DETERMINATION OF COMPLEX PERMITTIVITY OF LOW-LOSS DIELECTRICS

A new high-order-mode analytical method is described for calculating t he frequency-dependent complex permittivity of a low-loss dielectric i n a parallel-plate structure using a planar microwave circuit model, A n analytical expression for the complex permittivity is derived in ter ms of the terminal impedance at a modal resonant frequency of the stru cture. The derivation provides physical and mathematical insight into the relation between complex permittivity and port impedance, The tech nique is validated by good agreement between manufacturer's specificat ions and complex permittivity calculated from measurements near resona nt frequencies for a printed circuit board (PCB).