This work presents an approach for optimization of window coefficients for 5G user equipment side sensing, using orthogonal frequency division multiplexing radar-based range and velocity estimation, based on the sounding reference signal (SRS) from the 5G New Radio (NR) standard. The signal configuration and the corresponding waveform are generated in compliance with the 3rd Generation Partnership Project (3GPP) standard for 5G. The limitations of conventional signal processing for resources available for sensing with the SRS are highlighted. The proposed approach, which optimizes the window coefficients to improve the sensing capabilities, is implemented through two methods. The first method employs a decoupled optimization strategy for range and velocity, showing high computational efficiency. Our results demonstrate that this method significantly improves the peak sidelobe level (PSL) of the velocity profile by over $\mathrm{15}\,\mathrm{dB}$, although it does not address the issue of diagonally located sidelobes, which occur due to non-uniform resource distribution. The second method adopts a comprehensive full 2D optimization technique. While it requires more computational resources and does not improve the PSL beyond the first method’s achievements, it mitigates the diagonally located sidelobes issue. The level of these have been improved by more than $\mathrm{3}\,\mathrm{dB}$.

With the emerging developments in millimeter-wave/5G technologies, the potential for wireless Internet of things devices to achieve widespread sensing, precise localization, and high data-rate communication systems becomes increasingly viable. The surge in interest surrounding virtual reality (VR) and augmented reality (AR) technologies is attributed to the vast array of applications they enable, ranging from surgical training to motion capture and daily interactions in VR spaces. To further elevate the user experience, and real-time and accurate orientation detection of the user, the authors proposes the utilization of a frequency-modulated continuous-wave (FMCW) radar system coupled with an ultra-low-power, sticker-like millimeter-wave identification (mmID). The mmID features four backscattering elements, multiplexed in amplitude, frequency, and spatial domains. This design utilizes the training of a supervised learning classification convolutional neural network, enabling accurate real-time three-axis orientation detection of the user. The proposed orientation detection system exhibits exceptional performance, achieving a noteworthy accuracy of 90.58% over three axes at a distance of 8 m. This high accuracy underscores the precision of the orientation detection system, particularly tailored for medium-range VR/AR applications. The integration of the FMCW-based mmID system with machine learning proves to be a promising advancement, contributing to the seamless and immersive interaction within virtual and augmented environments.

Future communication and radar sensing systems will require synchronization methods which are more versatile in terms of the systems involved in the synchronization process. We present an over-the-air frequency synchronization algorithm based on the standard and the generalized Kuramoto model which uses continuous wave (CW) signals. In contrast to other approaches, all nodes of the network participate equally, and synchronization can even be achieved in presence of a non-cooperative node. By changing the parameters of the radar or by modifying the synchronization algorithm, synchronization accuracy can be adjusted as well. All claims are supported by measurements conducted with CW radars. It will be demonstrated that our algorithm enables synchronization accuracies down to 1.92 ppb and thus could provide sufficient accuracy for velocity measurements on pedestrians.

Frequency-modulated continuous-wave radar systems profit from increasing the absolute bandwidths of the generated frequency chirps to improve range resolution. As the relative bandwidth of SiGe-voltage-controlled oscillators (VCOs) is limited to about 80%, increasing the center frequency fundamentally or via frequency multiplication is the most direct way to increase that absolute bandwidth. However, as some applications require penetration depth, which dramatically decreases with frequency, other solutions are necessary. Therefore, state-of-the-art concepts rely on the down-conversion of generated frequency chirps via two separately stabilized frequency sources. This article implements a novel architecture, offering relative bandwidths of >100% within a single phase-locked loop (PLL). Therefore, two VCOs at different center frequencies are fed into a down-conversion mixer, whose output is directly stabilized via that PLL with one loop filter generating both tuning voltages. Those circuit blocks can be summarized as one equivalent VCO, offering a higher relative bandwidth and a significantly more linear tuning curve. Thereby, a solution to limited relative bandwidths with high VCO gain variation of single VCO synthesizers is offered while substantially reducing the hardware and implementation effort compared to the state-of-the-art.

In this paper, we investigate low-cost solutions for enabling ground moving target indication applications with multichannel mobile passive radar systems. As known, in order to be competitive with their active counterparts, passive radars are typically characterized by severe constraints in terms of cost, complexity, and compactness, especially when installed on moving platforms. On the one hand, carrying out the computations onboard requires processing techniques as simple as possible. On the other hand, the need for lightweight and compact systems that can be installed on a moving platform requires using a limited number of receiving channels. To meet these requirements, we propose a series of nonadaptive detectors based on multichannel displaced phase center antennas, which allow suppressing the Doppler-spread clutter component without requiring computationally intensive space–time adaptive processing techniques. Moreover, we explore the use of nonuniformly spaced array configurations on receive, which represent a good alternative to conventional uniform linear arrays when a limited number of receiving channels can be implemented. The effectiveness of the proposed processing techniques and antenna design solutions is demonstrated via numerical analysis for the case of a DVB-T-based mobile passive radar system.

