ARTICLE IDENTIFICATION APPARATUS AND METHOD

摘要

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