Abstract
A method has been developed to estimate the amount of inter-modulation distortion which may result in a broad-band, low-noise, nondegenerate parametric amplifier handling multiple f-m carriers in the presence of a comparatively strong interfering source, e.g. the leakage arising from the transmitter in a communication satellite earth station. In Chapter 2 the distortion due to nonlinearity of the charge-voltage relationship of the varactor is calculated. The modulation index of the f-m carriers is derived from C.C.I.R. recommendations based on Holbrook and Dixon's load rating theory. A formal analysis of the gain-bandwidth theory of the parametric amplifier is included. Chapter 3 deals with the distortion due to nonlinear phase-frequency relationship of the parametric amplifier. A differential equation approach is made to re-examine Van Der Pol's quasi-stationary approximation in a varactor diode type network. The group delay characteristics of the amplifier have been calculated, the results are verified by experiments on a practical amplifier and the crosstalk and harmonic powers interfering the baseband telephone channels (composite audio signals from different talkers) are calculated. Chapter 4 deals with the distortion due to A.M.-P.M. conversion effect in the parametric amplifier which arises from the finite gain slope in the amplifier passband. The A.M.-P.M. conversion coefficient is experimentally determined by a precision phase-bridge and the cross modulation ratios are calculated for different input carrier levels using the measured A.M.-P.M. transfer coefficient. In Chapter 5 the experiments on the multi-carrier behaviour of the amplifier are described. A two-carrier I.F. method is utilized to verify the theoretical prediction of the s.h.f. cross-product levels as described in Chapter 2. Eight c.w. carriers and a strong transmitter leakage signal are introduced into the amplifier and the intermodulation products falling within the band 3 to 5 GH[z] are also examined and the conclusions arrived at.