Design Con 2015

Radar challenges: T/R module testing comes up to speed

-September 20, 2013

Even a small array consisting of 100 elements has thousands of individual components that require perhaps 25,000 measurements per module for an eye-watering grand total of 2.5 million. Barry Manz talks about how T/R module testing is changing…

Production testing and calibrating the T/R modules in a phased-array radar has never been a task for the faint of heart. Even a small array consisting of 100 elements has thousands of individual components that require perhaps 25,000 measurements per module for an eye-watering grand total of 2.5 million. While the digital content in phased-arrays, specifically Active Electronically-Steered Arrays (AESAs) continues to increase, the microwave switches, phase shifters, variable gain amplifiers, and other RF and microwave components in transmit and receive paths continue to pose the greatest challenges. All of these components can (and often do) interact, so timing and control states of every module must be aligned within a few tenths of a decibel and a few degrees of phase. Insertion loss, impedance mismatches, and other artifacts must also be de-embedded from the results.

Until relatively recently, phased-array radars were characterized and calibrated using test routines and instruments cobbled together in the classic “siloed” approach so familiar in the defense industry. That is, radar manufacturers developed their own measurement systems and test routines tailored to only their own radars and sometimes to only a specific radar among them. This approach “worked” in the sense that the required measurements could be made and the system could be tweaked over time to produce impressive results, assuming the company had the time and talent to devote to this labor-intensive task. Even then, considerable measurement certainty and poor repeatability were possible, and using this system by different groups using different test equipment on different radars could produce widely varying results.

Today, as budget cutters in the federal government sharpen their knives, even such esoteric, low-volume systems are AESA radars must be characterized and aligned accuracy as quickly as possible without sacrificing accuracy -- which the use of commercial turnkey solutions dedicated to the task highly appealing and for larger radars essential.

Obviously, the greater the number of measurement points the greater the accuracy, but in practice there are limits on what any reasonable system can handle given the need to also achieve high measurement speed. Fortunately, these vendors have determined what accommodates both without sacrificing either, which not surprisingly varies between T/R module test system manufacturers. The resulting systems can make these tests in minutes or seconds per module rather than weeks. In addition, the ability to simultaneously test two T/R modules reduces test time per module by half and multiplexing four test fixtures allowing eight modules to be tested. Devices can be inserted into unused test fixtures while measurements are being performed in others, which provides more or less continuous high-speed testing. The Rohde & Schwarz R&S TS6710 is a good example of a system that employs all of these techniques.
 
So in short, the day of the one-off, homebrew phased-array test system are coming to a close, driven in no small measure by DoD’s snowballing drive to get more complex systems built and deployed faster at less cost. Automated measurements systems dedicated to the task that are fast, accurate, and easily (and securely) reconfigurable are their replacements. These test systems will have to be further enhanced in the future as the AESA architecture is employed not just in radars but in electronic warfare systems and multi-function systems in development that perform both functions, perhaps adding communications to the mix as well.

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Also See:
How to test modern radars
Phase noise and its changing roles in radar test
Profiles in Test: Jerry Lumurno, Eastern OptX
Fiber optic delay lines enable radar testing in the lab

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