler and phase shift elements. Measurement results show that the mutual coupling has improved by 30 dB.

Donya Jasteh

Papers

Experimental Low-Terahertz Radar Image Analysis for Automotive Terrain Sensing

Road Edge Recognition Using the Stripe Hough Transform From Millimeter-Wave Radar Images

Low-THz imaging radar for outdoor applications

Antenna range evaluations of low THz imagers for automotive applications

Feed network for antenna decoupling