In the following paper a microstrip patch antenna with a slot is designed on Fr4 substrate which has a dielectric constant 4.4. This antenna operates in ku band (12-18 GHz). The operating bandwidth of antenna is 12.029-13.255 GHz. The resonant frequency is 12.64GHz. This antenna is simulated on CST software. The maximum gain of antenna is 4.82 dBi with directivity 7.10 dB. The VSWR is 1.10.