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In this article, an improved model for the beam–wave interaction of sheet beam in traveling wave tubes (TWTs) considering ohmic losses and reflections is presented. The ohmic losses are obtained by field analysis and equivalent method. The space charge magnetic field is derived from the active Helmholtz’s equation. An algorithm to obtain the S-matrix by the equivalent circuit method is presented. The relativistic Boris method is applied to accelerate macroparticles. The exchanged power is computed by the work the electromagnetic field applied to the macroparticles. The theoretical model is applied for validation to a ${G}$ -band staggered double vane TWT and validated in comparison with CST Particle Studio and simulations without losses and reflections. The convergence of this algorithm is also discussed. The simulation time of the model is substantial faster than 3-D particle-in-cell (PIC) simulations.

5G and the future 6G ambitions will be real when wireless “unlimited data’ will be available. Multi-Gigabit per second or Terabit per second are the new units to measure the data demand of emerging applications such as 8K video, e-health, extended reality, vehicle to everything , and many others. Actual wireless networks are based on the fiber substrate that feeds, by fixed access points, a wireless layer for distribution to users at much lower capacity, posing a limit to the introduction of data hungry applications. To increase the area capacity of the wireless distribution layer, an ubiquitous data source is needed. A wireless layer to transport data at rooftop level is conceived to replicate wireless the data provision of the fiber substrate, with unlimited access flexibility. This new layer is fed by fiber and provides to the wireless distribution layer links arbitrarily distributed, for a ubiquitous data distribution. The architecture and enabling technology of the proposed wireless transport layer will be described.

High data rate wireless links are an affordable and easily deployable solution to replace or complement fibre. The wide frequency band available at millimetre waves above 100 GHz can support multi-gigabit per second data rate. However, the high attenuation due to rain and humidity poses a substantial obstacle to long-range links. This study describes a wireless system being developed for point-to-point links at D-band (DLINK), above 150 GHz, to enable a full fibre-on-air link with more than 1 km range and unprecedented data rate up to 45 Gb/s. The upper end of the D-band spectrum is used (151.5–174.8 GHz) in full frequency division duplex transmission. The DLINK system consists of a transmitter using a directly modulated resonant tunnelling diode oscillator powered by novel travelling wave tubes. The performance and the small footprint of the front end will make the DLINK system highly competitive to the point-to-point links presently available in the market at frequencies below 100 GHz. The innovative approach and the design are oriented to large-scale productions to satisfy the high data traffic demand of the new 5G infrastructure.

An improved topology of Extended interaction oscillators (EIO) is presented with enhanced efficiency at 0.35 THz. A bi-periodic ladder-type structure is used for optimizing the performance of the TM $_{{31}}- 2\pi $ mode operation, based on bi-periodic interaction gaps composed of staggered short and long slots. The bi-periodic interaction mechanism permits to operate the circuit with a standing-wave field between the $\pi $ and $2\pi $ modes, thus providing the potential to combine the advantages of both $\pi $ and $2\pi $ modes in terms of both coupling and output performance. The resulting transverse TM31 operating mechanism exhibits a good agreement with the bi-periodic structure in terms of coupling performance, with the short slot length positively correlated with the value of effective characteristic impedance ${M}^{\,{2}}{R}/{Q}$ . The circuit demonstrates attractive coupling and output characteristics by optimization of ${M}^{\,{2}}{R}/{Q}$ and ${Q}_{e}$ . A state-of-the-art value ${M}^{\,{2}}{R}/{Q}$ of 59.69 $\Omega $ and a moderate ${Q}_{e}$ of 2523.52 are achieved for a proposed eight-period ladder-type EIO. An RF power of 540 W is obtained with a 42.5 kV, 0.6 A sheet beam, with 2.1% electronic efficiency at 0.35 THz.

Meander lines have been lately studied as slow wave structures (SWSs) for millimeter-wave traveling wave tubes (TWTs) given their numerous benefits such as low beam voltage, high interaction impedance and straightforward manufacture. They are seen as a very promising candidate for a new generation of low-cost TWTs. The efforts are now focused on finding novel meander line configurations that could improve the overall performance of the TWT. This paper analyses the effect of the material underneath the meander line substrate and presents different alternatives to enhance the interaction impedance.

A slow-wave structure (SWS) with periodic coupling structure and reentrant cavity is proposed for extending the extended interaction klystron (EIK) technology. The conventional higher-order mode single-period cavities allow for larger sizes, corresponding to the G-band (220 GHz), but their low R/Q values are not facilitating the realization of extended interaction klystron (EIK). The newly proposed compact EIK topology is to support millimeter-wave higher-order mode operations. The slow wave structure facilitates the advantages of multi-layered processing.

