Tuesday, January 23, 2018

CST Filter Design Technology: a Powerful Toolkit for Microwave Engineers

In recent years, CST's filter design and analysis technology have continually improved, resulting in exciting new tools that facilitate design, analysis, and optimization. We spoke to one of CST’s resident filter experts, Dr. Theunis Beukman about the latest solvers and features that make CST STUDIO SUITE® such an excellent tool for designers.

If you want to learn more, our Filter Design Workshop is fast approaching and registration is open! The workshop will take place on February 27th outside Washington D.C. and will no doubt benefit filter designers of all levels and areas of focus. We also recommend checking out our 2017 eSeminar, "Overview of CST Filter Design Technology" you can watch on-demand.

What new features for filter design and tuning has CST recently introduced?
Fields in a multimode cavity filter
simulated in CST STUDIO SUITE® 

Over the past two years, in particular, we introduced many new features for filter design and tuning. A vital contribution in this regard came with CST Filter Designer 3D. This tool provides the capability for synthesizing a coupling matrix based on the user’s input of specifications –including arbitrarily placed transmission zeros for bandpass, bandstop or diplexer filters. CST Filter Designer 3D is much more than just a synthesis tool. It also has a unique feature that allows you to extract the coupling matrix from the S-parameters of your EM simulation model, which provides insight into the operation of this 3D model without having to dissect or analyze it using surrogate circuits. Another great feature is our moving mesh technology that helps overcome “mesh noise,” which is a common simulation issue. Moving mesh enables us to tune up very sensitive filters that can have fractional bandwidths of 1% and below.

How does CST’s new coupling matrix based optimization improve the filter design 
workflow?

I think any person who has tried to tune up a filter knows the cumbersome workflow and time-consuming routines they have to endure (perhaps with a minimal number of exceptions). What we’ve done is taken the new capabilities of CST Filter Designer 3D and implemented an optimizer dedicated for coupled-resonator filters. Our software eliminates that time-consuming effort when tuning and provides an efficient solution that is far more capable than brute-force optimization.

Besides EM, what multiphysics effects do filter designers also need to watch out for?

When it comes to transmitter systems, front-end filters typically need to be able to handle high input power. This can lead to various unwanted effects that require advanced simulation during the design phase. A very capable tool in our arsenal is SPARK3D, which uses advanced algorithms to calculate possible RF breakdown either in a vacuum or in gas – perhaps better known as multipaction and corona discharge. Another potentially harmful effect is heating due to power dissipation in a device or adjacent components. This can lead to substantial detuning of the filter structure and therefore requires both thermal and mechanical simulation which are available in CST STUDIO SUITE® 2018. At the workshop, we will have two dedicated sessions for these topics.

Speaking of the workshop, could you give us an overview of what will be covered? Who should be sure to attend and why?

This workshop is a fantastic resource for all filter designers, regardless of whether you are currently using CST STUDIO SUITE® or you’re just curious about the topic of filter simulation. This workshop will provide you with a solid overview of the complete set of simulation solutions that can be applied in practical filter design.

The program will include topics like synthesis, the realization of distributed models, tuning based on the coupling matrix and multiphysics analyses. There will be a focus on bandpass filter design, though we will also touch on other types such as lowpass/highpass and multiplexer filters. We will showcase the different tools that are applicable in each stage of the design workflow and highlight the underlying technologies that make it possible.

Register here for the CST Filter Design Workshop.


Dr. Theunis Beukman is an application engineer at CST - Computer Simulation Technology in Darmstadt, Germany. He received his MScEng (cum laude) and Ph.D. degrees in Electrical and Electronic Engineering from the University of Stellenbosch, South Africa, in 2011 and 2015 respectively. During his Masters, Dr. Beukman worked on tunable wideband filters for the Square Kilometre Array (SKA) project and spent several months as a visiting researcher with the filter group at Heriot-Watt University.

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