Design and Fabrication of E-Band Traveling Wave Tube for High Data Rate Wireless Links

${E}$ -band (71–76 and 81–86 GHz) is widely used for wireless point to point (PtP) links with a few gigabit/second data rate. ${E}$ -band front ends are powered by solid-state amplifiers with about 1-W output power per module. This level of output power limits range and spectral efficiency in rain condition and has to be compensated by high gain antennas or backup low-frequency links with reduced capacity. The availability of tens of watts of transmission power would allows higher spectral efficiency and long range, and the use of lower gain antennas for multibeam and area coverage. Millimeter wave traveling wave tubes (TWTs) are gaining interest due to their higher power, more than one order of magnitude, in comparison with solid-state devices. Helix TWTs, typically built at microwaves, are very arduous to fabricate due to the extremely small diameter of a helix at ${E}$ -band. This article reports the design and fabrication of the first ever ${E}$ -band TWT based on a full metal slow wave structure (SWS), the double corrugated waveguide (DCW). The TWT is designed to provide about 70-W power and more than 35-dB gain in the 71–76-GHz band. A test TWT using a single Section interaction structure is in the final assembly phase as proof of concept with about 2-W output power. The ${E}$ -band TWT performance will open new perspectives in the availability of long range wireless links with multi-Gb/s data rate needed for enabling 5G and 6G new networks.

I. Introduction

E-BAND (71–76 and 81–86 GHz) is of high interest having 10-GHz band allowed for wireless communications in point to point (PtP) [1], [2], [3]. High data rate links are fundamental for high capacity data distribution in support of 5G and 6G (G is generation) concepts. -band links are commercially available with data rate of a few gigabits per second (Gb/s) depending on the atmospheric conditions. However, the relatively low power of solid state amplifiers, in the range of 1-W per module, has to be compensated by high gain antennas to achieve range and signal-to-noise ratio (SNR) to satisfy the link budget for the typical availability of 99.99% in the rain zone of operation [4], [5], [6]. High gain antennas have relatively large footprint. In addition, if links with tens of Gb/s are needed, a cluster of front ends has to be used with a combined large footprint that makes difficult to find sites for its installation [7]. The availability of higher transmission power would enhance the spectral efficiency with increased data rate for the same frequency band and reduce the antenna footprint, making front ends more compact and easier to deploy.