RF Capacitor Measurement Standard

Measuring Complex Permittivity of Dielectric Materials at VHF/UHF Frequencies using a Radio Frequency Capacitive System

The RF Capacitor Measurement Standard is a test method to evaluate the intrinsic properties of dielectrics over a wide frequency range.

The fixture consists of a vertically oriented square coaxial transmission line where the center conductor is truncated to allow placement of the specimen in contact with the center conductor. A rectangular or cube-shaped specimen may be used if it is no wider than the center conductor.  

How Do I Use the RF Capacitor?

A shorting plate is placed on top of the specimen and secured to the outer walls of the square coaxial line to form a shorted transmission line with the specimen inside. Screws around the perimeter of the outer conductor are used to electrically connect the shorting plate to the outer conductor so that no RF energy leaks out of the fixture. A network analyzer is connected to the other end of the square coaxial line via a transition to excite the RF capacitor. A CEM-based inversion algorithm converts the measured amplitude and phase into a corresponding real and imaginary permittivity at each measurement frequency.

The electric field at the specimen location is vertically oriented between the truncated center conductor and the metal short on top of the specimen. For anisotropic materials, the measured permittivity is in this vertical direction.  

When Would I Use the RF Capacitor Measurement Standard Test Method?

Bulk materials are used to absorb, reflect, or guide electromagnetic energy in a variety of applications. The horizontal size of the center conductor in the fixture enables inhomogeneous composites (e.g. foams, honeycombs, and multilayer constructs) to be characterized as well as simple dielectrics.