ESCO Technologies ETS-Lindgren 7405, User Manual, Page: 39 / 49

www.ets-lindgren.com Common Diagnostic Techniques 39
A qualitative knowledge of the field impedance indicates how to approach the
EMC/EMI design for the problem. By determining the dynamics of the radiating
structure, it can be surmised what kinds of designs will be effective is solving the
radiation problem. A primarily H-field problem signifies that current flow
predominates.
The other possibility is that the problem is predominately electrical or E-field. In
this case the field impedance is relatively high. A high field impedance means
there is a potential build-up across some impedance, and this high potential
region is the radiating source.
A differential mode problem will respond to these types of remedies:
• Reducing circuit loop area.
• Reducing signal voltage swing.
• Shielding the entire radiating loop.
It will not respond well to partial shielding of the radiating loop. Partial
shielding typically occurs when the path of the return current is
mapped incorrectly and not included inside the shield.
• Filtering the radiating signal line.