Programming instructions

 National Instruments Corporation 14-1 Multisim Component Reference Guide
Chapter 14
RF Components
RF components are not available in all editions of Multisim.
14.1 RF Capacitor
RF capacitors at RF frequencies show behaviors different from the regular capacitors at low
frequencies. RF capacitors at RF frequencies act as a combination of a number of
transmission lines, waveguides, discontinuities, and dielectrics. The dielectric layers are
usually very thin (typically 0.2 Mµm). The equations governing these types of capacitors
follow those of transmission lines; therefore, each RF capacitor is described by inductance per
unit length, resistance per unit length, shunt capacitance per unit length, and shunt
conductance per unit length. Depending on the type of the technology used, practical
capacitance values are in the range between several picofarads and several nanofarads. These
capacitors are used for coupling or bypassing for frequencies up to approximately 20 GHz.
One type of RF capacitor is called an interdigital capacitor. Both conductors of the capacitor
are in the same plane, which is the top surface of the dielectric substrate used. Each conductor,
or external node of the capacitor, is structured by connecting a number of transmission lines in
parallel. In other words, the planar structure uses N thin parallel conducting strips of length L,
linked alternately to one or other two strips of length W running perpendicularly alongside
them, and the whole structure is deposited on a substrate, often of alumina. Capacitors of this
type capacitors appear to be lumped up to 3 GHz and values from 0.1 to 10 pF can be
achieved. However, because of their structure, they require a relatively large area.
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