Methods for Permittivity, Permeability, and Loss Measurements of Polymer Composite Magneto-Dielectric Laminates
(Room 203)
18 Oct 18
1:20 PM
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1:50 PM
Tracks:
Test & Measurement
It has been well known for more than 50 years to use high dielectric constant conductor clad substrates to reduce the size of wavelength dependent microstrip structures such as patch antennas. In the general case, the material’s impedance is √(μ_R/ε_R ) √(μ_0/ε_0 ) where〖 μ〗_R 〖 and ε〗_R are the relative permeability and permittivity, respectively, and the subscript 0 values are those of free space. The miniaturization factor (by which the material decreases the wavelength of an EM signal) is √(μ_R ε_R ). While all natural solid materials exhibit an ε_R value > 1, most materials are non-magnetic, with a μ_R = 1.0. Thus, the high dielectric constant results in a material impedance significantly lower than free-space and a reduction in both bandwidth and antenna efficiency of microstrip patch antennas. A recently developed PTFE – ferrite powder composite laminate exhibits μ_R ~ ε_R ~ 6 and low electrical and magnetic loss values at frequencies up to 500 MHz. This material has a miniaturization factor of a dielectric material with permittivity of 36, but with an impedance essentially matched to free space. Accurately measuring the permittivity, permeability, and loss values, however, presents challenges. In the present work, we compare data from widely different test methods, including the Keysight Impedance Analyzer with 16453A and 16454A permittivity and permeability fixtures, coaxial airline perturbation, “full sheet resonance,” split post dielectric resonator, and phase length, insertion loss and impedance of microstrip transmission lines over a frequency range of 40 MHz to 4 GHz. We explain the causes of both random measurement error and systematic error in the various test methods. Variation between test method results is often due to the anisotropy of the in-plane and z-axis permittivity and permeability and differences in the relative orientation of the electrical and magnetic fields in the test fixtures. Correctly modeling an antenna utilizing these recently developed materials requires an understanding of the anisotropy of these materials and the orientations of the electrical and magnetic fields in the antenna. In spite of requiring exacting sample preparation, the 25 mm coaxial airline yields the most reproducible data. Measured performance of transmission lines and antennas shows good agreement with Sonnet Software models using the measured values of permittivity and permeability.