A V-band substrate-integrated waveguide (SIW) leaky-wave antenna with enhanced frequency-scanning capability is presented. The antenna consists of a uniform fast-wave SIW radiating section excited through a grounded coplanar waveguide (GCPW)-to-SIW transition incorporating an etched magnetic-dipole (M-dipole) horn. Frequency-dependent beam scanning arises from the dispersive phase constant of the dominant TE\(_{10}\) mode in the SIW radiating section, while the GCPW transition couples quasi-TEM feed excitation into the TE\(_{10}\) SIW aperture mode. The etched M-dipole horn introduces a localized boundary perturbation at the excitation interface, producing a frequency-dependent change in the extracted effective phase constant and increasing the dispersion slope. As a result, the measured scanning range expands from 22\(^\circ\) for the standalone LWA to 40\(^\circ\) over 58.6–62.5 GHz, corresponding to a scanning rate of 621.11\(^\circ\) per unit fractional bandwidth. The fabricated prototype achieves 12.9 dBi peak realized gain and radiation efficiency exceeding 85%. The proposed transition-assisted scanning approach is suited for compact mmWave radar sensing, V2X short-range communication, UAV links, and beam-steerable front ends where periodic loading or multilayer slow-wave structures increase design complexity.
