At Collm (51.3 degrees N, 13.0 degrees E) mesosphere/lower thermosphere (MLT) zonal and meridional winds have been measured for more than four decades using low-frequency spaced receiver measurements on 177, 225, and 270 kHz, and very high frequency meteor radar observations on 36.2 MHz. We analyse the combined time series of monthly mean horizontal winds at 90 km height from 1979 to 2024 with respect to long-term changes, and in particular to the effect of the 11-year solar cycle (SC). In the 1980s and 1990s there is a negative correlation with solar extreme ultraviolet proxies in spring and early summer, with a weaker jet in the lower thermosphere during solar maximum. This correspondence weakens after the year 2000. In winter, there is a weak positive effect towards stronger westerly winds during solar maximum. Together, the results suggest that solar forcing remains an important, season-dependent driver of mid-latitude MLT dynamics, but its expression is modulated by the recently weakened SCs 24-25, or modified by changing trends of forcing from below. These results are largely in agreement with partial reflection radar observations of mesospheric winds over Juliusruh (54.6 degrees N, 13.4 degrees E) at 3.18 MHz. We also compare them with decadal variations of gravity wave proxies, but these results are partly inconclusive.
Polar mesosphere summer echoes (PMSE) are strong radar signals received at very high radar frequencies at altitudes between about 80 and 95 km at polar latitudes during summer. PMSE are caused by inhomogeneities in electron density on the radar Bragg scale of 3 m (for a monostatic 53.5 MHz radar), which originate from density fluctuations in negatively charged ice particles. Continuous monitoring of PMSE takes place on the northern Norwegian island of And & oslash;ya (69.3 degrees N, 16.0 degrees E) with the ALWIN (1999-2008) and MAARSY radars (since 2011), respectively. Both radars are calibrated which allows the conversion of the received PMSE echo strength to absolute signal power and the determination of the volume radar reflectivity eta , which is now available for more than a quarter of a century. The distribution of the mean volume reflectivity covers a range starting at the detection limit of the radars and extending to a maximum value of similar to 10 (- 9 )m(-1) with peak values at around 7.9 & times; 10 (- 15) and 1.6 & times; 10 (- 15) m(-1) for ALWIN and MAARSY, respectively. Seasonal, diurnal, and height variations of PMSE occurrence rates based on the 26-year data set of eta are presented. Since PMSE reflectivity is affected by ionization from solar radiation and high-energy particle precipitation, seasonal mean values of PMSE reflectivity have been analyzed with respect to solar and geomagnetic activity. Regarding long term trends, PMSE measurements from the ALOMAR SOUSY radar covering the period 1994-1997 are included which leads to a time series of 32 years, making it the longest measurement series of its kind worldwide.
Non-contact monitoring of vital signs has become increasingly important for enhancing patient comfort and reducing interference during medical assessments. Such methods are particularly valuable for addressing phenomena such as white-coat hypertension and for enabling more accurate diagnoses in home environments. This paper consolidates three innovative approaches for heartbeat detection using a dedicated 24 GHz frequency-modulated continuous-wave (FMCW) radar. First, a novel signal envelope analysis method is introduced, demonstrating its ability to extract heartbeat information and to validate the results against an ECG reference system (GE Healthcare CARESCAPE Monitor B650). Second, computationally intensive steps are optimized for real-time processing by replacing the Hilbert transform and smoothing functions with more efficient alternatives such as Moving-RMS and Moving-Average filters. These adaptations enable low-latency operation while maintaining reliable detection performance. Lastly, a convolution-based Gaussian pulse method is presented to extend the envelope analysis, followed by a time-domain plausibility check to refine peak detection. The modular radar system comprises a 2TX/4RX MIMO radar front-end, a filtering and amplification module, and a data acquisition module, all developed at the Laboratory of Applied Radar and Optical Systems (LaROS) at Trier University of Applied Sciences. Each proposed method has been optimized for the 24 GHz ISM band, offering a balance between real-time capability and detection accuracy. Validation against ECG benchmarks confirms the feasibility and effectiveness of the presented approaches, contributing to the advancement of non-contact vital sign monitoring technologies.
