Abstract-The microwave signal attenuation caused by dust is one of the major problems in utilizing microwave bands for terrestrial and space communication especially at desert and semi desert area. This paper presents a mathematical model developed to characterize the microwave signal attenuation due to dust. This model enables a convenient calculation of the microwave signal path attenuation which relates attenuation to visibility, frequency, particle size and complex permittivity. The predicted values from the mathematical model, which are compared with the measured values observed by the author in Sudan show relatively optimistic agreement.

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Figure 5 shows the simulated and measured results for return loss in the FCC-defined UWB. The measured impedance bandwidth is determined by a 10-dB return loss, and the bandwidth performance is sufficient for the UWB requirement. The radiation patterns shown in Figures 6-8, are measured at 4.0, 6.0, and 10.0 GHz, respectively. In addition, good omni-directional radiation characteristics can be observed in these figures. The cross-polarization radiation at the H plane is also negligible. Figure 9 shows the measured antenna gain. The maximum antenna gain is estimated at 3.857 dBi across the UWB band. CONCLUSIONSA new, low-profile planar circular disc-and-ring monopole antenna is proposed. A prototype for the UMTS/UWB dual-network applications has been built and demonstrated. As the measured and simulated results show, not only the omni-directional radiation characteristics but also the impedance bandwidth performance is suitable for the specified dual-network applications.ABSTRACT: In this paper, we present a novel domain decomposition finite-difference time domain technique for solving large electromagnetic radiation and scattering problems. In this method the computational domain is divided into manageable, moderate-sized subdomains with overlapping regions. PML layers are used for terminating the subdomains to absorb the outgoing waves. The tangential electric fields are stored on an interface plane to be used as a boundary condition to generate the field in the adjacent subdomain. These computations are applied in a serial manner to solve a problem that is too large to be solved in one step because of limitations in the available computational resources.ABSTRACT: In this paper, a compact coplanar waveguide-fed slot antenna that can operate over an octaveband (1.75-3.7 GHz) is presented. The novelty of this antenna is the wideband operation with the radial stub loading. The front-to-back ratio of the antenna with a back plate is better than 25dB in H-plane and better than 18 dB in E-plane. The cross polarization level is around Ϫ20 dB over the band and the worst being at Ϫ15 dB.

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