Dual microstrip antenna for rfid device

Abstract

Microstrip patch antenna ( 46 ), feed structure ( 48 ), and matching circuit ( 50 ) designs for an RFID tag ( 10 ) are disclosed. A balanced feed design using balanced feeds coupled by a shorting stub ( 56 ) creates a virtual short between the two feeds so as to eliminate the need for physically connecting the substrate to the ground plane. A dual feed structure design uses a four-terminal IC connected to two antennas ( 46 a, 46 b ) resonating at different frequencies to provide directional and polarization diversity. A combined near-field/far-field design using a microstrip antenna provides electromagnetic coupling for far-field operation, and a looping matching circuit provides inductive coupling for near-field operation. A dual-antenna design uses first and second microstrip antennas providing directional diversity when affixed to a cylindrical or conical object, and a protective superstrate ( 66 ) is applied. An annular antenna ( 46 c ) design for application to the top of a metal cylinder around a stem is disclosed.

1 . A radio frequency identification transponder comprising:
 a first layer including a substrate and a ground plane;   a second layer including—
 first and second microstrip patch antennas, with each patch antenna extending toward a different side of the second layer, 
 an integrated circuit, and 
 first and second matching circuits coupling the first and second microstrip patch antennas, respectively, to the integrated circuit. 
   
     
     
         2 . The radio frequency identification transponder as set forth in  claim 1 , wherein the first microstrip patch antenna extends toward a first side of the second layer, and the second microstrip patch antenna extends toward an opposite second side of the second layer, so as to achieve directional diversity. 
     
     
         3 . The radio frequency identification transponder as set forth in  claim 1 , further including a third layer including a superstrate protecting the second layer from an adverse condition of an operating environment. 
     
     
         4 . The radio frequency identification transponder as set forth in  claim 3 , wherein the superstrate of the third layer has a higher dielectric than the substrate of the first layer. 
     
     
         5 . The radio frequency identification transponder as set forth in  claim 4 , wherein the dielectric of the superstrate is less than 10. 
     
     
         6 . The radio frequency identification transponder as set forth in  claim 4 , wherein the dielectric of the superstrate is equal to or less than 6. 
     
     
         7 . The radio frequency identification transponder as set forth in  claim 3 , wherein the adverse condition is a physical impact. 
     
     
         8 . The radio frequency identification transponder as set forth in  claim 3 , wherein the adverse condition is a high temperature. 
     
     
         9 . The radio frequency identification transponder as set forth in  claim 1 , wherein the first and second layers are flexible so as to conform to a curved shape when applied thereto. 
     
     
         10 . In a radio frequency identification transponder for physical association with an object and for storing and communicating data regarding the object, the radio frequency identification transponder having an integrated circuit, the improvement comprising:
 a first layer including a substrate and a ground plane;   a second layer including—
 first and second microstrip patch antennas, with each patch antenna extending toward a different side of the second layer, 
 an integrated circuit, and 
 first and second matching circuits coupling the first and second microstrip patch antennas, respectively, to the integrated circuit; and 
   a third layer including a superstrate for protecting the second layer from an adverse condition of an operating environment.   
     
     
         11 . The radio frequency identification transponder as set forth in  claim 10 , wherein the first microstrip patch antenna extends toward a first side of the second layer, and the second microstrip patch antenna extends toward an opposite second side of the second layer, so as to achieve directional diversity. 
     
     
         12 . The radio frequency identification transponder as set forth in  claim 10 , wherein the superstrate of the third layer has a higher dielectric than the substrate of the first layer. 
     
     
         13 . The radio frequency identification transponder as set forth in  claim 12 , wherein the dielectric of the superstrate is less than 10. 
     
     
         14 . The radio frequency identification transponder as set forth in  claim 12 , wherein the dielectric of the superstrate is equal to or less than 6. 
     
     
         15 . The radio frequency identification transponder as set forth in  claim 10 , wherein the adverse condition is a physical impact. 
     
     
         16 . The radio frequency identification transponder as set forth in  claim 10 , wherein the adverse condition is a high temperature. 
     
     
         17 . The radio frequency identification transponder as set forth in  claim 10 , wherein the first, second, and third layers are flexible so as to conform to a curved shape when applied thereto. 
     
     
         18 . A radio frequency identification transponder comprising:
 a first layer including a substrate and a ground plane;   a second layer including—
 first and second microstrip patch antennas, with each patch antenna extending in a different direction, 
 an integrated circuit, and 
 first and second matching circuits coupling the first and second microstrip patch antennas, respectively, to the integrated circuit. 
   
     
     
         19 . The radio frequency identification transponder as set forth in  claim 18 , wherein the first microstrip patch antenna extends toward a first side of the second layer, and the second microstrip patch antenna extends toward an opposite second side of the second layer, so as to achieve directional diversity. 
     
     
         20 . The radio frequency identification transponder as set forth in  claim 18 , wherein the first and second layers are flexible so as to conform to a curved shape when applied thereto.