Abstract : Directive antennas are required for the development of high-power microwave (HPM) transmission system concepts. The type of system considered includes a single HPM source with waveguide output, the antenna, and the control/support equipment integrated onto a ground-mobile platform. A parabolic reflector with a custom-designed horn feed has been demonstrated as one antenna option that allows direct connection to the HPM source waveguide output. An alternative approach to reflector antennas is desired, so a slotted-waveguide array was selected to meet the operational requirements. The array design is modular (with four symmetric modules) to ease fabrication and to maximize transportability and repairability. A rectangular waveguide corporate-feed network is used to minimize the antenna subsystem volume (i.e., depth) and allow the HPM source to be integrated into the feed structure. An S-band array and feed structure were fabricated and assembled for laboratory evaluation. The array was fabricated from WR-284 copper waveguide with brass end caps to a +5-mil tolerance. The array design, fabrication, assembly, and testing are discussed. Preliminary test data for a single module of the four-module full array are presented. As expected, the array as fabricated requires "fine-tuning" to optimize performance. Empirical results will be used to evaluate design alternatives appropriate for particular HPM applications.