Spaceborne Multiple-Input Multiple-Output Synthetic Aperture Radar (MIMO-SAR) overcomes fundamental shortcomings of state-of-the-art SAR, such as the trade-off between swath width and spatial resolution, and offers a greater agility of the antenna beam steering. In addition, MIMO-SAR enables a wide variety of new operation and acquisition modes, such as the High-Resolution Wide-Swath (HRWS) mode. One demanding requirement in this subject is to design separable orthogonal waveforms which optimize the overall imaging performance. In the case of a SAR system, this is not an easy task due to the nature of the imaged scene consisting of a multitude of point and distributed targets. This paper summarizes the most promising waveforms in the literature and analyzes them in detail. The selected waveforms are investigated for the first time with respect to their use in SAR using the ambiguity function. As a conclusion, a catalogue of important waveform performance parameters and an ambiguity function analysis are provided, to support the modern MIMO-SAR designer in the form of decision rules for the optimal waveform selection.
This publication focuses on the production of low-cost prototypes of coaxial-waveguide transitions (CWTs) that achieve the performance level of industrial WR90 and WR187 CWTs. The assembly consists of a specially designed coupling element in stripline technology that merges into an SMA connector. It is embedded into a 3D printed housing treated with a metallic surface finishing to achieve compatibility with hollow waveguides. In the first part of this study, a copper spray varnish is used to create a conductive surface on the device under test (DUT). After assembly of the prototypes, network parameters will be extracted for one pair of transitions by carrying out a set of 2-port measurements. The individual performance of a singular DUT is then deembedded by using reference measurements of commercial-grade waveguides. This analysis shows that also S-parameter extraction on connectors with a poor transition is valid. Subsequently, the procedure for the developed WR90 CWT is applied to a WR187 waveguide standard, again followed by a performance analysis. The procedure briefly addresses the modified parameters and illustrates the results as S-parameters. A comparative analysis of the measurement results for each deembedded WR90 and WR187 prototype respectively, indicates a better performance for larger waveguide standards. In consistency with this observation, larger relative tolerances in manufacturing and difficulties in controlling a uniform metallization process are identified as the limiting factors of miniaturization. In the second part of this work, an alternative concept utilizing aluminum coating and a segmented manufacturing approach is developed, targeting reduced insertion loss but keeping the mechanical tolerance level. The redesign is based on the geometry of the prior WR90 prototype, but forming a plug-in kit with each body segment being clad in multiple thin layers of aluminum foil. The measurement results of these samples reveal the effects of increased conductivity and reduced irregularities in terms of significantly improved reflection and transmission parameters. The DUTs investigated in the third part of this work again originate from the initially manufactured variants. To investigate the effects of different metallic coatings, the copper varnish is now replaced by a silver based ink, which provides high conductivity and is therefore commonly used in additive manufacturing. The network measurements are repeatedly carried out with a varying number of layers of lacquer applications on the body's surface. By deembedding a singular part from the measurements, it is shown that increasing surface conductivity leads to a significant impact on transmission parameters. In direct comparison, the silver coated CWT outperforms both preceding variants with copper varnish or aluminum clad. With more than 95 % transmitted power, it is indeed competitive compared to the industrially manufactured WR90 CWT reference. To conclude, the study focuses on a comparison of three different additive manufacturing processes for equal hollow waveguide geometries at moderate frequencies. It proves that CWT parts are producible in a simple and rapid process. The production stages with the strongest impact on performance are identified and demonstrated to be controllable. The variant presented finally is able to achieve competitive performance compared to commercial-grade parts, especially when considering the enormous cost reduction. In addition, it is proven that the RF parameter extraction method for symmetric two-port networks presented earlier by the authors is also applicable when the DUT exhibits high insertion losses. The central aim of this work is to demonstrate that additive manufacturing combined with low-cost metallization techniques can produce coaxial-waveguide transitions that approach the performance of industrial WR90 standards. This novelty highlights the feasibility of achieving near-commercial-grade quality at a fraction of the cost, thereby extending the accessibility of high-frequency components to research and prototyping applications.
