This paper presents the design and numerical verification of a slotted waveguide antenna array (SWAA) that operates at 2.3 GHz, has an overall gain of 30 dB and is capable of handle high power (40 kW average). The array is going to be used as part of a narrow band high power microwaves (HPM) system capable of activate landmines from a safe distance. The numerical verification is made using CST Microwave Studio.