IEEE Transactions on Microwave Theory and Techniques
Highly accurate vibrometry and ranging are important topics in the industrialized economy. Wherev... more Highly accurate vibrometry and ranging are important topics in the industrialized economy. Wherever optical measurement technology fails due to its high prices and vulnerability within harsh environments, millimeter-wave (mmWave) radar technology is well suited. This article introduces a signal processing chain for ultrawideband frequency-modulated continuous-wave (FMCW) radar. It uses fast-time measurement to evaluate the instantaneous phase, thus allowing for spatially resolved sensing of multiple simultaneously vibrating radar targets, faster than the chirp rate. In order to accomplish this, a sophisticated error model and a calibration scheme were derived. We used three FMCW radar systems covering a broad range of the mmWave spectrum to demonstrate the signal processing approach. In contrast to the commonly used slow-time measurement principle, the highest detectable frequency was improved from 55 Hz to at least 16 kHz, which is the upper limit of the audio range. Up to 10 kHz could be measured with an underlying large-scale motion of 0.4 m/s, while the vibration displacement was at a minimum of 30 nm.
IEEE Transactions on Microwave Theory and Techniques
Radar imaging using the synthetic aperture radar (SAR) principle is a common method to obtain inf... more Radar imaging using the synthetic aperture radar (SAR) principle is a common method to obtain information about e.g., the surface of a target. However, most image formation algorithms for such systems assume (quasi-)static measurements. This may lead to errors in the processed images if the sensor is moving during the measurement process. This is especially the case for frequency-modulated continuous-wave (FMCW)based sensors since the signal duration is longer than in a pulsed system and the achievable bandwidth is much larger and introduces additional challenges. Motion compensation in the context of radar imaging is usually related to the correction of deviations from an ideal trajectory. In contrast, this article presents a method to take the sensor movement during a single FMCW ramp into account and therefore addresses the effects caused by a continuous path during the transmit/receive process. Hence, faster movement can be achieved during the scanning of the synthetic aperture without being bound by stop-and-go approximations. In addition, it will be shown that the algorithm is suitable to reduce systematic errors due to aliasing caused by spatial sampling below the Nyquist rate. For this purpose, this article presents simulations and measurement results, obtained by an ultrawideband D-band FMCW radar operating between 122 and 170 GHz.
IEEE Transactions on Microwave Theory and Techniques
With the integrated radar technology being increasingly common in the automotive segment, it beco... more With the integrated radar technology being increasingly common in the automotive segment, it becomes even more cost-effective in other applications as well. Taking into account its price and robustness, radar sensors can be considered as a potential replacement for laser interferometry which is being widely used for accurate contactless sensing. In this paper we describe a phase evaluation algorithm for highly accurate distance measurements using linear frequency modulated continuous wave (FMCW) radar systems, considering hardware dependent effects i. e. frequency responses of the signal paths. In several investigations we show that this novel algorithm is significantly more robust against disturbing radar targets or micro vibrations than typical techniques. Distance measurements were carried out using an 80 GHz wideband FMCW radar sensor on a maximum measurement range of 5.2 m with a movable radar target. For free space measurements the unambiguous measurement accuracy was improved to ±4.5 µm, using phase evaluation techniques in a non-ideal environment over the entire measurement range, which was previously around ±120 µm with frequency evaluation techniques. Due to its robustness and accuracy, the proposed algorithm is well suited for harsh industrial environments such as real time positioning of machine tools.
International Journal of Microwave and Wireless Technologies
This paper presents a W-band MIMO radar transceiver chipset for automotive applications, based on... more This paper presents a W-band MIMO radar transceiver chipset for automotive applications, based on a Silicon Germanium technology. It consists of a reference VCO, operating at a center frequency of 38 GHz and a companion IC that comprises a complete millimeter-wave transceiver at 76 GHz. This chipset enables building multipurpose MIMO radar systems that can be scaled in terms of transmitter and receiver count. What makes this system innovative is the fact that it is able to handle more broadband signals than systems presented in current literature and is furthermore not limited to one modulation scheme. The chipset is capable of transmitting and receiving any signal waveform. The main goal of this work was to create a functional version of a VCO and a one-channel transceiver MMIC. Furthermore a demonstrator for a proof of concept was designed to test the MMICs on a system level. The realized VCO MMIC achieves a tuning frequency range of 6 GHz with a center frequency of 38 GHz and con...
