| 摘要 |
Apparatus for the identification of articles (5) endowed with device for changing the polarization properties of the radiation, comprising a source (1) of non-randomly polarized microwave radiation, and a detector (3) for detecting the change in polarization properties of the radiation. The microwave radiation may have a first plane of polarization and, in use, the device for changing the plane of polarization properties of radiation may change the first plane of polarization to a second plane of polarization. The detector (3) for detecting the change in polarization properties of radiation may comprise a receiving antenna (4c) connected to suitable microwave detector (3), where the receiving antenna (4c) is arranged to favour reception of radiation having the second plane of polarization. For example, the transmitting (4b) and receiving (4c) antennas may be waveguide antennas. The device for changing the polarization of radiation may comprise a feature having an edge oriented at a nonzero angle to a direction parallel with, or orthogonal to, the first plane of polarization. Typically, the feature may be a linear metallic strip, or may be a feature having a crossed dipole antenna structure. The apparatus may also comprise a device for determining the orientation of the feature or features. The polarization changing device may also comprise a covert structure for preventing the changing of the polarization properties by the polarization changing device in one or more selected location, wherein the arrangement of the one or more selected location provides an identification code. |
