A fully-metallic periodic leaky-wave antenna well-suited for angle-of-arrival estimation with a reduced frequency bandwidth is presented. The design is based on a leaky rectangular waveguide loaded with corrugations and periodically modulated by longitudinal slots, which produces a frequency beam scanning in the H-plane. By exploiting multiple visible spatial harmonics, multiple beams are radiated for each frequency. This enables the antenna main beam to scan the 180 •-angular range with a bandwidth of only 3.7% at 27 GHz. Simulations show that using a frequency-domain MUSIC approach, it is possible to estimate angles-of-arrival of several incoming sources without ambiguity.