This research introduces an innovative phase inverter (PI) design using a substrate-integrated coaxial line (SICL). The proposed SICL PI is achieved by bisecting the SICL with two I-shape slots embedded on the top and bottom broad-side walls of the SICL. The central signal strip is also bisected, and the divided strips are diverted to the top/bottom walls on the other side of the slots through one or two via-holes. Thus, phase inversion is obtained by swapping the potentials of the central strip and the top/bottom walls. A transition between the feeding SMA and the SICL is also developed to facilitate measurements. Experimental results demonstrate that the proposed SICL PI exhibits a fractional bandwidth (FBW) of 2.74–4.66 GHz (51.8%) under the criteria of return losses greater than 10 dB, insertion losses less than 0.5 dB, and phase deviation within ±15°.
