A novel structure of metallic compound air-fed array (CAFA) antennas, as a kind of improved Fabry-Perot resonator (FRP), is proposed in this paper. With stepped metallic ground plate, metallic grating cover and open-ended waveguide feeding, this kind of antenna exhibits features of low profile, low cost and easy integration into microwave out-door unit (ODU). The operating principle, design procedure, simulation analysis and an experimental prototype for application of 13 GHz microwave radio-link are presented. The measured results exhibit: 19.2 dBi peak gain, 3.85% common bandwidth for both 3 dB gain-drop and VSWR≤1.5∶1, and good radiation characteristics.