This paper presents the development of a novel line-camera device in the lower THz-domain which i... more This paper presents the development of a novel line-camera device in the lower THz-domain which is capable of measuring minute differences in broadband spectral fingerprints of non-conducting materials. The primary focus is sorting black plastics in industrial recycling contexts, where large scale sorting of different types of black plastics remains a challenge. The system operates between 84 GHz and 96 GHz. As the relevant plastics exhibit no specific absorption lines in this frequency range, a broadband approach is necessary to accumulate slight differences in dielectric properties. Using this technique, enough entropy can be gathered that a machine learning algorithm can be trained to differentiate between different materials. This has to work even in the presence of contaminants such as flame retardants, color pigments and dirt. Preliminary results suggest that the THz sensor system is capable of achieving these goals.
IEEE Transactions on Microwave Theory and Techniques
In this paper, a fully integrated silicon-germanium (SiGe)-based compact high-resolution frequenc... more In this paper, a fully integrated silicon-germanium (SiGe)-based compact high-resolution frequency-modulated continuous-wave (FMCW) radar sensor working in a frequency range from 198 to 250 GHz is presented. The wide modulation bandwidth of 52 GHz enables a range resolution better than 3 mm combined with a measurement accuracy in the micrometer regime. Together with a low power consumption of approximately 3.5 W, a high-focusing Teflon lens antenna, and a compact and robust housing, the presented radar system is capable of satisfying the needs of several novel measuring tasks. A compensated measurement accuracy of down to −0.5-0.4 µm is achieved, which is demonstrated by distance measurements using a laser interferometer reference. Additionally, a calibration technique is shown enabling multi-target measurements reaching to the theoretical limit of the range resolution. As the fundamental feedthrough of common frequency doubler architectures cause false targets in the range profile, a dielectric fundamental frequency filter is presented as well, filtering the fundamental feedthrough signal and thus removing the false target, improving the unambiguousness of the presented radar sensor.
This paper presents SiGe-based transmitter and receiver chips for a radio frequency identificatio... more This paper presents SiGe-based transmitter and receiver chips for a radio frequency identification (RFID) frontend in the 61-GHz industrial, scientific, and medical (ISM) frequency band. The chips are fabricated in a modern 130-nm SiGe BiCMOS technology with HBTs offering an f T of 250 GHz and f max of 370 GHz. The presented transmitter consists of a fundamental voltage-controlled oscillator (VCO), a power amplifier (PA), lumped element Wilkinson power dividers, and a static divide-by-16 chain for stabilization within a phase-locked loop (PLL). Two variants of the transmitter are fabricated with supply voltages of 3.3 and 5 V, respectively. The transmitters are designed to provide an efficient signal source to supply a passive RFID tag with the maximum allowed 20-dBm effective isotropic radiated power (EIRP) for short-range devices. The 3.3-V transmitter chip achieves a peak output power of 17 dBm, PAE PA of 18.6% and dc-to-RF efficiency of 12.9% (excluding the divider). At 61 GHz, a phase noise of −102 dBc/Hz at 1 MHz offset is achieved. The power consumption for the 5-and 3.3-V transmitter chips is 710 and 482 mW, respectively. The receiver chip is implemented as two Gilbert cell mixers inphase quadrature configuration to compensate for destructive interference that may be caused by varying distance between reader and tag.
IEEE Transactions on Microwave Theory and Techniques
Phase-locked loops (PLLs) for ultra-wideband, low noise, and linear frequency ramp synthesis exhi... more Phase-locked loops (PLLs) for ultra-wideband, low noise, and linear frequency ramp synthesis exhibit a wide variation of the loop gain, if no compensation method is applied. This impairs the performance of the PLL and the corresponding microwave measurement systems. To overcome the disadvantages of existing compensation techniques, we present a new compensation method based on a phase-frequency detector gain modulation. This offers low hardware complexity and avoids additional noise. Furthermore, we present an ultra-wideband, low noise monolithic microwave-integrated circuit for 60-GHz PLLs. Based on this, a 60-GHz frequency synthesizer with a modulation bandwidth of 22 GHz and a jitter of less than 79 fs at the center frequency are realized. The new compensation technique reduces the variation of the loop gain from 14.2:1 to 1.67:1 and is compared with an existing compensation technique utilizing a voltage-dependent damping network, which reduces the variation of the loop gain to 1.78:1. Due to the reduction of the variation of the loop gain, the maximum ramp slope increases from 22 GHz/2.9 ms up to 22 GHz/0.35 ms. In addition, the time jitter of the output signal of the PLL decreases by up to 18%. Furthermore, the PLL performance is constant in the temperature range from 0 • C to 70 • C.
