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Radar-based gesture recognition can play a vital role in autonomous vehicles’ interaction with vulnerable road users (VRUs). However, in automotive scenarios the same gesture produces strongly differing radar responses owing to the wide range of variations such as position, orientation, or ego-motion. Since including all kinds of modifications in a measured dataset is laborious, gesture simulations alleviate the measurement effort and increase the robustness against edge and corner cases. Hence, this article presents a flexible geometric human target model allowing the direct introduction of a wide range of modifications, while it facilitates the handling of shadowing effects and multiradar constellations. Using the proposed simulation model, a dataset recorded with a radar sensor network consisting of three chirp sequence (CS) radars is resimulated based on the motion data simultaneously captured with a stereo video system. Completely substituting the measured by the simulated data for training, a convolutional neural network (CNN) classifier still achieves 80.4% cross-validation accuracy on a challenging gesture set, compared with 89.4% for training on the measured data. Moreover, using the simulated data the classifier is shown to successfully generalize to new scenarios not observed in measurements. [ABSTRACT FROM AUTHOR]

With radar networks, the resolution of critical radar parameters such as Doppler and angle can be improved compared to a single radar sensor. As the network’s aperture is considerably larger than that of a single radar, a much higher angular resolution is achieved. However, with a large aperture, range-dependent phase deviations, that is, near-field effects, occur and affect the angle estimation. In this work, these near-field effects are evaluated exemplarily for a coherent network. Furthermore, a new strategy to compensate for those network near-field effects is proposed and demonstrated based on measurements. The benefits of the near-field compensation are emphasized by comparing the network’s angle-estimation capabilities with and without compensated near-field effects. [ABSTRACT FROM AUTHOR]

The field of multicopter unmanned aerial vehicles (UAVs) has seen massive technological advances and decreasing costs over the last decade. Due to the higher prevalence and availability of these multicopter UAVs, there have also been rapid improvements in the software interfaceability, enabling the easy integration of custom software for flight planning and controllers. This opened up completely new possibilities, such as low-cost individual aerial photography, the most common civilian application. Furthermore, lightweight multicopters became widely accessible to the public, boosting the development of UAVs even more. [ABSTRACT FROM AUTHOR]

Reflectarrays and tunable surfaces receive increasing attention for wavefront engineering in the upper millimeter-wave range. As chip-based phase shifters can now be integrated with antenna elements, the performance verification at unit cell (UC) level is of great interest for a cost-efficient investigation of large-scale arrays. In this article, two UC designs with integrated phase shifter and on-chip antenna are evaluated experimentally at 240 GHz. For the first time, a single element is characterized above 100 GHz by applying the classic waveguide simulator technique. Since this method is mechanically problematic at high frequencies due to small dimensions and mechanical tolerances, an alternative approach involving a near-field probe is presented and investigated. The results for both measurement methods are compared and interpreted, assisted by full-wave simulations. [ABSTRACT FROM AUTHOR]

For autonomous driving vehicles, highly accurate representations of the environment are essential for both trajectory planning and self-localization. Different possibilities allow to generate detailed maps of the environment based on chirp-sequence radar sensors for advanced driver assistance systems (ADASs). For the first time, this letter shows a qualitative comparison between synthetic aperture radar (SAR)- and occupancy grid map (OGM)-based environment representation using identical measurement data. The differences of existing signal processing chains as well as a visual measurement-based comparison of the resulting environmental maps is presented. [ABSTRACT FROM AUTHOR]

This paper presents broadband multimode antennas for multiple-input multiple-output (MIMO) and diversity applications. The antenna system is not based on spatial diversity, as usual MIMO systems, but on a combination of pattern and polarization diversity. Different modes of self-complementary, thus extremely broadband, spiral and sinuous antennas are used to decorrelate the signals. It is shown that only one antenna is necessary to receive three uncorrelated signals, thus the space required to place the MIMO antenna is very small. Simulation results and measurements of a typical indoor scenario are given. Index Terms--Multimode diversity, multiple-input multiple-output (MIMO), sinuous antenna, spiral antenna.

A framework to analyze compact arrays for multiple-input-multiple-output (MIMO) is presented. Many handheld devices require very compact arrays. Small spacings between the antennas lead to mutual coupling, which decreases the efficiency of the antennas and therefor the signal-to-noise ratio and leads to correlated signals at the antennas. Both effects are completely taken into account in this framework; thus, it allows for a fair comparison of different antenna arrays for MIMO. It is distinguished between MIMO systems for multiplex transmission or pure beamforming, which have different requirements for the antennas. Different compact array configurations, which exploit spatial, polarization, and pattern diversity, are discussed and compared. For practical purposes, it is also shown how to connect this framework to standard path-based channel models. Index Terms--Antenna arrays, antennas for terminals, compact antennas, multiple-input-multiple-output (MIMO), mutual coupling, network theory, polarization diversity, terminals.

