Standard spherical dipole source

Abstract

A spherical dipole was developed to provide a source that can be characterized both by theory and experiment and integrated into modern automated test systems.The frequency and amplitude of the radiated electromagnetic field are established remotely using a signal generator. This signal and all other control features are transmitted to and from the sphere using fiber optic cable.The field measurements show good agreement with predictions over much of the frequency band.

A Standard source method for reducing antenna factor errors in shielded room measurements

“…A similar spherical dipole has also been used successfully by researchers in England [18,20,21] [7] was the question of loading, that is, the sensitivity of the source to nearby conducting objects. Some earlier resuUs had indicated little or no loading effect in a mode-stirred chamber [24], at frequencies of 1 50 MHz and higher, for a dipole-to-wall separation of at least 1 m. At the lower frequencies (<50 MHz) in a small transverse electromagnetic (TEM) cell there appeared to be an effect on the order of 3 dB with the sphere 30 cm from the surrounding walls. A third set of measurements [7] was performed on the OATS facility at five selected frequencies with the sphere located from 0.25to2.25m above the conducting ground plane.…”

“…[8,9] The next logical refinement then is to dampen the electromagnetic fields in the room so that the positioning specifications are practical. These documents [8,9] [23], and recently NIST has developed a new version making extensive use of optical fiber technology [24]. This design, which will be described shortly, is now available commercially.…”

Results of screened-room measurements on NIST standard radiators

“…The design, construction, and operation of the device are described in Refs. [1,2], which also present results of tests in various NIST facilities --the open area test site (OATS), anechoic chamber (AC), transverse electromagnetic (TEM) cell, and mode -stirred chamber.…”

“…The spherical radiator is a well controlled, well characterized source of electromagnetic radiation for the frequency range of about 5 MHz to over 1 GHz. As such, it can be used to test the ability of a laboratory to measure radiated electromagnetic emissions.…”

“…where M^(M 2 ) is the number of frequencies missed on day 1 (2) symmetry in the radiated pattern [1,2], but this is only of order 3 to 5 dB, and it occurs only for 600 MHz and above. Furthermore, the orientation of the 13 sphere was usually the same at a given laboratory, due to positioning of the fibers running into the sphere.…”