An accurate broadband equivalent circuit model of millimeter wave planar Schottky varistor diodes

A Broadband equivalent circuit model of a planar Schottky varistor diode is presented in this article to improve the accuracy of circuit design. Take advantage of a combination of 3-D full wave EM analysis and lumped parameters extraction approach, all the geometry-dependent parasitic elements are taken into account according to physical dimension of the diode, based on which the broadband equivalent circuit model is established. Herein, a T-type network is adopted to account for discontinuities between diode finger and pad. Effect of ambient channel around the diode together with losses caused by the diode material at millimeter wavelength is considered to improve the practical frequency response of the diode chip. Analysis results indicate that the characteristic of the diode especially the phase accuracy is greatly improved with the proposed model. To verify the validity of the circuit model, a prototype of W-band frequency tripler covering 75-110 GHz employing this model is designed and fabricated. The measured conversion loss is in agreement with the theoretical prediction.