Antenna Metrology

Antennas are the eyes, ears and voices of everything from cell phones to interplanetary spacecraft. The Antenna Metrology Program carries on PML'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 method, which transforms measurements taken at centimeter distances into accurate predictions of an antenna’s far-field, valid at distances of kilometers and beyond. Using mathematical tools developed at PML, the technique is used at hundreds of test ranges worldwide. Recent advances promise to extend the method’s use.

PML’s Antenna Metrology Program has for three decades served companies and government agencies seeking to maximize the efficiency of communications, relying on the world’s highest-performance antennas. Program physicists and engineers are leaders in testing key antenna performance characteristics used in some of the world’s most sensitive applications, such as those of radar and aircraft and of 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 — where an incremental pound can cost $10,000 to launch. Equally important, proper testing of antennas on scientific spacecraft costing hundreds of millions of dollars provides assurance that precious data will make it back to Earth.

PML 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. The private sector and other government agencies provide most testing services based on PML’s path breaking work. In hundreds of test ranges worldwide, engineers test antennas using probes designed to capture an antenna’s output. In the U.S., each antenna probe is NIST-traceable, or NIST-calibrated. Such testing measures an antenna’s near-field at close distances (a few centimeters), then uses mathematical algorithms developed at NIST to determine the far-field. 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 angular distribution of transmitted or received energy) of antennas operating at frequencies from 1.5 gigahertz to 110 gigahertz.

Project scientists recently scored a major success in the race to stay ahead of increasing antenna frequencies with their development of 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 life of some of the nation’s key antenna-testing infrastructure. Such higher frequencies hold significant promise in the areas of medical and security imaging and radiometer systems for improved weather and climate prediction. Project scientists are also working on imaging applications that could one day pinpoint undesired electromagnetic reflections in test chambers, enabling even more accurate antenna calibration.

• Completed and documented a method for estimating uncertainty due to the source of known brightness temperature being in the near-field of the radiometer.
• Determined gains and compared results of three antennas (one dual-port probe) using both the extrapolation and pattern integration methods.
• Established a test bed at 13.56 megahertz for testing radio-frequency identification (RFID) cards for load modulation (return signal strength) and durability when cards are exposed to electrostatic discharge or to high strength alternating electric and magnetic fields.

Associated Publications/Reports:

• M. Francis, R. Wittmann, “Near-Field Scanning Measurements: Theory and Practice,” in Modern Antenna Handbook, John Wiley, Ch. 19, pp. 929-976, 2008.
• R. Wittmann, M. Francis, R. Direen, “Chamber Imaging Using Near-Field Scanning,” in Proc. 2008 IEEE Antennas and Propagation Symposium (San Diego, CA), ID 10.1109/APS.2008.4619141, July 2008.
• J. Guerrieri, K. MacReynolds, M. Francis, R. Wittmann, D. Tamura, “Planar Near-Field Measurement Results Up To 94 GHz Using Probe Position Correction,” in Proc. 27th AMTA Symposium (Newport, RI), pp. 110-116, October 2005.