This paper presents angle-resolved radio channel measurements at 3.9 GHz and 28 GHz conducted in a densely packed industrial production hall. The channel was captured at 87 positions with 3D distances ranging from 13 m to 87 m. The power, delay, and angular characteristics are evaluated and compared with the 3GPP TR 38.901 Indoor Factory model. Frequency-dependent models for path loss, $K$-factor, RMS delay spread, and azimuth spread of arrival are extracted and crosscorrelations between the parameters are analysed. The results show that the $K$-factor and delay spread are nearly frequency independent, while the angle spread increases with frequency.

In this paper, two reconfigurable intelligent surfaces based on liquid crystal in the mmWave frequency range are presented and a characterisation of their amplitude and phase vs frequency is performed for different applied voltages. The two charaterized RIS are a single-polarization RIS based on multiple resonators while the other one is a novel dual-polarized phaseshift-based RIS whose phaseshifter has a high shrinking factor in order to compensate for the low tunability of the LC. Besides, the effect of the orientation of the LC-molecules in the performance is compared, as well as two different LC-mixtures: the GT7-29001 from Merck KGaA Darmstadt, Germany and the GT8-32003, also from the same company.

In this paper, a phased array for a hybrid beamforming system with a conformal array topology is discussed. The system is operating in the 5G-FR2 mm-Wave region and consists of 16 linear $4 \times 1$ patch antenna arrays, which are placed in a half-circular order, making a half-cylinder. The linear arrays consist from 4 aperture coupled patch antennas with fractional BW $(\text{FBW})>10 \%$ and dual-polarization. Each linear array is realized as a thin rectangular strip (array segment) with a width of approximately $0.8 \lambda_{0}$. The segments are connected via highfrequency coaxial connectors to a beamforming board containing 4 mm-wave quad-channel dual-polarization BFICs (Beamforming IC) from NXP. Phase shift values for the intended beamforming are being calculated based on a simple geometrical ray model that determines the center-to-element time delay of an incident wave from a given angle. The array is sector-wise operated, with two sectors independently and simultaneously radiating and operating in both uplink and downlink. Each sector covers an azimuthal scan range of $\pm \mathbf{6 0}{ }^{\circ}$ with fixed elevation on 90°. First measurements show successful beamforming with beamscanning capabilities with errors in gain and scan angles. This is due to varying channel behavior, which needs custom array calibration to compensate for these errors.

In this paper, we present a modular open radio access network (O-RAN) consisting of the 5G Core, a central (O-CU) and distributed unit (O-DU) by Software Radio Systems (SRS) and an O-RAN radio unit (O-RU), MODRAD-SC, by Massive Beams (MB). OCUDU provides an open source 5G-compliant O-CU and O-DU solution developed by SRS, while MB's radio unit is a fully O-RAN compliant category A O-RU. According to O-RAN split 7.2a, OCUDU performs higher layer functions up to the high physical (PHY) layer, while the O-RU handles low PHY and RF functions. This results in an O-RAN-compliant 5G gNodeB. In an alternative configuration, OCUDU and MODRAD-SC operate in a software-defined radio fashion corresponding to split 8, facilitating non-real-time experiments among others. In both cases, the system provides full control over O-CU, O-DU, and O-RU. In addition, we will discuss the possibility to attach an analog beamformer to the O-RU, enabling hybrid digital-analog beamforming. The flexibility and modularity offered by OCUDU and MODRAD-SC enable the practical realization of a multitude of applications, ranging from 5G demonstrators to pre-6G experiments. The system addresses the requirements of academia and industry and is well-suited as an easy-to-use platform for experimental and practical deployments.

In this work, a Reflective Intelligent Surface (RIS) is designed and evaluated. The design is based on aperture-coupled stacked patches, enabling compact array realization with dualpolarization capability and broadband behavior. Initially, a single antenna element was designed, based on which, two arrays were designed, one $2 \times 2$, to be used as the signal source for far-field RIS measurements and one $8 \times 8$, the RIS. To keep the design efficient, 2-bit switched delay line phase shifters are used for beam steering. All hardware elements were individually manufactured and tested. Additionally, the whole system was assembled and tested in a bi-static configuration. To ensure satisfactory performance, the phase distribution of the incident wave was determined directly. This was achieved by radio frequency connectors at each unit cell, bypassing the phase shifters. This modular design allows for easy identification of deviation sources from the ideal design and to perform better root cause analysis.

In this research, a Near-field Fed Reflective Intelligent Surface (NFED-RIS) System is evaluated in far-field as an alternative beamforming system for centimeter-wave operation. A dual-polarized $8 \times 8$ RIS within the centimeter-wave band was designed for this study. The NFED-RIS system, which is based on these two patch arrays, will be experimentally evaluated in a farfield anechoic chamber. The RIS is considered a passive reflect array antenna that can be utilized as an analog beamformer. This is achieved by dynamically reflecting incident waves from the Feeder, resulting in steerable beams in the far-field. The parabolic phase distribution of the impinging wave from the Feeder at the RIS needs to be compensated in such a way that the reflected wave has a uniform phase distribution which forms the basis to shape beams in the far-field. The NFED-RIS system demonstrates remarkable performance as an alternative cost-efficient beamforming system in comparison to conventional phased arrays.

