CST – Computer Simulation Technology

Test Equipment Plus Develops High-Performance Custom Filters with CST MICROWAVE STUDIO


The Signal Hound® product line from Test Equipment Plus comprises a series of compact, lightweight, and affordable spectrum analyzers. The Signal Hound equipment is built on the design philosophy of maximizing performance while minimizing cost, and as well as having a wide range of applications for general engineering labs, it has also found success in fields ranging from telecoms and spectrum monitoring to aerospace and defense.

Figure 1 Signal Hound BB60C, which includes filters designed in CST MICROWAVE STUDIO.  

To remain competitive, Signal Hound products are designed for portability, affordability, and performance, with a better price-performance ratio than other entrants in the spectrum analyzer market. When designing the latest generation of products – real-time, USB-powered spectrum analyzers operating in the 9 kHz–12.4GHz and 9 kHz–6.0GHz bands – Test Equipment Plus worked to maintain their core competency and produce products with an excellent price-performance ratio....


The first prototypes for the next generation Signal Hound products did not meet the required level of performance to be competitive in the market and maintain a good value to Test Equipment Plus’s customers. The most critical weakness turned out to be the discrete, off-the-shelf filters employed in the design. Even after cascading multiple filters together and shielding them, the spectrum analyzers did not achieve their target performance. Test Equipment Plus was in need of a spectral filtering solution that had professional grade performance, without adding serious cost to the bill of materials.

With CST MICROWAVE STUDIO® (CST MWS), Test Equipment Plus was able to make a paradigm shift from using discrete filter components and turn to buried printed filters. These filters can be built directly into PCB boards and the only cost they add is the additional engineering time, since the fabrication cost of the printed elements is already included in the production cost. This solution would not have been possible without full-wave 3D EM simulation.

Figure 2 CST Studio Suite model of a 9-element coupled line filter with a via post wall.

Figure 3 Simulated performance of a 9-element coupled line filter, both in ideal conditions and with manufacturing effects taken into account, as compared with the performance of a prototype measured with an HP 8510C VNA.

As a small company with limited resources, versatility was a key feature that Test Equipment Plus looked for in a 3D EM solver. Beyond that, accuracy, speed, and usability were also very important, as was the expandability to easily add additional capabilities and technologies, such as the thermal solvers in CST MPHYSICS® STUDIO.

CST MWS provided Test Equipment Plus with the ability to produce virtual prototypes, and this has led to substantial savings in time and money when developing new products. Additionally, by investigating the effect of changes to device parameters, the engineers were able to reverse-model their physical prototypes in order to better understand the effect of natural manufacturing and materials variations; information that is invaluable for producing robust and manufacturable products.


Using the time domain solver in CST MWS with GPU acceleration, Test Equipment Plus was not only able to design custom filter solutions, but also to validate those designs by taking into account PCB manufacturing tolerances, aging effects and environmental variations (see Figure 3). This allowed them to design filters that are robust enough to withstand manufacturing variations and the effects of long-term use.

The filters enhance the spectral purity of the analyzers, offering an extra 35 dB of spurious-free dynamic range. CST MWS was the “silver bullet” for achieving this impressive performance gain over predecessor products. Without the capability that CST MWS provided, Test Equipment Plus would have had to drastically increase the product’s cost and change the form factor, or settle for lesser performance.

The design capability afforded through the use of full-wave 3D simulation helped Test Equipment Plus to evolve their products and take them to the next level. In addition, the technical support, user interface and workflow of CST Studio Suite made it easier to get started with the product and get accurate results effectively.

I have been very satisfied with the level of service CST has provided. I get more support now than I have ever had for any software or product. The fact that I can call tech support and speak with someone I already have a good working relationship with is invaluable. I have had some challenges with getting going with CST and the response has been more than satisfactory. I don’t expect a product to always work perfectly, in my view a company makes their bread in how they respond to hiccups and problems. CST has done a great job in addressing my specific challenges and continues to do so. Thanks for everything!


Morgan Roddy
  • Morgan Roddy
  • Microelectronics Physicist and Field Applications Engineer, Test Equipment Plus, Inc.

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Test Equipment Plus, Inc. provides top quality, affordable service and support for the used test and measurement market. They service equipment from HP/Agilent exclusively and also design, manufacture and sell the Signal Hound line of portable, affordable spectrum analyzers. With distributors on five continents, TEP has been able take great strides to level the playing field between them and the major players in the test equipment industry. Test Equipment Plus was founded in 1996 and is based in La Center, Washington, USA.
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