Antenna Metrology Project

Antennas are the eyes, ears and voice boxes of everything from cell phones to interplanetary spacecraft. The Antenna Metrology Program carries on NIST's pioneering work on testing high-end antennas for critical hardware such as communications satellites, scientific spacecraft, radar and aircraft. The program focuses on improving its near-field scanning technique, which transforms measurements taken at distances of a few centimeters into accurate predictions of an antenna’s performance at distances of millions of kilometers. Using mathematical algorithms developed at NIST, the technique works for antennas operating at frequencies as high as 110 gigahertz and is used at hundreds of test ranges worldwide. Recent advances promise to extend the method's capability to still higher frequencies.

NIST’s Antenna Metrology Program has for three decades served companies and government agencies seeking to maximize the clarity and efficiency of communications relying on the world’s highest-performance antennas. Program physicists and engineers are leaders in defining and testing key performance characteristics of antennas used in some of the world’s most sensitive and unforgiving applications, such as those on radar and aircraft. NIST also supports out-of-this-world antennas — on satellites and spacecraft vital for communications, weather prediction, and space science. Precise understanding of antenna performance enables designers of television satellites and spacecraft bound for other planets to avoid overbuilding antennas and related power sources, such as batteries and solar panels. They can thereby minimize spacecraft weight — and costs — in an environment where an incremental pound can cost $10,000 to launch. Equally important, proper testing of antennas on scientific spacecraft costing hundreds of millions of taxpayer dollars provides assurance that precious data will make it back to the tiny speck called Earth. NIST scientists pioneered the near-field scanning technique — now the standard method for testing high-performance antennas designed to communicate across tens, thousands or even millions of kilometers — and continue to advance it both theoretically and experimentally. Although project scientists test selected antennas at the Boulder antenna range, the private sector and other government agencies provide most testing services based on NIST’s pathbreaking work. NIST focuses on advancing the science of antenna metrology.

In hundreds of testing ranges worldwide, engineers test antennas using probes designed to capture an antenna’s output. Each antenna probe is NIST-traceable, meaning that NIST physicists have established the probe’s accuracy or, more commonly, that industry engineers used a NIST-calibrated probe to calibrate others for actual antenna testing. Such testing involves measuring an antenna’s near-field performance at distances as close as a few centimeters, then using mathematical algorithms developed at NIST to determine far-field performance. Near-field scanning allows for accurate assessment of the gain (the amount of power transmitted or received in the antenna’s primary direction), polarization (the orientation of the electromagnetic field) and pattern (the distribution of transmitted or received energy) of antennas operating at frequencies from 1.5 gigahertz (GHz) to 110 GHz.

Project scientists recently scored a major success in the race to stay ahead of increasing antenna frequencies. The computations yielding far-field performance estimates require near-field scans measured with an antenna measurement probe placed at points on a grid with a precision of one fiftieth of a wavelength. With higher frequencies come shorter wavelengths. Weather-watching satellite radiometers and satellite-to-satellite communications can run at 500 to 600 gigahertz, corresponding to wavelengths of about half a millimeter. The necessary accuracy for placing the probe cannot be achieved mechanically. Project scientists have developed a dynamic laser-based antenna-probe tracking system with probe-position correction algorithms, which enable the use of existing near-field scanning ranges at much higher frequencies than previously attainable — thereby extending the useful life of some of the nation’s key antenna-testing infrastructure to the benefit of government and industry alike. Such higher antenna frequencies hold significant promise in the areas of medical and security imaging as well as in radiometer systems for improved weather prediction.

Antenna Metrology Project scientists are also working on microwave imaging applications that could one day pinpoint currently undetectable electromagnetic reflections in antenna-testing chambers, enabling even more accurate antenna calibration.