Abstract: An antenna structure comprises a substrate, a first antenna unit and a second antenna unit. The substrate comprises a first surface and a second surface opposing the first surface. The first antenna unit is disposed on the first surface, and comprises at least a first slot with a wider inside and narrower outside at the edge of the first antenna unit. The second antenna unit is disposed on the second surface, and is connected to the first antenna unit through a hole in the substrate. The radius of the at least one first slot is one-fourth the wavelength of the central frequency of the antenna structure.

Abstract: The invention relates to a method for testing the authenticity of documents, in particular bank notes, documents of value or security documents, by authenticity criteria. To increase the reliability of authenticity testing of documents, at least two different authenticity classes each with one or more authenticity criteria are provided, the individual authenticity classes differing in at least one authenticity criterion. An authenticity class is selected from the different authenticity classes and the document tested by the authenticity criteria of the selected authenticity class. The document is assigned the selected authenticity class if the document meets the authenticity criteria thereof. This obtains higher reliability of authenticity testing since this method makes it possible to determine those documents that meet higher authenticity requirements, i.e. stricter authenticity criteria, than the other documents and are therefore authentic with higher probability.