• Which Products are you interested in ?

    CST offers a wide range of EM simulation software to address design challenges across the electromagnetic spectrum, from static and low frequency to microwave and RF, for a range of applications, including EDA & electronics, EMC & EMI and charged particle dynamics.

  • CST STUDIO SUITE
  • CST EMC STUDIO
  • CST BOARDCHECK
  • Antenna Magus
  • IdEM
  • FEST3D
  • Optenni Lab
  • Looking for a Training, Workshop or eSeminar ?

    CST STUDIO SUITE® is being demonstrated at trade shows and workshops all over the world. Take a look at the list of conferences and exhibitions CST will be attending and get further information regarding CST workshops, eSeminars and training days.

  • TrainingsRegular training courses are held in CST's offices in Asia, Europe, and North America. Please check our trainings section for detail of trainings in all over the globe. Advance registration is normally required.

  • WorkshopsCST hosts workshops in multiple languages and in countries around the world. Workshops provide an opportunity to learn about specific applications and refresh your skills with experienced CST support staff. Make sure you visit our workshop section.

  • eSeminarsThroughout the year, CST simulation experts present eSeminars on the applications, features and usage of our software. You can also view past eSeminars by searching our archive and filtering for the markets or industries that interest you most.

  • Check our latest Events
  • Why create a MyCST Account ?

    A MyCST account may facilitate your access to many of the offerings on the CST website, for example the registration for eSeminars and the watching of eSeminars recordings, setting email preferences, and there is more functionality to come. It is required to participate in workshops and trainings.

  • Personal PreferencesAllows you to update your email preferences and areas of interest. It helps us to personalize your experience.

  • EventsSearch for events by location, industry and application. Once you are registered, you will be able to manage your registrations and check important details about your events. This section also provides you with a repository for Workshop & Training material.

  • LibraryYou can collect articles you find on the CST website to reference or read later by clicking on the “Add this article” button at the bottom of the article page.

  • Create Your Own Account
  • Need technical Support ?

    Customers can customize their accounts once they have completed the account creation process. This platform acts as vivid interface between CST and our customers.

    We therefore offer access to the latest Service Packs (including an automatic notification that a new Service Pack is available), a steadily growing database of Frequently Asked Questions (FAQs), Application Notes and Training Videos, as well as an individual FTP section for easy exchange of large files with our support team.

  • Do I need an Account?To access the Support Site a valid maintenance contract and a one-time registration is required.

    Please note that your Support login does not work for the MyCST account.

  • Get Support
  • How to request a Trial License ?

    Get your license in only three steps:

    1. Fill in the required fields in the contact form on the right and click "Send Us Your Request".

    2. Lean back and wait until one of our CST Experts contacts you.

    3. Enjoy a our trial license.

  • Student Edition

    Student Edition The CST STUDIO SUITE® Student Edition has been developed with the aim of introducing you to the world of electromagnetic simulation, making Maxwell’s equations easier to understand than ever. With this edition you have, bar some restrictions, access to our powerful visualization engine and some of the most advanced solvers of CST STUDIO SUITE.

    Student Edition

CST – Computer Simulation Technology

Simulation of 650 GHz Backward Wave Oscillators

Similar to traveling wave tubes, a backward wave oscillator (BWO) is a device for converting DC power into RF power. Furthermore, it uses also the same working principle, namely the application of DC power to an electron gun resulting in a steady electron beam. This electron beam interacts with a slow wave structure to excite RF power. While the backward wave (the wave travelling in the opposite direction as the electrons) in a traveling wave tube is a limiting factor, it is exactly this wave which is used in backward wave oscillators. The intensity of the backward wave is dependent on the beam current level, the slow wave geometry, focusing and the transition regions to absorb the final RF wave. The frequency of the backward wave is determined by the transit time or velocity of the particles and therefore simultaneously by the initially applied DC power. More information can be found in [1]....

The design of the backward wave oscillators was invented and published by Carol L. Kory and James A. Dayton Jr., Teraphysics Corporation, USA [2]. One device (shown in figure 1 left) is based on a biplanar interdigital slow wave structure, where the beam moves between the opposing fingers.

The other device (shown in figure 1 right) is realized by a helical structure, where the beam moves outside of the helix.



