Figures of Merit for Field Homogeneity in TEM Waveguides

The homogeneity of the transverse electromagnetic (TEM) field in a TEM device is a necessary condition for the compliance of emission and immunity measurements in TEM test facilities with standards. Under these conditions, the behavior of the TEM mode over the desired frequency range has to be verified. This homogeneity, indeed a figure of merit of the waveguide, is investigated using the generalized postulates presented in this work in combination with some calibration procedures defined in the standards. Verification of the postulates provides a valuable insight into the field distribution within the considered TEM line facility, since the obtained results are in excellent agreement with the measured fields. The maximum transverse and longitudinal polarization errors, which can be normally tolerated in order for the field to be considered as a TEM wave, are derived from the copolar field. As a result, the savings in the measurements are achieved. Finally, the consistency obtained upon direct comparison of different TEM test facilities confirms the applicability of the model.     

Calibration cell for E-field sensors in water environment

Compact and nonperturbing E-field sensors are used for antenna near field measurements. For application in the research area of hyperthermia these sensors are used in a water environment. Owing to the high dielectric constant of water in the frequency range from DC to ~1 GHz the sensitivity is changed. To perform a calibration of E-field sensors, a water-filled TEM-cell has been developed. The technique employs a transverse electromagnetic (TEM) transmission cell that operates as a 50 W impedance matched system. A uniform TEM-field is established inside the cell     

On the Interplay Between the Equipment Under Test and TEM Cells

In all applications of the gigahertz transverse electromagnetic (GTEM) cell, there is an interplay between the equipment under test (EUT) and the cell reflecting metal walls, as represented by images of the EUT. Moreover, owing to the multiple reflections within the cell and to its tapering structure, the phenomenon of illumination and reillumination of the EUT can hardly be avoided. These problems, known as reactive effects of the cell, are investigated in this paper. A simple new approach for an efficient investigation of the interactions between the EUT and the cell is provided. Closed-form expressions for the reflection coefficient, the relative deviation in field, and the relative error in the induced current caused by the reactive effect of the cell are derived. Each of these expressions encompasses both the mutual influence of the EUT's radar cross section (RCS) and the reactive effects of the cell. It is shown that depending on the frequency-dependent phase factor e^jpsi, strong and weak test conditions may occur since the overall incident field will exhibit maxima and minima. Hence, evidence showing that the total incident field impinging on the EUT generally deviates from the primary excited TEM field is provided. Moreover, the relative deviation in the field and the relative error in the induced current are quantified. Finally, the frequency dependence of the well-known one-third-rule of thumb is demonstrated.     

RF radiation properties of printed-circuits boards in a GTEM cell

The behavior of reradiated fields from printed-circuits boards (PCBs), with the radar cross section being the main parameter of interest, is investigated in this paper. A rigorous approach to predict radiation from PCBs in a gigahertz transverse electromagnetic cell is presented. The analysis is based upon the use of the reciprocity theorem in combination with the method of moment applied to the scattered field, thus yielding a generalized impedance matrix, whose determinant represents the characteristic polynomial of the scattering system. The effectiveness of the method is demonstrated by investigating some canonical circuit configurations and structures illustrating sources of fundamental electromagnetic interference mechanism. The validity and the accuracy of the analysis becomes obvious in view of the one-to-one correlation with measurements.     

Assessment of Shielding Effectiveness of Gaskets by Means of the Modified Bethe's Coupling Theory

This paper investigates estimates for the shielding effectiveness (SE) of finger stock gaskets. Valuable insight into the nature of the openings principally responsible for coupling between gasket and mating surfaces are gained via a dipole characterization. It is shown that through visualization of the real contact area, the overall length of the engaged active contact region between fingers and their mating surfaces is generally smaller than the finger's width, thus leading to an additional ldquoellipse-like' shape opening between two adjacent fingertips, which is much greater than the spacing slot. As a consequence, the dipole moment exhibited by the elliptic aperture is dominant and is responsible for the radiated fields into or from a shielding enclosure. Modified Bethe's coupling theory for small apertures is applied to derive these fields and assess the SE of the gaskets. The validity and accuracy of the analysis become obvious in view of the good correlation with measurements.