The radiofrequency behavior of passive circuit components: The capacitor – Part 2

Starting from Tutto_Misure n. 4/2010 we begin to address a basic and important topic for those involved in Electromagnetic Compatibility (EMC) measurements and design: the radio–frequency (RF) behavior of passive circuit components. The discussion will be limited to linear components: resistors, capacitors, inductors and mutually–coupled inductors. Also, in a broad sense of the term “component”, we will also include in the list the short circuit and the open circuit. At RF it is essential to know the real behavior of components. Indeed, at RF the real behavior is markedly different from the ideal one and this fact may be at the origin of unexpected experimental situations. For example what was designed does not work or does not fulfill specifications, or neither the measurement results nor the qualitative behavior correspond with expectations. This first article deals with the analysis of ceramic and electrolytic capacitors. In particular, we will present the equivalent lumped circuits which describe their RF behavior and we will discuss the physical origin of each element in the equivalent model. Particular emphasis will be placed on the type of component assembly: Surface Mount Device (SMD) or Through–Hole (TH).