Design of a conical terminated TEM cell for EMC testing

Abstract

This research focuses on the design, manufacture, and testing of a conical terminated Transverse Electromagnetic (TEM) cell. The conical terminated TEM cell will be used for precompliance electromagnetic testing at the Cape Peninsula University of Technology. The requirement is focused on designing such a cell that is suitable for desktop use and capable of operating across a frequency range of DC to 1.0 GHz with a working volume of 10 × 10 × 10 cm. This thesis presents a comprehensive overview of the principles as laid out by Giri and Baum, 1996. Design considerations are discussed after which calculations, determining the cell geometry, are performed. The conical terminated TEM cell is simulated in AltairFeko and various adjustments are made to determine which model results in an S11 lower than -10 dB across the prescribed frequency range. The S11 study includes the determination that the model is negligibly affected with the insertion of, and in the absence of a device under test. S11 measurements are conducted up to 2.5 GHz, to test the S11 response at a frequency higher than what the cell is designed. Electromagnetic studies are conducted in AltairFeko to determine the largest achievable working volume by investigating electric field uniformity. These studies also include the worst-case effect that a device under test of ≈ 10 × 10 × 10 cm has on the working volume. The model that meets the criteria is manufactured. Manufacturing components are dictated by guidelines based on the literature study. S11 measurements are conducted using a nanoVNA vector network analyzer and then using a RF analyzer with a vector network analyzer capability, in an unshielded laboratory environment. Measured results are then analyzed in AltairFeko and Matlab. From 0.4 GHz to 2.5 GHz the S11 remains below -10 dB. Considering the measured results with and without a DUT we observe similar results with the insertion of a DUT having a negligible effect on the S11. As verification, the working volume is simulated and analyzed using 3 electromagnetic slices closest to the ground plane, intersecting the middle of the volume parallel to the top-plate and another slice closest running parallel to the top-plate. These studies are observed at 0.5 GHz and 1.0 GHz, with and without a device under test. Field uniformity was validated by the IEC 61000-4-3 standard; with 75 % of the measured points within the working volume measured to be within 0 dB to + 6 dB. This confirms that the manufactured conical terminated TEM cell complies to the relevant standards for use as an EMC pre-compliance test setup.