For unmanned aerial vehicles (UAVs), grid maps can be a versatile tool for navigation and self-localization. In general, payload is critical for UAVs and every additional sensor limits the flight duration. Due to its robustness and the ability to directly measure velocities, radar sensors are well suited for sense and avoid applications (SAAs) for UAVs. It would be advantageous if these sensor data could be used to generate grid maps instead of mounting additional sensors such as light detection and ranging (LiDAR). This letter demonstrates that using the data from high-resolution multiple-input–multiple-output (MIMO) imaging radars, high-resolution 2-D and 3-D radar grid maps can be created. The necessary adaption of the sensors free-space model for MIMO radar-based occupancy grid maps is presented in detail. UAV-borne measurements resulting in 2-D and 3-D grid maps with an adequate representation of the environment validate this approach. [ABSTRACT FROM AUTHOR]

Biomimetic antenna arrays inspired by the fly Ormia ochracea showed a promising improvement of the angle estimation capabilities of radar sensors. So far, there is usually a loss of output power associated with this improvement decreasing the detectability of weak radar targets. In this letter, an electronically switchable two-element biomimetic antenna array is presented for the first time. This array provides the possibility to switch between a biomimetic antenna mode with enhanced phase sensitivity and a conventional antenna mode with a better signal-to-noise ratio. Circuit requirements are discussed, the design process is described, and a realization in the 77 GHz range using p-i-n diodes as switching elements is presented. Radar measurements verify the concept. By switching, the phase sensitivity of the realized array can be enhanced by a factor of three with a relative power loss of maximum 14 dB. [ABSTRACT FROM AUTHOR]

The improvement of the angular resolution of radar sensors is one of the crucial goals of current radar research. A promising approach to achieve this goal is inspired by the ears of a fly called Ormia ochracea. The working principle was adapted for antennas, and the so-called biomimetic antenna arrays (BMAAs) aroused the interest of several research groups. In this work, BMAAs are incorporated into multiple-input multiple-output (MIMO) arrays, a very common approach of improving the angular resolution, to gain more degrees of freedom in array design. The MIMO BMAAs are modeled utilizing the effective biomimetic antenna distance, a fundamentally new measure introduced in this article to translate the special biomimetic phase progression into a spatial quantity. We present straightforward antenna configurations but also describe how a genetic algorithm can be utilized to optimize both antenna positions and BMAA parameters. The proposed arrays show various beneficial effects such as a wider angular range for unambiguous angle estimation or a narrower beamwidth. The impact of MIMO BMAAs on the angular resolution is thoroughly analyzed both theoretically and by radar measurements in the range of 77 GHz. The measurements confirm the modeling method very well and show a significant increase in the angular separability. [ABSTRACT FROM AUTHOR]

Lidar is considered to play an essential role on the road towards fully autonomous driving. In this context, coherent lidar systems hold the potential for lean, efficient and inexpensive sensors, but their performance depends significantly on suitable modulation and signal processing methods that can handle high Doppler shifts and enable high measurement rates at low computational complexities. This paper presents four novel phase-modulation-based approaches that utilize pseudo-random binary sequences to estimate target distances up to 180 m and the absolute value of target velocities up to 80 m/s. The corresponding system setup is lean, as it is based on only one phase modulator and one non-quadrature demodulator. The proposed methods are assessed analytically and by simulations and are compared in terms of computational complexity, detection performance, measurement rate and accuracy. The results demonstrate that while each approach has individual advantages and limitations, the proposed methods offer essential advancements in terms of measurement rate, multiplexing potential and multi-target capability, compared to already known methods. The feasibility of all presented approaches is validated by measurements. [ABSTRACT FROM AUTHOR]

In order to test and verify radar-based systems for advanced driver assistance systems, radar target simulators offer a test environment for reproducible dynamic automotive scenarios. This article presents a system capable of generating multiple targets with individual ranges and velocities for chirp-sequence frequency modulated continuous waveform radars. The novel approach allows to generate targets without prior knowledge about the radar sensor by estimating the radar’s waveform parameters. The proposed simulator offers high flexibility at low costs by performing the estimation on undersampled data. Finally, an automotive scenario of a spatially extended target is simulated for a radar sensor with the proposed system. [ABSTRACT FROM AUTHOR]

Emerging digital radar concepts such as orthogonal frequency-division multiplexing (OFDM) allow flexible signal generation. This opens up new opportunities in waveform design in a multiple-input multiple-output (MIMO) system such as introducing coding for signal multiplexing. In this article, coded MIMO OFDM waveforms are proposed and investigated that allow continuous and simultaneous wideband transmission for all transmitters of a multiple transmit and receive antenna array for spatial radar environment perception. Challenges for coded MIMO OFDM radar operation are derived, and three coded MIMO strategies are introduced and analyzed. Their potential is validated and compared to the standard subcarrier interleaving OFDM approach using simulations and measurements of an experimental 4 ×  $ 4$ MIMO OFDM radar at 77GHz. [ABSTRACT FROM AUTHOR]

