Abstract This chapter deals with architectures for wideband channel sounders suitable for characterising THz wave propagation. A maximum-length binary-sequence (MLBS) sounder, a vector network analyser, and an arbitrary waveform generation-based sounder are presented as implementation examples of THz channel sounders. Sounding is usually concerned with several measurement dimensions. We are discussing impacts on the architecture if directional channel information is to be captured. This includes improvements in dynamic range when using mechanically rotated antennas. Finally, a front-end design for capturing polarimetric channel information is presented.

In this work, we introduce a thorough comparison between ray tracing (RT) simulations and multi-band measurements in a complex scenario such as an industrial environment. The RT model was generated from precise 3D laser scans in a small machinery room. A 3D model was recreated and processed using commercial and non-commercial software. Simultaneously, double-directional dual-polarized ultra-wideband measurements at 6 GHz, mmWave, sub-THz, and THz were also carried out for calibration and validation purposes. The RT simulations were conducted in the open-source tool for physical channel modeling Sionna. Afterwards, the measurement set-up was emulated by embedding the measurement bandwidth and antenna patterns into the RT simulations for a fair comparison. The results show a good agreement on the location of the dominant scatterers.

The utilization of the sub-THz frequency range for industrial applications has gained relevance in the latest years. The free blocks of available spectrum and the need of implementing high gain radio interfaces result in high resolution systems, ideal for sensing applications as well. This contribution shows novel results on ultra wide-band measurements of Doppler and micro-Doppler at 170 GHz inside industrial machines with the objective of characterizing propagation for integrated sensing and communications. The results have shown complex patterns from the interaction of multiple-paths with different typical Doppler signatures.

This paper describes an experimental performance validation of Fisher information-based waveform designs for channel sounding and high-resolution propagation parameter estimation. These waveform designs require prior knowledge about the parameters which can be estimated from a preceding measurement. We describe a setup to implement this intermediate parameter estimation and waveform optimization step. A subsequent performance validation via the empirical MSE derived from measurement-based Monte Carlo trials is also presented. This paper builds upon a previous simulation-based study that found that the CRB for delay estimation improves using the optimized waveforms. This finding can be reproduced for the delay MSE with the presented experiments. An additional insight is that the accuracy of the intermediate estimates does not significantly impact the MSE, as long as the SNR is sufficient to detect the required paths reliably.

Understanding the hardware impairments and the effect of the postprocessing algorithms on an unknown channel sounder (CS) requires a comparison with a calibrated instrument with a known error model. In this study, we use a vector network analyzer (VNA) with error models and theoretical calculations to characterize two correlation-based, purpose-designed CS test instruments operating around 200 and 300 GHz, respectively. We conducted a series of controlled measurements, including both line-of-sight (LoS) and nonline-of-sight (NLoS) scenarios. Key aspects investigated include VNA calibration accuracy, noise performance, and power delay profile (PDP) peak magnitude and delay drift. For the correlation-based CSs, we investigate the impact of dc offset and in-phase and quadrature (IQ) imbalance on measurements. The measurement scenarios enabled detailed characterization of the antennas under test, the VNA's nonlinearity, and the total spectrum of the CSs. We examined the feasible bandwidth in terms of PDP path gain and delay deviations, comparing results with VNA measurements to ensure accuracy. Additionally, multipath measurements using various reflectors provided insights into the system's response to different multipath components, presenting the influence of reflectors on path gain and measurement uncertainties. Some of the findings demonstrated combined uncertainties of +/- 0.22 and +/- 0.51 dB for the WR05 and WR03 VNA measurements, respectively. The CS measurements displayed a standard deviation of 0.4 dB and 0.3 both before and after applying the Hann window for 5 GHz bandwidth for the WR05 band. At the WR03 CS 5-GHz bandwidth, the deviations were 1.4 and 1 dB before and after applying the Hann window, respectively.

Developing channel models typically requires aggregating channel measurements and the corresponding extracted propagation parameters from different research institutions to form a sufficiently large data basis. However, uncertainties arising from limitations of the sounding hardware and algorithms may greatly impact the comparability between sounding results. Especially, (sub-)THz channel sounders do not allow simultaneous spatially and timely resolved measurements as known from sub-6 GHz and mm-wave applications (right now), limiting the possibilities of a hardware-independent channel characterization. At the same time, a high Doppler bandwidth may occur due to the high carrier frequencies, limiting the time spans for coherent or incoherent data processing. Hence, assessing the sounder’s performance and limits is important before interpreting the measurement results. Evaluating the sounder performance requires a traceable reference allowing tracing back measurements (or estimated propagation parameters) to a physical ground truth. Therefore, we propose and discuss an over-the-air artifact allowing a joint verification of delay and Doppler parameters in a multipath scenario. The evaluations of exemplary sub-THz measurements with a multicarrier-based sounder highlight the strong interplay between sounder hardware and estimation algorithms, especially when coping with the mutual interference of parameters from multiple propagation paths. Hence, a metrological assessment always requires considering the full processing pipeline from the unprocessed measurements up to the extracted propagation parameters.

