In this paper the results of an extensive study of the effects of the drift region width on the performance of LHL-GaAs-IMPATT diodes are presented. These results have been obtained using an IMPATT-diode full scale computer simulation program. It is demonstrated that the transition between the regular IMPATT mode and the high-efficiency modes becomes more abrupt as the drift region width is increased. It is also found that when the diode operates according to the highefficiency modes the efficiency is not a sensitive function of the drift region width. The anomalous behaviour of the admittance of the diode is found to be caused by the increase of the component of the total current.contributing to the power generation mechanism at the expenense of the cold-capacitive current. It is demonstrated that for the diodes whose drift region width is optimized for the regular IMPATT mode the efficiency remains always high and the hysterises in the tuning characteristics are less significant

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This paper is a comparative study between the performances of conventional terrestrial multicell Multiple Input Multiple Output (MIMO) working in a Rayleigh fading environment and its corresponding High Altitude Platform (HAP) system working under a different Path Loss (PL) model with the capacity as the performance metric of interest, calculated using the Singular Value Decomposition (SVD). Both systems are assumed to be affected by cochannel interference users in other cells .Simulation results show that the performance of multicell MIMO HAP dependent system outperforms its corresponding that works in terrestrial environment in terms of per user channel capacity.

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A special waveform is proposed and assumed to be the optimum waveform for p-type InP IMPATTs. This waveform is deduced after careful and extensive study of the performance of these devices. The results presented here indicate the superiority of the performance of the IMPATTs driven by the proposed waveform over that obtained when the same IMPATTs are driven by the conventional sinusoidal waveform. The results presented here are obtained using a full-scale computer simulation program that takes fully into account all the physical effects pertinent to IMPATT operation. In this paper, it is indicated that the superiority of the proposed waveform is attributed to its ability to reduce the bad effects that usually degrade the IMPATT performance such as the space-charge effect and the drift-velocity dropping below saturation effect. The superiority is also attributed to the ability of the proposed waveform to improve the phase relationship between the terminal voltage and the induced current.