SAE - ARP958E
(R) Electromagnetic Interference Measurement Antennas; Calibration Method
|Publication Date:||1 September 2021|
This SAE Aerospace Recommended Practice outlines a standardized and economical method for the checkout and calibration of electromagnetic interference measurement antennas. Its application is for use when measuring a source 1 m from the antenna in a shield room. This is the typical distance used in performing military EMC testing. The influence of the shield room on the measured field strength is not considered. This standard does not address the measurement of emissions from an unknown distributed source, yet it attempts to resemble reality by using another antenna, in the calibration method, that represents a distributed source. This document presents a technique to determine antenna factors for antennas used primarily in performing measurements in accordance with References 2.1 and 2.2. The purpose of Revision B was to include the calibration of other antennas, such as biconical, horn, monopole and small loop antennas that are also specified for use in these same references. Revision D includes a specific procedure for loop antennas that are separated by 1 m from the device under test. Revision E adds the inclusion of modern instrumentation, instruction on how to calibrate the hybrid antenna, and attempts to improve upon the clarity of this document for the user.
Typical antennas being considered are the following:
b. Resonant dipole
c. Log-periodic dipole array (LPDA)
d. Log spiral
e. Double ridged waveguide horns
f. Standard gain horns
g. Loop antennas
h. Monopole (i.e., rod)
i. Hybrid antenna (bilog/biconilog)
The use of such antenna, as listed, is limited by particular testing standards and the inclusion here should not be considered as endorsement for use universally. The standard measurement distance on the hybrid antenna shall be measured in the same way as that of the LPDA.
General Background and Limitations
The original 1968 version of ARP958 was limited to determining antenna factors for conical logarithmic spiral antennas over the frequency range 200 MHz to 1 GHz. The standard has been expanded to cover other antennas as indicated in 1.2. Antenna factors can be determined and calculated for the far field condition independent of ground reflections. The methods, described in this document, of moving from the far field to a 1 m distance results in changes in antenna factors of typically zero to four dB, but in the case of log-periodic antennas these changes intentionally correct the field strength from the position of the phase center on the antenna at each frequency to the position of the tip of the antenna, being 1 m away from the source. The primary conditions which influence the antenna factors are the antenna separation, the height of the antenna above the ground plane, the orientation of the antenna relative to the ground plane, and the size, flatness and conductivity of the ground plane. However for an antenna separation of 1 m the calibration methods found in Section 4 are intended to reduce the influence of the ground plane.