A Ka-band microstrip antenna based on PIN diodes with accurate extraction of equivalent circuit parameters for pattern reconfigurability is proposed in this work. With the increase in operation frequency, the parasitic effect introduced by PIN diodes has tremendous influence on the performance of reconfigurable antennas; hence, the conventional equivalent circuit parameters of the PIN diodes are not applicable for higher-frequency applications, such as millimeter-wave circuits and antennas. Therefore, accurate equivalent circuit models of the conventional PIN diodes are essential in the millimeter-wave reconfigurable antenna design. Based on the combination of simulation and experimental results, accurate equivalent circuit model parameters for the millimeter-wave range of the PIN diode are extracted, with a pattern-reconfigurable antenna being developed afterwards. The proposed antenna consists of two PIN diodes, two interdigital capacitors, an L-shaped slot, and their bias networks. Particularly, the interdigital capacitors are utilized to isolate direct current (DC) from radio frequency circuits, which is able to improve the economic efficiency of the antenna notably as compared with conventional chip capacitors in the Ka-band. By combining a suitable arrangement of the diodes' location and the DC bias networks, the main beam direction of the proposed antenna can be switched between −60° and 60°. To demonstrate the proposed idea, a prototype antenna is fabricated and measured. The measured results agree with the simulation quite well, with a good performance around 30 GHz and a gain greater than 5 dBi for both modes being achieved. [ABSTRACT FROM AUTHOR]

Presents information on the TC-29 Aerospace Microwave Systems-Technical Committee Report. [ABSTRACT FROM AUTHOR]

Next-generation radar sensors require imaging capabilities with high angular resolution. As for a single sensor, the aperture, and thus the achievable resolution, is limited due to the constraints of the front end, radar networks consisting of multiple sensors are a possible solution. However, their incoherency usually makes joint angle estimation impossible. This article presents a network concept consisting of an orthogonal frequency-division multiplexing (OFDM) radar and repeater elements, which receive the reflections from targets and retransmit them back to the radar. Thereby, any frequency conversion from radio frequency to baseband and vice versa is omitted such that the signal remains coherent to the initial transmit signal. To distinguish the bistatic signal transmitted by the repeater from the monostatic one of the OFDM radar, the orthogonal subcarrier structure of OFDM waveforms is exploited by combining a sparse radar transmit signal with a low-frequency modulation in the repeater. This allows to evaluate the bistatic signals at the radar with standard multiple-input–multiple-output (MIMO)-OFDM signal processing, leading to separate range–Doppler images for each virtual channel. Finally, it is shown that this method offers a coherent angular estimation based on the extended aperture of the network. For this purpose, a method to establish phase coherency by a reconstruction of the modulation phase is presented. The network concept is proved with measurements at 77 GHz. [ABSTRACT FROM AUTHOR]

In order to improve the resolution of imaging radars, electrically large arrays and a high absolute modulation bandwidth are needed. For radar systems with simultaneously high range resolution and very large aperture, the difference in path length at the receiving antennas is a multiple of the range resolution of the radar, in particular for off-boresight angles of the incident wave. Therefore, the radar response of a target measured at the different receiving antennas is distributed over a large number of range cells. This behavior depends on the unknown incident angle of the wave and is, thus, denoted as range-angle coupling. Furthermore, the far-field (FF) condition is no longer fulfilled in short-range applications. Applying conventional signal processing and radar calibration techniques leads to a significant reduction of the resolution capabilities of the array. In this article, the key aspects of radar imaging are discussed when radars with both large aperture size and high absolute bandwidth are employed in short-range applications. Based on an initial mathematical formulation of the physical effects, a correction method and an efficient signal processing chain are proposed, which compensate for errors that occur with conventional beamforming techniques. It is shown by measurements that with an appropriate error correction an improvement of the angular resolution up to a factor of 2.5 is achieved, resulting in an angular resolution below 0.4° with an overall aperture size of nearly 200 $\lambda _{0}$. [ABSTRACT FROM AUTHOR]

Have you read everything about direction-of-arrival estimation in textbooks but are still uncertain how to realize it in practice? This tutorial-like article will help to link the theory with a practical approach for direction-of-arrival estimation using millimeter-wave (mm-wave) radar systems, and it deals with arising challenges. Step by step, it is explained how to move from the measured time domain data to the estimated angular position of the target. Since the target angle estimation is usually carried out after range-velocity processing, the required preprocessing steps are described. [ABSTRACT FROM AUTHOR]

For highly integrated imaging systems above 100 GHz, the complexity and chip area increase significantly with an increasing number of channels. In addition, bulky dielectric lenses prevent applications in spatially restricted surroundings. The presented concept of an imaging monopulse radar with a mechanically flexible front end reduces the required chip area and allows the antenna to be placed in any desired position apart from the sensitive electronics. The radar system is based on a two-channel 160-GHz microwave monolithic integrated circuit (MMIC) feeding a flexible dielectric waveguide. Depending on the angle of the incidence signal, a sum mode (HE11 mode) and a difference mode (HE21 mode) are excited in the dielectric waveguide. MMIC and waveguide are connected by a self-aligning transition reducing the requirements for packaging accuracy. The required chip area of the transition is only $0.022\lambda ^{2}$ with a spacing between the on-chip antennas of $\lambda /4$. The measured ambiguity-free region between −18° and 15° is defined by the modified elliptical lens antenna focusing in the $E$ -plane only. A mechanical bending of the flexible waveguide is possible down to a radius of at least 2 cm without affecting the angle estimation capability. [ABSTRACT FROM AUTHOR]

