TWEETHER aims to achieve a milestone in millimetre wave technology with the realization of the first W-band wireless system for distribution of high speed internet everywhere. This system merges for the first time novel approaches in vacuum electron devices, monolithic millimetre wave integrated circuits and networking paradigms to implement a novel transmitter to foster the future wireless communication networks.
In particular, the main technological challenges to be faced are:
Novel, compact, affordable millimetre wave Travelling Wave Tube (TWT) with 40W output power.
Only vacuum TWTs, among all the available technologies, have been demonstrated to provide wideband operation and high power capabilities. The design of W-band TWTs for communication networks to be low cost, reliable and with a long lifetime requires a leap beyond the state of the art of current technologies and design approaches. At W-band numerous formidable challenges have to be tackled to achieve the defined specifications: fabrication tolerances, limits of the available microfabrication techniques (cylinder shapes cannot be realised by mechanical microfabrication or photolithograpy), ohmic losses, difficult assembling, production yield and long lifetime.
The first prototype of the Traveling Wave Tube has been designed. In particular, a folded waveguide (FWG) has been chosen for the well-known properties of wide band and relatively easy fabrication (Fig. 1).
Fig. 1. Longitudinal Section (one half) of folded waveguide
Simulation results show that the FWG TWT gain obtained with this design is over 40 dB in the whole frequency range (Fig. 2).
Fig. 1. FWG TWT Gain
First samples of the fabricated FWG are shown in Fig. 3. The small section of the waveguide, 1890x300 mm2, requires a high precision CNC milling to be realized with tolerance in the a few micron range. The beam optics is also in advanced fabrication phase.
Fig. 3. W-band metal interaction structure fabrication
Advanced affordable and high performance chipset.
The chipset is a coherent set of the various monolithic microwave integrated circuits (MMICs) enabling the low power operation of the system. Due to the very high cost of the mask set at W-band Silicon-Germanium (SiGe) is not suitable for small to medium quantities. In addition, high power levels of hundreds of milliwatts are not feasible with SiGe technology at W-band. For this reason the technology of choice is definitively the short gate length GaAs.
The high number of chips and the specifications represent a formidable challenge in terms of design and fabrication effort. The power amplifier, is one of the most challenging components and has to be designed to provide a Psat of about 23 dBm along the required bandwidth (92-95 GHz). First samples of MMIC power amplifiers have been successfully fabricated and measured.
W-band transmission hub and receiver integration.
The complete front end will be realized with advanced micro-electronics and micro-mechanics. Then it will be assembled and packaged with interfaces and antennas for the field trial at the UPV facilities. There are 3 subassemblies to integrate and test:
- Packaged TWT and power supply for the hub.
- Packaged Transmitter and Receiver hub module with synthesizer and synchronization function.
- Packaged Transceiver radio module for the terminal will comprise an RF board on which all the MMIC will be integrated.