A phase-locked loop (PLL) based frequency synthesizer capable of generating highly linear broadba... more A phase-locked loop (PLL) based frequency synthesizer capable of generating highly linear broadband frequency sweeps as signal source of a high resolution 80 GHz FMCW radar system is presented. The system achieves a wide output range of 24.5 GHz starting from 68 GHz up to 92.5 GHz. High frequencies allow the use of small antennas for small antenna beam angles. The wide bandwidth results in a radar system with a very high range resolution of below 1.5 cm. Furthermore, the presented synthesizer provides a very low phase noise performance of −80 dBc/Hz at 80 GHz carrier frequency and 10 kHz offset, which enables high precision distance measurements with low range errors. This is achieved by using two nested phase-looked loops with high order loop filters. The use of a fractional PLL divider and a high phase frequency discriminator (PFD) frequency assures an excellent ramp linearity.
ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences
Airborne SAR on small and flexible platforms guarantees the evaluation of local damages after nat... more Airborne SAR on small and flexible platforms guarantees the evaluation of local damages after natural disasters and is both weather and daylight independent. The processing of circular flight trajectories can further improve the reconstruction of target scenes especially in complex urban scenarios as shadowing and foreshortening effects can be reduced by multiple views from different aspect angles (hyper- or full- aspect). A dataset collected with the Miranda 35 GHz radar system with 1 GHz bandwidth on a small ultralight aircraft on a circular trajectory over an urban scene was processed using a time domain approach. The SAR processing chain and the effects of the navigational data for such highly nonlinear trajectories and unstable platforms are described. The generated SAR image stack over the entire trajectory consists of 240 individual SAR images, each image visualizing the scene from a slightly different aspect angle. First results for the fusion of multiple aspect views to cre...
Especially production quality assurance and non destructive testing applications demand for cost ... more Especially production quality assurance and non destructive testing applications demand for cost effective and high resolution imaging sensor systems. In this contribution 3D synthetic aperture radar (SAR) images in the upper millimeterwave region are presented. All measurements are performed using a SiGe MMIC based ultra-wideband frequency modulated continuous wave (FMCW) radar with on-chip antennas at 240 GHz. The on-chip antennas together with integration of all high frequency parts into a single transceiver chip will allow low-cost high-volume production of complete sensor chips at frequencies close to the THz region in near future.
IEEE Transactions on Microwave Theory and Techniques
Highly accurate vibrometry and ranging are important topics in the industrialized economy. Wherev... more Highly accurate vibrometry and ranging are important topics in the industrialized economy. Wherever optical measurement technology fails due to its high prices and vulnerability within harsh environments, millimeter-wave (mmWave) radar technology is well suited. This article introduces a signal processing chain for ultrawideband frequency-modulated continuous-wave (FMCW) radar. It uses fast-time measurement to evaluate the instantaneous phase, thus allowing for spatially resolved sensing of multiple simultaneously vibrating radar targets, faster than the chirp rate. In order to accomplish this, a sophisticated error model and a calibration scheme were derived. We used three FMCW radar systems covering a broad range of the mmWave spectrum to demonstrate the signal processing approach. In contrast to the commonly used slow-time measurement principle, the highest detectable frequency was improved from 55 Hz to at least 16 kHz, which is the upper limit of the audio range. Up to 10 kHz could be measured with an underlying large-scale motion of 0.4 m/s, while the vibration displacement was at a minimum of 30 nm.
IEEE Transactions on Microwave Theory and Techniques
Radar imaging using the synthetic aperture radar (SAR) principle is a common method to obtain inf... more Radar imaging using the synthetic aperture radar (SAR) principle is a common method to obtain information about e.g., the surface of a target. However, most image formation algorithms for such systems assume (quasi-)static measurements. This may lead to errors in the processed images if the sensor is moving during the measurement process. This is especially the case for frequency-modulated continuous-wave (FMCW)based sensors since the signal duration is longer than in a pulsed system and the achievable bandwidth is much larger and introduces additional challenges. Motion compensation in the context of radar imaging is usually related to the correction of deviations from an ideal trajectory. In contrast, this article presents a method to take the sensor movement during a single FMCW ramp into account and therefore addresses the effects caused by a continuous path during the transmit/receive process. Hence, faster movement can be achieved during the scanning of the synthetic aperture without being bound by stop-and-go approximations. In addition, it will be shown that the algorithm is suitable to reduce systematic errors due to aliasing caused by spatial sampling below the Nyquist rate. For this purpose, this article presents simulations and measurement results, obtained by an ultrawideband D-band FMCW radar operating between 122 and 170 GHz.
