Termination Transfer Impedance Z TT

The measurement of termination transfer impedance of terminating shielding devices such as shield grounding flanges and chassis mount shielding connectors is accomplished utilizing a recently developed ground return current sensor. An appropriately driven load or loaded transformer imparts current to a short coaxial fixture with its input and output isolated by the fixtured sample which shorts the coax conductors. The resistive coaxial current sensor is in the current return path and encircles the sample. The transfer resistance of the sensor and sample are measured with D.C. and the equivalent measurement verified at low frequency. Ground loop currents or ground loop resonance are minimized using special fixturing. Two fixtures are identified to test large samples from D.C. to 200 MHz and small samples from D.C. to 3 GHz. Applicability of transfer impedance and shielding effectiveness is discussed relative to wavelength and sample size.