Study of an Attenuator Supporting Meander-Line Slow Wave Structure for Ka-Band TWT

Hexin Wang,Huarong Gong,Zhaoyun Duan,Shaomeng Wang,Duo Xu,Yubin Gong,Tenglong He,Zhanliang Wang,Zhigang Lu,Xinyi Li

doi:10.3390/electronics10192372

Hexin Wang, Huarong Gong + Show 8 more

Open Access

https://doi.org/10.3390/electronics10192372

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Abstract

An attenuator supporting meander-line (ASML) slow wave structure (SWS) is proposed for a Ka-band traveling wave tube (TWT) and studied by simulations and experiments. The ASML SWS simplifies the fabrication and assembly process of traditional planar metal meander-lines (MLs) structures, by employing an attenuator to support the ML on the bottom of the enclosure rather than welding them together on the sides. To reduce the surface roughness of the molybdenum ML caused by laser cutting, the ML is coated by a thin copper film by magnetron sputtering. The measured S11 of the ML is below −20 dB and S21 varies around −8 dB to −12 dB without the attenuator, while below −40 dB with the attenuator. Particle-in-cell (PIC) simulation results show that with a 4.4-kV, 200-mA sheet electron beam, a maximum output power of 126 W is obtained at 38 GHz, corresponding to a gain of 24.1 dB and an electronic efficiency of 14.3%, respectively.

Highlights

With the large-scale application of 5G communication networks and the rapid development of 6G, the demands for high-power, high-efficiency millimeter wave sources are increasing rapidly [1,2,3,4,5] in recent years
The traditional traveling wave tube (TWT) usually has disadvantages, such as large size and weight, high operation voltage and so on, which make it difficult to meet the requirements of the communication industry for miniaturization and mass production
The measured S-parameters characteristics of the slow wave structure (SWS) shows during the designed band of 36–39 GHz, the S11 is below −20 dB and the S21 of the ML varies around −8 to −12 dB and the S21 of the attenuator is below −40 dB

Summary

Introduction

With the large-scale application of 5G communication networks and the rapid development of 6G, the demands for high-power, high-efficiency millimeter wave sources are increasing rapidly [1,2,3,4,5] in recent years. The typical planar SWS, formed by periodically bending a thin metal line on the dielectric substrate, is a kind of microstrip meander line This process can be seen as flattening the traditional helix SWS into a flat structure. The measured S-parameters characteristics of the SWS shows during the designed band of 36–39 GHz, the S11 is below −20 dB and the S21 of the ML varies around −8 to −12 dB and the S21 of the attenuator is below −40 dB This new structure inherits the characteristics of the ML, such as high output power, planarization and low working voltage, further reducing the difficulty of processing and assembly which makes it easier to manufacture and mass produce.

Structure Model and High Frequency Characteristics of the ASML SWS

The Surface Roughness Measurement

S-Parameters Measurements