Stub-Loaded Via Transition for Wideband Impedance Matching of Sub-THz 6G Antenna-in-Package
This paper introduces new impedance matching technique for via transition of multi-layer PCB based sub-THz antenna-in-package (AiP). In the proposed design, multiple resonating stubs are cascaded in vertical direction along via transition to create multi-stage wideband impedance matching network. The resonating stub employs rectangular ring to reduce the stub length by increasing parasitic capacitance around the ring. The impedance matching technique presented in this paper is demonstrated through design, fabrication, and measurement of subarray for the next generation’s sub-THz 6G AiP operating from 136 to 148 GHz. In the subarray design, four antenna elements are combined with 4-way power divider to form 4×1 array. The 4×1 subarray is then connected to the proposed stub-loaded via transition for input impedance matching looking from bump pad of beamforming integrated circuit. This stub-loaded via transition for impedance matching of the 4×1 subarray shows more than 17.6% fractional bandwidth (FBW) with return loss of 10 dB. Since the impedance matching network provides much wider bandwidth than the antenna element and 4-way power divider, it does not limit the 4×1 subarray performance. The designed 4×1 subarray is fabricated with advanced printed circuit board technology using modified semi-additive process. Both simulated and measured FBW of the 4×1 subarray shows more than 13.2% with return loss of 10 dB. The measured gain of the 4×1 subarray is greater than 8.9 dBi within the bandwidth.