Millimetre wave double corrugated waveguide TWT

行波管（twt）是最古老的电子放大器之一，发明于1943年，但它们仍然是唯一能够在微波和毫米波频率的宽频段提供高功率的设备。没有行波管，就不可能有卫星通信、高速无线通信、雷达和许多其他基本应用。行波管由缠绕成螺旋状的细丝组成，在其中产生电子束。螺旋由纵向介质杆支撑，这些介质杆与金属真空外壳同心。电磁波以与电子相同的速度减速，导致电子聚集。反过来，电磁场延缓了束，它们的动能被转移到振荡场，从而放大了它。目前的制造技术允许实现直径小于1毫米的螺旋，原则上支持频率高达60 GHz左右。组装具有这些尺寸的螺旋需要高度熟练的操作员，并且需要很长时间。此外，小零件制造的不确定性导致成品率低。这种毫米波管的成本非常高，大约1万英镑，限制了它在某些特定应用中的使用。相反，对高功率毫米波放大器的需求正在增长。无线千兆数据通信是一项全球业务，需要在50千兆赫以上的频率上进行宽带、高功率放大，以支持多千兆自由空间传输。改进后的行波管直接解决了这一市场需求。该项目旨在通过引入一种新的双波纹波导（DCW）来代替螺旋波波导，从而克服螺旋波管的频率限制。DCW是由PI构思的，允许设计和制造第一个1太赫兹，1000千兆赫，行波管放大器。将研究DCW作为慢波结构在较低频率下的行为，这种慢波结构具有与螺旋结构相似的性能，但更容易制造。精密数控铣削，具有微米级的精度，将用于定义DCW。DCW相对于螺旋的巨大优势是易于组装：DCW是由两个部分组成的金属结构，可以通过特征对齐，然后简单地夹在一起。一部分是中空的矩形金属波导，沿波导有两排平行的金属柱；另一部分是顶板，用于闭合和完成波导。不需要精确对准，装配时间最小：装配者的技能已被加工的精度所取代。在行波管中引入DCW将大大降低制造成本并克服螺旋的频率限制。双波纹波导将带来的创新是非常重要的，它将促进低成本、高性能真空电子器件新家族的发展，这将给英国带来出色的市场前景和就业机会。兰开斯特大学在该领域享有很高的国际声誉，将设计新型行波管，同时研究基于新型DWP结构的设备可以放大的频率范围。英国主要真空电子公司e2v将以其制造经验和设施支持设计过程。E2v还将对完成的器件进行电磁表征。双波纹波导的设计将由毫米波技术集团最先进的微加工设备实现，该技术集团是STFC卢瑟福阿普尔顿实验室RAL空间部门的一部分。在项目结束时，将实现首个用于毫米波频率范围的双波纹波导行波管的优化设计，并在e2v下进行实验验证。这一成功的实现将成为后续生产工程最终商业供应的原型演示。

Traveling wave tubes (TWTs) are among the oldest electronic amplifiers, invented in 1943, but they remain the only devices able to provide high power in a wide frequency band at microwave & millimetre wave frequencies. Without TWTs, no satellite communications, high-speed wireless communications, radars and many other fundamental applications would be possible. A TWT consists of a filament wound in helical shape where an electron beam is generated. The helix is supported by longitudinal dielectric rods that are placed concentric to a metal vacuum envelope. The electromagnetic wave is slowed at about the same velocity as the electrons, causing bunching of the electrons. In turn, the electromagnetic field retards the bunches and their kinetic energy is transferred to the oscillating field, thereby amplifying it. Current fabrication technology permits the realisation of helices with diameters below 1mm that support frequencies up to around 60 GHz in principle. To assemble a helix with these dimensions requires a highly skilled operator and takes a long time. Further, the uncertainty in the fabrication of the small parts causes a low yield. The cost of such a millimetre wave tube is very high, >£10k, limiting its use to some specific applications. On the contrary the demand for high power millimetre waves amplifiers is growing. One application, wireless gigabit data communications is a global business that requires wide band, high power, amplification at frequency above 50 GHz to support multigigabit free space transmission. An improved TWT addresses this market need directly. This project aims to overcome the frequency limitation of the helix TWT by introducing a novel double corrugated waveguide (DCW), in place of the helix. The DCW was conceived by the PI to permit the design and fabrication of the first 1 THz, 1000 GHz, TWT amplifier. The behaviour of the DCW at lower frequency as a slow wave structure with similar performance to a helix, but much easier to manufacture, will be investigated. Precision CNC milling, with micrometer accuracy, will be used to define the DCW.The great advantage of the DCW over the helix is the ease of assembly: the DCW is a metal structure made from two parts that can be aligned by features and then simply clamped together. One part is a hollow rectangular metal waveguide with two parallel rows of metal pillars along the guide: the other part is a top plate to close and complete the waveguide. No precision alignment is required and the assembly time is minimal: the skill of the assembler having been replaced by the precision of the machining. The introduction of the DCW in TWTs will substantially reduce the fabrication cost and overcome the frequency limitation of the helices. The innovation that the double corrugated waveguide will bring is of great importance and will foster the development of a new family of low cost, high performance vacuum electron devices, that will give the UK outstanding market perspective and employment opportunities. Lancaster University has a strong international reputation in the field and will design the novel TWT, also investigating the range of frequencies that can be amplified by devices based on the new DWP structure. e2v, the main UK vacuum electronics company will support the design process with its fabrication experience and facilities. e2v will also characterise electromagnetically the completed devices. The designs of double corrugated waveguide will be realised by state-of-the-art microfabrication facilities in the Millimetre Wave Technology Group, part of the RAL Space department at the STFC Rutherford Appleton Laboratory. At the end of the project an optimised design of the first double corrugated waveguide TWT for millimetre wave frequency range will be realised for experimental verification at e2v. This successful realisation will be the prototype demonstrator for the following production engineering for eventual commercial supply.