Reflective-Type Phase Shifter Design with a Patch Antenna for a 250 GHz On-Chip Beamforming System

Kyoungmin Lee; Yunkyeong Koh; Moonil Kim

doi:10.23075/jicas.2025.11.1.005

Kyoungmin Lee Korea University
Yunkyeong Koh Korea University
Moonil Kim Korea University

DOI: https://doi.org/10.23075/jicas.2025.11.1.005

Keywords: Terahertz beam-forming system, Reflective-type phase shifter, defected ground patch, beam-steering simulation, SiGe HBT process

Abstract

This paper introduces a reflective-type phase shifter (RTPS) and a defected ground patch antenna design for configuring a 4-bit 250 GHz on-chip beamforming system using a SiGe HBT device. The patch antenna is designed to operate at 250 GHz, with a defected ground structure implemented to address the issue of narrow bandwidth. Four ground slots, each sized 50 x 121 mm², are fabricated, and measurement results show that the patch antenna operates within the 240-257 GHz band. The RTPS is designed using a 90^o hybrid coupler and variable loads using varactors. The 90^o hybrid coupler is made compact by overlapping two adjacent 50-W quarter-wavelength lines and forming a slot on the ground plane. The varactor is based on a diode-connected SiGe HBT device, and its size is selected as the largest available 9 mm in length to maximize the capacitance variation with the bias input. Two RTPS unit cells are connected in series to achieve a 360^o phase shift, and the measurement results demonstrate a 4-bit phase shift.

Author Biographies

Kyoungmin Lee, Korea University

Kyoungmin Lee received the B.S. degree in electrical engineering from Korea University, Seoul, South Korea, in 2015, where he is currently working toward the Ph.D. degree. His research topics include development of antenna and passive microwave sensor system for millimeter wave band. His current research is design detector and antenna based on InP DHBT in terahertz region and package integrated circuits in waveguide and lens antenna.

Yunkyeong Koh, Korea University

Yunkyeong Koh is currently an undergraduate student in electrical engineering at Korea University. Her research interests are design and measurements of terahertz integrated circuits that include power amplifiers and oscillators.

Moonil Kim, Korea University

Moonil Kim is a currently professor in Electrical Engineering, Korea University. His current research interests include development of both passive and active circuit components required in construction of terahertz communication and imaging systems.