Planar circuit analysis of ultra-wideband millimeter-wave inductor using transmission line sections

Regarding the capacitive nature of input/output impedances of millimeter-wave amplifiers, it is necessary to utilize wideband inductive elements for the design of input/output impedance matching circuits. In this paper, the design and optimization of an ultra-wideband transmission line inductor with an inductance of less than 100 pH are introduced for using at frequencies above 50 GHz. The reason of using this inductor is its superior performance compared to that of a spiral inductor and single-coil inductor. The inductor consists of three rectangular microstrip line segments with nonequal and variable characteristic impedances. The design is done by calculating the impedance matrix using planar circuit analysis (PCA) based on a planar waveguide model, segmentation/desegmentation methods, and an intelligent algorithm in MATLAB. With this design method, the effect of discontinuities, fringing fields at the edges of the microstrip, and the conductor as well as dielectric losses can be considered while minimizing the dispersion effect. In this study, to reduce the calculation time of the impedance matrix, the doubly infinite series are reduced to a singly infinite series by summing the inner sum for a rectangular segment whose one side is shorted and three other sides are open.