Abstract:  To meet the demands of future high-data-rate communication systems in the millimeter-wave frequency band, this paper proposes a Butler matrix-based multi-beam horn array antenna capable of achieving four distinct beam directions across the full W-band. The antenna is realized by integrating an H-plane horn array antenna with a Butler matrix feeding network, featuring a compact structure and ease of fabrication using E-plane split computer numerical control (CNC) machining. The main contributions include: the design of a 1×4 H-plane horn array antenna; the realization of high-performance couplers as key components within the matrix; the development of a Butler matrix that provides stable output signals across the full W-band; and the integration of the H-plane horn array antenna with the Butler matrix feeding network. The multi-beam antenna was fabricated using mainstream CNC technology. Measured results demonstrate that the antenna achieves a return loss better than -10 dB across the entire W-band, and at the center frequency of 92.5 GHz, four beam directions of 12.7°, -40.6°, 42.8°, and -12.1° are realized, resulting in a beam coverage range of ±55.7°.