Electronic measurement systems in the THz frequency range are often bulky and expensive devices. While some compact single-chip systems operating in the high millimeter-wave frequency range have recently been published, compact measurement systems in the low THz frequency range are still rare. The emergence of new silicon-germanium (SiGe) semiconductor technologies allow the integration of system components, like oscillators, frequency multipliers, frequency dividers, and antennas, operating in the low THz frequency range, into a compact monolithic microwave integrated circuits (MMIC), which contains most components to implement a low-cost and compact frequency-modulated continuous-wave-radar transceiver. This article presents a single transceiver solution containing all necessary components. It introduces a $0.48\,\mathrm{THz}$ radar transceiver MMIC with a tuning range of $43\,\mathrm{GHz}$ and an output power of up to $-9.4\,\mathrm{dBm}$ in the SG13G3 $130\,\mathrm{nm}$ SiGe technology by IHP. The MMIC is complemented by a dielectric lens antenna design consisting of polytetrafluoroethylene, providing up to $39.3\,\mathrm d\mathrm B\mathrm i$ of directivity and half-power beam widths of 0.95∘ in transmit and receive direction. The suppression of clutter from unwanted targets deviating from antenna boresight more than 6∘ is higher than $24.6\,\mathrm d \mathrm B$ in E- and H-Plane.

In missile test ranges, complex missions demand precise trajectory generated by radar. Both the radar and Global Navigation Satellite System (GNSS) signals are affected by atmospheric effects, degrading their accuracy and performance. The Indian Regional Navigation Satellite System/Navigation with Indian Constellation (IRNSS/NavIC) transmits signals in the S-band together with the L-band. This paper presents a novel experimental technique to improve the tracking accuracy of S-band radars using the concurrent NavIC S-band signal. The ionospheric delay using the NavIC S-band signal is calculated first, and the results are used to improve the trajectory data of simultaneously operating S-band radars. This is a unique application of the NavIC S-band signals apart from its conventional usage. During a launch mission, for low elevation angles, the ionospheric error is found to be ~130 m while at higher elevation angles the error values are found to be ~1–3 m. The concept is validated using data from a missile test mission. This report on the use of S-band GNSS signals for the correction of S-band radar range data offers a clear advantage of simplicity and accuracy.

Modern radar sensors are gaining more and more relevance for several industrial measurement applications. To achieve the required range resolution and measurement accuracy, the use of higher frequencies beyond 100 GHz is beneficiary. A commonly used signal generation concept in fully integrated radar transceivers is to use a fundamental oscillator with subsequent frequency multiplication. Depending on the overall system concept, this type of signal generation suffers from a fundamental feed-through signal which generates false targets in frequency modulated continuous wave operation. Additionally, those unwanted signal components radiated by the sensors might be problematic for legal conformity or electromagnetic (EM) interference compliance. This paper presents a novel concept for frequency filtering dielectric lens antennas, to suppress unwanted signal components at harmonic frequencies based on interference filtering effects. Besides the EM simulations to theoretically prove this concept, multiple prototypes of filtering lens antennas were fabricated by conventional mechanical and additive manufacturing. Using a self-developed, ultra-compact radar sensor, measurements were taken to compare the lens antenna prototypes in terms of filtering performance and how the material characteristics affect the filtering performance. Within these measurements, the successful suppression of false targets caused by fundamental feed-through signals is demonstrated.

The development of a millimeter-wave transparent antenna integrated inside a headlamp for automotive radar application is presented. The antenna consists of two radiating elements: the primary and secondary ones. The primary antenna is the one that is fabricated on RF PCB material (e.g., patch, slot, sectoral horn) and connected directly to the transceiver chip, while the secondary antenna is made of optically transparent materials such as glass, but with a optical transparent electrically conductive coating, well known as transparent conductive oxide (TCO). This antenna is realized as a planar offset reflector to collimate and shape the incoming wave from the primary antenna. This reflector is designed based on the Fresnel theory and the reflectarray concept. The division of the primary and secondary antenna enables the placement of the radar module (that contains the primary antenna) at the base of the headlamp, and therefore it is concealed from the surroundings and hidden from the optical path of the light. The secondary antenna is inserted in the space between the headlamp cover and the light unit. The main challenge here is to provide a maximum on transparency in the visible range of the spectrum with a specially designed and laser-based generated microstructure for the resonant reflection of the radar wavelength. An antenna demonstrator has been fabricated, and together with the headlamp cover, the radiation pattern and realized gain are measured. We reported here the measurement results for several reflector designs and concluded that the headlamp cover gives minimal influence on the antenna performance.

