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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]

The coupling matrix model is a helpful tool during synthesis and analysis of coupled resonator filters. Application of the coupling matrix for filter synthesis often requires the designer to reconfigure the coupling matrix to yield a specific matrix structure matching the topology of the filter. Currently, there is no closed-form solution known to this matrix reconfiguration problem. This paper proposes a new approach to solve this problem for coupling matrix representations of general lossy filters. The method is based on infinitesimal matrix rotations and can be considered as a continuous analog to the well-known coupling matrix similarity transforms. The results shown indicate good convergence behavior of the reconfiguration algorithm, as well as the ability of the method to always keep the desired scattering parameter goal. Based on this algorithm, a method for coupling matrix extraction of lossy filters is presented and successfully evaluated using simulated and measured scattering parameter data. [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 wily 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. [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]

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]

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]

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]

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]

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]

As driver assistance systems and autonomous driving are on the rise, radar sensors become a common device for automobiles. The high sensor density leads to the occurrence of interference, which decreases the detection capabilities. Here, digital beamforming (DBF) is applied to mitigate such interference. A DBF system requires a calibration of the different receiving channels. It is shown how this calibration completely changes the DBF beam pattern required to cancel interferences, if the system has no IQ receiver. Afterward, the application of DBF on a multiple-input multiple-output (MIMO) radar is investigated. It is shown that only the real aperture and not the virtual one can be used for interference suppression, leading to wide notches in the pattern. However, for any target the large virtual aperture can be exploited, even if interferers are blinded out. Moreover, the wide notches for interference suppression of the real aperture appear narrow in the virtual aperture for target localization. The results are verified by measurements with time-multiplexing MIMO radar. [ABSTRACT FROM AUTHOR]

In this paper, an incoherent radar network based on integrated radar sensors is presented. It consists of radar sensor nodes with independently generated frequency-modulated continuous wave-modulated transmit signals, performing both monostatic and bistatic distance measurements. An architecture to operate such a cooperative bistatic network is introduced and an optimal parameterization of the system is presented. Several nonidealities of frequency synthesizers, that are important for such cooperative radar networks, are discussed and their influence on system performance is evaluated. A prototype of the cooperative bistatic network has been realized using highly integrated radar sensors at 122 GHz. Radar measurements using the prototype prove the feasibility and potential of the network approach. The complete signal processing chain is presented, including an adapted multilateration algorithm for target position estimation using all measured distances. [ABSTRACT FROM PUBLISHER]

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]

• A covariance matrix model for data sets gathered by MIMO sensing systems is presented. • A ML estimator is proposed to estimate the model parameters, which gives a non-convex cost function. • Generalised eigenvalue decomposition is used to efficiently calculate the inverse and log-determinant of the covariance matrix. • Gradient-based optimisation using an approximate Fisher matrix is proposed for numerical efficient optimisation of the ML cost function. • MIMO FMCW radar measurements are used to demonstrate the performance of the novel covariance model. A novel model for the covariance matrix of sampled observations by multiple-input-multiple-output (MIMO) sensing systems with parallel receiver channels will be presented. The model is of shifted Kronecker structure and accounts for two mutually independent noise processes: a coloured and a white one. The maximum-likelihood (ML) estimator is applied to identify this covariance model from observations. The ML estimator gives rise to a non-convex optimisation problem. Since no closed-form solution is available, an iterative, space-alternating Gauss–Newton algorithm is proposed to solve the optimisation problem. This approach repeatedly requires the evaluation of the ML cost function. Since the cost function composes of the inverse and determinant of the covariance matrix, its evaluation can be memory exhaustive, numerically unstable and computationally complex. A computational method is developed to overcome these issues, using the simultaneous matrix diagonalisation and exploiting the properties of the Kronecker product. Measurements by a MIMO radar are used to identify the covariance model and to demonstrate its benefits. The identified covariance model is used to whiten the measurements. The whitening reduces interfering, noise-like components, which enhances the signal-to-interference ratio and hence facilitates the target detection. [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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

Feeding integrated antennas during a measurement requires special feeding structures. Due to the small antenna dimensions, these feeding structures are often much bigger than the antenna under test (AUT) itself and with chip sizes of around 1 mm2, the achievable separation between antenna and feed is limited. Wafer probes have to be used to feed the AUT during passive antenna measurements and present a large reflective surface in close proximity to the AUT. Reflections from the wafer probe cause interference on the measurement surface and distort the results. The same is true for active antenna measurements, where bondwires and the package can have a significant effect on the radiated fields. The fragility and size of the components do not allow to reduce reflections with absorbers, which is why modal filtering was used in this paper to mitigate undesired reflections and improve the measurement result through postprocessing. Two issues that limit the performance of the algorithm are discussed, namely, phase center inaccuracies of the AUT and a limited measurement surface. It is shown that modal filtering is applicable to integrated antenna measurements at frequencies over 100 GHz and that a significant improvement in the measured radiation pattern can be achieved. Furthermore, it is shown that the postprocessed results make it possible to measure the directivity of integrated antennas, despite strong probe reflections. [ABSTRACT FROM AUTHOR]

