Antenna Calibration: Exploring the New C63.5-2006

Sherrie Conroy, Editor

In December 2004, ANSI ASC C63 published its long-awaited antenna calibration standard. The standard replaces the 1988 and 1998 versions, which had both met with controversy. Late last year, the subcommittee added a flowchart and an interpretation to this standard that clarified some of the confusing text.

The new standard takes into account the errors that are introduced when using certain broadband antennas, particularly those at frequencies below 200 MHz. The standard provides correction factors for these antennas when they are used for site validation. It also introduces alternative measurement techniques for determining antenna factors for other types of antennas.

In August, a workshop will lead users through the new document, highlighting which technique should be used based on the type of antenna being calibrated. The workshop is slated for Saturday, August 12, during the IEEE EMC Symposium. The workshop will be held at Northwest EMC in Hillsboro, OR.

“[Northwest EMC] is letting us use its large semianechoic chamber and antennas,” notes Don Heirman, an author of the standard and the workshop’s director. “We will have software to operate the test instrumentation. Being with those of us who wrote the standard or have been close to it will give the attendees an opportunity to talk to us one-on-one during the class. That is much more valuable than just reading the standard,” adds Heirman.

Knowing the type of antenna is essential to ensure that the right antenna factor is used, especially when validating semianechoic chambers. Attendees will get a chance to apply what they learn through both problem solving and performing an antenna calibration in the lab at the meeting venue. Heirman says that the workshop will have a two-hour segment in the afternoon where teams will calibrate two types of antennas and discuss what they learned.

Specifically, the workshop will address the following issues:

• General test conditions.
• Appropriate measurement geometry.
• Methods to determine antenna factors.
• Application of standard site method.
• Reference antenna method.
• Equivalent capacitance substitution method.
• Discrete- and continuous-frequency calibration considerations.
• Rationale for geometry-specific correction factors for biconicals.
• Guidelines for measurement uncertainty.
• Hands-on participation in a state-of-the-art 10-m chamber.

The link between the use of an antenna and the method of antenna calibration has been confusing. Understanding available techniques for site validation is critical to improving methods for achieving accurate and meaningful results. This workshop should be enlightening.