Shielding Quality Of Cables And Connectors: Some Basics For Beller Understanding Of Test Methods

In wide frequency ran es the electromagnetic coupling through a cable shieldmay be well simulated with a longitudinal1 homo eneous set-up (transfined: (surface) transfer impedance Z, b / m ) and capacitive coupling impedance Z, (Q/m). They are not dependent on the test set-up, in contrary to the "shielding attenuation". The coupling transfer function (T) throu h the shield nuation into ZT and ZF, at any frequency where ZT and Z, may be defined. The shielding quality (and intrinsic shield parameters) may be tested also with "field methods", some of them not having a basic upper frequency limit of application. The concepts used for coaxial cables may be a p p lied to multi-wire cables and to connectors and cable asmission line). The intrinsic CO L 9 le shie d ammeters are dei s given. It allows to convert the test data or s f ielding atteGlossary of Important Terms 1 and 2 = outer and inner circuit, see fig. 2 n and f = near and far end (seen from generator) Subscripts only used if distinction i s necessary (surface) transfer impedance (of a cable ihield) ' transfer impedance [of a connector) capacitive coupling impedance (of a cable shield) capacitive coupling impedance (of a connector] through capacitance (of a cable shield) i d T 1 3 characteristic impedances of the transmission lines formed by circuits (1 ) and (2) , see fig. 2 max IZ,+ZTl length of cable section under test shield diameter coupling (transfer) function shielding attenuation As = 20 log IT I summing function, argument I-f 4 7 7 2