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5.4 Independence of the common mode coupling from the horizontal trace routing

It has previously been mentioned that only the vertical current segments of the trace
couple to the cavity. Therefore, the trace introduction method only considers these
vertical source and load currents in (5.6). Transfer impedance
comparisons as described before are carried out for the two trace routings in
Figure 5.7, to validate the independence of the coupling from the
horizontal trace segments. The trace length in both models is l=110mm, the trace width
=2mm, the trace hight above the ground plane is d=0.65mm, and the enclosure
dimensions are (L=134mm, W=104mm, h=7mm). The comparison of the transfer functions to the
meas port at (x=67mm, y=104mm) for the models in Figure 5.7(a) and in
Figure 5.7(b) are depicted in Figure 5.8 and
Figure 5.9 respectively. Comparison results of the transfer
impedance to the other two measurement ports are presented in
Appendix A.2

Magnitude and phase comparisons show a very good agreement of both models in
Figure 5.7(a) and in Figure 5.7(b) to the results obtained
with (5.6), (5.9) and the impedance
matrix (4.17) from the model in Figure 5.7(c). That
confirms the independence of the common mode coupling from the horizontal trace routing
and validates the trace introduction method.

(a) Model a with trace. | (b) Model with a different trace routing. |

(c) Model with ports at the trace source- and load positions. |

**Figure 5.7:**
HFSS

^{®} models with a different trace routing between identical
source and load positions.

Load: 0 Ohm, magnitude. | Load: 0 Ohm, phase angle. |

Load: 1e9 Ohm, magnitude. | Load: 1e9 Ohm, phase angle. |

Load: 50 Ohm, magnitude. | Load: 50 Ohm, phase angle. |

**Figure 5.8:**
Transfer impedance from the trace source current to the slot measurement port at (67mm,104mm). Comparison of HFSS results from a model with a trace (Figure

5.7(a)) to the results obtained with (

5.6), (

5.9) and a HFSS model with ports.

Load: 0 Ohm, magnitude. | Load: 0 Ohm, phase angle. |

Load: 1e9 Ohm, magnitude. | Load: 1e9 Ohm, phase angle. |

Load: 50 Ohm, magnitude. | Load: 50 Ohm, phase angle. |

**Figure 5.9:**
Transfer impedance from the trace source current to the slot measurement port at (67mm,104mm). Comparison of HFSS results from a model with a trace (Figure

5.7(b)) to the results obtained with (

5.6), (

5.9) and a HFSS model with ports.

*C. Poschalko: The Simulation of Emission from Printed Circuit Boards under a Metallic Cover*