In this article, an imaging system is presented, which is solely based on distributed radar sensors mounted on a mobile platform, such as a robot or vehicle. The data of multiple distributed sensors, which perform fast chirp-sequence measurements, are processed together. This enables both a highly accurate ego-motion estimation and a coherent synthetic aperture radar (SAR) imaging based on it. This system is independent of any additional sensors, such as an inertial measurement unit (IMU) for motion estimation or a global navigation satellite system (GNSS) for self-localization. Measurements using four sensors are carried out at 77 GHz to verify simulations. [ABSTRACT FROM AUTHOR]

Monostaticmultiple-input–multiple-output (MIMO) radar configurations using the same antenna array for transmission and reception inherently lead to redundant virtual antenna positions within the virtual MIMO aperture. This article presents a new method for designing monostatic MIMO radars where this disadvantage may be overcome and nonredundant virtual arrays are yielded by exploiting biomimetic antenna arrays (BMAAs). The new concept of biomimetic MIMO is introduced and thoroughly investigated in this article. Its working principle is compared with conventional monostatic MIMO and verified by radar measurements. The new approach is intended to improve the angle estimation capability of, in particular, small radar systems. Therefore, the concept is applied to an ultracompact two-channel radar monolithic microwave integrated circuit (MMIC) with fully integrated antennas for range and angle measurements in the 150-GHz range. The chip features two monostatic transmit–receive (TRX) channels with an antenna spacing of $\lambda /4$ and occupies less than 3 mm2 of space. By applying biomimetic MIMO, a virtual aperture consisting of four unique antenna positions and an equivalent total size of around $1.5\lambda $ is achieved. [ABSTRACT FROM AUTHOR]

This work introduces a method for coherent multiin multiout (MIMO) processing over a network of frequency-modulated continuous wave (FMCW) radar sensor nodes with independent signal synthesis. The coherency between the bistatic channels is established algorithmically based on the frequency and phase-offset estimation from pairs of sensor nodes and subsequent least-squares estimation on the overdetermined equation system. For the chirp-sequence radar, the proposed processing allows range and speed measurements, as offsets are estimated and corrected for each individual ramp. The applicability of the method is demonstrated in a prototypical setup of a radar network with three sensor nodes comprising integrated 122-GHz transceivers. The obtained bistatic phase precisions of < 0.1 rad approximately match those of the monostatic measurements of the same radar nodes. For a sequence of 30 ramps of 1-ms duration, this translates to ambiguous range precisions $ < 10~\mu \text{m}$ and speed precision < 1 mm/s. The absence of wired high-frequency links between the nodes makes the approach well suited for short-range radar networks in cost-sensitive applications. [ABSTRACT FROM AUTHOR]

Imaging radars are usually realized fully coherently. However, the distribution of one common radio frequency signal to all transmit and receive paths requires a high degree of hardware complexity. In order to reduce the hardware effort significantly, a novel phase synchronization method for incoherent and quasi-coherent frequency-modulated continuous-wave (FMCW) imaging radars with individual signal synthesis per channel is presented. The quasi-coherent setup uses one common oscillator for all frequency synthesizers. It is shown that in the case of the quasi-coherent system, only a phase difference between the calibration and the measurement has to be corrected to achieve coherence. In comparison, an incoherent system causes additional time, frequency, and FMCW ramp slope errors due to the different behavior of the oscillators. In order to achieve phase coherence and to correct the error sources, a calibration-based method using a defined signal path as part of the radar system is proposed. The imaging radar used for verification of the theory consists of individual single-channel radar monolithic microwave integrated circuits (MMICs) at 160 GHz; each MMIC fed by an individual frequency synthesizer. As shown by measurements, it is possible to achieve phase coherence for both system approaches and to perform angle estimation. [ABSTRACT FROM AUTHOR]

In this article, a method for the assessment of the performance and for the design of a 2-D-array for multiple input multiple output (2-D-MIMO) radar applications is presented. The proposed approach is based on the analysis of the ambiguity function associated with the array. Such analysis leads to the definition of an area in the 2-D-angular field-of-view of the radar, denoted as ambiguity-free region, characterized by a low probability to obtain ambiguities in direction of arrival estimation. Simulations of a basic 2-D-MIMO array are used to explain the proposed method, which is then employed as the main criterion for the optimization of a 2-D-MIMO sparse array composed of four transmitters and eight receivers. The optimization is performed through a genetic algorithm. The resulted element positions guarantee an ambiguity-free region span in the azimuth and elevation angles greater than 120° and angular resolutions of 8° and 5.9° on the azimuth and elevation angles, respectively. The optimized positions are then used to realize a 2-D-MIMO sparse array that is integrated in a radar system operating at a center frequency of 76.5 GHz. Such an array is calibrated, and comparisons between the simulated and measured ambiguity functions show the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The packaging technology for transitions to dielectric waveguides in the frequency range above 100 GHz is complex and must be highly precise, and the waveguides are usually permanently connected. This letter presents a transition from a monolithic microwave integrated circuit (MMIC) to a flexible dielectric waveguide at $G$ -Band (140–220 GHz), which is self-aligning and, thus, reduces the requirements for packaging accuracy. Furthermore, the transition is mechanically decoupled to avoid mechanical stress to the MMIC and to reconnect it arbitrarily often. A patch radiator on a quartz-glass carrier is excited by a coupler on the MMIC. It feeds the $\mathrm {HE_{11}}$ mode into a rigid, high-permittivity dielectric dome, which increases the coupling efficiency. The flexible dielectric waveguide is placed above the dome and fixed with Rohacell half shells. The minimum insertion loss measured with a back-end-of-line (BEOL) MMIC is 3.0 dB at 168 GHz. [ABSTRACT FROM AUTHOR]

