W-band millimeter wave vialess microstrip-to-microstrip vertical transition in multilayer LCP substrate

In this paper, a W-band broadband vialess microstrip(MS)-to-MS vertical transition in multilayer liquid crystal polymer(LCP) substrate is presented, which consists of two MS lines in the top layer, a common ground plane and slotline resonators in the second layer, and a close-loop transmission-line in the third layer. To increase the passband of the vialess vertical transition, an H-shaped slotline resonator is introduced, which greatly improves the impedance performance of the slotline resonator, and the full-wave simulated results indicate that insertion loss(IL) is less than 2 dB and return loss(RL) is better than 10 dB at W-band. To verify this design, the broadband vertical transition is fabricated and measured. The measured results indicate that a broadband vertical transition with RL better than 10 dB and IL less than 5.67 dB can be obtained in the frequency range from 70.00 GHz to 104.09 GHz. Due to the fabrication error in the preparation process, the measured results are deteriorated compared to the simulated results, and the investigation indicates that the deviation is caused by the thickness error of the LCP substrate.