Novel wideband 3D transitions on Liquid Crystal Polymer for millimeter-wave applications up to 100 GHz

Abstract

This paper reports on two novel broadband vertical transitions on flexible organic Liquid Crystal Polymer (LCP) substrate which show superior characteristics- Return Loss below -10 dB, Insertion Loss better than -2.5 dB from 60 to 100 GHz. The presented Coplanar Waveguide-Coplanar Waveguide-Microstrip (CPW-CPW-MSTRIP) and CPW-CPW-CPW 3D transitions require strategically placed vias and tapering of the CPW ground planes in order to suppress radiation loss and optimize the performance over a very broad frequency range. These transitions are simple to realize and are compatible with low-cost substrate fabrication guidelines allowing for the easy feeding of embedded IC's in 3D modules, especially in compact automotive radar applications and beam-steering wideband antenna arrays. To estimate the effect of practical fabrication variations, a sensitivity analysis was performed against the lateral misalignment of via to pad defined by commercial fabrication houses and shows a worst case scenario of a 5dB RL and 0.2dB IL degradation compared to the ideal case. The measurement results of the reported transitions exhibit very good performance up to 100 GHz and show reasonable agreement with simulation.