Microstrip antenna miniaturization using partial dielectric material   filling
  In this paper we study microstrip antenna miniaturization using partial filling of the antenna volume with dielectric materials. An analytical expression is derived for the quality factor of an antenna loaded with a combination of two different materials. This expression can be used to optimize the filling pattern for the design that most efficiently retains the impedance bandwidth after size reduction. Qualitative design rules are given, and a miniaturization example is provided where the antenna performance is compared for different filling patterns. Results given by the analytical model are verified with numerical simulations and experiments.   Key words: Microstrip antenna, miniaturization, partial filling, impedance bandwidth, quality factor. 
Olli Luukkonen, Pekka Ikonen, and Sergei Tretyakov