D-band TWTs (151 – 161.5 GHz) are the enabling devices for long range links with high capacity at sub-THz frequency. The EPSRC DLINK project aims to produce a front end to provide about 45 Gb/s for 1 kilometre range in point to point with 99.99% availability in ITU zone K. The design and fabrication of the TWTs is in progress. The short wavelength at D-band needs high precision fabrication and strict tolerances. This paper will discuss the impact of variation of dimensions against the nominal design value of the double corrugated waveguide for a 151 – 161.5 GHz TWT, highlighting the design parameters that needs higher accuracy.

The European Commission Horizon 2020 ULTRAWAVE “Ultra capacity wireless layer beyond 100 GHz based on millimeter waves” is in the final stage of development. The first ever field test of a D-band point to multipoint wireless system will be performed in a real environment. The ULTRAWAVE wireless system comprises a D-band Transmission Hub to produce a 30 degree sector with 600 m radius with multi gigabit per second data rate and a number of compact D-band terminals. The terminals will be distributed at different distances from the transmission hub to recreate real deployment condition. The paper describes the latest update on the development of the ULTRAWAVE systems and the field test set up.

Meander lines are promising slow-wave structures (SWSs) for millimeter-wave traveling-wave tubes (TWTs) due to low-cost manufacture, low-voltage operation, and high interaction impedance. However, experimental results on meander lines are rare in the literature. Phase velocity and interaction impedance are the most important parameters for the design and characterization of TWT SWSs. Their experimental determination in meander lines is crucial for validating simulations and developing new topologies. Based on a new theoretical model, this article presents an experimental procedure to determine the phase velocity and the interaction impedance. The method is validated on four different Ka -band (33–37 GHz) meander-line SWSs, including two of a novel topology.

The rising traffic demand in mobile networks is pushing the capacity need, especially in the access network. Wireless access integrated with the operator optical fiber network offers mobility and easiness of deployment. The challenge is the provision of wireless broadband capacity paired with the increasing traffic demands. The paper describes a point-to-multipoint fronthaul distribution wireless network at D-band (141 – 148.5 GHz) fed with point-to-point backhaul transport links at G-band (275 – 305 GHz), providing tens of Gb/s data rate. The system is under development in the frame of the European Commission Horizon 2020 ULTRAWAVE “Ultra capacity wireless layer beyond 100 GHz based on millimeter wave”. The D-band transmission hubs are connected to the optical core network through Gb/s class G-band links, based on a microwave photonic transmitter employing uni-traveling-carrier photodiodes (UTC-PD). A field test in real environment is planned to demonstrate the ULTRAWAVE system breakthrough.

With the advent of newer technologies in the electronic and telecommunication sectors, the extent of electromagnetic (EM) pollution is growing at an alarming pace. This is mostly due to the intermixing of EM signals emitted out from electronic modules that are mostly powered by microwave radiations. Hence, there is humungous interest among researches to design and fabricate high-performance microwave-absorbing materials that can address this undesired phenomenon. In this context, plant-derived cellulose nanofibers are considered as one of the most promising bionanomaterials for designing next-generation sustainable microwave absorbers. Nanocellulose can be utilized to fabricate flexible, robust nanopapers and highly porous aerogels that can find potential application as efficient microwave absorbers. This chapter encompasses on various strategies adopted to design and fabricate conducting nanocellulose-based functional constructs by incorporating various 1D and 2D nanostructures. The potential ways to enhance the overall microwave absorption by these shields has also been discussed in detail.

The first Transmission Hub for Point to multipoint wireless distribution at D-band (141 – 148.5 GHz) is presented. The paper reports the development of the main components of the transmission hub, including MMIC chipset, TWT, Image rejection filter and horn antennas.

The unfeasible fabrication of helix slow wave structures in W-band traveling wave tubes makes necessary to find alternative slow wave structures in order to amplify the RF signal to the output levels required to overcome atmospheric attenuation in satellite communications. Meander lines are nowadays being studied as slow wave structures for W-band traveling wave tubes due to their favorable properties compared to full metal alternatives. A novel meander line topology is introduced in this work, showing that high gain and output power can be achieved using a low-voltage electron beam. Cold and large signal simulations are presented in this work.

A novel front end for high data rate point to point links at D-band (151 – 174.8 GHz) will provide up to 45 Gb/s over 1 km range. The low power signal generation is provided by a low cost Resonant Tunnelling Diode (RTD) oscillator. The RTD oscillator is connected to a Traveling Wave Tube that provides up to 10 W transmission power.

