Abstract-A new variety of millimeter-wave Fresnel-zone plate lens with enhanced focusing quality is described. Each full-wave zone of the lens is divided into four quarter-wave subzones, which are covered by dielectric rings having equal thickness but different permittivities. More practical equations are derived for the radii of the zones, and for the thickness of the lens by taking into account the angle of incidence of the electromagnetic wave.A Fresnel-zone plate antenna (FZPA) consisting of a quarterwave lens and a scalar feed is developed and analysed theoretically. Equations for the aperture field and far field are derived using multiple ray tracing through dielectric plates and vectorial Kirchhoff diffraction theory, respectively. It is demonstrated that the proposed transmissive-type FZPA has an aperture efficiency of more than 50% in the 60 GHz frequency band. This computed efficiency agree with the measured overall efficiency reported by other researchers for an X-band quarter-wave reflector-type FZPA.

Abstract-This paper presents a model for the scattering of radiowaves from the canopy of a single tree. The canopy is modeled as a cylindrical volume containing randomly distributed and oriented cylinders, representing the branches, and thin disks, representing the leaves. A simple expression for the incoherent scattered field outside the canopy is obtained using Twersky's multiple scattering theory. This expression is shown to agree well with results of scattering measurements on a live tree typical of those found in urban environments. The scattering model can be readily incorporated in ray-based propagation prediction tools that assist the planning of microcellular radio networks. This involves the use of so-called tree-scattered rays, which interact at the tree centers. Path loss predictions generated with the aid of the new model are shown and compared with measured data to illustrate the considerable improvement in prediction accuracy that can be achieved in realistic urban microcellular scenarios by taking into account the scatter from trees.

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Abstract-This paper investigates diversity for dual-antenna systems operating in indoor environments. First, an approximated equation of the diversity gain is derived for different combining techniques. These theoretical results show that the two-term approximation, as generally used in the literature [5], is too rough an estimate. Consequently, a new six-term approximation is derived. Next, it is demonstrated by a comparison of theoretical and experimental diversity gain values that, due to mutual coupling between the two antennas in practice, the diversity gain will not approach 0 dB if the distance between the two antennas approaches zero. Finally, it is concluded from measurements at 900 MHz that antenna-pattern diversity is a better choice than space diversity for use at handhelds.

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