Figure 1: Slow wave structure of the interdigital BWO (left) and helical BWO (right)

Both backward wave oscillators are designed to provide an output power at a frequency of 650 GHz. The beam profiles of the new designs are represented by the emission surfaces shown in figure 2. The beam voltage is in both cases 12 kV. The current is 2 mA in the interdigital and 10 mA in the helical case, respectively.



Figure 2: Emission surfaces of the interdigital BWO (left) and the helical BWO (right)

The time signal of the output power is directly recorded with waveguide ports known also from CST MICROWAVE STUDIO® (CST MWS). The waveguide ports are positioned according to figure 3.



Figure 3: Waveguide port for receiving the output power in case of the interdigital BWO (left) and helical BWO (right)

Figure 4 shows on the left hand side the signal received at the waveguide port for the interdigital BWO including conductor losses. Obviously, the steady state condition has been reached. Since the signal is recorded in terms of wave amplitudes, the resulting output power can be easily determined by taking the square of the time signal. The spectrum of the signal, evaluated with the template based postprocessing, shows nicely the peak at 650 GHz for which the BWO was designed.



Figure 4: Time signal received at the waveguide port (left) and corresponding spectrum

The time dependent particle trajectory of the beam is shown in figure 5 from initial to steady state condition. The color indicates the velocity of the particles. Thus, the modulation of the particle velocity due to the interaction of beam and slow wave structure can be seen.



Figure 5: Time dependent particle trajectory

The phase space plot for an instance of time, where the steady state condition is reached, is shown in figure 6. The aforementioned modulation of the particles becomes again obvious. Furthermore, the energy transfer between particles and RF wave is demonstrated by the decreasing average energy.



Figure 6: Phasespace plot at 5.2 ns

So far only the results of the interdigital BWO including conductor losses have been demonstrated. The time signal and spectrum of the lossless interdigital BWO, the lossless helical BWO and the helical BWO with conductor losses are quite similar. They of course differ in the steady state amplitude. The table below gives an overview of the different output powers obtained with the classical analysis (see [2] and references [3,4]), MAFIA and CST PARTICLE STUDIO® (CST PS). The results are courtesy of Teraphysics Corporation, USA.



Figure 7: Comparison of theoretial and simulated output power

The results of CST PS show excellent agreement with classical analysis. The lossless simulations can already in principle be performed within MAFIA, the predecessor of CST PS. However, the lossy simulations need either additional approximations or are even impossible. Since CST PS benefits from many features initially developed for CST MWS, for example waveguide ports, lossy metal models and PERFECT BOUNDARY APPROXIMATION (PBA)®, such a simulation can conveniently be performed with CST PS.

References

[1] A. S. Gilmour Jr., "Principles of Travelling Wave Tubes", Artech House, Inc, Norwood, MA, USA, 1994.

[2] C. L. Kory and J. A. Dayton, Jr., "Interaction Simulations of Two 650 GHz BWOs Using MAFIA", Proceedings of the IVEC 2008, Monterey, USA, April 22-24, p. 390-391, 2008.

[3] J. W. Gewartowski, H. A. Watson, "Principles of Electron Tubes", D. Van Nostrand Company, Inc, New York, 1965.

[4] R. Grow, D. Gunderson, "Starting Conditions for Backward Wave Oscillators with Large Loss and Large Space Charge", IEEE Trans. ED, Vol. ED-17, No. 12, 1970.

Rate this Article

0 of 5 Stars
5 Stars
0%
4 Stars
0%
3 Stars
0%
2 Stars
0%
1 Stars
0%
contact support

Your session has expired. Redirecting you to the login page...

We use cookie to operate this website, improve its usability, personalize your experience, and track visits. By continuing to use this site, you are consenting to use of cookies. You have the possibility to manage the parameters and choose whether to accept certain cookies while on the site. For more information, please read our updated privacy policy


Cookie Management

When you browse our website, cookies are enabled by default and data may be read or stored locally on your device. You can set your preferences below:


Functional cookies

These cookies enable additional functionality like saving preferences, allowing social interactions and analyzing usage for site optimization.


Advertising cookies

These cookies enable us and third parties to serve ads that are relevant to your interests.