The current work presents the first experimental demonstration of real-time Ethernet (ETH) trial services and 4K-Ultra High Definition (UHD) video application transmission over a 2λ Wavelength Division Multiplexing (WDM) analog Fiber-Wireless (FiWi) mmWave X-haul network, supporting dynamic flexible capacity allocation through an integrated silicon photonic Si ₃ N ₄ Reconfigurable Optical Add Drop Multiplexer (ROADM) and 60 GHz wireless transmission across a 7 m V-band link distance, while controlled by a Software Defined Network (SDN) controller based on Open Daylight. Analog X-haul transport of the radio signals is based on an Intermediate Frequency over Fiber (IFoF) scheme centered at 1.5 GHz using an Orthogonal Frequency Division Multiplexing (OFDM) radio-waveform with a bandwidth of 204 MHz, generated by a Field Programmable Gated Array (FPGA)-based RF System-on-Chip (SoC) processor that converts on-the-fly the real-time ETH downlink traffic to analog radio and vice-versa for the uplink. Dynamic allocation of the X-haul traffic capacity is handled through the use of the 802.1Q Virtual Local Area Network (VLAN) tag-mechanism, which controls the forwarding operation to the proper DAC and InP EML for optical modulation using Intensity Modulation/Direct Detection (IM/DD) schemes, while the wavelength routing operation is handled by the low-loss four-port Si ₃ N ₄ ROADM featuring only 2.5 dB fiber-to-fiber losses based on a cascaded MZI-interleaver design on the TriPleX platform, routing the real-time traffic to a second mmWave antenna site. Detailed measurements and traffic statistics indicate end-to-end latency of less than 260 μs and a packet loss less than 0.0054% across a dynamic range of at least 6.5 dB in the optical domain, while the high user bandwidth and signal quality are validated by an uninterrupted 4K-UHD video transmission across the FiWi X-haul mmWave transport network. The current work aims to shape a complete technology roadmap for Point-to-Multipoint FiWi transport network architectures with high spectral efficiency X-haul transport for dense areas and 5G/6G hotspots of future mmWave Centralized Radio Access Networks (C-RANs).

A novel technique is presented for the design and optimization of waveguide antenna arrays based on overlapping sub-arrays for limited field-of-view applications. Each sub-array consists of one directly-fed antenna element and several passive reactive-loaded elements. The proposed overlapping scheme exploits a free-space reactive coupling instead of more conventional schemes based on complex beamforming networks. This results in a drastic reduction in the number of waveguide components required in the feeding network. The optimization of the considered class of array structures using a full-wave EM solver is extremely time-consuming even in the presence of sub-arrays with a reduced number of passive elements. To overcome this limitation, an effective semi-analytical design algorithm has been specifically developed. Using this algorithm, a novel sub-array structure with a predefined pulse-shaped radiation pattern was synthesized. The designed sub-array is inherently matched and features reduced spurious electromagnetic coupling level with adjacent sub-array elements. In particular, the analysis of an array consisting of 38 such sub-array elements has been carried out with the main goal of illustrating the effect of the sub-array pattern on the total array characteristics. To validate the sub-array overlapping scheme, an array composed by 3 contiguous sub-arrays has been realized and measured experimentally. In this way, a scan range in the field of view [-4°; 4°] with 15dB grating lobe suppression has been demonstrated.

This work aims at the establishment of a methodology providing the characteristic modes of mobile devices realistic models including their metallic parts as well as their material-dielectric loading. A modified integral equation Moment method is employed to yield the impedance matrix of such metal-dielectric structures. In turn the characteristic mode approach is employed to formulate and solve the related eigenproblem.

