Fixed-Beam High-Gain Millimeter-Wave Leaky-Wave Slot Antenna with Small Cross Section Using Micro-Metal Additive Manufacturing Process

Leaky-wave antennas (LWAs) are prominent candidates for millimeter-wave (mmW) applications due to their high-gain radiation and simplified topologies. While the inherent frequency-scanning capability of LWAs is advantageous for radar sensing and detection, it constitutes a critical limitation for point-to-point communications requiring stable beam alignment. For the fundamental suppression of beam scanning, a design strategy based on an air-filled micro-coaxial line (MCL) is proposed to construct a fixed-beam LWA. The beam stability is achieved by exploiting the naturally low-dispersive quasi-TEM mode of the MCL combined with a dispersion-compensating E-plane probe transition. The antenna comprises an E-plane probe transition and a composite triple-slot array designed for miniaturization and high gain, both fabricated by micro-metal additive manufacturing (M-MAM) and assembled with a computer numerical control (CNC)-machined split-block waveguide fixture. Benefiting from the independence of the coaxial mode from cross-sectional dimensions, the design achieves an ultra-compact cross-section of 0.4×0.08 λ₀², which is the smallest among reported mmW fixed-beam LWAs. Experimental results demonstrate a -10-dB impedance bandwidth of 54.9–58.5 GHz with a negligible beam deviation of 1.9° and a peak gain of 11.3 dBi.