This paper presents metrics and measurement methods for the experimental characterization of helicopter rotor blade modulation of the wireless propagation channel. Broadband bistatic channel measurements were conducted at three widely separated carrier frequencies (302 MHz in the UHF band, 4.9 GHz in the C-band, and 27.1 GHz in the Ka-band) for three military helicopters (CH-53, Tiger, and UMAT) at the Bundeswehr Technical and Airworthiness Center for Aircraft in Manching, Germany. The time-variant channel was analyzed in terms of the Doppler Power Spectrum and the RMS Doppler spread, the Doppler spectrogram, and the Power Time Profile. The RMS Doppler spread values were found to be moderate (up to 106 Hz), which is attributable to the predominantly lateral blade motion relative to the line-of-sight path. The Power Time Profiles revealed periodic blockage attenuations of up to 15 dB at Ka-band, increasing significantly with the carrier frequency; at 302 MHz, the blockage attenuation does not exceed 2.3 dB and the RMS Doppler spread stays below 10 Hz. The measured blockage attenuation was modeled using the double knife-edge diffraction model, showing good agreement with the measurements. The distinct micro-Doppler signatures visible in the spectrograms are identified as a potential resource for helicopter classification and passive radar applications.

This paper presents the Geometrical Optics (GO) and Physical Optics (PO) techniques for calculating the radiation pattern of a dielectric lens mounted on top of an open-ended WR6 waveguide. A ray tracing tool is used, and the far-field radiation pattern is calculated by applying Kirchhoff's Diffraction Theory on the lens surface. The results from the asymptotic methods are compared with full-wave simulation and far-field measurements at 160 GHz, with good agreement of the main lobe.

This paper presents results of a channel measurement campaign carried out in a production hall of Rohde & Schwarz in Memmingen, Germany. The channel measurements were performed with a novel time-domain correlative channel sounder operating in the D-Band at a carrier frequency of 160 GHz. The channel measurements were performed and an-alyzed with respect to the topic of beam-steering and macro-diversity gains. It was found out that an average macro-diversity gain of 3.2 dB for line-of-sight and 5.7 dB for non-line-of-sight is achieved.

This paper presents a D-band (150-170 GHz) $16 \times 2$ planar patch antenna array, integrated with a dielectric lens, designed to facilitate dual-beam (hybrid) beamforming capabilities. The configuration employs both the array factor and the lens to achieve beam collimation across distinct focal planes. The patch antenna array elements are designed based on a band-pass filter topology on high-resistive silicon substrate, and optimized for the PTFE dielectric lens material situated atop the array. The extruded elliptical dielectric lens with the patch antenna array reported in EM simulation a gain of 26.8 dBi and scan angle of +/−30° at 150 GHz. Furthermore, an asymptotic analysis method has been employed to investigate the variations in beam tilt relative to the size of the dielectric lens.

In this paper, we introduce a novel time domain correlation based channel sounder that operates at 485 GHz. The channel sounder targets the Y-band ($330 \text{GHz}-500 \text{GHz}$) and covers a center frequency up to 500 GHz. The setup has been validated in the laboratory for conducted and over-the-air measurements. The conducted measurements report a dynamic range of around 80 dB without spurious peaks, and a linear behavior between added attenuation and dynamic range with constant relative noise floor. The over-the-air measurements report a match of the line-of-sight path's propagation length and normalized received power.

This paper proposes a novel independently controllable dual-polarized 2-bit unit cell with excellent cross-polarization isolation (XPI) for reconfigurable intelligent surface (RIS) applications with $\mathbf{4 0 0} \text{MHz}$ bandwidth centered around 15 GHz. The proposed RIS unit cell is based on orthogonally placed slotted bowtie elements loaded with varactor diodes, square rings to increase phase shift range, and dummy square patches to minimize the reflection loss. The full-wave electromagnetic simulation results of the unit cell demonstrate the reflection phase shift up to 270 degrees, a maximum reflection loss of 4.1 dB, and 55 dB of XPI within the operating bandwidth. Furthermore, $16 \times 16$ element panel simulations of the RIS have been performed for different reflection angles under TE and TM-polarized illuminations. The results indicate a wide-angle scanning range within -60 to +60 degrees with a maximum of 1.7 degrees of beam pointing error. The proposed RIS also demonstrates precise control under wide-angle excitation.

This paper presents THz channel propagation measurements at 300 GHz conducted in a conference room environment, targeting both static and dynamic sensing scenarios involving a metallic reflector and a human subject. The measurements were analyzed in terms of power delay profile (PDP), Doppler spread, and radar cross section (RCS), revealing the system’s high sensitivity and precision. Utilizing an 8 GHz bandwidth, the setup achieved millimeter-level sensing accuracy, highlighting its potential for fine-grained detection and characterization in indoor environments.