A new project to realize a point to point wireless system above 150 GHz with multigigabit per second data rate is in progress. The upper side of the D-band (151 -174 GHz) offers about 20 GHz with 3 GHz forbidden band for full duplex transmission. The aims it to enable fiber on air capacity with more than 1 km range to provide up to 45 Gb/s data rate. The wireless system works in Frequency Division Duplexing and consists of two front-ends, each of them with a transmitter powered by novel traveling wave tubes (TWT) fed by a directly modulated Resonant Tunnelling Diode (RTD) oscillator. Two TWTs are designed using the double corrugated waveguide at 151 – 161.5 GHz and 161.5 – 174.8 GHz.

The D-band (141 - 178 GHz), due to relatively low attenuation and about 27 GHz available bandwidth, is attractive for point to multipoint backhaul. However, solid state power amplifiers at those frequencies do not have sufficient power to assure a long propagation range with 99.99% availability. This paper will describe the design and fabrication of a novel D-band traveling wave tube power amplifier to enable the first point to multipoint wireless system at D-band. The design approach is for potentially large scale production. For the first time, a new topology of double corrugated waveguide, used as slow wave structure, has been fabricated and measured at D-band. The D-band TWT provides about 35 dB gain and more than 12 W output power.

Planar meander lines have been recently studied in detail due to their favorable properties as slow wave structures for traveling wave tubes. However, the interaction of a cylindrical electron beam with this kind of structures is not efficient enough in order to achieve the output power levels required for space applications at W-band. A new design, suitable and optimized for the cylindrical beam geometry, is introduced in this work. Cold and large signal results are presented in the paper.

A G-band (210 – 250 GHz) Traveling Wave Tube (TWT) is in the fabrication stage. The TWT specifications are gain in the range 25 - 35 dB with more than 1 W output power. The double corrugated waveguide is chosen as the slow wave structure for the relatively easy fabrication. The TWT is based on a single SWS section, instead of the typical configuration with two sections separated by a sever typical at microwave frequency. The short wavelength at G-band determines the size of the parts to be less than 100 microns. The design and the fabrication had to be harmonised to achieve a high precision fabrication. A high end Computer Numerically Controlled milling machine was used. The fabrication result confirms the capabilities of the fabrication process.

The multi-Gigahertz bands available above 100GHz have huge potential to support high capacity wireless communications. However, technology advancements are needed. This paper will describe the architecture and system proposed in the EU H2020 ULTRAWAVE “Ultra capacity wireless layer beyond 100 GHz based on millimeter wave Traveling Wave Tubes” focused on the first D-Band Point to Multi Point system for very high capacity distribution.

The first Point to MultiPoint wireless system at D-band has been designed and is in advanced development. The European Commission H2020 ULTRAWAVE "Ultra capacity wireless layer beyond 100 GHz based on millimeter wave Traveling Wave Tubes" project aims to respond to the demand of high capacity at level of tens of Gigabit per second, in urban areas, where fiber backhaul is not economically viable and high density small cell architectures are deployed. A transmission hub powered by a novel D-band TWTs will feed a number of terminals arbitrarily allocated in the corresponding area sector. This paper illustrates the main characteristics, advantages and networking aspects and provide a summary of the latest results of the ULTRAWAVE project.

The folded waveguide (FWG) traveling wave tube (TWT) developed in the frame of the Horizon 2020 TWEETHER project for enabling a novel ${W}$ -band (92–95 GHz) high capacity wireless network for 5G is presented. The FWG TWT was designed by particle-in-cell (PIC) simulations. The technology and the results in terms of measured RF losses and beam transmission from the realized beam tester are presented. Amplification on the first TWT breadboard has been observed but with a poor multireflection pattern resulting from spurious burrs inside the FWG. It indicates, however, that the FWG technology offers great manufacturing simplification compared to conventional helix TWTs, thus enabling a low-cost device with large series production suitable for the wide market of wireless communications.

Sheet beam vacuum electron tubes are an attractive solution for high-power sources or amplifiers at millimeter-waves. In this article, a novel ${W}$ -band slow wave structure (SWS) for traveling wave tube (TWT) amplifiers supporting a sheet beam is proposed. The SWS is based on a rectangular waveguide with ${H}$ - and ${E}$ -plane loaded (HEL) metal corrugations. A test structure of the proposed HEL SWS with purposely designed input and output couplers was built in the frequency range of 91–98 GHz ( ${W}$ -band). The measured scattering-parameters agree well with the simulations showing ${S}_{11} dB over 10-GHz bandwidth. A TWT was designed and simulated with the HEL SWS. It shows very good gain-bandwidth performance. The SWS is easy to manufacture by low-cost computer numerical controlled (CNC)-milling. The results demonstrated that the HEL SWS is a very good solution to build high-power, wideband millimeter-wave TWTs for a wide range of applications that need high power in a broad frequency range.

