UHF-band inductively-coupled RFID antenna with near-isotropic radar cross section patterns

This paper presents a RFID tag antenna at 911 MHz which has near-isotropic radiation patterns and easy conjugate impedance matching property by adopting an inductively- coupled feeding. With a typical antenna impedance of 2+j146Omega, the proposed tag of compact size 40 x 46 mm(0.12x0.14lambda) has the simulated maximum and minimum RCS' of -16.75 dBm 2 and -21.47dBm 2 , respectively, depending on the incident angles. The difference of about 4.7 dB (3.0 in measurement) is very small compared with that (about 70dB~80dB) of dipole-type tags. The designed antenna has been fabricated and its RCS' have been measured varying the angles of incidence. The measured RCS' have been found to have good agreement with the simulated ones.