In this work, a Near-field Fed Reflective Intelligent Surface (NFED-RIS) System is designed and evaluated in preparation of the usage as an alternative beamforming system. The conceptual architecture of this smart antenna system has been developed and validated using a system model presented in this paper. Subsequently, a dual-polarized $8 \times 8$ RIS array and $2 \times 2$ Feeder array within the centimeter-wave band were designed and validated through an electromagnetic simulation prior to fabrication. The NFED-RIS system, which is based on these two patch arrays, will be experimentally evaluated and compared to the results of electromagnetic simulations, including potential deviations caused by imperfections not captured in the simulation model. Consequently, the RIS is regarded as a passive reflect array antenna that can be utilized as an analog beamformer. This is achieved by dynamically reflecting incident waves from the Feeder, resulting in steerable beams in the far field. The distance between the two arrays is critical to ensuring optimal system performance. One of the objectives of the experiments is to identify the optimal distance between RIS and Feeder through the analysis of the near field channel (S21 over-the-air measurements) across all antenna elements, excluding the RIS phase shifters. In addition to delivering deep insights and design trade-offs of the NFED-RIS system, the measurement provides the magnitude and phase distribution at the optimal distance on the RIS, which is crucial for determining the beamforming steering vectors for future far-field experiments.

We present a model of the classic Fabry-Perot resonator with one of the metal mirrors being replaced by a dielectric mirror. This modification enables efficient filtering of the resonator's eigenmodes without degrading the working oscillation's frequency or quality factor. The results of numerical experiments demonstrate the feasibility of constructing such a quasi-optical resonator whose dimensions exceed the working wavelength by more than an order of magnitude, and which supports a single dominant eigenmode within the $0-178 \text{GHz}$ frequency range. The proposed design technique for quasi-optical resonators may be of interest in applications requiring generation and/or selection of oscillations with low phase-noise levels.

This paper evaluates the performance of a WR6.5 rotary joint utilizing two 3D-printed TE01 mode transducers. The rotary joint, fabricated from AL6061 alloy, was tested in a measurement setup using a vector network analyzer across a frequency range from 140 to 170 GHz. The findings indicate that the rotary joint demonstrates an average insertion loss of approximately -2 dB over a usable bandwidth of 15.85 GHz ranging from 145.25 to 161.1 GHz with phase angle variation of less than 15.3° over a full rotation. The results highlight the viability of 3D printing for creating waveguide structures while also acknowledging limitations in surface finish and dimensional accuracy.

In this paper a novel frequency-scalable rotary platform design is introduced which allows for flexible directional channel measurements using different types of antennas, and which can also be used with frequency extenders for measurements up to the THz region. The measurement platform has been applied to measure the channel properties including the direction of arrival at the FR3 frequency 14 GHz and in the D-band at 160 GHz in a large hall indoor environment with LOS distances up to 40 m. The results show very good agreement of strong path components for both frequencies as well as interesting dependencies of delay spread, angular spread, and Ricean K- factor on distance and frequency and can be used to parameterize a path loss model.

An innovative planar single layer off-chip antenna for the use in broadband communication and sensing applications in the 220 GHz to 330 GHz frequency range is presented. The antenna employs the use of double U-shaped slots as loading for a rectangular patch to introduce coupled resonances, leading to a broadband radiation characteristic. As an off-chip design, low permittivity substrates, such as fused silica, can be used, ensuring good radiation characteristics. An impedance transformer is added to the microstrip antenna feed line allowing to match a 50 ohm bondwire connection to the 65 ohm antenna input impedance, satisfying the condition of a reflection coefficient of less than -10 dB over the whole desired frequency range. Simulation and measurement show good accordance, with the antenna having a peak gain of 6.2 dBi at the centre frequency of 300 GHz, only 0.4 dB less than the simulated value. In the measurements a bandwidth of at least 13.3% is achieved, more than four times the bandwidth of a standard rectangular patch antenna on the same substrate.

This paper presents channel measurements and modeling at 28 and 160 GHz in an industrial-style open office environment with angular information at the receiver. Channel impulse response snapshots are captured at 135 measurement positions for both frequencies and are evaluated in terms of power metrics, delay, and angular characteristics. Frequencydependent models for path loss, delay, and angular spread of arrival and K-factor are estimated, and large-scale parameter cross-correlations are evaluated. The results show that delay and angle spread are not frequency dependent in this environment although twice as many multi-path components were identified at 28 GHz compared to 160 GHz.

This paper presents the design and implementation of an agile sub-terahertz (sub-THz) broadband time-domain photonic channel sounder, capable of characterizing wireless propagation channels within the 100 GHz to 500 GHz frequency range. The sounder employs a hybrid architecture that combines photonic carrier generation through heterodyne mixing of continuous-wave lasers locked to a frequency comb, along with electronic components for broadband sounding sequence synthesis and digitization. This design enables precise and tunable carrier frequency generation, overcoming the limitations of traditional electronic-only systems. Experimental evaluations highlight the system's high temporal resolution, phase stability, and broadband performance, including over-the-air calibration and monostatic channel measurements across three sub-THz bands (160 GHz, 300 GHz, and 450 GHz). The results establish the feasibility of the time-domain photonic channel sounder as a powerful and versatile tool for measuring various, widely scattered, and spread sub-THz bands.