
Metamaterials 
It has been demonstrated recently by a number of researchers that a periodic arrangement of closely spaced conducting wires and loops give rise to double negative (i.e., negative and negative ) materials, known popularly as metamaterials, over a certain range of frequencies. While it may be of interest, in practice, to know the effect of material tolerances on the double negative properties, we are also studying the effect of a nonperiodic lattice on the dielectric and magnetic properties of metamaterials. We are exploring whether periodicity is not a requirement for achieving negative and . Our results indicate that a completely random array of conducting wires having the same wire density as the periodic case gives rise to essentially the same dielectric properties.

MIMO Communications Systems 
Multiple Input Multiple Output (MIMO) communication, whereby multiple antennas are used at both the ends of a communication system, are being studied by a number of research groups for boosting the system capacity when the spectral resources are limited. We are studying the effects of element correlation due to insufficient spacing and electromagnetic mutual coupling on the system capacity. Our results indicate that when elements are densely packed in a limited spatial region, the information theoretic capacity does not increase linearly as is commonly assumed. Indeed the capacity drops with increasing number of elements due to electromagnetic mutual coupling.

Modeling Propagation Over Rough Ocean Surface 
The US Navy is interested in understanding the combined effect of surface roughness and atmospheric refraction on the propagation of radio waves. We are developing parabolic equation (PE) based techniques for this purpose by describing the surface roughness in terms of an equivalent impedance of a flat plane. The equivalent impedance is found to be angle dependent and a splitstep based parabolic equation solution of radio wave propagation on a nonconstant impedance is being utilized in the study. The properties of the impedance surface at low grazing angles is being studies using a variety of techniques

Modeling Wireless Propagation 
We are developing a 3D vector parabolic equation technique for predicting path loss and angular spread in an outdoor multipath environment. The technique being developed incorporates lateral and rooftop propagation of waves and is suitable for predicting both the copolarized as well as the cross polarized component. The normalized field behind a rectangular, lossy building predicted by the 3D vector PE is being compared with measurements in the figure PE1. Figure PE2 shows yet another comparison of the copolarized field in the shadow of a lossy building with measurements. 