The phase-correcting Fresnel zone plate antenna has been studied extensively at microwave and millimeter-wave frequencies in the past few years, in part because it offers advantages of low weight, cost, and loss. Scores of articles have appeared describing fundamental characteristics and methods of improving the efficiency, gain, and multiple- frequency band performance. As a result of these studies, one can now optimize the design, and an optimized zone plate antenna can provide performance superior to a standard lens or paraboloid antenna, especially at millimeter wavelengths. There are many differences between performance at optical wavelengths and microwaves/millimeter-waves, and these differences are described. A new planar design with non- parallel surfaces is discussed. This configuration offers further improvement in diffraction efficiency.