The Case for RF & Microwave Core Test Systems

Cut development, manufacturing, and documentation time and cost

by Bob Twiggs, Vice President, Business Development, In-Phase Technologies

Systems designed today are more complex than ever and harder to test. Test engineers are faced with finding budget money to face the most challenging obstacles. For example, what happens when a new GaAn-rich macroherz super-dynamic phase correlating power receiver hits your company? How do you test it?

Your company’s test engineers are faced with finding new budget money to buy a test system. What to buy? How long will it last? In the meantime, the test engineers are already supporting dozens of existing products in the pipeline. 

How Will This Get Accomplished?

RF and microwave test systems and their components continue to improve. As these technologies quickly evolve, methodologies and focus on testability have leaped forward. By default, test systems must continue to improve also. Analog and digital test systems have already started to embrace a new concept called Core Test Systems.  It is time for the RF and microwave community to do the same.

The fundamental concept of Core Test Systems is not new. Many engineers have thought about or even tried to produce a Core Test System. Every test engineer imagines designing a universal test system. Imagine a new Core Test System that would test everything by simply changing software or changing the Interface Test Adapter (ITA) or the Unit Under Test (UUT) interfaces!

The test industry and the Defense Department invested millions of dollars in an attempt to create a true Universal Test System.  This was met with mixed results. By now, most engineers have discovered that there is no such thing as a universal test system. You’ve probably become quickly stymied if you attempted to design and maintain one single system. In the meantime, the technology and test challenges keep changing. Roll-up or add-on instruments are one way to compensate for this—but the whole process involves a significant amount of new non-recurring engineering (NRE) costs. What happens to those instruments when you are finished testing the new technology, which is already getting old? Probably they end up in a warehouse or on the shelf somewhere. 

Thus, the main concept behind Core Test Systems is to invest NRE up-front. Engineers need to take the time upfront time to build a foundation for a Core Test System. It would have pre-engineered components, saving on continuing recurring development costs.

Invest the NRE time and money into a base set of system components.

Ideally, for all Core Test Systems, this would include:

• Equipment enclosure
• Wire management system
• PXI instrument chassis
• High-density interface with pre-defined signal paths
• Select common PXI and/or rack mounted
• COTs instruments.

This set of instruments is a core platform to produce multiple test sets for testing similar items. The Core Test System is then fitted to a new testing need by adding a personality in the form of an Interface Test Adapter (ITA) and software. You may also change some of the Commercial-Off-The-Shelf (COTS) instruments to fit your specific frequency or dynamic range requirements.

In RF and microwave systems, this configuration might look like a base Core Test System design capable of morphing into four different test sets: 

• One test set to test amplifiers
• One to test transmitters 
• One to test receivers  
• One to test a transceiver or radar 

What differentiates these systems from one another are a few COTS instruments that can be added or removed between systems to produce all four. Configuration-controlled documentation becomes an easy task. You will have one set of drawings and documents that reflect the base core system released under a common part number.  If your configuration management system allows it, the four above examples could be separate drawing group numbers. This will greatly simplify the task of producing and storing your test system released drawings.

A good starting point for an RF and microwave “kitchen sink” approach to Core Test Systems would include:

• equipment enclosure (rack) system
• computer, power and wire management system, 
• PXI instrument chassis, PXI or rack mounted COTS instruments in the form of: 
  • power meter 
  • vector signal generator 
  • arbitrary waveform generator
  • spectrum analyzer 
  • network analyzer
  • power supplies 
  • high speed A-D and D-A converters
  • high density interface (like a Virginia Panel system)
  • instrument drivers to support all of the instruments

The Design of the Initial Core Test System is Not a Trivial Task

The work should be done thoughtfully. The goal is to have a system to withstand the rigors of each test requirement and adapt as technology advances.  

