-a high gain broadband antenna using a cylinder hollow-cavity microstrip structure with multilayer H-shaped slots is presented, which can be realized by microwave multi-layers technology (MLT). The measured impedance bandwidth of the proposed antenna is 32.3% with the reference of Sl1 -lOdB, and the measured gain of the antenna is 5.75dBi @ 16.1GHz and 6.2dBi @ 20GHz, which indicates a low gain fluctuation in the whole bandwidth of the antenna.