The present paper compares double-directional ultra-wideband measurements at 187.5 GHz with ray tracing (RT) simulations using the open-source tool Sionna. The objective is to validate a model obtained from precise light detection and ranging (LiDAR) scans. The measurements emulated a sensing system in a situation of blockage by a forklift truck in an industrial scenario. The results show, despite expected differences, a good agreement between the measurements and simulations, enabling this model for further investigations on machine learning (ML)-based integrated sensing and communication (ISAC) algorithms.

The large blocks of free instantaneous bandwidth at (sub-)THz and the utilization of high gain radio interfaces makes the (sub-)THz suitable for sensing applications. In this paper we present the analysis of novel dual-polarized double directional measurements at 190 GHz in an industrial setting with integrated sensing and communication applications in view. The set-up consists of a bi-static configuration emulating two access points with beam-steering capabilities in a machine room. One access point serves a machine with a wireless link, while the other access point senses the environment to detect moving objects. The objective is to detect possible obstructions that could interrupt the communication link or cause accidents on the production line. The results have shown that the system aspects as narrow beams and large bandwidths allow the early identification of objects in the environment from the measured channel impulse response.

The upcoming 3GPP global mobile communication standard 6G strives to push the technological limits of radio frequency (RF) communication even further than its predecessors: Sum data rates beyond 100 Gbit/s, RF bandwidths above 1 GHz per link, and sub-millisecond latency necessitate very high performance development tools. We propose a new SDR firmware and software architecture designed explicitly to meet these challenging requirements. It relies on Ethernet and commercial off-the-shelf network and server components to maximize flexibility and to reduce costs. We analyze state-of-the-art solutions (USRP X440 and other RFSoC-based systems), derive architectural design goals, explain resulting design decision in detail, and exemplify our architecture’s implementation on the XCZU48DR RFSoC. Finally, we validate its performance via measurements and outline how the architecture surpasses the state of the art with respect to sustained RF recording, while maintaining high Ethernet bandwidth efficiency. Building a 6G integrated sensing and communication (ISAC) example, we demonstrate its real-time and rapid application development capabilities.

We perform simultaneous multi-band ultra-wideband dual-polarized double-directional measurements at sub-6 GHz (center frequency, 6.75 GHz), mmWave (74.25 GHz), and sub-THz (305.27 GHz) in line of sight (LOS) and non-LOS in a small industrial scenario (machine room). The aim is to characterize the propagation at THz taking as a reference the lower bands and identifying shared and distinguishing features. The spatial/temporal analysis of the measurements shows strong similarities in multi-path components (MPCs) between the different bands. Moreover, high order reflections have been identified at THz. Overall, the results indicate that THz channels exhibit significant multipath, with some specular MPCs unique to the band and with lower contribution by the diffuse components. Finally, path-loss has also been computed and compared with existing multi-band models.

The mmWave and sub-THz bands are foreseen as candidates to achieve the data-rate demands in the beyond 5G and 6G wireless communication networks. The co-existence of multiple radio interfaces at several bands enables data fusion and the utilization of the similarities and differences on propagation and system properties for communication and sensing applications. MmWave radio interfaces rely on directive beams that require high training overhead for beam steering. Sensors in the network infrastructure and co-located radio interfaces at sub-6 GHz and mmWave can be used to assist the beam-forming process at mmWave. In the present paper we investigate the performance of multi-band assisted beam-forming in an industrial environment. We empirically demonstrate from real-world measurements that even in NLOS, the direction of the beams estimated at sub-6 GHz can be used to established a link at mmWave.

In the present paper we introduce novel ultra-wideband (UWB) dual-polarized double-directional measurements at sub-THz (300 GHz) in an access point to inside of machine application in an industrial scenario. The results show a sparse spatial/temporal channel with multiple paths from the different metallic objects and their influence on polarization. In addition, different LOS blockage situations were investigated, showing the presence of alternative paths for communications.

