Fraunhofer Institute for High Frequency Physics and Radar Techniques

The present work intends to characterise the combination of two netted software defined radios (SDR) and different radio frequency (RF) front‐ends installed in them, together with a two‐stratum time dissemination and synchronisation system. A modified implementation of the Network Time Protocol is used as coarse event synchronisation for either SDR back‐end. The White rabbit light embedded node implementation of the commonly known white rabbit synchronisation system (IEEE 1588 PTP‐2019) or arbitrary wave form generators are used as fine time dissemination system for either SDR. The resulting netted transceiver system is intended to compose a demonstrator for proof‐of‐concept experiments. The findings presented in this article show that the chosen combination of hardware and software is suitable for radar applications operating within L‐, S‐ and C‐bands. A channel coherency throughout the network with a relative modified Allan deviation of less than 80 fs for averaging intervals of 1 s, a phase noise better than −118 dBc/Hz at 10 Hz frequency offset and a fractional frequency lower than ±2.5⋅10−13 $\pm 2.5\cdot 1{0}^{-13}$ was measured. Within a single transceiver node, a fractional frequency lower than ±2⋅10−13 $\pm 2\cdot 1{0}^{-13}$ and phase noise of −124 dBc/Hz at 10 Hz frequency offset were measured as well. Multistatic radar systems exploit wide spatial diversity to enhance target detection and tracking, albeit with increased complexity when compared to a monostatic configuration. To exploit these benefits, all participating transceiver nodes within the netted radar need to synchronise to a common time base t0 $\left({t}_{0}\right)$. The achieved synchronisation level increases the accuracy with which the chain of timed events at the transmitter and at the receiver side occur, intending to maximise the signal‐to‐noise ratio available at the receiver. The Universal software radio peripheral model X310 with two different daughterboard models as RF front‐end was used as SDR on either radar node. A network combining data and synchronisation purposes allowed the radar nodes under test to operate synchronously. The two‐stratum synchronisation system used glass fibres between 2 m and 5 km of length or coaxial cables with 2 m in length for network traffic, time and frequency dissemination purposes. The multiple RF front‐ends were stimulated by means of arbitrary waveform generators with calibrated traceability. Up‐chirp and sinusoid waveforms were used as stimuli for measuring the offset of either channel with regards of t0 ${t}_{0}$ to ultimately estimate the achievable coherency limits of the system under test. Both analogue and digital evaluation methods were considered.

This article presents an approach in the design of voltage-controlled oscillators (VCOs) that aims to provide robust low-noise performance while also being resistant to high-temperature conditions. The proposed design methodology is grounded in the principles of the negative resistance model. For demonstration purposes, a D -band oscillator is realized in a SiGe BiCMOS technology and evaluated, which significantly corroborates the design approach. For frequency doubling, two concepts, the push–push principle (VCO1) and Gilbert cell mixer (VCO2), are implemented and compared with a special focus on load pulling effects. Both realizations target the D -band center frequency of 140 GHz with a tuning range of around 13 GHz. The VCO core draws a current of 40 mA and the on-chip frequency divider 32 mA from a 3.3-V source. A uniform differential output power of about $-$ 1.5 dBm ( $-$ 8 dBm) without buffer and low phase noise of $-$ 98.7 dBc/Hz ( $-$ 95 dBc/Hz) and the VCO remains remarkable phase noise performance up to temperatures $>$ 200 $^{\circ}$ C.

This work shows the hetero-integration of an InP resonant tunneling diode (RTD) on a SiGe-BiCMOS mm-Wave integrated circuit (MMIC) for near-field wireless fundamental injection locking. We observe injection locking within a locking range of 26 GHz and a total power during injection locking of $-$ 3.4 dBm. The SiGe-based local oscillator (LO) is integrated with a frequency doubler and an on-chip patch antenna that operates between 220 and 247 GHz, providing a maximum output power of $-$ 7 dBm. The LO is near-field coupled to an InP RTD oscillator integrated into a slot antenna which reaches a free running maximum output power of $-$ 6.2 dBm. The chip-to-chip integration is carried out through flip-chip bonding.

Automotive self-localization is an essential task for any automated driving function. This means that the vehicle has to reliably know its position and orientation with an accuracy of a few centimeters and degrees, respectively. This paper presents a radar-based approach to self-localization, which exploits fully polarimetric scattering information for robust landmark detection. The proposed method requires no input from sensors other than radar during localization for a given map. By association of landmark observations with map landmarks, the vehicle’s position is inferred. Abstract point-and line-shaped landmarks allow for compact map sizes and, in combination with the factor graph formulation used, for an efficient implementation. Evaluation of extensive real-world experiments in diverse environments shows a promising overall localization performance of 0.12m RMS absolute trajectory and 0.43 $^\circ$ RMS heading error by leveraging the polarimetric information. A comparison of the performance of different levels of polarimetric information proves the advantage in challenging scenarios.

