Complementarily Coupled C-Shaped Microstrip Patches With Wide-Range Frequency Tuning Capability for Metal-Applicable UHF RFID Tag Design

A single-layer patch antenna, which is constructed using two complementarily placed C-shaped patches, has been proposed for designing a metal-mountable tag with a wide range of frequency tuning capability. The two patches are closely coupled for generating sufficient antenna reactance, which is in turn employed as a tuning mechanism. With only the employment of this tuning mechanism, the tag’s resonant frequency can be successfully tuned over a broad range covering 920 MHz–1.18 GHz without using any other external lumped components, shorting stubs, or vias. Good read performance is sustainable as the tuning can be performed without changing the antenna structure much. A transmission line model has also been constructed for the design and characterization processes. The proposed tag is compact ( $0.154\lambda \times 0.154\lambda \times 0.010\lambda$ ), and it can be read from ~9 m with 3.28 W effective isotropic radiated power (EIRP).