Harmonic and higher order mode mm-wave klystrons
Lead Research Organisation:
Lancaster University
Department Name: Engineering
Abstract
The Klystron is a well-known, high efficiency amplifier, with a simple structure and scalable dimensions. It is typically designed with cylindrical reentrant cavities in the fundamental mode. However as the frequency of the device increases the size of the structure decreases. At mm-wave frequencies this leads to two problems:
1) Manufacturing the complex small scale structures.
2) The gap voltage decreases as the gap gets shorter leading to less gain.
Most mm-wave klystron concepts reported in the literature are simply smaller versions of microwave klystrons. Even if, in principle the dimensions can be scaled according to the frequency increase, the fabrication challenges and the beam characteristic represent a huge obstacle to the realization of a working device when frequency is higher than 50 GHz. This is consequently true for the frequency range around 94 GHz, which is of great interest for communication and radar applications.
This proposal is aimed to overcome of the above-mentioned obstacle to the design and realization of a 94 GHz klystron by two innovative design solutions.
The first solution is to operate the cavity at a higher order mode, chosen with similar Ez field distribution on the gap cross-section as the fundamental mode. The design will adopt reentrant cavities with square or rectangular shape, to be compatible with a photolithographic fabrication technique. The higher mode operation permits to design the cavities with dimensions larger (at least 4 -5 times) than in case of fundamental mode operation. This eases the technological effort and makes possible a high quality fabrication by mechanical micromachining or by photolithographic processes. Further, the beam tunnel can be larger than in fundamental mode, to support higher beam current. In order to increase the interaction a number of intermediate buncher cavities, spaced all along the drift tube, will be used to increase the beam current modulation.
A separate approach uses a lower frequency input cavity to modulate the beam current. As the beam travels down the drift tube beam harmonics start to form hence a higher order mode output cavity at an integer harmonic frequency of the input cavity can be exited hence acting as a high power frequency multiplier. As the input can be a readily available high power microwave source we are able to overcome the low gain of the device.
1) Manufacturing the complex small scale structures.
2) The gap voltage decreases as the gap gets shorter leading to less gain.
Most mm-wave klystron concepts reported in the literature are simply smaller versions of microwave klystrons. Even if, in principle the dimensions can be scaled according to the frequency increase, the fabrication challenges and the beam characteristic represent a huge obstacle to the realization of a working device when frequency is higher than 50 GHz. This is consequently true for the frequency range around 94 GHz, which is of great interest for communication and radar applications.
This proposal is aimed to overcome of the above-mentioned obstacle to the design and realization of a 94 GHz klystron by two innovative design solutions.
The first solution is to operate the cavity at a higher order mode, chosen with similar Ez field distribution on the gap cross-section as the fundamental mode. The design will adopt reentrant cavities with square or rectangular shape, to be compatible with a photolithographic fabrication technique. The higher mode operation permits to design the cavities with dimensions larger (at least 4 -5 times) than in case of fundamental mode operation. This eases the technological effort and makes possible a high quality fabrication by mechanical micromachining or by photolithographic processes. Further, the beam tunnel can be larger than in fundamental mode, to support higher beam current. In order to increase the interaction a number of intermediate buncher cavities, spaced all along the drift tube, will be used to increase the beam current modulation.
A separate approach uses a lower frequency input cavity to modulate the beam current. As the beam travels down the drift tube beam harmonics start to form hence a higher order mode output cavity at an integer harmonic frequency of the input cavity can be exited hence acting as a high power frequency multiplier. As the input can be a readily available high power microwave source we are able to overcome the low gain of the device.
Publications
Castilla A
(2022)
Ka-band linearizer structure studies for a compact light source
in Physical Review Accelerators and Beams
Constable D
(2016)
2-D particle-in-cell simulations of high efficiency klystrons
Description | A low cost medium power millimeter wave upconverter. It converts 33GHz radiation to 100 GHz with a maximum output power of 200 Watts |
Exploitation Route | As part of Radar or security scanning equipment. |
Sectors | Aerospace Defence and Marine Electronics Security and Diplomacy Transport |
Description | We are currently preparing a patent. |
First Year Of Impact | 2014 |
Sector | Electronics,Security and Diplomacy,Transport |
Impact Types | Economic |
Description | Engineering of Accelerators |
Organisation | Elekta Inc |
Country | Sweden |
Sector | Private |
PI Contribution | Co-founder of the network. |
Collaborator Contribution | Presentations at the kick-off meeting. |
Impact | Multi-disciplinary, mechanical, electrical and electronic engineering |
Start Year | 2014 |
Description | Engineering of Accelerators |
Organisation | Science and Technologies Facilities Council (STFC) |
Country | United Kingdom |
Sector | Public |
PI Contribution | Co-founder of the network. |
Collaborator Contribution | Presentations at the kick-off meeting. |
Impact | Multi-disciplinary, mechanical, electrical and electronic engineering |
Start Year | 2014 |
Title | An Electromagnetic Wave Frequency and Amplitude Modifier |
Description | The device is an RF device that generates an output at the 3rd harmonic of the input at a higher power. The device uses harmonic cavities in order to make the device large enough to be manufactured by conventional facilities at high frequencies. |
IP Reference | GB1520498.5 |
Protection | Patent application published |
Year Protection Granted | 2016 |
Licensed | No |
Impact | None yet |
Description | Accelerators: Powering Cutting Edge Reserach |
Form Of Engagement Activity | A magazine, newsletter or online publication |
Part Of Official Scheme? | No |
Type Of Presentation | Paper Presentation |
Geographic Reach | National |
Primary Audience | Policymakers/politicians |
Results and Impact | We have created a brochure aimed at policy makers in collaboration with the IoP and STFC Communications. The brochure is on the applications of particle accelerators. It was printed in 2015 None yet, but it hasn't been printed yet. |
Year(s) Of Engagement Activity | 2013,2014,2015 |
Description | IMAEGMOOH |
Form Of Engagement Activity | Engagement focused website, blog or social media channel |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Schools |
Results and Impact | I participated in the STFC sponsored I'm an engineer get me out of here competition, where I did live webchats with several schools all over the UK answering questions over a two week period. |
Year(s) Of Engagement Activity | 2019 |
URL | https://energym19.imanengineer.org.uk/ |