Selectively coupling to feed points of an antenna system

• US 7,936,268 B2
• Filed: 08/31/2007
• Issued: 05/03/2011
• Est. Priority Date: 08/31/2007
• Status: Expired due to Fees

• Current Assignee: Round Rock Research LLC
• Original Assignee: Round Rock Research LLC
• Inventors: Tuttle, John R
• Primary Examiner(s): Lee; Benjamin C
• Assistant Examiner(s): King; Curtis J
• Application Number:
  US11/848,295
• Publication Number:
  US 20090058649A1
• Time in Patent Office: 1,341 Days
• Field of Search: 340/572.7
• US Class Current: 340/572.1
• CPC Class Codes: H01Q 1/2225 used in active tags, i.e. provided with its own power source or in passive tags, i.e. deriving power from RF signal

Abstract

Selectively coupling to feed points of an antenna system. At least some of the illustrative embodiments are systems comprising an antenna system, an antenna communication circuit, a first diode coupled between the antenna communication circuit and a first feed point of the antenna system, and a second diode coupled between the antenna communication circuit and a second feed point of the antenna system. The antenna communication circuit is configured to couple the antenna communication circuit to the first and second feed points by forward biasing the diodes.

Claims

1. A system comprising:

an antenna system having a single antenna structure, the single antenna structure having a first feed point coupled to a first capacitor, and a second feed point coupled to a second capacitor, wherein the first feed point transmits a first interrogation signal in response to a first antenna current and the second feed point transmits a second interrogation signal in response to a second antenna current;

an antenna communication circuit configured to output an alternating current signal having an average value of zero;

a first current source coupled to the antenna communication circuit and configured to output a first direct current signal responsive to an antenna selecting signal from the antenna communication circuit, wherein the first direct current signal has a greater magnitude than a peak-to-peak value of the alternating current signal;

a first diode coupled to the antenna communication circuit to receive the alternating current signal, and coupled to the first current source and the first capacitor, wherein the first diode is forward biased by the first direct current signal to output a first diode alternating current signal with a first direct current component to the first capacitor, the first capacitor removing the first direct current component from the first diode alternating signal to provide the first antenna current to the first feed point;

a second current source coupled to the antenna communication circuit and configured to output a second direct current signal responsive to an antenna selecting signal from the antenna communication circuit, wherein the second direct current signal has a greater magnitude than a peak-to-peak value of the alternating current signal; and

a second diode coupled to the antenna communication circuit to receive the alternating current signal, and coupled to the second current source and the second capacitor, wherein the second diode is forward biased by the second direct current signal to output a second diode alternating current signal with a second direct current component to the second capacitor, the second capacitor removing the second direct current component from the second diode alternating signal to provide the second antenna current to the second feed point.

2. The system according to claim 1 wherein the antenna structure further comprises:

a radiative patch that defines a perimeter; and

a ground element, the radiative patch parallel and proximate to the ground element;

wherein the first and second feed points are one or more selected from the group consisting of;

within the perimeter; and

disposed on the perimeter.

3. The system according to claim 1 wherein the antenna structure further comprises:

a first antenna having a first polarization when the first feed point is used; and

a second antenna having a second polarization when the second feed point is used.

4. The system according to claim 1 wherein the antenna communication circuit is one or more selected from the group consisting of:

a radio frequency identification (RFID) reader; and

a RFID circuit within an RFID tag.

6. The system according to claim 1 wherein the antenna communication circuit is a radio frequency identification (RFID) reader;

and the system further comprises a RFID tag communicatively coupled to the RFID reader.

7. The system according to claim 6 wherein the RFID tag further comprises:

a tag antenna having a plurality of third feed points;

a RFID circuit; and

a plurality of third diodes, wherein at least one of the third diodes is coupled between each of the plurality of third feed points and the RFID circuit;

wherein the RFID circuit is configured to selectively apply an antenna signal to the tag antenna through at least one of the third diodes.

8. The system according to claim 7 wherein when the RFID circuit selectively applies the antenna signal the RFID circuit is configured to apply a bias current to a selected one of the plurality of third diodes.

9. The system according to claim 7 further comprising a power source coupled to the RFID circuit.

5. A semiconductor device comprising:

a substrate;

a first diode engaging the substrate, wherein the first diode is coupled to a first feed point of a single antenna structure of an antenna system, the first feed point transmitting a first interrogation signal in response to a first antenna current;

a first capacitor disposed between the first diode and the first feed point;

a second diode engaging the substrate, wherein the second diode is coupled to a second feed point of the single antenna structure of the antenna system, the second feed point transmitting a second interrogation signal in response to a second antenna current;

a second capacitor disposed between the second diode and the second feed point;

a radio frequency identification (RFID) circuit engaging the substrate, wherein the RFID circuit comprises an antenna signal line coupled to the first and second diodes, the RFID circuit outputting to the antenna signal line an alternating current signal having an average value of zero; and

a current source coupled to the RFID circuit, the first and second diodes, and the first and second capacitors, wherein the current source is configured to output a direct current signal having a greater magnitude than a peak-to-peak value of the alternating current signal, the first and second diodes being forward biased by the direct current signal responsive to a respective antenna selecting signal from the RFID circuit,

wherein the forward biased first diode outputs a first diode alternating current signal with a first direct current component to the first capacitor, the first capacitor removing the first direct current component from the first diode alternating signal to provide the first antenna current to the first feed point, and

wherein the forward biased second diode outputs a second diode alternating current signal with a second direct current component to the second capacitor, the second capacitor removing the second direct current component from the second diode alternating signal to provide the second antenna current to the second feed point.

10. A method comprising:

outputting an alternating current signal from an antenna communication circuit to a first diode and to a second diode, wherein the alternating current signal has an average value of zero;

selectively coupling the antenna communication circuit to first and second feed points of an antenna system, wherein the first feed point is coupled to the first diode and the second feed point is coupled to the second diode and the first and second diodes are coupled to the feed points through a first capacitor and second capacitor, respectively, the selectively coupling comprising;

selectively applying a constant first forward biasing current to forward bias the first diode to select communication through the first feed point such that the first diode outputs a first diode alternating current signal with a first direct current component, wherein the constant first forward biasing current has a greater magnitude than a peak-to-peak value of the alternating current signal;

removing the first direct current component from the first diode alternating current signal with the first capacitor resulting in a first antenna current being provided to the first feed point;

selectively applying a constant second forward biasing current to forward bias the second diode to select communication through the second feed point such that the second diode outputs a second diode alternating current signal with a second direct current component, wherein the constant second forward biasing current has a greater magnitude than a peak-to-peak value of the alternating current signal; and

removing the second direct current component from the second diode alternating current signal with the second capacitor resulting in a second antenna current being provided to the second feed point.

11. The method according to claim 10 wherein selectively coupling further comprises selectively coupling the antenna communication circuit to a patch antenna embodying said first and second antennas and having the first and second feed points.

12. The method according to claim 10 wherein selectively coupling further comprises selectively coupling the antenna communication circuit to at least one selected from the group consisting of:

a first antenna having the first feed point; and

a second antenna having the second feed point.

13. The method according to claim 10 wherein the antenna communication circuit is a radio frequency identification (RFID) reader.

14. The method according to claim 10 wherein the antenna communication circuit is a radio frequency identification (RFID) circuit.