Fraunhofer Institute for High Frequency Physics and Radar Techniques

Abstract The airborne circular synthetic aperture radar (CSAR) can be used for the continuous and daylight independent surveillance. In case of small flying platforms, it is attractive to use a broadband frequency-modulated continuous wave (FMCW) radar and to transmit the sensor data to a ground station inside the measurement area for CSAR signal processing to save on-board resources. Thus, a joint FMCW radar and wireless communication system is needed. We propose and investigate frequency division multiplex (FDM) of broadband FMCW radar and single-carrier quadrature phase-shift keying (QPSK) communication using a single high power amplifier (HPA) for saving weight, size, power consumption and costs. Because of the HPA characteristics it is necessary to insert a frequency gap between the broadband linear chirp and the communication bandwidth. In case of an example scenario, the increase in overall bandwidth is only around 2.5 % of the radar bandwidth at 500 m flight altitude. It is shown that the transmit power of the communication part can be reduced to 13.4 dBm compared to the radar part with 30 dBm for maximal 500 m altitude. This enables power balancing for reducing intermodulation products of the HPA. Therefore, the reduction of the overall bandwidth by using a 70 % smaller frequency gap between the two frequency bands is possible. By using this power balancing the spectral efficiency is increased from 0.67 bps/Hz to 1.03 bps/Hz, but the power efficiency of the HPA is decreased by only 2.41 %. Therefore, it shows better performance for such applications than the linearity-hungry orthogonal FDM technique.

In modern integrated automotive radar systems, conventional methods for measuring the antenna's radiation pattern are often prohibited due to limited access to the antenna feed point. Thus, the two-way radiation pattern of a frequency-modulated continuous wave (FMCW) radar is measured against a reflector. In this context, the polarization scattering matrix of the reflector and the impact of necessary post-processing steps are crucial for obtaining reliable results. The findings for circular polarization and both equal and orthogonal polarization combinations demonstrate an overall good recovery of the main beam over frequency. Within post-processing, the range gating and different windowing for the fast Fourier transform (FFT) and inverse FFT (IFFT) are analyzed. Among these, the Hann window yields the best result.

The detection and classification of radar emitters from the electromagnetic spectrum is an essential task for electronic support. This article introduces an innovative method that directly estimates the radar emitters from the spectrogram of received data in a single step, utilizing a convolutional neural network. The processing does not rely on the typically used sequence of pulse detection, pulse deinterleaving, and emitter identification and does not require the creation of pulse descriptor words. The approach can detect multiple interleaved emitters in a spectrogram and is, therefore, a multilabel classification task. The feasibility of this single-step approach is evaluated for a library of 50 emitters, which includes high parameter agility. The results show that the proposed approach provides a high detection probability of up to 98 % while maintaining a low false alarm rate of only 0.02%. In addition, we propose an explainable artificial intelligence technique based on occlusion that is well suited to radar emitter recognition in spectrogram data. A final evaluation of the trained neural network with test signals generated in the lab investigates the robustness to some real-world radio frequency effects.

This work presents a broadband generation of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{4 5}^{\circ}$</tex> phase-shifted signals in the W-Band in a 90 nm SiGe BiCMOS technology. It is designed for IQ modulation in the D-Band, where the use of subharmonic system architectures is beneficial with regard to efficient signal generation. However, the subharmonic factor, which is two for this work, reduces the required phase shift for IQ modulators from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{9 0}^{\boldsymbol{\circ}}$</tex> to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{4 5}^{\boldsymbol{\circ}}$</tex>. Our approach utilizes an integrated Lange Coupler to generate <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{4 5}^{\boldsymbol{\circ}}$</tex> phase-shifted signals by adding the Lange Coupler's in-phase and quadrature output signals. Accepting a phase error of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\pm 5^{\circ}$</tex> a relative bandwidth of 51.5% is achieved at a center frequency of 83.5 GHz, which represents the highest published operating frequency for an integrated generation of a 45° phase shift. Embedded into a subharmonic IQ modulator, a sideband suppression of more than <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$25 dB$</tex> is achieved over a bandwidth of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$60 GHz$</tex>, covering a large portion of the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$D$</tex> band.

