Compact Folded Dipolar Patch Antenna With Broad Tuning Range for On-Metal Tag Design

A compact dipolar patch antenna, which is embedded with a middle-layer patch internally, is proposed for designing an on-metal tag. Multiple tuning mechanisms have been employed for enabling frequency tuning over a wide bandwidth. First, the antenna’s shorting stubs are displaced diagonally to two opposite corners for lengthening the current paths. Then, the two patches are coupled capacitively for generating additional tuning reactance. Finally, multiple inductive slits have been incorporated with the patches for lowering the tag’s resonant frequency. Employment of the tuning mechanisms has successfully brought the tag resonance down to the UHF RFID passband. Notably, adjusting the slit length $(i_{2})$ allows the tag’s resonant frequency to be tuned across a broad range from 834 MHz to 964 MHz. Despite its compact size of $25\times 25\times 3.3$ mm3, the proposed tag can be read from a distance of 16 m (with 4W EIRP), which is much longer than most of the contemporary on-metal tags of this size.