Ultra-Wideband Microstrip Line-to-Microstrip Line Transition in Multilayer LCP Substrate at Millimeter-Wave Frequencies

In this letter, an ultrawideband microstrip line (MSL)-to-MSL transition in multilayer liquid crystal polymer (LCP) substrate is presented for millimeter-wave applications. The proposed transition consists of three circuit layers and three LCP layers. The MSLs' signal lines are in the top circuit layer, while their grounds are distributed in the inner and bottom layers, respectively, and are connected using through vias. Full-wave simulation reveals an insertion loss of less than 1.1 dB for the proposed transition from dc to 110 GHz. To experimentally demonstrate this design, its back-to-back transition was fabricated and characterized. The measured insertion loss and reflection of the back-to-back transition are less than 2.5 and -13 dB below 110 GHz, respectively, showing a good agreement with the simulated data.