To process images of a prism-shaped aperture in a radar imaging context, a hybrid algorithm is derived. This hybrid algorithm combines the benefits of backprojection and the Omega-K algorithm in terms of computational performance and flexibility. As a demonstration for an application of this algorithm, a 3D inspection system based on millimeter wave imaging is introduced. The system scans through the object, while it is passing on a conveyor belt. It comprises a curved antenna layout, which is able to synthesize the prism-shaped aperture. This aperture is shown to have superior resolution capabilities compared to a planar aperture. Some potential pitfalls when implementing the hybrid algorithm are assessed. Approximation formulae to estimate the achievable resolution are derived. The introduced algorithm is analyzed regarding its point spread function and compared to backprojection with the help of numerical simulations to demonstrate its potential.
This study introduces a novel frequency-selective radar system for street condition monitoring (SCM) that eliminates the cost-intensive dedicated monolithic microwave integrated circuit (MMIC) channels approach by sharing radar channels across different frequency bands. The proposed design uses a step-impedance filter (SIF) to allow the radar to perform standard operations at 76.5 GHz while adding SCM capabilities at 80.5 GHz. The radar system ensures robust frequency selectivity, meeting strict isolation requirements to minimize mutual coupling between the antennas operating at different frequencies. An intensive investigation is conducted to determine the minimum co-polar to cross-polar isolation required for effective frequency-selectivity in the system. Simulations show how the SCM antenna affects the primary radar antenna at 76.5 GHz and how the primary radar antenna affects the SCM antenna at 80.5 GHz. The results confirm that this design can integrate SCM without affecting the main radar's performance, offering a practical and cost-effective solution for autonomous vehicles.
This work investigates the process by which electromagnetic waves heat solid surfaces, potentially leading to the ignition of explosive atmospheres. Initially, the temperature increase of various lossy materials exposed to electromagnetic waves at 92 GHz is experimentally determined. Based on these observations, material samples are prepared, and ignition tests are conducted based on test specifications for small hot components in diethyl ether-air and carbon disulfide-air mixtures. These experiments provide a foundation for determining safe power limits for the application of electromagnetic waves in explosive atmospheres.
This work presents the application of two movable antennas in a compact radar test range for testing the angular resolution of radar systems in an automotive environment. The goal is to simulate two targets in the azimuth direction, which are measured by a radar placed in the quiet zone. At first, a mathematical approach to the problem is presented. Afterwards, a ray tracer in MATLAB is used for the setup simulation, and measurements are carried out to validate the calculation and simulation results. The effects occurring in the simulation and measurements are analyzed, and strategies to mitigate them are presented. Overall, the results look promising, and the system is suitable for testing the angular resolution of radar systems.
This study explores the extraction of the radiation mode field from backscattering field components of a composite right/left-handed (CRLH) leaky wave antenna (LWA) to estimate the relative angle to the radiation mode field within its frequency band of operation. Two methods, transmission line delay (TLD) and impedance loading (IL), for extracting the radiation mode from backscattering field components, are employed to isolate the radiation mode field of a CRLH LWA. In the IL method, backscattered fields are measured by terminating the CRLH LWA with short and open load impedances to express the radiation mode and structure mode field components. The TLD method uses a coaxial transmission line to connect the CRLH LWA to a high-gain X-band horn antenna, enabling isolation of the radiation mode field component from the backscattered field components, using time gating. This analysis employs two measurement setups for TLD, one in which both the CRLH LWA and the horn antenna rotate along the azimuth and the other in which only the CRLH LWA rotates. The analysis shows the frequency-angle relationship of the CRLH LWA radiation mode field, which reveals the frequency-dependent features of the CRLH LWA. Additionally, an evaluation of frequency ambiguity is done to provide more insights into the effectiveness of each approach for angle estimation of CRLH LWA relative to the incident wave.
