Scale modelling and computer non-linear analysis of a Schottky barrier structure at 35 GHz

Within the field of millimetric RADAR mixer receiver protection, there exists a need to characterize and explain the behaviour of diode power samplers at 35 GHz. Such characterisation is important in being able to extend capability to higher frequencies, notably 94 GHz, to optimise performance and thereby fulfill more demanding specifications, and to improve production yields. No published data on this subject is known to exist. Specifically, this thesis seeks to allocate measured values to an equivalent circuit for a combined loop antenna, Schottky Barrier diode, co-axial line, frequency dependant lossy termination, and a simplified P.I.N. diode load. Using an HP8510B network analyser these measured values are obtained using a 4.666:1 scaled model at 7.5 GHz for the antenna and line. Measured values for the Schottky diode were obtained using various techniques from d.c. to 22 GHz, again with an HP8510B. Particular attention has been paid to reconciling diode and transmission line measured values with those predicted for this co-axially mounted 'seven dot chip' structure. In this application, the diode is often exposed to comparatively high powers and high junction voltages. Previous authors do not account for the increase of diode series resistance with high junction voltage; this is believed to be an unacceptable simplification in this context. Runge-Kutta analysis of the composite antenna, transmission line, and non-linear diode model has been used to equate modelled and practical 35 GHz characteristics for rectified current as a function of P.I.N. diode load, and input power. Sensitivity of the model to variations in most diode and line parameters has been evaluated.