An antenna is one of the prime important parts in the radar system to transmit and receive the electromagnetic signal. In order a coastal radar is able to detect an object at the sea and minimize sea clutter, it is needed to have horizontal polarization signal, and therefore a narrow wall slotted waveguide antenna is designed. This paper describes the design and fabrication of a narrow wall slotted waveguide antenna with 12 slots. The objective of this antenna design is to operate in X-band with center frequency at 9.4 GHz, VSWR ≤ 1.5, bandwidth ≥ 100 MHz. There are many studies which discuss narrow wall slotted waveguide antenna by using the quadratic equation to obtain a slot angle from each slot. However only one the quadratic equation can result in center frequency at 9.4 GHz. To validate the result of the antenna designed, fabrication and measurement were conducted. From the measurement results, the antenna produces 145 MHz bandwidth with VSWR ≤ 1.5 and the center frequency is 9.35 GHz at −27.098 dB minimum return loss. While the antenna simulation results generated 159 MHz with VSWR ≤ 1.5 and the center frequency is 9.4 GHz at −22.076 dB minimum return loss. The simulation and measurement results show similar results.