The growing demand for ubiquitous broadband connectivity in 5G/6G Radio Access Networks (RANs) has turned Centralized RAN (C-RAN) and reconfigurable Point-to-MultiPoint (PtMP) network topologies into the mainstream approach for keeping pace with the vastly increasing traffic capacities and connection densities. Relying on an all-passive Arrayed Waveguide Grating Router (AWGR), we propose and demonstrate reconfigurable allocation of multiple parallel Fiber-Wireless (FiWi) millimeter wave (mmWave) analog (Intermediate Frequency over Fiber) IFoF interfaces. The proposed technology provides a framework for the implementation of reconfigurable multiple FiWi backhaul /midhaul/fronthaul (X-haul) connections. The use of AWGR enables wavelength slicing and the co-existence of multiple transport links over the same X-haul network infrastructure. The proposed concept is experimentally validated by two sets of experimental measurements. More specifically a 4λ- Wavelength-Division Multiplexed (WDM) signals modulated by IFoF signals are routed through the AWGR and wirelessly transmitted over the air across a 1m V-band distance by two different pairs of mmWave 60 GHz antennas. In the first experiment, a Phased Array Antenna (PAA) operating at 60 GHz is utilized achieving a 2.5 Gb/s data rate per wavelength and beam pair with an Error Vector Magnitude (EVM) of less than 12.5% and an aggregate 10 Gb/s traffic capacity. The achieved performance meets for the first time the respective 5G Key Performance Indicator (KPI) requirements for EVM quality and peak data traffic while supporting the link reconfiguration wavelength routing and mmWave beam direction. In the second experiment, the PAA is replaced by a point-to-point 60 GHz link utilizing a high-end mm-wave transmitter, thus achieving a data rate of 12.75 Gb/s per wavelength-beam with an EVM of less than 6.5% and an aggregate capacity of 51 Gb/s. To this end, the proposed solution is shown to form a promising roadmap toward flexible and reconfigurable 5G/6G mmWave C-RAN architectures where multiple Mobile Network Operators (MNOs) can share the same network infrastructure and dynamically allocate fiber, antenna beams and wavelengths.

This paper presents an antenna array organized in sub-arrays and composed of densely spaced dielectric-based radiating elements. To reduce the number of active components required in the array beamforming network, each sub-array consists of a single active element, directly fed, and several passive reactively loaded elements. State-of-the-art implementations of such arrays are typically based on rectangular air-filled waveguide radiators which provide a limited bandwidth and support a single linear polarization only. By utilizing the dielectric-based radiators presented in this work, a significant increase in the operating bandwidth of the array can be achieved. In this case, the aforementioned reactive loading is implemented through short-circuited dielectric-filled waveguides. By optimizing the position of the short circuits, the radiation pattern of the sub-array can be controlled and synthesized according to a given mask. To create a larger design flexibility, one can design the sub-array in the presence of the adjacent sub-arrays, so achieving their effective overlapping. By employing the considered design technique, a sub-array featuring flat-top radiation pattern characteristics in combination with low side-lobe levels and high gain was developed, manufactured, and thoroughly analyzed. An additional benefit of such design choice is the possibility of supporting two orthogonal polarizations.

The rise of the 6G era promotes massive broadband wireless connectivity in dense multi-user networks, equipped with flexible X-haul transport schemes. This work presents the first experimental demonstration of the end-to-end signal flow of a flexible THz Fiber Wireless (FiWi) X-haul that aggregates and simultaneously transports the multiple Intermediate Frequency over Fiber (IFoF) streams of a mmWave Multiple Input Multiple Output (MIMO) antenna on a single wavelength in the analog domain. Specifically, the FiWi X-haul transmission relies on a pair of 150 GHz antennas with 256 radiating elements placed after a 7 km-long fiber spool, acting as a THz wireless bridge that provides flexible, seamless last mile connectivity. In turn, mmWave access in the Radio Access Network (RAN) segment is provided by means of a cascaded MIMO Phased Array Antenna (PAA) hosting three analog Intermediate Frequency (IF) input ports with microwave filtering and RF beamsteering. The proposed THz FiWi multi-IFoF X-haul link transports three different V-band user beams, each supporting a 250Mbd QPSK signal with individual analog RF beamsteering anywhere within a 90^o sector, mapping each beam at a different transport IF. The proposed system distributes a 1.5 Gb/s data rate in three steerable beams anywhere in the 90° field of view of the MIMO antenna or to unleash a peak aggregate rate of >10 Gb/s at a single beam-direction, forming a flexible THz multi-IFoF X-haul of a multi-beam mmWave antenna on a single-wavelength and a promising roadmap for future multi-user 6G RANs.