The number of environment-detecting sensors inside cars continuously increases, to enable failsafe autonomous driving. With more sensors, the probability of performance degrading interferences increases. A promising solution to the interferences is orthogonal frequency division multiplex (OFDM) radar. Due to the complex modulation scheme, the analog front end, especially the power amplifier in the transmitter, has to deal with a high peak-to-average power ratio. Therefore, conventional amplifiers have to be operated in power back-off to maintain linear operation at the drawback of reduced power-added efficiency. To mitigate this problem, a Doherty power amplifier for an automotive radar transceiver is proposed. In this work, we present a design methodology for an integrated Doherty amplifier for automotive radar applications, focussing on the theory of operation by analyzing transistor-level simulations. Small- and large signal simulations analyze the concept of load modulation for a Doherty amplifier in the automotive frequency band from 76--81 GHz. Using a fully differential transmission-line-based approach, we showcase the superior performance of an automotive Doherty amplifier over an conventional state-of-the-art reference amplifier. In measurements, the proposed Doherty amplifier achieves a saturated output power of 17.2 dBm with a peak power-added efficiency of 11.6%. When operating in 6 dB back-off, the PAE still amounts to 6.1%. Thereby we propose to improve conventional automotive power amplifiers by incorporating them into a Doherty amplifier.

Radars on unmanned aerial vehicles (UAVs) can be used in indoor rescue scenarios to detect missing people based on their motion. The phase of the radar signal provides information about sub-millimeter changes in distance to the reflecting objects. However, in order to evaluate the motion of a missing person, the relative position variation of the unmanned vehicle itself must be known and compensated for. To estimate the position variation of the unmanned vehicle, the radar system measures the phase information for multiple static objects in the radar’s environment. A model describing how a position change of the radar affects the phase signals is used to build a system of equations with the current position being the solution. The accuracy of the estimated position depends on how accurately the phase measurements represent the model. By analytically decomposing the errors in the measurement model, it is shown that the radar’s limited angular resolution induces a significant error. To mitigate this source of error, a weighted least squares approach that minimizes the influence of the angular resolution on the position error is derived. By calculating the position error distribution with and without the weighting approach, the benefits of the proposed algorithms are stated. Furthermore, the results are validated using simulations and real world measurements, showing that the proposed algorithm achieves sub-millimeter position accuracy.

The need for size and cost-efficient vector network analyzer (VNA) frequency extension modules (VNAX module) is driven by new applications in research and industry. Responding to this potential demand, we present a novel D-band VNAX module based on a single SiGe MMIC. Our work addresses the challenges associated with integrating components on a single chip compared to conventional commercial modules, which typically rely on discrete components. We provide a comprehensive discussion covering the performance of system blocks, such as multiplier chains and receivers, and their impact on the module's performance. In addition, we present extensive measurements of the entire system, including magnitude-and phase stability and dynamic ranges. At a resolution bandwidth (RBW) of 10 Hz, our module shows a system dynamic range (SDR) above 90 dB for the frequency range of 110 GHz to 151 GHz and a maximum SDR close to 100 dB at 122 GHz. The corresponding receiver dynamic range within the D-band ranges from 113 dB to 125 dB, and the Test Port power is between −27 dBm and −16 dBm. In addition, we present and evaluate several measurements of different passive components that verify the calibration capability of our module.

The critical role of specifying micro‐Doppler mode performance in the modelling and development of modern radar systems is investigated. The authors focus on the detection of micro‐Doppler modulation from light aircraft, analysing data from eight helicopters and nine propeller aircraft. With the growing need for accurate target classification in radar technology, incorporating micro‐Doppler detection metrics into radar performance specifications has become increasingly important. This research offers a novel approach to measuring the detectability of micro‐Doppler modulation relative to returns from the main fuselage. The investigation covers the impacts of various preprocessing techniques, polarisation, and aspect angle on detection capabilities. Findings reveal that, on average, micro‐Doppler modulation from propellers is detectable at distances between 50% and 100% of the range at which the fuselage is detected. For helicopters, this range decreases to between 30% and 80%. Additionally, the study introduces empirically derived statistical models designed to predict micro‐Doppler detection ranges in relation to fuselage returns, enhancing the predictability and specificity of radar system performance. This novel contribution presents a basis for improving radar system specifications, leading ultimately to more predictable and reliable light aircraft classification.