The growing interest in wireless high-data-rate communications at millimeter waves for both terrestrial networks and satellite communications is stimulating novel solutions to overcome the strong atmospheric attenuation. In particular, the development of high-throughput satellite communication systems for Internet distribution is fundamental to complementing the terrestrial networks and to cover regions not connected to terrestrial backbones, such as at sea or remote areas. Ku-band and Ka-band satellite systems are presently available. Recently, the W-band (71–76 GHz and 81–86 GHz) has been allocated for multigigabit transmissions, providing 5-GHz bandwidth for both uplink and downlink. However, it has been estimated that for enabling high-throughput W-band satellite communication systems, transmission power higher than 50 W is needed. In this paper, a 71–76 GHz double-corrugated waveguide (DCW) traveling-wave tube (TWT) is designed as an amplifier for high-data-rate satellite downlink, with about 70-W output power. The dispersion characteristic of the designed DCW is experimentally validated by a cold test. The proposed TWT is also a test vehicle, scaled in frequency, for a future novel 220-GHz DCW TWT for terrestrial wireless networks.

A novel Lagrangian code for fast simulation of non-rotationally symmetric slow wave structure for millimetre wave Travelling wave tubes is proposed. Novel slow wave structures (SWS) suitable for fabrication at millimetre wave frequencies often have non-rotationally symmetric, differently from the helix that has a cylindrical symmetry. This prevents the use of conventional Lagrangian simulators valid for symmetric cylindrical symmetry. A modified Lagrangian simulator to simulate arbitrary symmetry SWS is proposed. The proposed simulator permits a very fast simulation of the large signal performance of the novel SWS, as the Double Corrugated Waveguide.

This paper investigates the performance of the W band millimeter wave (mmWave) backhaul network proposed by our EU TWEETHER project. We focus on the downlink transmission of the mmWave backhaul network, in which each of the hubs serves a cluster of base stations (BSs). In the considered backhaul network, available frequency resources are first allocated to the downlink links with the consideration of fairness issue. In order to mitigate interference in the mmWave backhaul network, each hub operates the proposed algorithm, namely cooperation and power adaptation (CPA). Our simulation results show that, the backhaul network with mmWave capabilities can achieve a significant better throughput performance than the sub-6 GHz ultra high frequency (UHF) backhaul network. Furthermore, our simulations also reveal that the proposed CPA algorithm can efficiently combat interference in the backhaul network.

The design and fabrication aspects of a novel D-band (141 GHz-148.5 GHz) Traveling Wave Tube (TWT) for enabling the first point to multipoint front end at D-band, objective of European Commission H2020 ULTRAWAVE is presented. The ULTRAWAVE system will provide unprecedented wireless area capacity over wide area sectors, with radius up to 500 – 600 m for the future 5G high density small cell deployment. The design and fabrication processes adopted for the TWT are focused to find new low cost solutions for TWTs at millimetre waves to satisfy the requirements of the wireless market. The proposed TWT will provide more than 10 W saturated output power for achieving more than 100 Gb/s/km2 of area capacity over 600 meters radius wide angle sector, with 99.99% availability in ITU zone K.

The first point to multipoint wireless system at D-band (141 - 148.5 GHz), providing high capacity area sectors fed by high data rate G-band (275 - 305 GHz) links connected to fiber access points, will be described. It is the objective of the European Commission H2020 ULTRAWAVE “Ultra capacity wireless layer beyond 100 GHz based on millimeter wave Traveling Wave Tubes”. The high transmission power provided by novel millimeter wave traveling wave tube will allow an unprecedented range and data rate at this frequency band. A novel MMIC chipset including components built by GaAs and InP processes to realize a full electronics solution for the sub-THz wireless communication system will be described.

International audience; We present in this paper an ongoing project will is targeting the combination of several technologies to achieve high-data-rate and long-range links using a mW level source with fast modulation, waveguide coupled to drive a traveling-wave tube amplifier towards a modulated in the 210-250 GHz range. In this project we are also investigating antennas structures, high-gain for outdoor links and using lens or cassegrain design or lower gain systems with steerable capability for indoor links.

A variable aperture horn antenna, for flexible coverage area in point to multipoint at millimeter wave, is proposed. The antenna is intended to be implement in future 5G high capacity wireless backhaul networks to respond to traffic variations and coverage needs. Design and test results of the variable aperture antenna at scaled 35 − 40 GHz frequency band are reported.