Spectral characterisation of devices at high frequencies and measurement methods
The properties of nonlinear devices, semiconductor diodes, were determined at high frequencies using the method of spectral characterisation. Such characterisation was carried out employing a specially developed technique where the components of the harmonic spectrum generated within these diodes at radio and microwave frequencies were measured. The theory of spectral analysis, based on Fourier principles, was reviewed. It was applied to the periodic gate function, which plays a fundamental role in signal analysis, in order to lay the foundation for the theoretical investigation carried out between pulses of known shapes and their corresponding spectra. Some useful relationships were established and applied in the evaluation of devices. Based on the fundamental properties of the periodic gate function, two new sampling procedures were introduced. The harmonic generating properties of practical diodes, where the nonlinearity in the element is an inherent condition, were examined. It was established that the spectrum generated within the device, at a particular drive level, gives the "fingerprint" of the diode, i.e. represents fully its nonlinearity. Measurement methods, both at low and high frequencies, were also discussed. The new technique, called the Multiple Reflections Resonant Line (MRRL) method was developed and described in the thesis to measure a complete spectrum. The method employed a coaxial slotted line system terminated by the device under test. The basic transmission line theory was extended to include the phenomena of multiple reflections along and resonance of, the line. The properties of the standing waves were then related to the device parameters. The twelve microwave diodes were successfully modelled which included parasitics using the new spectral technique. An attempt was made to evaluate these devices for particular applications.