Employing frequency bands above 100 GHz for future frequency-modulated continuous-wave (FMCW) radar applications necessitate hardware realizations as monolithic microwave integrated circuit (MMIC). Spurious signals stemming from hardware impairments deteriorate target detection performance, but hardware-based mitigation is not preferred, given the increased cost and size of the integrated circuits. Instead, signal processing-based mitigation is favored. In this article, an approach is proposed to mitigate hardware impairments by parametric, model-based signal processing. For one particular FMCW radar operating at 160 GHz, a behavioral model of the radar device is developed, which accounts for the hardware impairments. This device model is incorporated in the data model of a maximum-likelihood parameter estimator that both resolves target ranges and mitigates spurious signal components. The mitigation performance and the improved robustness of target detection of this approach in the presence of hardware impairments are demonstrated by measurements. [ABSTRACT FROM AUTHOR]

Antipersonnel fragmentation mines are relatively large metallic mines, which are only partially buried and often triggered by a metallic tripwire. In humanitarian mine clearance, the search for the wires is usually carried out manually. As a new approach, an airborne system for the detection of tripwires using a synthetic aperture radar is presented. The system consists of an industrial multicopter, a frequency-modulated continuous-wave radar, and a real time kinematic global navigation satellite system. For image formation, a backprojection algorithm is used. Measurements with tripwires attached to a dummy mine successfully demonstrate the functionality of this system approach. In addition, the influence of wire length, vegetation, and incidence angle are investigated. It is shown that several overflights with different directions of flight are required to detect randomly oriented tripwires. [ABSTRACT FROM AUTHOR]

A hybrid thin film multilayer antenna for automotive radar is presented in this work. A 2 × 8 aperture coupled stacked patch antenna array is realized on a single layer printed circuit board (PCB) using a novel thin film-based approach. Using a compact 180° phase difference power divider, inter-element spacing in a 2×2 sub-array is reduced. Measurement results show a 19% (67.9–82.5 GHz) impedance bandwidth and a wideband broadside radiation pattern, with a maximum gain of 15.4 dBi realized gain at 72 GHz. The presented antenna compares favorably with other multilayer PCB antennas in terms of performance, with the advantage of simpler manufacturing and robust design. The antenna can be employed in mid-range automotive radar applications. [ABSTRACT FROM AUTHOR]

This letter demonstrates different planar highly efficient on-chip antennas at 165 GHz with high gain utilizing a standard silicon-Germanium bipolar-complementary metal-oxide-semiconductor (Bi-CMOS) process with a localized backside etching (LBE) feature that allows cutting air trenches in the silicon. A dipole antenna, a folded dipole antenna with air trenches around the radiator, and a single-ended patch antenna with air trenches at the radiating edges are designed, fabricated, and characterized in the D-band (110–170 GHz). The geometry of each individual antenna and the LBE air trenches are optimized to meet both process reliability specifications and radiation performance simultaneously. Metal fillings effects on the radiation pattern and matching are also studied. [ABSTRACT FROM AUTHOR]

Digital modulations such as orthogonal frequency-division multiplexing (OFDM) have received increasing interest for radar. However, the required fast analog-to-digital (AD) and digital-to-analog (DA) converters providing the necessary bandwidth have not been feasible for automotive applications so far. In this paper, the first highly integrated, fully coherent OFDM radar capable of multiple-input multiple-output (MIMO) and stepped-carrier OFDM for automotive applications is presented. The stepped-carrier OFDM approach is adopted to reduce AD/DA requirements using an analog local oscillator (LO) frequency step generator. The capability to generate frequency steps with a duration of a few microseconds required for automotive applications is demonstrated. Calibration steps that are required with the new architecture are discussed and measurements are done to validate the functionality of the system. Also, possibilities for adaptive reconfiguration of the radar sensor in the presence of ambiguities are demonstrated. [ABSTRACT FROM AUTHOR]

