A design method of offset Fresnel zone plate reflector as receiving antenna

The Fresnel zone plate reflector (FZPR) as a receiving antenna consists of a Fresnel zone plate lens (FZPL), a reflecting plate (reflector) placed a quarter wavelength from the FZPL and a conical horn for the receiver. Usually the FZPR uses the non-blocking offset configuration, by which the FZPL is composed from elliptical zones. The FZPR is also called an offset phase reversal zone plate reflector and is the object for study in this paper. The paper describes a calculation method for the characteristics of the FZPR based upon Kirchhoff's diffraction integral formula. The method shows how to determine an optimum position and diameter of the conical horn and calculates the relation between offset angles and receiving powers. Then the calculation method is verified by building and measuring four FZPRs with 90/spl deg/ offset angle and different focal length.