Here, a hybrid backed-cavity with electromagnetic band-gap (EBG) structure and a perfect electronic conductor (PEC) is proposed for an Archimedean spiral antenna. This cavity makes the spiral antenna work operate over the 10:1 bandwidth and without the loss introduced by absorbing materials that are used conventionally to broadband spirals. Based on the artificial magnetic conductor (AMC) characteristic, an EBG is placed in the outer region of backed-cavity to improve the blind spot gain at low frequency. A PEC at the center of the structure is used to obtain high gain at high frequency. The antenna performances are improved significantly for of the low profile spiral antenna is improved significantly. A typical spiral antenna with a hybrid backed cavity is fabricated and studied experimentally. The experimental data are consistent with that of the simulation results.