In the present paper we introduce the empirical results of measurements with an over-the-air based propagation artifact for verification and validation of sub-THz and THz channel sounders and parameter estimation algorithms. This experiment produces a fixed number of multipath components with traceable propagation properties in the different domains that can be used to test resolution and performance. Because of the inherent characteristics of the measurement hardware, we have introduced an adaptation on a parametric high resolution estimation algorithm to account the imperfections of the channel sounder. The results have shown to account for a relative good performance of the sounder and the tested parametric and non-parametric estimation algorithms.

In the present paper we introduce simultaneous multi-band measurements at sub-6 GHz and two mm-wave bands with the objective of characterizing propagation for multi-band channel modelling purposes in industry scenarios. The marginal power profiles show that the dominant scatterers are common in the different frequencies. In addition, a relation of decreasing average delay and angular spreads with increasing frequency is observed. The different measured parameters are contrasted with the 3GPP model for indoor factories.

In this paper, we present the ray tracing (RT) simulation in the 3D model of one highly dense clutter industrial hall, which is scanned by laser scanner and reconstructed based on accurate point cloud. The whole processing chain from the scanning of the physical environment to running the simulation is presented in detail. To validate the simulation results, the synthetic channel characteristics and large-scale parameters, including delay spread (DS), angular spread (AS) and path loss (PL), are compared with those obtained from channel sounding measurement in both LOS and NLOS cases, at 6.75 GHz, 30 GHz and 60 GHz. The simulation results show that some scatters are significant in all bands and may be well identified and tracked. This indicates that our target to generate a deterministic channel model or a hybrid channel model at multi-band for industrial scenario may be possible.

The lower THz bands are foreseen as candidates to achieve the data-rates demanded in the sixth generation (6G) of wireless communications. Hence, multiple measurements for characterization of propagation at these frequencies in different scenarios are being conducted all around the world. This also impulses activities on standardization of measurement equipment and methodologies to define common practices and make measurements from different actors comparable. Therefore, in the present paper we investigate the accuracy of a dual-polarized ultra-wideband channel sounder in the time, angular, and polarization domains by means of a verification methodology based on interferometry.

In this paper we describe the architecture and design of a non-blocking 4×4 switch matrix module for mm-wave satellite communications, where flexible signal distribution becomes increasingly relevant. Following the successful on-orbit verification of a blocking 4×4 switch matrix for a reconfigurable Ka-band input multiplexer aboard the planned German Heinrich Hertz mission, the non-blocking switch matrix module offers relevant advantages in terms of signal routing and total power consumption. The non-blocking switch matrix utilizes hybrid-integrated precision laser-trimmed Wilkinson power splitters and low microwave-loss absorptive transistor-based SPST-switches.

This chapter discusses the general requirements for microwave applications. Substrates for microwave circuits are required to have a low dielectric loss tangent (tan δ < 0.001 across the range of frequencies of interest) and high frequency and temperature stability of permittivity. Multilayer ceramic technologies such as low temperature co-fired ceramic (LTCC) offer options to implement three-dimensional waveguide, biasing, and control structures and components in addition to better shielding opportunities in the substrates. The chapter provides an overview about different technologies to structure the lateral conductor pattern on LTCC tapes and substrates. The use of LTCC is a promising technology for the realization of satellite payload modules and subsystems, since it provides good microwave performance, multilayer capabilities with three-dimensional microwave circuitry and high wiring densities, moderate production costs, and hermetic packaging. Cavities in the LTCC are used to align the monolithic microwave integrated circuits (MMIC) surface to the substrate surface.

In this paper we describe the development of a compact and lightweight reconfigurable 4×4 switch matrix module for geostationary satellite communications in Ka-band (17…22 GHz), where signal routing becomes more and more relevant. The module is based on a space-qualified low-temperature co-fired ceramic multilayer technology. Following a successful on-orbit verification aboard a low-earth orbit satellite mission, the switch matrix has undergone major design revisions, aiming at an industry-scale manufacturability without compromising the advanced functional performance. By applying a system-in-package approach including automated hybrid assembly, a fully operational breadboard version has been developed, which upon further space qualification steps is intended to become part of a reconfigurable input multiplexer aboard the geostationary Heinrich Hertz satellite. Combining a ceramic package, an organic multilayer interface, wire-bonded coaxial connectors into an aluminum housing, the dimensions measure 126 mm × 87 mm × 11 mm with a weight of 193 g, corresponding to a reduction of 60 % in volume and 40 % in mass compared to a previous electronic version, and orders-of-magnitude better than coaxial switch matrices.