A Variable Position, Gravity Down G-TEM Configuration
H. Stephen Berger · 1995
This article reports on the development and implementation of a new configuration of the GTEM cell, called the Extended Hyper Rotation GTEM. This configuration introduces two improvements over other designs. First, the EUT holds its normal orientation, with gravity down relative to the EUT. Secondly, the cell rotates, so that sufficient information may be derived to solve for the magnetic and electric dipole moments separately. The magnetic and electric dipole moments model the EUT emission at any given frequency. Further, the design allows full automation of the testing. The movement scheme used allows automation of algorithms that assume the far-field condition and newer, low frequency algorithms that do not make this assumption. The Extended Hyper Rotation GTEM was designed with accuracy as the primary objective. Speed and ease of testing were very important secondary objectives. This meant that the EUT must remain in its normal orientation throughout the test. Secondly, it was desired that the cell be constructed so that sufficient data could be obtained from any given EUT to solve for the magnetic and electric dipole moments without having to assume far-field conditions. The primary purpose of this cell was to test telephones. Thus a major consideration was that data cables from the EUT be handled accurately. These objectives were achieved by first designing a turntable to hold the EUT in the cell. This allows for the EUT to be rotated 360°, in the horizontal plane. Next, a gimbaled cradle was designed to hold the turntable. This gimbaled turntable insured that the EUT would remain level while the GTEM was rotated around an axis oriented at 45° to the cell centerline. Therefore, two independent degrees of motion were achieved. Further, the axis of rotation includes the hyper-rotated position, where the GTEM is placed at 54.7°, but extends beyond it, hence the name Extended Hyper Rotation. The hyper-rotated position greatly simplifies testing to the three input equations and also allows for an elegant solution for the accurate testing of EUT’s which have cables which must exit the cell.