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Ferroelectrics in microwave antenna systems offer benefits of electronic tunability, compact size and light weight, speed
of operation, high power-handling, low dc power consumption, and potential for low loss and cost. Ferroelectrics allow
for the tuning of microwave devices by virtue of the nonlinear dependence of their dielectric permittivity on an applied
electric field. Experiments on the field-polarization dependence of ferroelectric thin films show variation in dielectric
permittivity of up to 50%. This is in contrast to the conventional dielectric materials used in electrical devices which
have a relatively constant permittivity, indicative of the linear field-polarization curve. Ferroelectrics, with their variable
dielectric constant introduce greater flexibility in correction and control of beam shapes and beam direction of antenna
structures. The motivation behind this research is applying ferroelectrics to mechanical load bearing antenna structures,
but in order to develop such structures, we need to understand not just the field-permittivity dependence, but also the
coupled electro-thermo-mechanical behavior of ferroelectrics. In this paper, two models are discussed: a nonlinear
phenomenological model relating the applied fields, strains and temperature to the dielectric permittivity based on the
Devonshire thermodynamic framework, and a phenomenological model relating applied fields and temperature to the
dielectric loss tangent. The models attempt to integrate the observed field-permittivity, strain-permittivity and
temperature-permittivity behavior into one single unified model and extend the resulting model to better fit experimental
data. Promising matches with experimental data are obtained. These relations, coupled with the expression for operating
frequency vs. the permittivity are then used to understand the bias field vs. frequency behavior of the antenna. Finally,
the effect of the macroscopic variables on the antenna radiation efficiency is discussed.
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