IEEE Transactions on Microwave Theory and Techniques
With the integrated radar technology being increasingly common in the automotive segment, it beco... more With the integrated radar technology being increasingly common in the automotive segment, it becomes even more cost-effective in other applications as well. Taking into account its price and robustness, radar sensors can be considered as a potential replacement for laser interferometry which is being widely used for accurate contactless sensing. In this paper we describe a phase evaluation algorithm for highly accurate distance measurements using linear frequency modulated continuous wave (FMCW) radar systems, considering hardware dependent effects i. e. frequency responses of the signal paths. In several investigations we show that this novel algorithm is significantly more robust against disturbing radar targets or micro vibrations than typical techniques. Distance measurements were carried out using an 80 GHz wideband FMCW radar sensor on a maximum measurement range of 5.2 m with a movable radar target. For free space measurements the unambiguous measurement accuracy was improved to ±4.5 µm, using phase evaluation techniques in a non-ideal environment over the entire measurement range, which was previously around ±120 µm with frequency evaluation techniques. Due to its robustness and accuracy, the proposed algorithm is well suited for harsh industrial environments such as real time positioning of machine tools.
International Journal of Microwave and Wireless Technologies
This paper presents a W-band MIMO radar transceiver chipset for automotive applications, based on... more This paper presents a W-band MIMO radar transceiver chipset for automotive applications, based on a Silicon Germanium technology. It consists of a reference VCO, operating at a center frequency of 38 GHz and a companion IC that comprises a complete millimeter-wave transceiver at 76 GHz. This chipset enables building multipurpose MIMO radar systems that can be scaled in terms of transmitter and receiver count. What makes this system innovative is the fact that it is able to handle more broadband signals than systems presented in current literature and is furthermore not limited to one modulation scheme. The chipset is capable of transmitting and receiving any signal waveform. The main goal of this work was to create a functional version of a VCO and a one-channel transceiver MMIC. Furthermore a demonstrator for a proof of concept was designed to test the MMICs on a system level. The realized VCO MMIC achieves a tuning frequency range of 6 GHz with a center frequency of 38 GHz and con...
This paper presents the development of a novel line-camera device in the lower THz-domain which i... more This paper presents the development of a novel line-camera device in the lower THz-domain which is capable of measuring minute differences in broadband spectral fingerprints of non-conducting materials. The primary focus is sorting black plastics in industrial recycling contexts, where large scale sorting of different types of black plastics remains a challenge. The system operates between 84 GHz and 96 GHz. As the relevant plastics exhibit no specific absorption lines in this frequency range, a broadband approach is necessary to accumulate slight differences in dielectric properties. Using this technique, enough entropy can be gathered that a machine learning algorithm can be trained to differentiate between different materials. This has to work even in the presence of contaminants such as flame retardants, color pigments and dirt. Preliminary results suggest that the THz sensor system is capable of achieving these goals.
IEEE Transactions on Microwave Theory and Techniques
In this paper, a fully integrated silicon-germanium (SiGe)-based compact high-resolution frequenc... more In this paper, a fully integrated silicon-germanium (SiGe)-based compact high-resolution frequency-modulated continuous-wave (FMCW) radar sensor working in a frequency range from 198 to 250 GHz is presented. The wide modulation bandwidth of 52 GHz enables a range resolution better than 3 mm combined with a measurement accuracy in the micrometer regime. Together with a low power consumption of approximately 3.5 W, a high-focusing Teflon lens antenna, and a compact and robust housing, the presented radar system is capable of satisfying the needs of several novel measuring tasks. A compensated measurement accuracy of down to −0.5-0.4 µm is achieved, which is demonstrated by distance measurements using a laser interferometer reference. Additionally, a calibration technique is shown enabling multi-target measurements reaching to the theoretical limit of the range resolution. As the fundamental feedthrough of common frequency doubler architectures cause false targets in the range profile, a dielectric fundamental frequency filter is presented as well, filtering the fundamental feedthrough signal and thus removing the false target, improving the unambiguousness of the presented radar sensor.