Noncoherent detection schemes are an appealing and low-complexity alternative in multi-user massive MIMO uplink systems compared to classical coherent detection algorithms, since no actual channel knowledge is required at the receiver. For noncoherent multi-user detection to function, the induced power at the base station is utilized to separate the different users. However, spatial separation is impossible when the users are located in the far-field of the receiving antenna array. Consequently, noncoherent detection fails in such scenarios. To this end, beamspace techniques can be applied, focusing the energy of the incident wave to a smaller subset of the receive antennas and enabling again the noncoherent detection scheme. This paper analyzes the beamspace capabilities of a dielectric lens and an analog beamforming network applied at the receiver. Furthermore, a sub-array architecture is proposed, relaxing the design requirements for practical implementation. It is shown that noncoherent detection in combination with beamspace techniques performs comparably to channel-estimation-based detection. In addition, the sub-array architecture revealed a significant performance enhancement accompanied by a reduced user separability. [ABSTRACT FROM AUTHOR]

In this paper, a coherent multistatic radar network with a novel system architecture is presented, which circumvents the general problems of clock distribution and phase noise-related signal-to-noise ratio (SNR) issues. The proposed network consists of a variable number of multiple-input multiple-output (MIMO) radar sensors and a variable number of repeater tags, all of which operate incoherently on the hardware level. In a minimum configuration, the network only consists of one MIMO radar sensor and a repeater tag. The theory behind such a multistatic network is mathematically derived, and simulations are presented to show key aspects of the network, i.e., multistatic range and Doppler measurements, as well as high-resolution angle estimation, exploiting a very large virtual aperture spanning the whole network. Measurements with one sensor and one repeater tag at 77 GHz are carried out to verify the simulations. The measurements show that the bistatic path between the sensor and the repeater tag retains coherency. [ABSTRACT FROM AUTHOR]

A high-resolution frequency-modulated continuous wave imaging radar for short-range applications is presented. A range resolution of about 1 cm is achieved with a bandwidth of up to 16 GHz around 160 GHz. In order to overcome losses and large tolerances on a printed circuit board (PCB), eight coherently coupled monolithic microwave integrated circuits (MMICs) are used, each with one transmit and receive antenna on-chip and each representing a single-channel radar system. The signals on the PCB are below 12 GHz, which facilitates fabrication and enables a design with low-cost substrates. The MMIC comprises a phase noise (PN)-optimized architecture with a fully integrated on-chip frequency synthesizer. Due to partly uncorrelated PN between the frequency synthesizer components, the noise level is increased in bistatic radar measurements between two different MMICs, which is explained by a thorough PN analysis. Time-division multiplexing is used to realize a multiple-input multiple-output system with a virtual array of 64 elements and an angular resolution better than 1.5° for the designed array. The positioning tolerances of the MMICs are included into the design resulting in a robust array design. The high-resolution radar performance is proven by imaging radar measurements of two exemplary scenarios. [ABSTRACT FROM AUTHOR]

Autonomous driving is currently the focus of considerable media attention, and the automotive industry is working on harnessing technological advances to accelerate development. In doing so, different levels of automated driving must be mastered (Table 1) and defined [1]. At higher automation levels, the execution, monitoring, and fallback performance are increasingly handled by the system and not the human driver, resulting in more demanding requirements for the sensor system. As shown in [2], radar sensors are a key technology to enable Society of Automotive Engineers level 5, full automation. [ABSTRACT FROM AUTHOR]

Biomimetic antenna arrays (BMAAs) are antenna systems enabling an improved angle estimation for small apertures by mimicking the hearing system of the fly Ormia ochracea. This is achieved by a special kind of coupling applied to the antenna elements inspired by the insect. However, recent designs of BMAAs rely on a strong mutual coupling between the antenna elements. In this paper, it will be shown that the strong mutual coupling is not needed for a BMAA at the antenna side, and a generalized model of the biomimetic antenna system is theoretically derived, evaluated, and verified by measurements. This new model also gives an intuitive insight into the working principle of the biomimetic antenna system. [ABSTRACT FROM AUTHOR]

Modern consumer and industrial unmanned aerial vehicles (UAVs) are easy-to-use flying sensor platforms. They offer stable flight, good maneuverability, hovering, and even waypoint flights in autopilot mode. For stabilization and localization, sensors such as inertial measurement units (IMUs)-including gyroscopes and accelerometers-barometric sensors, and the Global Navigation Satellite System (GNSS) are used. To sense the UAV?s direct environment, e.g., for collision avoidance or fully automated flight, additional sensors are needed. State-of-the-art combinations of infrared, ultrasonic, and vision-based sensors (monocular and/or stereo vision) capture the close vicinity. Using radar sensors is advantageous, as they are able to directly sense range and velocity and are not affected by lighting conditions and contrast. With the help of a multichannel radar, the angular information may also be extracted. [ABSTRACT FROM AUTHOR]

