Spectral characterisation of variable reactance devices

Abstract

Low Noise Figure communication receivers require more efficient frequency converters. Frequency conversion and multiplication processes cannot take place without the existence of harmonics in the system and the inherent property of a nonlinear element is to generate a harmonic spectrum. Such non1inearity, in general, may be provided by semiconductor diodes. This research project deals with the theoretical analysis as well as the properties of a nonlinear reactive device, i.e. Varactor Diode. The power series solutions for the exponential diodes do not normally converge quickly enough to be of practical value for numerical evaluations. A different approach is proposed for the evaluation of harmonic amplitudes and phases. The harmonic generating properties of four diodes of the same type were examined using two different approaches and a good agreement was found between the two methods. Many analyses published over the years have tended to introduce severe approximations which were only valid in practice over limited ranges of operation. However, it is believed that the new sampling method presented here evaluates fully the capabilities of these diodes in practice.