In this contribution, the authors present guidelines for an effective design of an X-band 2D array of slotted waveguides for surveillance applications. The radiation pattern, with a narrow beam and cosec² profile, respectively, in azimuth and in elevation, is obtained by a beam forming network based on a hybrid architecture, in which the main corporate feed line feeds identical 11-element travelling wave slotted arrays. The latter produces a radiation pattern that is frequency-independent in azimuth and only slightly frequency-dependent in elevation. The fabricated antenna features a horizontal beam width (at −3 dB) of 1.16°, gain >31 dBi, and 30 dB sidelobe level in the 300 MHz operative band. The overall array is made up of three stacked layers: the first two for the corporate feed line and the third for the travelling wave radiating elements, resulting in remarkably compact external dimensions (170 cm × 25 cm × 2 cm) and relatively low weight (8 kg in total).