The approach of multipole-based generalized source integral equation (GSIE) formulations for the scattering by essentially-convex impenetrable objects is extended to dyadic problems. This is demonstrated through the two-dimensional (2-D) problem of transverse-electric (TE) scattering. For this case, the principles of multipole-based generalized source design are utilized within the framework of dyadic TE-GSIEs introduced recently for reflective shield sources. The derivation of the dyadic auxiliary contribution to the modified Green's function is presented in detail and is shown to provide similar superior low-rank compressibility of off-diagonal method-of-moments' matrix blocks as its transverse-magnetic counterpart, while maintaining error controllability. The extension enables the treatment of impedance boundary scatterers in 2-D and is a crucial stepping stone toward a full three-dimensional vector formulation that is expected to exhibit enhanced low-rank compressibility for a broad range of scatterer geometries.
At Collm (51.3° N, 13.0° 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° N, 13.4° 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 Andøya (69.3° N, 16.0° 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 η, 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 ∼10-9 m−1 with peak values at around 7.9×10-15 and 1.6×10-15 m−1 for ALWIN and MAARSY, respectively. Seasonal, diurnal, and height variations of PMSE occurrence rates based on the 26-year data set of η 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.
