An automated simulation-based design cycle has become a fundamental part of the success of one of today’s leading designers of traveling wave tube (TWT) microwave amplifiers.

Testing a TWT: Automated simulation using Opera software is a fundamental part of the design of microwave amplifiers at TMD.

TMD Technologies (Middlesex, UK) produces a wide range of TWTs, a core component of many radar and missile seeker, electronic counter measure (ECM), and electronic warfare (EW) systems. TWTs are vacuum devices that amplify by producing an electron beam and coupling it with a microwave frequency electromagnetic signal. Synchronization is achieved by means of a “slow wave structure” that employs geometry such as a helix, ring bar, or ring loop to precisely delay the microwave signal by forcing it to meander back and forth.

By using scripting tools built into Opera electromagnetic design software from Cobham Technical Services (Aurora, IL), the company has created a custom tool that automatically builds a three-dimensional (3D) model of a new TWT, simulates it, and analyzes the results, all within the space of about five minutes. This speed of design provides the engineering team with a means of rapidly creating highly optimized solutions for new TWT applications.

Automation of the design process is critical, as simulation is the main means of understanding the effects of design changes on TWT performance. Along with frequency and amplification specifications, there are often severe weight, size, power consumption, and heat dissipation targets, for example, as systems might be installed on satellites or aircraft. The ability to design a TWT that is compatible with the voltage levels of an existing power supply is another common demand, as this can substantially reduce project costs and timescales.

The Opera-based electromagnetic design tool provides TMD with a means of exploring the solutions to these design challenges. The tool has a library of generic parameterized models of TWT tube designs, containing unique intellectual property on the design of component parts of TWTs, and all the engineer needs to start creating a custom TWT is to enter some of the model geometry parameters using dialog boxes, which takes only a few minutes. The package will then automatically simulate and post-process the results to provide custom, high-level views of the resulting performance.

Assembling a traveling wave tube (TWT).

This process typically takes less than five minutes, so it is easy for TMD to modify the design parameters and repeat the analysis to locate the optimum solution within any chosen design space. TMD also has built in special features to the custom design software to improve the optimization process, such as making it easy for users to suspend simulation and change parameters on the fly, or to “bracket” a design topology and then create an interpolated data file that can be used to explore the intervening design space. Using a highly automated design optimization, this phase of the total TWT design process can often be accomplished within a couple of days. TMD has also produced similar script sequences that partially automate the design of the electron gun and magnetic focusing elements of a TWT.

TMD has been using the Opera software suite for more than 10 years. The company utilizes many of the special electromagnetic design solvers developed by Cobham, including those for simulating charged particle beams, for static and time-varying magnetic field analysis, and for modeling thermal effects. The accuracy of the finite element analysis design software has been proven for the company by comparing actual measured results from the finished real-world products with the predictions obtained from the simulation models.

This article was contributed by Cobham Technical Services, Aurora, IL. For more information, Click Here 

RF & Microwave Technology Magazine

This article first appeared in the April, 2013 issue of RF & Microwave Technology Magazine.

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