Orientation Effect of the Electromagnetic Field Coupling for Device in a TEM Cell

In this article, the orientation effect of electromagnetic coupling for a device in a transverse electromagnetic (TEM) cell is explained in the frame of the model with intercoupling of equivalent electric and magnetic dipoles taken into account. Different from the widely used model, which predicts a half-circle period of the orientation effect, the proposed model predicts a full-circle period due to the introduced intercoupling. The intercoupling of the electric and magnetic field interaction inside the TEM cell and the full-circle period orientation effect is demonstrated first by simple straight and meander microstrip lines, which is then compared to a segment of an integrated circuit (IC). For the application of the proposed model to a complex device, a limited number of pairs of intercoupling electric and magnetic field dipoles can be introduced to predict the complicated orientation effect of a running large-scale IC in TEM cell measurement. The extracted dipoles are in good agreement with the near-field scanning results. The widely used Wilson model should be checked carefully in the application of field to line analysis.

I. Introduction

The electromagnetic coupling for a device in a transverse electromagnetic (TEM) or gigahertz TEM (GTEM) [1], [2] cell is basic for the application of measuring the radiated electromagnetic emission [3], [4] and susceptibility [5] of integrated circuits (ICs) [6], [7]. To evaluate the radiated electromagnetic emission and susceptibility of ICs, the TEM cell measurement method has been widely used [3], [8], [11]–[14] and also adopted by the international electrotechnical commission (IEC) [15], [16]. Although the TEM cell measurement method is suggested for many years, the method is still attractive in current days. For example, designing an improved TEM cell was suggested [17] for the test of radiated susceptibility and emissions of ICs in a wider frequency. For the application in higher frequency up to tens of gigahertz, a GTEM cell [1], [18] is also suggested [15] for the IC emission measurement. Usually, in (gigahertz) TEM cell, measurement of emission the testing board with the mounted IC is rotated at four directions (0°, 90°, 180°, and 270°) to quantify the electromagnetic interference (EMI) by finding the maximum emission level, and then, the maximum emission of the IC is represented by an equivalent electric or magnetic dipole [15], [19]. However, whether the real emission maximum occurs in the four directions actually depends on the orientation effect of the studied device placed in the TEM cell. To find the real emission maximum, the measurement has been applied in more directions [20], [21], such as 24 orientations with an angle changing of 15°. Although the measurement in multiple angles would be proper to find the maximum emission level, the orientation effect is still important to understand the electromagnetic coupling inside the TEM cell.