October 2009

Antenna Test Systems Evolve to Commercial-Off-the-Shelf Products
Near-Field Test Methods Drive Faster Test Times and Economical Production
By Daniël Janse van Rensburg, Sales & Marketing Manager,
Nearfield Systems Inc.

The microwave antenna test industry has, over the last decade, seen the introduction of Commercial-Off-the-Shelf [COTS] test systems that allow manufacturers to approach antenna testing in much the same way as benchtop network analysis. The subsequent savings in time and efficient use of facilities is helping to drive down the cost of production and improve quality for a wide range of microwave antenna applications.

This wasn’t always the case. The antenna test industry initially focused on outdoor Far-Field testing, where the source and receiver were separated by a sufficiently large distance such that the radius of curvature of the wave front hitting the antenna under test appears to be locally flat. For electrically large antennas (that is, antenna dimensions large in terms of wavelengths), this distance can become prohibitively large. This space limitation, in addition to other factors like exposure of the test article to the elements and the fact that the purity of the plane wave illuminating the antenna can be greatly compromised by reflections from surrounding structures, lead to the desirability of indoor testing and subsequent development of alternative test methods.

Near-Field Testing Provides the Solution
Using Near-Field techniques, antennas can be characterized through testing in very close proximity to the device in an environmentally stable anechoic chamber and then, relying on mathematical transformation, the desired Far-Field radiation characteristics may be obtained.

Near-Field techniques allow for very efficient use of space and lower cost anechoic environments compared to outdoor Far-Field testing. In addition, the introduction of modern automated network analyzers provide for highly accurate and readily available RF subsystems. This has allowed antenna testing to become an integral part of the production process rather than an expensive field exercise.

Today, Near-Field scanning hardware is integrated with these RF subsystems through software, making Near-Field antenna test systems easily accessible COTS tools. Many turn-key Near-Field test systems can be installed in as little as eight hours, allowing engineers to obtain highly accurate antenna test characteristics within minutes after installation.

Looking to the very near future, new planar and spherical scanners combined with vector network analyzers make high speed, multi-frequency antenna testing commonplace. In the case of planar Near-Field scanners, testing within an office environment is feasible.

Near-Field test and measurement techniques, combined with COTS analyzers and components, will continue to reduce the cost and improve the efficiency of microwave antenna testing for years to come. For more information, visit www.nearfield.com

Nearfield Systems Inc.
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