Antenna for a backscatter-based RFID transponder
View Patent ↗An antenna for a backscatter-based RFID transponder is provided that has an integrated receive circuit having a capacitive input impedance for receiving a radio signal spectrally located in an operating frequency range. The antenna includes two antenna branches that extend outward from a connecting region in which the antenna branches can be connected to the integrated receive circuit, and a yoke-shaped first trace segment that is designed to connect the two antenna branches together. Each antenna branch can have a U-shaped second trace segment connected to the connecting region, and a U-shaped third trace segment connected to the second trace segment and extending parallel to the second trace segment. The invention further relates to a backscatter-based RFID transponder with such an antenna.
1. An antenna comprising:
two branches that each extend outward from a connecting region where the branches are connected to an integrated receive circuit of a backscatter-based radio frequency identification (RFID) transponder, each of the branches comprising a first trace segment connected to the connecting region and a second trace segment connected to the first trace segment, each of the second trace segments extending substantially parallel to its first trace segment, each of the first and second trace segments being substantially U shaped, each of the first and second trace segments being formed from three legs, each of the legs of each the first trace segments being spaced apart from an adjacent one of the legs of its second trace segment; and
a third trace segment that connects the two branches to each other, the third trace segment being substantially yoke shaped;
wherein, in each of the branches:
each of the first and second trace segments has a first end and a second end;
the first end of the first trace segment is connected to the first end of the second trace segment;
the second end of the first trace segment is connected to the second end of the second trace segment; and
the second end of the first trace segment or the second trace segment is connected to the connecting region.
2. The antenna of claim 1 , wherein the first and second trace segments of the same antenna branch extend at a substantially constant spacing from one another.
3. The antenna of claim 1 , wherein, in each of the branches:
the first trace segment forms an inner area and the second trace segment is located in the inner area; or
the second trace segment forms the inner area and the first trace segment is located in the inner area.
4. The antenna of claim 1 , wherein the first and second trace segments are each piecewise linear.
5. The antenna of claim 1 , wherein each of the first and second trace segments has a first trace width.
6. The antenna of claim 5 , wherein the third trace segment has a second trace width that is smaller than the first trace width.
7. The antenna of claim 1 , wherein, at least in part because of one or more design aspects of the third trace segment, the antenna has an inductive input impedance in an operating frequency range that approximates complex conjugate values of a capacitive input impedance of the integrated receive circuit, substantially obviating a circuit arrangement for impedance matching between the antenna and the integrated receive circuit.
8. The antenna of claim 1 , wherein, at least in part because of one or more design aspects of the third trace segment, the antenna has values of an inductive input impedance in an operating frequency range with its real component below 35 ohms and its imaginary component having a magnitude above 170 ohms.
9. The antenna of claim 1 , wherein each of the branches comprises a fourth trace segment that connects the connecting region to the first trace segment of the branch, the fourth trace segment being substantially serpentine in shape.
10. The antenna of claim 9 , wherein the third trace segment connects the fourth trace segments of the two branches to one another.
11. The antenna of claim 9 , wherein, in each of the branches, the second end of the first trace segment or the second end of the second trace segment is connected to an end of the fourth trace segment that faces away from the connecting region.
12. The antenna of claim 9 , wherein:
the fourth trace segment has a first trace width;
each of the first trace segments has a second trace width; and
each of the second trace segments has a third trace width;
the first trace width being smaller than the second or third trace width.
13. The antenna of claim 12 , wherein the first trace width is substantially equal to a fourth trace width of the third trace segment.
14. The antenna of claim 1 , wherein the antenna further comprises a fourth trace segment that connects the second ends of the second trace segments to one another.
15. The antenna of claim 1 , wherein the branches are substantially symmetrical to one another in shape.
16. The antenna of claim 1 , wherein the branches are substantially planar in design and substantially lie in a common plane.
17. The antenna of claim 1 , wherein the antenna is an electrically small antenna.
18. The antenna of claim 1 , wherein an operating-frequency range of the antenna lies in the UHF or microwave frequency range.
19. The antenna of claim 1 , wherein, at least in part because of one or more first design aspects of the first and second trace segments, the antenna has an input impedance in an operating-frequency range with an inductive reactance that has a frequency response with an inflection point in the operating-frequency range.
20. The antenna of claim 19 , wherein, at least in part because of one or more second design aspects of the first and second trace segments, the frequency response of the reactance has a local maximum value or a local minimum value within the operating-frequency range.
21. The antenna of claim 20 , wherein the one or more first design aspects and the one or more second design aspects comprise the same one or more design aspects.
22. The antenna of claim 19 , wherein, at least in part because of trace lengths along the first and second trace segments, the frequency response of the reactance has an inflection point, a local maximum value, or a local minimum value in the operating frequency range.
23. A transponder comprising:
an integrated receive circuit with a capacitive input impedance; and
an antenna connected to the integrated receive circuit, the antenna comprising:
two branches that extend outward from a connecting region where the branches are connected to the integrated receive circuit, each of the branches comprising a first trace segment connected to the connecting region and a second trace segment connected to the first trace segment, each of the second trace segments extending substantially parallel to its first trace segment, each of the first and second trace segments being substantially U shaped, each of the first and second trace segments being formed from three legs, each of the legs of each the first trace segments being spaced apart from an adjacent one of the legs of its second trace segment; and
a third trace segment that connects the two branches to each other, the third trace segment being substantially yoke shaped;
wherein, in each of the branches:
each of the first and second trace segments has a first end and a second end;
the first end of the first trace segment is connected to the first end of the second trace segment;
the second end of the first trace segment is connected to the second end of the second trace segment; and
the second end of the first trace segment or the second trace segment is connected to the connecting region.
24. The transponder of claim 23 , wherein the integrated receive circuit is located in the connecting region of the antenna.
25. The transponder of claim 23 , wherein each of the branches comprises a thin conductive layer that is formed on a substrate and the integrated receive circuit is formed on the substrate.