k‐Selective Electrical‐to‐Magnon Transduction with Finite‐Element‐Resolved Sub‐Micron Nanoantennas

ABSTRACT Controlling wave‐vector‐selective coupling between microwave antennas and spin waves is a central challenge in magnonic transducer design. In all‐electrical propagating spin‐wave spectroscopy, the launched ‐spectrum is set by Fourier transform of the perpendicular near‐field component of the antenna, but realistic sub‐micron antennas exhibit skin and proximity effects, impedance mismatch, and electromagnetic leakage from feed tapers that uniform‐current models cannot capture. We introduce a coupled finite‐element–finite‐difference (FE–FD) framework linking impedance‐matched nanoantenna geometries to propagating spin‐wave dynamics. Finite‐element simulations yield the full complex vector RF near field, projected onto the precession‐driving perpendicular component, discretised onto a grid, and injected into micromagnetic Landau–Lifshitz–Gilbert simulations. The antenna wave‐vector weighting and excitation intensity are extracted by Fourier analysis and compared with experiment. Applying this framework to coplanar‐waveguide and stripline nanoantennas on a yttrium‐iron‐garnet film, we achieve quantitative agreement in dispersion ridges, group velocities, and wave‐vector peak positions. The simulations resolve how antenna width, ground‐return symmetry, taper geometry, and leakage shape the launched ‐spectrum, providing design rules for wave‐vector‐selective spin‐wave excitation in classical and quantum magnonic devices. We further quantify leakage from feed tapers, identify dominant loss channels, and compare CPW and stripline performance, providing routes to efficiency optimization.