This paper presents SiGe-based transmitter and receiver chips for a radio frequency identificatio... more This paper presents SiGe-based transmitter and receiver chips for a radio frequency identification (RFID) frontend in the 61-GHz industrial, scientific, and medical (ISM) frequency band. The chips are fabricated in a modern 130-nm SiGe BiCMOS technology with HBTs offering an f T of 250 GHz and f max of 370 GHz. The presented transmitter consists of a fundamental voltage-controlled oscillator (VCO), a power amplifier (PA), lumped element Wilkinson power dividers, and a static divide-by-16 chain for stabilization within a phase-locked loop (PLL). Two variants of the transmitter are fabricated with supply voltages of 3.3 and 5 V, respectively. The transmitters are designed to provide an efficient signal source to supply a passive RFID tag with the maximum allowed 20-dBm effective isotropic radiated power (EIRP) for short-range devices. The 3.3-V transmitter chip achieves a peak output power of 17 dBm, PAE PA of 18.6% and dc-to-RF efficiency of 12.9% (excluding the divider). At 61 GHz, a phase noise of −102 dBc/Hz at 1 MHz offset is achieved. The power consumption for the 5-and 3.3-V transmitter chips is 710 and 482 mW, respectively. The receiver chip is implemented as two Gilbert cell mixers inphase quadrature configuration to compensate for destructive interference that may be caused by varying distance between reader and tag.
IEEE Transactions on Microwave Theory and Techniques
Phase-locked loops (PLLs) for ultra-wideband, low noise, and linear frequency ramp synthesis exhi... more Phase-locked loops (PLLs) for ultra-wideband, low noise, and linear frequency ramp synthesis exhibit a wide variation of the loop gain, if no compensation method is applied. This impairs the performance of the PLL and the corresponding microwave measurement systems. To overcome the disadvantages of existing compensation techniques, we present a new compensation method based on a phase-frequency detector gain modulation. This offers low hardware complexity and avoids additional noise. Furthermore, we present an ultra-wideband, low noise monolithic microwave-integrated circuit for 60-GHz PLLs. Based on this, a 60-GHz frequency synthesizer with a modulation bandwidth of 22 GHz and a jitter of less than 79 fs at the center frequency are realized. The new compensation technique reduces the variation of the loop gain from 14.2:1 to 1.67:1 and is compared with an existing compensation technique utilizing a voltage-dependent damping network, which reduces the variation of the loop gain to 1.78:1. Due to the reduction of the variation of the loop gain, the maximum ramp slope increases from 22 GHz/2.9 ms up to 22 GHz/0.35 ms. In addition, the time jitter of the output signal of the PLL decreases by up to 18%. Furthermore, the PLL performance is constant in the temperature range from 0 • C to 70 • C.
A phase-locked loop (PLL) based frequency synthesizer capable of generating highly linear broadba... more A phase-locked loop (PLL) based frequency synthesizer capable of generating highly linear broadband frequency sweeps as signal source of a high resolution 80 GHz FMCW radar system is presented. The system achieves a wide output range of 24.5 GHz starting from 68 GHz up to 92.5 GHz. High frequencies allow the use of small antennas for small antenna beam angles. The wide bandwidth results in a radar system with a very high range resolution of below 1.5 cm. Furthermore, the presented synthesizer provides a very low phase noise performance of −80 dBc/Hz at 80 GHz carrier frequency and 10 kHz offset, which enables high precision distance measurements with low range errors. This is achieved by using two nested phase-looked loops with high order loop filters. The use of a fractional PLL divider and a high phase frequency discriminator (PFD) frequency assures an excellent ramp linearity.
ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences
Airborne SAR on small and flexible platforms guarantees the evaluation of local damages after nat... more Airborne SAR on small and flexible platforms guarantees the evaluation of local damages after natural disasters and is both weather and daylight independent. The processing of circular flight trajectories can further improve the reconstruction of target scenes especially in complex urban scenarios as shadowing and foreshortening effects can be reduced by multiple views from different aspect angles (hyper- or full- aspect). A dataset collected with the Miranda 35 GHz radar system with 1 GHz bandwidth on a small ultralight aircraft on a circular trajectory over an urban scene was processed using a time domain approach. The SAR processing chain and the effects of the navigational data for such highly nonlinear trajectories and unstable platforms are described. The generated SAR image stack over the entire trajectory consists of 240 individual SAR images, each image visualizing the scene from a slightly different aspect angle. First results for the fusion of multiple aspect views to cre...
Especially production quality assurance and non destructive testing applications demand for cost ... more Especially production quality assurance and non destructive testing applications demand for cost effective and high resolution imaging sensor systems. In this contribution 3D synthetic aperture radar (SAR) images in the upper millimeterwave region are presented. All measurements are performed using a SiGe MMIC based ultra-wideband frequency modulated continuous wave (FMCW) radar with on-chip antennas at 240 GHz. The on-chip antennas together with integration of all high frequency parts into a single transceiver chip will allow low-cost high-volume production of complete sensor chips at frequencies close to the THz region in near future.
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Papers by Nils Pohl