This paper presents a single-layer SIW longitudinal slot array antenna optimized for high gain and low side lobe levels (SLL) in the W-band, designed for LMRR (Long Medium Range Radar) applications. This design enhances detection range at high frequencies. It also provides a wider azimuth field of view (FOV) at lower frequencies. The approach improves compactness and reduces costs. It eliminates the need for multiple antennas in different radar ranges. The system includes two band pass filters (BPFs) and one power divider. These components integrate into four antenna arrays, each with six slots. The results show a 4.6 dB gain improvement between lower and higher frequency bands. The antenna extends the maximum detection range by 168 m for a vehicle with an RCS of 10 dBsm in a lossless system. Additionally, the study analyses the normalized admittance of the antenna. It examines the effects of slot length, width, and displacement on conductance and susceptance. These findings confirm the antenna's efficiency for radar applications. A comprehensive tolerance analysis was performed to assess the proposed design's robustness under variations in key parameters.
The paper deals with a new spherical-multipole solution for the scattering of an arbitrary incident wave by a circular aperture in an acoustically soft or hard plane. The boundary-value problem is formulated as a three-domain problem. In each of the domains the field is expanded by means of a complete spherical-multipole expansion, which automatically satisfies the soft or hard boundary condition on the plane, if applicable. The multipole amplitudes of the incident field in the presence of the soft or hard plane are supposed to be given and explicitly derived for a plane wave and for a uniform Complex-Source Beam (CSB). The unknown multipole amplitudes are found from the conditions of continuity of the field and its normal derivative at the boundaries between the domains, leading to a quadratic system of linear equations. All coupling integrals are solved completely analytically. Possible and expected zeros and singularities of the field values or their derivatives at the rim of the aperture develop in the course of an increasing number of multipoles, while at the other locations a finite number of multipoles is sufficient to represent the field. The numerical evaluation validates and improves numerical results found in the literature for the geometrically complementary case of acoustically hard and soft circular discs. Further numerical results for the near- and far field exemplarily prove the robustness and convergence of the proposed method.
In this work, current and voltage time series are analyzed using the continuous wavelet transform (CWT). It is shown that, in contrast to a Fourier transform, a CWT enables the detection and analysis of transient and short-term disturbances in power grids. This is particularly important during the commissioning and maintenance of power systems. So-called Daubechies wavelets are used as purposes. In addition, the family of complex Gaussian wavelets also allows resonance mode analysis. This approach enables the real-time series of current and voltage to be transformed into a complex time series. This shows that wavelets can be used to make statements about the active power transit even in the case of short-term disturbances in the power grid. Finally, practical examples of the application of this method complete this work.
It is investigated how the antenna reflection coefficient (ARC) of directional radio link antennas changes over time when the antenna radome gets wet and dries off afterwards. A hand sprayer is used to deposit droplets on antenna radomes manually. Next, ARC measurements are performed repeatedly using a vector network analyzer and the ARC variation over time and frequency during the drying process is recorded into consecutive frequency response data sets. These vividly demonstrate a continuous drift from the altered, i.e., wet state back to the initial dry state. Previous work has shown that the ARC is a very useful reference for determining the wet antenna attenuation (WAA) that occurs during and also after rain events. It did, however, not explain the observed significant differences in the relation between ARC and WAA with different antennas and at individual frequencies. Inverse Fourier transforms of the recorded frequency domain ARC show a clustered concentration of variations within the unambiguous range in the near vicinity of the antenna. This supports the assumption that the changes in ARC are exclusively caused by moisture on the radome. Our findings match with measurements from previous investigations, reaffirm the expedient value of ARC to support WAA estimates, and explain why different antennas exhibit very different ARC-WAA relations.
The ground-wave signals of terrestrial radio navigation systems, which operate in the medium and low frequency band, are sensitive to changes in the electrical parameters of the Earth's surface between the transmitter and receiver. Sea ice affects the electrical parameters of the sea and leads to an additional signal phase delay compared to the propagation over salt water. To ensure the uniform performance of the navigation receivers for these systems throughout the year, the impact of sea ice on the signal has to be known. A challenge here is the high spatial and temporal dynamic of sea ice in some regions. Earth observation data can be used to obtain information regarding the world-wide sea-ice coverage and further electrical ground parameters. In this paper, our proposed model for the ground-wave propagation and Copernicus data are used to compute the impact of varying conditions on the signal propagation. Simulation results for a real-world scenario show that the signal propagation delay caused by sea ice can lie in the order of 20 ns with respect to sea water.
