Abstract: In this paper,a new model of Gunn diode VCO is established on the basis of computing the coupling disc capacitance between Gunn diode land varactor using spectral-domain Hankle transformation.The non- linear analysis of Gunn diode VCO has been developed by using har- monic balance lechnique.A Ka-Band hybrid integrated Gunn diode VCO has been fabricated and the experimental results of the output power and frequency are compared with the computed results.In addition,the dependence of tuning bandwidth on the coupling between Gunn diode and varactor is also investigated.It is shown that the developed model and analysis program are available and effective.On the basis of nootinear analysis,a special optimization procedure is proposed to find the doping power factor of varactor in order to get the optimal tuning linearity.