Design of a Zeroth Order Resonator UHF RFID Passive Tag Antenna with Capacitive Loaded Coplanar Waveguide Structures

The use and development of Radio Frequency Identification (RFID) systems has undergone substantial growth in the past decade in many new areas. Some of these areas include wire‐ less sensor systems, metamaterials and compact antennas [1-8]. However, much of this new growth has required more performance from traditional passive RFID systems. In particu‐ lar, the need for more compact antennas with performances comparable to much larger res‐ onant antennas is one such condition. To fulfill the requirements of compact antennas, researchers have developed various novel RFID antenna designs [2-4], including metamate‐ rial-based RFID antenna designs [1,5-8] to improve the performance of RFID systems. Using composite right/left-handed (CRLH) transmission line (TL) based metamaterials to show the unique property of zeroth-order resonance (ZOR) [9,10] is one such method to reduce the overall size of an antenna. More specifically, a ZOR-TL can be used to make an electrically small antenna to appear electrically large; which leads to improved matching and radiation properties. This is done by producing a zero phase constant at a non-zero frequency (i.e. the wavelength of the travelling wave becomes infinite) on the TL. This is a unique property which makes the resonance condition independent from the physical dimensions of the an‐ tenna or TL [11-13] so it can be used to design miniature antennas for passive UHF RFID applications. The resonance of such antennas at any operating frequency only depend on its CRLH characteristics to acquire ZOR at that frequency and less to do with the physical di‐ mensions of corresponding antenna.