The dynamic range of frequency modulated continuous wave (FMCW) radar sensors is often limited by the phase noise of the ramp signal. Especially at millimeter wave (mm-wave) frequencies, a low phase noise signal is very difficult to obtain. In this paper, a new system architecture, which is implemented in a low-cost, ultracompact FMCW radar monolithic microwave integrated circuit (MMIC) at 160 GHz, is proposed to address this topic. The approach is based on a frequency offset synthesizer, whose upconverting mixer is driven by a stabilized low phase noise local oscillator (LO) signal. This LO is generated by a fixed-frequency phase locked loop with a 2^N divider. The upconversion of the ramp signal with the stabilized LO signal leads to an excellent mm-wave phase noise of −89 dBc/Hz at a frequency offset of 1 MHz. By integrating the antennas on the MMIC, interconnects at mm-wave frequencies to package or printed circuit board are avoided and a simple assembly and interconnection technology is feasible. The ultracompact MMIC is realized on an area of only 2 mm2, including the integrated antennas. A precision below 5 \mu \textm for range measurements is demonstrated with the radar sensor. Additionally, the radar performance is evaluated with two different voltage-controlled oscillators for the generation of the ramp signal. [ABSTRACT FROM AUTHOR]

This paper introduces a novel target height estimation approach using a Frequency Modulation Continuous Wave (FMCW) automotive radar. The presented algorithm takes advantage of radar wave multipath propagation to measure the height of objects in the vehicle surroundings. A multipath propagation model is presented first, then a target height is formulated using geometry, based on the presented propagation model. It is then shown from Sensor-Target geometry that height estimation of targets is highly dependent on the radar range resolution, target range and target height. The high resolution algorithm RELAX is discussed and applied to collected raw data to enhance the radar range resolution capability. This enables a more accurate height estimation especially for low targets. Finally, the results of a measurement campaign using corner reflectors at different heights are discussed to show that target heights can be very accurately resolved by the proposed algorithm and that for low targets an average mean height estimation error of 0.03m has been achieved by the proposed height finding algorithm. [ABSTRACT FROM AUTHOR]

With new generations of high-resolution imaging radars, the orientation of vehicles can be estimated without temporal filtering. This enables time-critical systems to respond even faster. Based on a large data set, this paper compares three generic algorithms for the orientation estimation of a vehicle. An experimental MIMO imaging radar is used to highlight the requirements of a robust algorithm. The well-known orientated bounding box and the so-called L-fit are adapted for radar measurements and compared with a brute-force approach. A quality function selects the best fitted model and is a key factor to minimize alignment errors. Moreover, the reliability of the estimation is evaluated with respect to the aspect angle, the distance to the target, and the number of sensors. An approach to estimate the reliability of the current orientation estimation is introduced. It is shown that the root mean square error of the orientation estimation is 9.77° and 38% smaller compared with the common algorithm. In 50% of the evaluated measurements the orientation estimation error is smaller than 3.73°. [ABSTRACT FROM AUTHOR]

The market for driver assistance systems based on millimeter-wave radar sensor technology is gaining momentum. In the near future, the full range of newly introduced car models will be equipped with radar based systems which leads to high volume production with low cost potential. This paper provides background and an overview of the state of the art of millimeter-wave technology for automotive radar applications, including two actual silicon based fully integrated radar chips. Several advanced packaging concepts and antenna systems are presented and discussed in detail. Finally measurement results of the fully integrated radar front ends are shown. [ABSTRACT FROM AUTHOR]

The increasing number of radar sensors in commercial and industrial products leads to a growing demand for system functionality tests. Conventional test procedures require expensive anechoic chambers to provide a defined test environment for radar sensors. In this paper, a compact and low cost dielectric waveguide radar target generator for level probing radars is presented. The radar target generator principle is based on a long dielectric waveguide as a one-target scenery. By manipulating the field distribution of the waveguide, a specific reflection of a radar target is generated. Two realistic scenarios for a tank level probing radar are investigated and suitable targets are designed with full wave simulations. Target distances from 13 cm to at least 9 m are realized with an extruded dielectric waveguide with dielectric losses of 2 dB/m at 160 GHz. Low loss (0.5 dB) and low reflection holders are used to fix the waveguide. Due to the dispersion of the dielectric waveguide, a detailed analysis of its impact on frequency-modulated continuous wave (FMCW) radars is given and compared to free-space propagation. The functionality of the radar target generator is verified with a 160-GHz FMCW radar prototype. [ABSTRACT FROM AUTHOR]