Equivalent Networks of Two In-line RLTs in Millimeter Wave VCO Waveguide Cavities

In the design of millimeter wave voltage control oscillators (VCOs), it is fairly important to establish the relationship between load impedance looking outward from active device and the impedance of varactor diode, so that load impedance can be related to the variation of varactor diode's impedance due to changing its dc bias voltage. In this paper, self impedance of radial line transformer (RLT) mounted on Gunn device has been calculated with mode matching methods at first. Numerical results of self impedance with respect to various circuit parameters are presented. General rules concerning self impedance by virtue of various structural parameters of the VCO have been deduced. Furthermore, an equivalent two-port network is presented in terms of impedance matrix, which is constructed by self impedance embedded on Gunn device and mutual impedance of two RLTs which has been calculated previously. The equivalent two-port network, which describes the relationship between load impedance and impedance of the varactor diode, is useful for the design and testing of the millimeter wave varactor VCO with two in-line RLTs.