This paper discusses applications of the Fresnel zone‐plate (FZP) made of metal foil to microwave antennas. First, the focusing effect and the far‐field pattern for the FZP are analyzed using the Kirchhoff‐Huygens diffraction integral. It is found that a phase‐reversing FZP, in which the phase of either its even or odd zones is inverted, has a sharp beam with a low sidelobe level. On the basis of the fundamental analysis, an antenna syctem in which a reflector‐type FZP fed by a backfire helix is proposed as an application of the phase‐reversing FZP. It is pointed out that a sharp circularly polarized beam with a half‐power beam‐width of 9 deg is obtained when the outermost radius of the FZP is about 4 wavelengths. Next, the gain variation by the change in the ground plate radius of the axial‐model helical antenna is explained by the Fresnel zone principle, and an axial‐mode helical antenna with a zoned ground plate is proposed. An absolute gain of 12.2 dB is realized by a two‐turn short helix with a zoned ground plate.