Transponder employing modulated backscatter microstrip double patch antenna

• US 5,771,021 A
• Filed: 10/31/1995
• Issued: 06/23/1998
• Est. Priority Date: 10/04/1993
• Status: Expired due to Term

• Current Assignee: Amtech Systems LLC (Roper Technologies, Inc.)
• Original Assignee: Amtech Corporation (McClarin Plastics LLC)
• Inventors: Veghte, Richard L., Koelle, Alfred R., Landt, Jeremy A., Carrender, Curtis L.
• Primary Examiner(s): Le, Hoanganh T.
• Application Number:
  US08/550,628
• Time in Patent Office: 966 Days
• Field of Search: 343/700 MS, 342/51, 342/175, 342/42, 342/44, 342/50
• US Class Current: 343/700.0MS
• CPC Class Codes: G01S 13/756 using a signal generator for modifying the reflectivity of the reflector G01S13/758 takes precedence
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
• CPC Class Codes: G06K 19/07786 the antenna being of the HF type, such as a dipole
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G06K 7/10316 using at least one antenna particularly designed for interrogating the wireless record carriers antennas in general H01Q1/22
• CPC Class Codes: G06K 7/10346 the antenna being of the far field type, e.g. HF types or dipoles
• CPC Class Codes: H01Q 1/247 with frequency mixer, e.g. for direct satellite reception or Doppler radar
• CPC Class Codes: H01Q 1/3233 particular used as part of a sensor or in a security system, e.g. for automotive radar, navigation systems
• CPC Class Codes: H01Q 1/38 formed by a conductive layer on an insulating support patch antennas H01Q9/0407; microstrip dipole antennas H01Q9/065; microstrip slot antennas H01Q13/106; transmission line microstrip antennas H01Q13/206; manufacturing reflecting surfaces using insulating material for supporting the reflecting surface H01Q15/142
• CPC Class Codes: H01Q 21/29 Combinations of different interacting antenna units for giving a desired directional characteristic H01Q25/00 takes precedence
• CPC Class Codes: H01Q 21/293 one unit or more being an array of identical aerial elements adaptive arrays H01Q3/2605
• CPC Class Codes: H01Q 3/44 varying the electric or magnetic characteristics of reflecting, refracting, or diffracting devices associated with the radiating element
• CPC Class Codes: H01Q 3/46 Active lenses or reflecting arrays
• CPC Class Codes: H01Q 9/0407 Substantially flat resonant element parallel to ground plane, e.g. patch antenna dipole H01Q9/285; monopole H01Q9/40
• CPC Class Codes: H01Q 9/0442 with particular tuning means

Abstract

A reader interrogates a transponder attached to a remote object. The transponder includes a microstrip patch antenna having two segments connected together by a switch, each segment being one-half wavelength, the antenna being a full wavelength at the frequency of the interrogating signal. In response to a control signal, the switch is opened and closed, thereby coupling and decoupling the two segments of the microstrip antenna. When the switch is in the closed position, the two segments are out-of-phase with one another, thereby producing a maximum reflected signal. When the switch is in the open position, the two segments act in concert to produce a minimum backscattered signal. The backscatter signal is thus modulated in accordance with the control signal and is received at the reader where it is subsequently decoded to identify the remote object.

Claims

1. A system including a reader and a transponder displaced from the reader for identifying an object associated with the transponder, said system comprising:

interrogating means at the reader for transmitting interrogating signals at an RF frequency to the transponder;

a microstrip patch antenna at the transponder for receiving the interrogating signals and for transmitting backscatter-modulated signals in response to the interrogating signals in accordance with a modulating signal produced by modulating means at the transponder, the modulating signal identifying the object associated with the transponder, the antenna comprising two one-half wavelength segments, at least one of which has an input line for receiving an external signal, connected together by a switch having a closed position and an open position, the antenna being full wavelength at the RF frequency, the two segments of the antenna being out-of-phase with each other when the switch is in the closed position, whereby a backscatter signal is reflected back to the reader, and the two segments of the antenna acting in concert when the switch is in the open position, whereby a minimum backscatter signal is reflected back to the reader;

and a switching circuit for actuating the switch between the open position and the closed position in response to the external signal.

2. A system according to claim 1 wherein each of the segments has linear polarization.

3. A system according to claim 1 wherein each of the segments has circular polarization.

4. A method of identifying a remote object using an interrogator and a transponder located at the remote object comprising the steps of:

transmitting an interrogating signal from the interrogator, the interrogating signal being at an RF frequency;

receiving the interrogating signal at the transponder, the transponder comprising a microstrip patch antenna, the microstrip patch antenna comprising two one-half wavelength segments, at least one of which has an input line for receiving an external control signal associated with the remote object, connected together by a switch having a closed position and an open position, the microstrip patch antenna being full wavelength at the RF frequency;

responding to the interrogating signal via a backscatter-modulated signal produced by the microstrip patch antenna, wherein when the switch is in the closed position, the two segments of the microstrip patch antenna are out-of-phase with each other, thereby producing a backscatter signal as seen by the reader, and when the switch is in the open position the two segments of the microstrip patch antenna act in concert, whereby a minimum backscatter signal is produced, the switch being opened and closed by a switching circuit in response to the external control signal associated with the remote object; and

receiving the backscatter-modulated signal at the reader and demodulating the backscatter-modulated signal to produce an identifying signal associated with the remote object.

5. A transponder comprising:

a modulator generating a control signal; and

a patch antenna coupled to the modulator for emitting backscatter-modulated signals at a fundamental frequency in response to a received signal, the patch antenna comprising two one-half wavelength segments, at least one of which has an input line for receiving an external signal, connected together by a switch having a closed position and an open position, the antenna being full wavelength at the fundamental frequency, the two segments being out-of-phase with each other when the switch is in the closed position, whereby a backscatter signal is emitted in response to the received signal, and the two segments of the antenna acting in concert when the switch is in the open position, whereby a minimum backscatter signal is emitted in response to the received signal, and the two segments of the antenna acting in concert when the switch is in the open position, whereby a minimum backscatter signal is produced in response to the received signal;

a switching circuit for actuating the switch between the open position and the closed position in response to the external signal;

wherein the switch opens and closes in response to the control signal.