In this paper, the design of a broadband multi-layer microstrip antenna is presented. The broadband characteristics are the results of coupled resonances of the patch and transmission line through the resonant aperture. For this purpose, a cross-shaped transmission line, a ring slot, and a shaped ring patch are used. The simulation and measurement results indicate that a wide impedance bandwidth of 70% for |S11| < −10 dB and a perfect impedance matching 35% for |S11| < −20 dB are achieved. The gain is stable over the impedance bandwidth. The maximum gain of the proposed antenna is 8.8 dBi at 5 GHz. The radiation pattern, radiation efficiency, and cross-polarization are also suitable throughout the impedance bandwidth.