Time invested in a Core Test System can pay off in the form of:

• Upwards of a 50% reduction of NRE costs are realizable per new system
• Reduced total documentation: one set of Core Test System design documents; each of the four systems can be a variation contained in the same release
• Increased measurement accuracy and repeatability
• Reduced test times 
• Document storage and configuration control costs; a single copy of design documents is all that is needed for the core of all new test systems
• Support costs: Supporting/troubleshooting systems is easier because the basis for each is the same; inventory of spare instruments is greatly reduced
• Reduced total test set footprint: Maximizing the use of modular test instruments decreases floor space requirement

And most of all:

• Having a flexible, scalable, and obsolescence-resistant common test set

Producing an amplifier, receiver, transmitter, transceiver or other test set from the Core Test System is then just a matter of adding or removing the PXI or rackmount instruments. For each Core Test System, keep in mind the frequency, dynamic range, power and modulation requirements. If the Core Test System allows and provides for interconnecting the above instruments to a high density interface, using in-house designed or by obtaining a vendor’s pre-configured PXI interconnect adapters, then morphing the Core System into what is needed becomes a more trivial, less NRE intensive task.

Aside from the morphing with instrumentation, configuring the Core Test System to meet your needs involves creating a personality in the form of ITA and measurement software.  For a long time, this has been a common task in some industries. At the Department of Defense they are referred to as Test Program Sets or TPS.

Every Core Test System is engineered with instrument drivers and pre-defined signal pins on the ITA mass interconnect receiver.  The task of developing the TPS becomes easier as each ITA mass interconnect signal pin is pre-defined and drivers are pre-written.

The ITA is designed to interface the Core Test System to the Unit Under Test (UUT). Use the proper signal routing needed for your application and add ancillary items that may be unique to your test requirements. You can even provide some integrated test points for signal probing or verification. This is the only electrical and mechanical design effort required to reuse the Core Test System for a new product requiring testing.

Software design becomes an easier task when the instruments are common.  Code reuse can be exploited to further reduce costs. When a Core Test System is used across an entire Enterprise—and a common software test language is chosen (i.e. LabVIEW, ATEasy etc.)—core measurement modules can be developed and stored in software libraries. The libraries are brought out, combined, and sequenced into a complete test execution.  This obviously reduces software NRE between systems, easing software configuration management. This provides the proven consistency of measurement methodology across multiple Enterprise test systems The results are increased repeatability, measurement reliability, and less buggy test systems.

When designing the measurement software, it’s a good idea to use a common user interface to reduce operator training and capitalize on the Core Test System benefits.  It is also important keep in mind hardware and measurement abstraction. Changing instruments and test requirements are easily mitigated. Now you have a more obsolescence-resistant test system that provides the end user with a test tool that works the same time every time across every Core Test System.

The best time to invest in a Core Test System is now.  Putting in the NRE time now will yield results far in excess of the NRE and thought process invested.  Be very deliberate in the way the core is designed.  

Keep system complexity low, system commonality high, and strive for a Core Test System that will serve as your basis for all new ATE system designs.  When the NRE and effort are poured into a Core Test System base system, your future design efforts, maintenance costs, user training, configuration management, and overall system cost will all be reduced.  Steal this article’s ideas and make them your own.  It may just result in a great raise or promotion. 

Finally, if you’re working in a busy manufacturing facility with limited engineering resources—who isn’t? —seek out a proven test systems company that offers Core Test Systems experience. That way, you can take advantage of a system that is already designed and ready for immediate use.  

As time and technology race onward, we fully expect to see instrument minimization take place with leaps in frequency, dynamic range, and overall performance increases.  

A good Core Test System will be ready for these changes and ready to suit your exact needs. 

About The Author

Bob Twiggs is VP of Business Development at In-Phase Technologies (IPT), a position he has held for 24 years. Prior to IPT, Bob was a test engineer and manufacturing manager for 12 years at RCA Astrospace, now doing business as Lockheed Martin. He holds a B.S.E.E.T. in electrical engineering from Temple University. He can be reached at +1(609) 298-9555 or bob.twiggs@in-phasetech.com

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