Radiation properties of microstrip elements in a dispersive substrate of permittivity less than unity

We present the design of a dispersive medium with a permittivity regime less than unity and investigate the radiation characteristics of elementary printed antennas within such a grounded substrate. The study is motivated by the possibility of minimization or elimination of surface waves in this permittivity region irrespective of the substrate thickness. The novel material is resynthesized as an amorphous ensemble of spherical particles composed of a low-loss dielectric core coated with a highly resonant dielectric layer and embedded into a dielectric host. The resulting complex structure is transparent over its entire spectrum except of two narrow-band opaque windows of adjustable depth, shape and positioning. The effective permittivity function is obtained according to the classical theory of effective media and exhibits a characteristic region with the real permittivity function /spl epsiv//sup r//sub eff/<1. We discuss the non-local but causal character of wave propagation in this permittivity region and examine the application of the novel medium in printed circuit antennas. A horizontal elementary microstrip dipole is pieced on a grounded substrate layer composed of this complex medium. The radiation pattern is examined within the region /spl epsiv//sup r//sub eff/<1 as a function of the constitutive media parameters and the of the inclusions geometry.