Time series of mesosphere/lower thermosphere half-hourly winds over Collm (51.3° N, 13.0° E) have been obtained from 1984–2007 by low frequency (LF) spaced receiver measurements and from 2004 to date by very high frequency (VHF) meteor radar Doppler wind observations in the height range 82–97 km. These observations are analysed with respect to gravity wave (GW) climatology and trends. From half-hourly differences of zonal and meridional winds, GW variance proxies have been calculated that describe amplitude variations in the period range 1–3 h. After applying corrections to account for instrumental differences, the GW climatology and time series have been obtained. The mean GW activity in the upper mesosphere shows maximum amplitudes in summer, while in the lower thermosphere GWs maximize in winter. At altitudes around 90 km, positive/negative long-term trends are visible in winter/summer, consistent with increasing/decreasing mesospheric winds. In the lower thermosphere, however, long-term amplitude trends are generally positive. We notice qualitative correspondence of these trends with those derived from satellite observations of potential energy despite of different wavelength ranges seen by radar and satellite. Quasi-decadal and interannual variations of GW amplitudes and mean winds are also visible, showing a possible influence of the 11-year solar cycle or lower atmosphere circulation patterns.
This paper is a direct continuation of "AI Assisted Interference Classification to Improve EMC Troubleshooting in Electronic System Development" . The previous paper aimed to classify the electromagnetic compatibility (EMC) problem classification, while this paper addresses two primary issues: the data and the technique. The technique used in the previous study involved a principal component analysis (PCA) to generate input features for the neural network. However, since PCA only encodes linear relations from the samples, autoencoder (AE) models are now used to encode the data into a latent vector that better represents the data. The latent vectors will ultimately be used as input to classify the EMC problems. A neural network and a random forest classifier were utilized to develop a classification model, wherein the random forest demonstrated superior performance in comparison to the neural network.
Within the project progressivKI, research is carried out to improve the analysis of schematics that depict an electrical circuit. Lots of manual efforts are necessary to validate a design, as schematics are handed in as image data. They neither follow a standard nor contain any meta information that can be obtained to automatically check certain conditions. Furthermore, even the visual representation of components like diodes, capacitors or resistors can differ depending on the design tool used.In this paper, we present an approach to decompose the problem into three different parts and describe their current status: (i) detection of the components like resistors, capacitors, or diodes (ii) detection of lines and their junctions (iii) detection of textual data placed next to components (like voltage or resistance). For each of the given areas we employ deep-learning methods as a basis. The training data is provided by Microchip in the form of link-annotated PDFs. In a preprocessing phase, the data is programmatically scanned for useful information like component names and bounding boxes to pre-annotate them before human correction. The final step is to fuse all information from (i)-(iii) to obtain a netlist that can be automatically validated with given rules.While most work has been carried out in (i) and (ii), a more general workflow including supportive tools has been established to extend our approach to PDFs from other design tools. The results show that recent deep-learning methods are capable of detecting components with a high accuracy given training data of good quality (no false labels).
In this study, the impact of local oscillator cable movements or drift during VNA measurements using frequency extenders is investigated. A non-reciprocal measurement error caused by alterations of the local oscillator signal in R 900 (WR 10) waveguide measurements from 75 to 110 GHz is observed and systematically analyzed. Furthermore, the theory behind this effect and its implications on measurement results are discussed, as well as possible corrections for both calibrated and raw measurement data.
In this work the determination of measurement uncertainties in scattering parameter measurements for waveguide interfaces ranging from R 100 (WR 90) to R 2.6k (WR 3, WM-864) is presented. For each waveguide band a Thru Reflect Line calibration is performed including uncertainties for calibration standards, cable movement, interface repeatability and the characteristics of the vector network analyzer. For reflection and transmission coefficients, envelopes of uncertainties are determined for magnitude and phase angle respectively. In addition, an experiment on connection (interface) repeatability for R 140 was carried out to systematically investigate the influence of shifting and rotating of waveguide flanges. Translation values in steps of 0.3 mm up to 1.5 mm are examined in simulation as well as measurement. The findings of these investigations can be extended and applied to other waveguide bands.