On-chip antennas are frequently used as radiating elements for monolithic microwave integrated circuits (MMICs) operating above 100 GHz. Their radiation pattern is wide since the radiator extension is typically about half wavelength. In a package, the wide radiation pattern is easily disturbed by interference from parasitic radiation of the package. In this paper, an approach to minimize and adjust the interference of the package is proposed and applied to a quad flat no leads (QFN) package housing. A structured metal sheet positioned between chip and exposed pad is used to generate enough degrees of freedom for the optimization of the 3-D-radiation pattern in open-cavity and molded QFN packages. For the open-cavity QFN package, a U-shaped slot is introduced, which reduces the propagation of surface waves to the sides and creates a uniform radiation pattern. For the molded QFN package with opening around the on-chip antenna, a corrugated metal sheet is introduced. This leads to a robust packaged radar MMIC with an on-chip antenna at 160 GHz, which provides a directed radiation pattern to boresight. Both optimized radiation patterns are well suited for the illumination of dielectric lenses, which results in a higher lens gain and a lower sidelobe level of the lens pattern compared to the standard QFN packaging. The proposed concepts are verified by measurements for the open-cavity and molded QFN packages at 160 GHz. [ABSTRACT FROM AUTHOR]

A number of millimeter-wave (mm-wave) integrated radar sensors above 100 GHz were proposed in the past five years. The comparability between these radar systems is limited due to different semiconductor processes, synthesizer topologies, and external periphery. Especially, the issue of using a monostatic or bistatic radar monolithic microwave integrated circuit (MMIC) for single-chip sensors is not discussed in detail. This paper provides a comparison between the different properties of bistatic and monostatic MMICs based on two realized almost identical silicon germanium (SiGe)-MMICs at 154 GHz. In the monostatic case, the influence of the transmit–receive coupler on the performance of the system is explained. In the bistatic case, the illumination of a focusing lens and the leakage from transmitter to receiver are investigated. All properties are verified by measurements. The system performance of the monostatic and bistatic MMIC are compared by the calculated link and noise budget. The detection performance and the signal-to-noise ratio performance are evaluated in two radar measurements. Limitations and suggestions for improvement are given for monostatic and bistatic mm-wave frequency-modulated continuous-wave radar MMICs. [ABSTRACT FROM AUTHOR]

Leakage in frequency-modulated continuous-wave (FMCW) radar with a homodyne receiver induces strong signal components in the lower frequency parts of the radar observations. There, the dynamic range of the observations has been reduced, such that close and weak targets are hard to detect. In this letter, a signal processing method is proposed to mitigate the leakage. First, background subtraction is applied to cancel the leakage. As the cancellation is imperfect, a noisy signal portion remains: the leakage noise. A statistical model is developed to describe the leakage noise as a colored noise process. This model is parameterized from measurements and used to whiten the observations. As a result, the dynamic range is improved, and the close targets become better detectable. [ABSTRACT FROM AUTHOR]

The aerospace sector has experienced major evolutions over recent years through structural changes, initiated a couple of decades ago, that led to the very dynamic field we witness today. This triggered the need for a dedicated IEEE Microwave Theory and Technology Society (MTT-S) Technical Committee (TC) addressing this broad topic. As a result, the TC-29 on Microwave Aerospace Systems was founded in 2020 and recently reported on its activities. It covers the wide range of aerospace applications, from the ground to the space segment and everything in between, including unmanned aerial vehicles (UAVs), high-altitude platforms, and more generally, atmospheric satellites. This focused issue is the first of two focused issues sponsored by TC-29, providing a good overview of key areas of development related to microwave systems for aerospace applications. [ABSTRACT FROM AUTHOR]

A robust and wideband differential microstrip line-to-WR6-waveguide transition for mixed multilayer PCBs at $D$ -band is presented. The PCB stack is composed of three standard RF core materials with standard thicknesses. Compared to other inline transitions above 90 GHz, which are designed for single substrates, it can be applied to mixed multilayer circuits. The tapered transition is only 8.0-mm wide and 2.5-mm long, has an insertion loss between 1.2 and 1.8 dB, and a return loss higher than 10 dB for 30-GHz bandwidth around the center frequency of 120 GHz. [ABSTRACT FROM AUTHOR]

Multicarrier waveforms such as orthogonal frequency-division multiplexing (OFDM) found their way into radar applications in the last few years. However, currently, typically only a fraction of the large baseband bandwidth required to obtain high resolution is available in practice due to hardware limitations. In this paper, we propose a frequency-agile sparse OFDM radar processing that allows the transmission of consecutive bandwidth-reduced OFDM pulses on different carriers, and thereby covering a much larger measurement bandwidth in a measurement frame. Through joint processing of multiple narrowband pulses and compressed sensing methods, high resolution and unambiguity in the joint range-velocity profile are obtained comparable to an equivalent wideband OFDM. It shows that a baseband bandwidth of 20% of the full channel bandwidth is sufficient to reliably obtain the same result as for an equivalent wideband OFDM signal. The proposed processing scheme is validated using simulations and radar measurements at 77 GHz. [ABSTRACT FROM AUTHOR]

The requirement of fast analog-to-digital (AD) and digital-to-analog (DA) converters is a challenge for high-resolution orthogonal frequency division multiplexing (OFDM) radars. This paper introduces a method to increase the modulation bandwidth of an OFDM signal by using an additional frequency modulated continuous wave carrier to reduce the requirements for the AD/DA converters while maintaining a high unambiguous velocity range. Multiplexing of transmit antennas with OFDM is still possible with the combined modulation. The presented approach is verified by simulations and measurements. A reduction of AD/DA converter bandwidth by factor eight is achieved. [ABSTRACT FROM AUTHOR]