Standards IEC 62288:2014 and MSC.191(79) require information on the displays of shipboard navigation systems to be logically grouped, but only provide limited specification for this ‘logical’ criterion. Meanwhile, complex interfaces and information overload remain as major design issues, being connected to several maritime accidents. To address this matter, a three-phase study was conducted to develop a pattern to organise essential information on Radar and Electronic Chart Display and Information System (ECDIS) displays and their equivalent modules on integrated navigation systems and integrated bridge systems. The first phase involved identifying the information most essential for safe navigation using cognitive task analyses, equipment performance standards and frequency of use. The second phase involved a card-sorting experiment with seafarers (n = 63) to develop an initial grouping pattern for the identified essential information. The third phase involved validating the initial grouping pattern with a new sample of seafarers (n = 35). The result is a pattern to group 48 types of information on shipboard navigation displays into 13 groups. The paper details the selected methods and the findings, and provides implications for future research.

In this paper, a wideband ultrathin metasurface absorber is investigated. The proposed absorber comprises a periodic array of a unit cell ring structure. The ring structure and patch inside are tuned to realize the desired frequency bandwidth. The structure has a frequency bandwidth of 7.4 GHz with a center frequency of 15 GHz and fractional bandwidth of 50%. Simulated and measured results show that the absorption at normal incidence is above 90% in the frequency range of 11.3–18.7 GHz. Furthermore, the thickness of the structure is 1.6 mm. The physical mechanism of the metasurface absorber has been analyzed and justified experimentally.

This paper introduces a new maritime search and rescue system based on S-band illumination harmonic radar (HR). Passive and active tags have been developed and tested while attached to life jackets and a small boat. In this demonstration test carried out on the Baltic Sea, the system was able to detect and range the active tags up to a distance of 5800 m using an illumination signal transmit-power of 100 W. Special attention is given to the development, performance, and conceptual differences between passive and active tags used in the system. Guidelines for achieving a high HR dynamic range, including a system components description, are given and a comparison with other HR systems is performed. System integration with a commercial maritime X-band navigation radar is shown to demonstrate a solution for rapid search and rescue response and quick localization.

Next-generation automotive radar sensors are increasingly becoming sensitive to cost and size, which will leverage monolithically integrated radar system-on-Chips (SoC). This article discusses the challenges and the opportunities of the integration of the millimeter-wave frontend along with the digital backend. A 76–81 GHz radar SoC is presented as an evaluation vehicle for an automotive, fully depleted silicon-over-insulator 22 nm CMOS technology. It features a digitally controlled oscillator, 2-millimeter-wave transmit channels and receive channels, an analog base-band with analog-to-digital conversion as well as a digital signal processing unit with on-chip memory. The radar SoC evaluation chip is packaged and flip-chip mounted to a high frequency printed circuit board for functional demonstration and performance evaluation.

In this work, the scattering characteristics of 3D-printed samples are being investigated by using a single-polarized and a cross-polarized radar system. The 3D-printed technology participates in a wide range of applications nowadays. The idea of synthetic aperture radar (SAR) has been utilized to investigate the reflected electromagnetic energy from the 3D-printed samples by setting each of the radar systems in a fixed position and the mounting sample on an x-y positioning table which has been used to achieve rectangular-scan mode for SAR. The data have been ported and processed by the matched filter approach. For better image interpretation, the data have been further processed by the median filter in order to reduce noise level while preserving the main image details. Afterwards, the data have been further investigated for determining and classifying any possible defects. This process has been accomplished by deploying the unsupervised learning concept to cluster the SAR responses into two groups, compromising the defected positions responses and the non-defected responses. The obtained results of both radar sensors have been compared and evaluated using different quality assessment factors. Moreover, unsupervised learning techniques have been investigated and the obtained results show a high degree of efficiency in clustering the SAR responses.

This paper considers the ability of polarization measurements for microwave remote sensing of clouds and precipitation. The simulation of reflections from liquid hydrometeors with a multi-polarization radar system is presented. The mathematical expression of energy received by a radar antenna with arbitrary polarization is obtained. The simulation of the energy redistribution of the signal reflected from liquid hydrometeors assembled over the antennas of multi-polarimetric radar for different wind conditions and different drop-size distributions is obtained and analyzed. The simulation results demonstrate the possibility to register wind and wind-related phenomena by polarimetric radar. The results of the paper can also be used to exclude an impact of drop vibration or oscillation into the radar signal to eliminate errors and underestimation during parameter measurements. The approach to segregate the reflected signal magnitude variations due to the wind-related phenomena from other factors is discussed.