Foreign Object Debris (FOD) at airport runways is a hazard that can cause accidents during takeoff and landing. A high accuracy detection system is critical to prevent any possible incidents. A radar system has become a technology for object detection, including FOD detection, by taking advantage of electromagnetic radiation emitted and detected by a high gain antenna. This research proposes a 64 element array series of rectangular patch microstrip antenna optimized by using array series method for radar FOD detection. The proposed microstrip antenna uses the Rogers RT / Duroid 5880 substrate with dielectric constant 2.2. The antenna size is 232.8 mm x 6 mm x 1.575 mm. Simulation results using CST Microwave Studio show that the antenna design can operate in a range frequency of 37.563 GHz-38.863 GHz or 1.3 GHz (3.4%) bandwidth. The simulated gain, E-plane and H-plane beamwidths are 16.66 dBi, 75.5 degrees and 2.8 degrees, respectively. Measurement results show that the antenna can operate at frequency range of 37.47 GHz-38.8 GHz or 1.33 GHz (3.49%) bandwidth, which has similar performances as simulation. In addition, the simulation of 128 x64 element series linear array achieved gain 41.36 dB, unidirectional radiation patterns, E-plane beamwidth 0.4 degrees and H-plane beamwidth 1.5 degrees. The proposed antenna is potential for radar FOD detection applications.