An aperture-coupled multi-layer broadband microstrip array antenna with coupling ring slots and modified ring patches is presented. The structure of the array consists of a 3-dB 180°-phase shifter, two 1-port's and two 2-port's aperture-coupled microstrip antennas. All parts of the array antenna are designed for broadband operation. The array antenna works based on the back coupling to the microstrip line of 2-port aperture-coupled antenna. Simulation results of the array display encouraging properties, such as wide impedance bandwidth of 77% for |S₁₁| < -10dB and nearly stable gain. The maximum gain of the array antenna is almost 12.65dBi at 5GHz. The radiation efficiency, radiation pattern, side-lobe level and cross-polarization are also adequate within the impedance bandwidth between of 3.34 and 7.53GHz.