Abstract: The present invention relates to a transponder comprising an antenna structure (31) configured to receive an incoming signal with RF power of a first frequency f1 and to retransmit the incoming signal as a transparent output signal with RF power of a second frequency f2 when hit by the incoming signal. The transponder further comprises: an amplifier (39) configured to provide an amplified transparent output signal based on the incoming signal; a frequency converter (35) configured to frequency convert the incoming signal into the transparent output signal; and a first frequency filter (33) connected to the antenna structure. The first frequency filter is tuned to the first frequency f1 to avoid amplifying incoming signals with RF power of frequencies other than the first frequency f1.

Abstract: The present invention relates to a transponder comprising an antenna structure (31) configured to receive an incoming signal with RF power of a first frequency f1 and to retransmit the incoming signal as a transparent output signal with RF power of a second frequency f2 when hit by the incoming signal. The transponder further comprises: an amplifier (39) configured to provide an amplified transparent output signal based on the incoming signal; a frequency converter (35) configured to frequency convert the incoming signal into the transparent output signal; and a first frequency filter (33) connected to the antenna structure. The first frequency filter is tuned to the first frequency f1 to avoid amplifying incoming signals with RF power of frequencies other than the first frequency f1.

Abstract: A passive transponder includes an antenna having two electrically conductive parts; a diode connected to the antenna; and a transmission line connected to the antenna and to the diode. The transmission line is adapted to match the impedance of the diode to an impedance of the antenna. The passive transponder, when hit by radio frequency (RF) power of a first frequency f1, retransmits RF power of a harmonic frequency fh. Each electrically conductive part of the antenna includes a flexible conductive thread having a first end and a second end, and the diode is connected to a first end of the flexible conductive thread. An item, such as a fabric or adhesive label, includes at least one passive transponder.