Dividing a System on Chip (SoC) into multiple smaller chiplets and embedding them into a single package has gained significant traction in recent years through more widespread adoption in digital circuitry. Despite benefits of reduced interference, protection against environmental influences and overcoming the “Interconnection Gap”, its usage in integrated analog circuits fails to match pace with digital designs. Adoption is likely impeded by an over-reliance on single-chip packages as they prioritize high-frequency performance over integration densities. We therefore demonstrate the first modular system approach with an embedded Wafer-Level Ball grid array (eWLB) package that does not compromise on either integration density nor performance. Restricted only by the maximum package dimensions, the number of channels can be adjusted application-specifically. This allows the system to scale down for low-cost, low-power applications while conversely facilitating massive MIMO. Exemplarily, a 4 × 4 radar System in Package (SiP) with five 130 nm B11HFC SiGe chiplets in a small form factor of 7.8 mm × 8.8 mm was manufactured for this work. It contains a central VCO that feeds four transceivers of identical design that can be configured as receivers or transceivers through the package’s layout. The configuration is solely package-based, enabling chip designs to be reused and thus drastically reducing development time. It also permits homogeneous or heterogeneous substitution of the chiplets based on available fabrication facilities and economic considerations. With its 15.6 dBi comb-line antennas, target detection within 76–77 GHz has been verified up to 36 m in range and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula>30° in azimuth. Adverse to single-chip solutions, this novel chiplet approach splits up temperature hotspots into smaller, localized areas of elevated temperature. While advantageous for the dissipation of heat, it imposes additional challenges thermomechanically as well as electromagnetically. The compromise between performance and reliability is therefore addressed with a detailed examination of the solderball placement and package-to-PCB interfaces.

Abstract This article presents a highly integrated 300-GHz frequency-modulated continuous wave radar sensor using a custom-developed dual-function transceiver MMIC. The system can either be configured as a stand-alone ultra-wide-band radar sensor or as a flexible RF front-end, enabling up-conversion and down-conversion of modulated signals to and from the terahertz range. The transceiver MMIC is manufactured using a 90 nm SiGe BiCMOS process, featuring high-speed hetero-junction bipolar transistors with an $f_{\rm{T}}$ of 300 GHz and $f_{\rm{max}}$ of 520 GHz. Using on-chip antennas and a focusing lens, the EIRP of the system for radar operation is greater than 3.2 dBm in a bandwidth of 54 GHz. The full potential of the system’s 90 GHz tuning range is demonstrated in radar measurements. A calibration method is applied to expand the usable tuning range, achieving an extraordinary spatial resolution of 1.97 mm with a frequency sweep from 330 to 240 GHz in 5 ms for a target at a distance of 0.35 m. The potential industrial use of this spatial resolution is demonstrated in a plastic thickness measurement scenario. Additionally a 100 Mbd OKK communication link with a BER of 0.55% is presented using two systems at 0.3 m distance.

In contrast to conventional radar, harmonic radar systems utilize two different frequencies for transmission and reception. Therefore, a desired target is equipped with a tag that includes a frequency doubler. It exclusively reflects the signal at twice the originally sent out frequency, making this specific target unique. Thus, enabling the key advantage of harmonic radar systems: clutter rejection. However, the range equation of such a system deviates significantly from conventional radar. This is mostly due to the power transfer function of the required doubler. Therefore, achieving sufficient range to satisfy a desired application is challenging. In this article, the measures with which state-of-the-art systems address those challenges are reviewed and explained with the help of this deviating range equation. Furthermore, this article highlights the potential of utilizing active tags as well as other research to increase realizable ranges and the frequencies of harmonic radar into the mmWaves, respectively.

In this paper a method for simultaneous radar sensing and low-bandwidth data transmission using commercially available automotive radar transceivers is presented. The underlying principle for setting up a half-duplex data link is explained. Furthermore, the hardware setup and firmware implementation of the experimental system and results of first experiments are described.

We want to present a method to estimate the velocity of a moving person in security scanning based on a correlation approach for subimages. The velocity estimate will give a signifikant gain in image quality and is performed without any additional sensors using only the imaging system. It is shown and verified that a high precision velocity estimate may be achieved by thinning out the full image to 1/25 of its original size.

The THz gap has been a significant research objective for photonics and electronics for decades. This work introduces a fully integrated frequency modulated continuous wave (FMCW) radar sensor with a center frequency of 0.48 THz, realized in a silicon-germanium (SiGe) technology. The sensor consists of a THz MMIC integrated onto a front-end printed circuit board (PCB) with FR4 substrate used for frequency synthesis and IF signal amplification. A dielectric polytetrafluoroethylene (PTFE) lens is mounted above the MMIC to act as transmitter (Tx) and receiver (Rx) lens as well as a physical protection for the bond wires of the MMIC. A back-end PCB generates the supply voltages and control signals, and its analog-digital-converter (ADC) samples the IF signal. The whole sensor is just 4.9 cm by 4.3 cm in size and is cost-efficient due to its design with FR4 PCBs. The MMIC reaches an output power of up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-9$</tex-math></inline-formula> dBm. In FMCW operation with the full sensor, a tuning range of 49 GHz is reached along an equivalent isotropic radiated power (EIRP) of up to 22 dBm. Distance measurements were successfully tested for distances of up to 5 m, and a radiation pattern is presented. In summary, this article demonstrates the potential of SiGe technology in the THz range for applications like localization, material characterization, and communication.