Patent ID: 6885342

Claim:
An antenna for sending and receiving microwave radiation for use in a transponder system for wireless toll payment, comprising: a dielectric antenna supporter ( 11 ) having a bearing surface ( 12 ), a frame shaped or loop shaped excited antenna element ( 13 ) extending in a first plane disposed on the dielectric antenna supporter bearing surface ( 12 ), a polarization transformer ( 22 ), wherein the excited antenna element is linearly polarized and disposed at a predetermined distance from the polarization transformer ( 22 ) to transform linearly polarized radiation to circular or elliptical polarized radiation, and wherein the polarization transformer ( 22 ) operates as a director, a reflector disposed at a predetermined distance from the excited antenna element, at least one parasite element or director placed in a predetermined distance from the excited antenna element, wherein the frame or loop antenna comprises two substantially equal shaped frames or loops placed at a predetermined distance, and a diode ( 25 ) connected to the frames or loops ( 14 , 15 ) for demodulation, and a capacitor ( 23 ) connected to the frames or loops ( 14 , 15 ).