US 4,816,839 A · Transponder antenna

Abstract

An antenna in a transponder receives signals from a reader, modulates them, and reflects them back to a reader to pass the information contained in the transponder to the reader. The system includes a thin planar dielectric material having first and second opposite surfaces, preferably with the approximate dimensions of a credit card. First conductive material is disposed on the first surface of the dielectric member at a first end of the member. Second conductive material on the second opposite surface of the dielectric member at the second end of the member defines a dipole with the first material. The second material, preferably triangular in configuration, extends from the second end to a median position between the opposite ends. An electrical circuitry module on the dielectric member produces reflected signals modulated at a particular frequency from the signal transmitted by the reader to pass information contained in the transponder to the reader. The third conductive material on the second surface of the member is electrically coupled with the second conductive material and extends from the triangular apex toward the first end to enhance an impedance match between the dipole and electrical circuitry. The third material has a first low impedance portion split into two parts connected in parllel to provide an extended effective length in a relatively small distance, and has a second portion, preferably a "pigtail", of substantially higher impedance than the first portion connected in series with the first portion.

Claims21

Dependent claims

In a transponder which includes a dipole antenna, a signal-modulating module and an impedance-matching module for matching the impedance of said antenna to that of said signal-modulating module, the improvement comprising:

a transmission line coupled between said dipole antenna and said impedance-matching module having a first portion having an impedance lower than that of said dipole antenna and a predetermined width comprised of two oppositely disposed parts connected in parallel, and a second substantially narrower portion with substantially higher impedance than the impedance of said first portion, connected in series with said first portion.

In combination in an antenna in a transponder for transmitting signals to a reader containing information from the transponder,

a planar dielectric member having first and second opposed surfaces,
first conductive material on the first surface of the dielectric member at one end of the dielectric member,
second conductive material on the second opposed surface of the dielectric member at the other end of the dielectric member,
the first and second conductive materials being separated from each other in the direction between the first and second ends of the dielectric member by a distance to define a dipole having a first impedance,
a split conductive path extending from the end of the second conductive material nearer to the first conductive material to a portion over the first conductive material, the split conductive path defining a second impedance less than the impedance of the dipole antenna at the junction with the second conductive material, and
a pigtail extending from the split conductive path and defining a third impedance greater than the second impedance.

3 more elements

In combination in an antenna in a transponder for receiving signals from a reader and for modulating and reflecting said signals back to the reader to pass information from the transponder to the reader,

a planar dielectric member having first and second opposite surfaces,
a first conductive material on the first surface of the dielectric member at a first end of the dielectric member,
a second conductive material on the second surface of the dielectric member at a second end of the dielectric member opposite the first end of the dielectric member to define a dipole with the first conductive material,
the lengths of each of the first and second opposed ends of the dielectric material defining less than a quarter of a wavelength at the frequency at which the dipole is to be operated, and
means disposed on the dielectric material and electrically contiguous with the second conductive material for reducing the capacitive impedance of the antenna to compensate for the additional capacitive impedance resulting from the length of each of the first and second conductive materials being less than a 1/4 of a wavelength.

2 more elements

Dependencies are inferred from the claim text.

Transponder antenna

Life of this patent

Transponder antenna

Life of this patent

Abstract

Claims21