The characteristics of three-dimensional (3D) multilayer coplanar waveguide (CPW) lines incorporating a 90 o vertical interconnection structure have been investigated using a full wave analysis. Possible coupling effects between CPW lines in different layers have been taken into account, with results showing that such effects could be very strong if the adjacent CPW lines are too close. As the distance between the adjacent lines increases, the coupling effects become weak; nevertheless it is not completely negligible for many practical applications. Equivalent circuits including such weak coupling effects which comprises of mixed lumped components and transmission lines have been developed. A good agreement with the full wave analysed results over ku, k and ka bands has been achieved. In addition to fundamental propagation mode, higher order mode effects have also been examined. The simulation results indicate that the second or third order modes might become dominant propagation mode at higher frequency depending upon the CPW structure and its layer distance.ud
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