Abstract: A radio-frequency identification (RFID) transponder (tag) in accordance with the principles of the invention includes a patch antenna. The patch antenna may be co-located with RFID circuitry and an impedance matching circuit on one side of a substrate. A ground plane may be formed on the opposite side of the substrate. A quarter wave transformer may provide an “RF short” to ground to connect the RFID circuitry on one side of the substrate with a ground plane located on the opposite side of the substrate.

Abstract: An impedance matching circuit in accordance with the principles of the present invention employs series-connected transmission lines to match a high reflection coefficient source impedance with a load impedance. The matching circuit is formed on a dielectric substrate material and accommodates the relatively limited capabilities of photo-lithographic circuit production. The new impedance matching circuit may be constructed of three series-connected transmission line sections. A first section, the section that is to be connected to the source, transforms the high source impedance into a relatively low valued impedance that is substantially resistive. The reflection coefficient of the first section is substantially equal to the reflection coefficient of the source. A second may be implemented as a quarter-wave transformer that transforms the low impedance developed by the first section into an intermediate impedance value.