Ultra-Wideband Vialess Microstrip Line-to-Stripline Transition in Multilayer LCP Substrate for $E$ - and $W$ -Band Applications

In this letter, we present an ultra-wideband microstrip line (MSL)-to-stripline (SL) transition without using vias or coupled slot in multilayer liquid crystal polymer (LCP) substrate at millimeter-wave frequencies. The proposed transition is achieved by using an asymmetric parallel SL to connect MSL and SLs signal lines in different layers, and its full-wave simulation predicts an insertion loss of less than 1.1 dB at E- and W-bands. To demonstrate this design experimentally, an MSL-to-SL-to-MSL transition was fabricated and characterized. The measured insertion loss of this back-to-back transition is less than 2 dB with a return loss higher than 13 dB from 60 to 110 GHz, showing good agreement with the simulated data.