An optically linked three-loop antenna system for determining the radiation characteristics of an electrically small source

Abstract

This paper presents the experimental results of an antenna system for determining the radiation characteristics of an electrically small source. Three orthogonal loop antennas, each terminated at diametrically opposite points with identical loads, encircle the source and characterize its equivalent electric and magnetic dipole moments. The total radiated power can be determined from this near-field measurement of the device under test. The test system operates from 3 kHz to over 100 MHz with up to 90 dB of dynamic range.

On determining the maximum emissions from electrically large sources

“…The total radiated power over the measurement bandwidth may be efficiently determined using the three-loop method at lower frequencies and the reverberation chamber at higher frequencies. Kanda's three-loop method is detailed in [6] and [7]. The EUT is centered inside the loops and the electric and magnetic dipoles determined by forming the sum (related to ) and differences (related to ) of the currents at the loads.…”

“…The EUT is then substituted for the calibration source and the received power measured over the same set of paddle positions. The total radiated power determined via [11] is then (7) where denotes average. The reverberation chamber method works well as long as the mode density in the chamber is suf-ficiently high to yield meaningful statistics.…”

“…To avoid the rotation problem, Kanda et al at the National Institute of Standards and Technology (NIST) proposed a rotationless method for determining the radiation characteristics of electrically small sources [6], [7]. The method makes use of loops with identical loads at two diametrically opposite points, in the manner used in Kanda's development of simultaneous electric-and magnetic-field sensors [8].…”

Selected EMC standards and regulations:

“…NIST's competence: Our established method of TEM cell in the difference mode [4] or the method of three orthogonal loops under investigation [5], both with detailed measurement procedures and error estimates, can be used to achieve the same objective with much improved accuracy and easier analysis of uncertainties.…”

“…Physical parameters to be measured: Electric field, voltage and current, in peak, quasi-peak, rms , or average values, narrow band or broadband (impulsive noise), and frequency. 5. Accuracy requirements; ±2 dB in volts, ±3 dB in fields, and ±2% in frequency.…”