TABLE OF CONTENTS EMC measurements can be complex and inherently unrepeatable. This is particularly true when making radiated emission or susceptibility measurements in anything other than ideal free-space test conditions. Military EMC standards usually require measurement to be made in screened chambers which may or may not have radio absorbent material (RAM) to damp out electromagnetic wave reflections; if uncontrolled these lead to an increase in measurement uncertainty.
System-level tests on large items of equipment may have to be made on an open range in the presence of ambient electromagnetic noise, an uncertain ground plane and possible reflections from nearby objects. All these effects can increase measurement uncertainty. Standards covering radiated emission testing of commercial electronic equipment, and particularly information technology products, usually specify testing on a specific type of open test site that has to be carefully calibrated before use. Repeatability of test results measured on an open range is however also open to question and continues to stimulate debate in the EMC community. See Chapter 3 References 11, 12, 15 17 and 19.
Whether the radiated emission testing is carried out in screened rooms or on an open field test site the antennas used are the key components in the measurement chain. What these various antennas actually measure, and the influence that surroundings have on these measurements, is often not straightforward and can lead to considerable misunderstanding and error.
Electromagnetic antenna theory is complex and rather mathematical and much has been written on the basic theory of antennas [1 4]...
