A hybrid numerical simulation method is presented to model and analyze integrated terahertz (THz) photomixer antennas. The proposed computational method combines an optoelectronic solver and a full-wave electromagnetic solver to rigorously model continuous wave (CW) THz photomixer sources. In this hybrid computational approach, the photomixer source is modeled in a rigorous manner without any approximation. The optoelectronic solver is used to find absorbed optical intensity and optical carrier generation rate inside the fast photoconductive region through solving an optical scattering problem. Then, the equations governing the charge carrier transport inside the photoconductor are solved to give THz photo-current by considering realistic material parameters. Finally, through a full-wave electromagnetic solver, and using calculated photo-current from the optoelectronic simulator, antenna parameters and radiated THz power are obtained. Using the proposed hybrid simulation method the effects of photomixer parameters on the THz photo-current and radiated power is rigorously investigated for several geometries. Moreover, results of a parametric study on various factors such as carrier lifetime of material, incident optical power density, applied bias voltage, THz beat frequency, and the gap size are presented. The method can be used for accurate design refinement at pre-fabrication stage.

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This paper mainly discusses the ITU-R P.530 flat fading model in fixed wireless channels.This empirical model introduces a more precise model than the traditional models. To evaluate the effect of this model on the system performance, the PDF of this flat fading model has been derived and used in the Monte Carlo simulation. According to the simulation results, the behavior of ITU-R P.530 model is significantly different from the lognormal model used conventionally in fixed wireless channel modeling, so using the lognormal distribution drastically causes to overestimate or underestimate the system power and fade margin in fixed wireless systems. INTRDUCTIONA microwave radio link suffers various signal fluctuation in time for a number of reasons. In fixed/mobile radio links, radio wave that propagates from transmitter to receiver, traveling through free space, undergoes absorption, reflection, refraction, diffraction, and scattering. In multi path situation, several rays with different delays and amplitudes, receiving by the receiver antenna, add to the ray of direct or line-of-sight (LOS) path constructively or destructively which introduce signal fluctuation. These signal random variations around the nominal receive level are commonly referred to as fading [1,2]. A receiver signal is said to undergo flat fading if the radio channel has a constant gain and linear phase response over a wideband larger than the bandwidth of the transmitter signal [3]. The multi path signals are not fixed in number, amplitude, phase, and arrival times, and the ability to predict these parameters is a continuing challenge for even the more advance site-specific propagation models [4]. ITU-R P.530-11 [5] includes the most practical and reliable prediction models in fixed LOS radio links. According to the measured results, [5] and [6] introduce outage prediction methods in multi path fading (flat and selective fading) conditions in worst month of year. Methods of converting from average worst month figures to the average annual figures are also given. The organization of this paper is as follow: First, the prediction method of flat fading is based on ITU-R P.530 standard reviewed. Then, the numerical simulation has been performed to demonstrate how different the system performance is by using ITU-R P.530 model and the conventional model (Lognormal Model). Finally, the simulation results are considered and concluded.