Automotive radar sensors for driver assistance systems are usually installed behind the bumper of the car. Multiple reflections between radar and bumper can occur and may lead to a wrong estimation of the direction of arrival of the signal reflected by the target. This paper presents an effective solution to improve the hidden integration of radars in a vehicle. In particular, this paper proposes the design of a low-radar cross section (RCS) millimeter-wave antenna array to reduce the reflections toward the car fascia. The design exploits the properties of artificial magnetic conductors (AMCs) to cancel out the wave backscattered by the antenna array. The integration of the AMC with the antenna array is analyzed in detail. The experimental results prove that the array with low RCS can mitigate the multiple reflections. Moreover, the measurement results show that the proposed antenna has 20 dB RCS reduction at 76 GHz. [ABSTRACT FROM PUBLISHER]

Recent publications show that the potential of using orthogonal frequency division multiplexing waveforms as radar signals. Since the range resolution is proportional to the RF bandwidth, the major obstacle that obstructs the practical use in automotive and other low-cost radars is the requirement to sample the received signal at sampling rates that span the whole RF signal bandwidth requiring ADCs with sampling rates in the order of GHz. This paper presents a method to achieve the high range resolution induced by a large RF bandwidth, but with a much lower baseband bandwidth, consequently requiring a much slower ADC while at the same time delivering a velocity profile for each subcarrier. In addition, the processing scheme induces a range migration compensation, independent of the number of targets. This is achieved with barely increased computational effort. The scheme is verified with simulations and measurements at 77 GHz. [ABSTRACT FROM PUBLISHER]

Due to various error sources, accurate integrated antenna measurements can be difficult to achieve. This study analyses the accuracy of a measurement set-up for radiation pattern (RP), directivity and gain measurements. The main sources of uncertainty are pointed out and the overall achievable accuracy is determined. The expanded uncertainty budgets for RP, directivity and gain measurements are 0.2, 0.2 and 1.7 dB, respectively. Furthermore, the phase centre of the antenna under test (AUT) is calculated for a more accurate and faster antenna alignment. The standard deviation of the calculated phase centre position is 50 μm on each axis. [ABSTRACT FROM AUTHOR]

A novel hybrid approach to designing multilayer antennas for automotive radar using a thin single layer printed circuit board and multilayer thin films is presented in this paper. A new substrate integrated waveguide (SIW) slot fed stacked grid antenna element is designed using this approach. The flexibility of this approach in designing antenna arrays is shown by integrating the same antenna element with three different feed networks based on SIW, grounded coplanar waveguide (GCPW), and microstrip (MS) transmission lines. The antenna is designed to operate in the frequency band between 77 and 81 GHz for automotive radar. Measurement results on $1\times 4$ arrays show an impedance matching bandwidth and a realized gain of 7.8% (76.3–82.5 GHz) and 9.2 dBi, respectively, for SIW feed antenna, 11.3% (76.3–85.5 GHz) and 10.7 dBi, respectively, for GCPW feed antenna, and 11.3% (75.7–84.8 GHz) and 12.1 dBi, respectively, for MS feed antennas. The proposed antenna can be used for medium- and short-range automotive radar applications. [ABSTRACT FROM PUBLISHER]

In radar measurements, the observed area is limited by the antenna beamwidth, and due to the usually fixed transceiver position, only unhidden targets in a small observation area can be detected. Furthermore, bulky lens dimensions prevent the use of radar systems in constricted surroundings despite the small dimensions of microwave monolithic integrated circuit (MMIC) radars. To avoid this issue, a new system concept for a flexible and low-cost 160-GHz radar sniffer probe is presented. The flexible sniffer probe is an extremely low-loss dielectric waveguide with a dielectric elliptical lens (28 dBi) at the end. The dielectric waveguide has dielectric losses of 4.5 dB/m at 160 GHz and high flexibility, supporting bending radii of 1.5 cm with negligible losses. To feed the dielectric waveguide, a metallic waveguide with a duplexer is used, which is fed by a special MMIC-to-metallic waveguide transition. The proposed system expands the known radar measurement scenarios with new industrial, medical, and security applications. [ABSTRACT FROM PUBLISHER]

The increasing demand for radar sensors and the wide distribution of handheld communication devices push the development of low-cost components with a small form factor. One approach to achieve smaller, low-cost devices is the integration of the required components on a monolithic microwaveintegrated circuit (MMIC). At frequencies above 100 GHz, passive components are small enough to be integrated onto a chip, and the advances in semiconductor technology make it possible to build active components that can operate at millimeter (mm)-wave frequencies [1], [2]. The available bandwidths of several gigahertz at mm-wave frequencies offer high data rates for communication devices or high resolution for remote-sensing applications. By integrating the radio-frequency (RF) components and the antennas, lossy off-chip transitions can be avoided, thus limiting the required connections to the power supply and baseband signals. [ABSTRACT FROM PUBLISHER]