In this paper, an experimental methodology for the characterization of the impedance of balanced RF identification (RFID) tag antennas is presented, and the application of the proposed method in RFID tag co-design is demonstrated. The balanced tag antenna is considered as a two-port network and the impedance of the antenna is characterized using network parameters. In the measurement, the antenna is connected to the two ports of a vector network analyzer through a test fixture. The influence of the test fixture is deembedded by using a port-extension technique and the antenna impedance can be extracted directly from the measured S -parameters. The proposed method is useful in practical RFID applications for co-designing the RFID tag with the attached platforms for enhancing the tag performance. An example of co-designing an ultra-high-frequency RFID tag with a plastic Sushi plate is demonstrated. The co-designed tag antenna achieves conjugate matching with the application-specific integrated circuit so that the reading range of the RFID tag is greatly enhanced.

Impedance Characterization of RFID Tag Antennas and Application in Tag Co-Design

Several compact, low profile and metal-attachable RFID tag antennas with a loop-fed method are proposed for UHF RFID systems. The structure of the proposed antennas comprise of two parts: (1) The radiator part consists of two shorted patches, which can be treated as two quarter-wave patch antennas or a cavity. (2) A small loop printed on the paper serves as the feeding structure. The small loop provides the needed inductance for the tag and is connected to the RFID chip. The input impedance of the antenna can be easily adjusted by changing loop dimensions. The antenna has the compact size of 80 mm × 25 mm × 3.5 mm, and the realized gain about dB. The measured results show that these antennas have good performance when attached onto metallic surfaces.

Compact Metallic RFID Tag Antennas With a Loop-Fed Method

A novel dual-layer electrically small radio-frequency-identification (RFID) tag antenna is proposed for metallic object applications. With a proximity-coupled feed method, two rotationally symmetric loaded via-patches are fed through an embedded dual-element planar inverted-F antenna (PIFA) array. With this configuration, the antenna volume is reduced to 0.08 λ×0.04 λ×0.007 λ while the measured antenna gain is 0.08 dBi at the frequency of 923 MHz. Studies demonstrate that the proposed antenna is a good candidate for ultra-high-frequency RFID tags to be mounted on metallic surfaces, especially in size-constrained scenarios. Meanwhile, a figure of merit, namely, NBG, is presented, with which a comparison among electrically small tag antennas is carried out. Finally, several guidelines are given out to facilitate the miniaturization of RFID tag antennas for metallic object applications.

A Novel Metal-Mountable Electrically Small Antenna for RFID Tag Applications With Practical Guidelines for the Antenna Design

A novel differentially fed dual-band implantable antenna is proposed for the first time for a fully implantable neuro-microsystem. The antenna operates at two center frequencies of 433.9 MHz and 542.4 MHz, which are close to the 402-405 MHz medical implant communication services (MICS) band, to support sub-GHz wideband communication for high-data rate implantable neural recording application. The size of the antenna is 480.06 mm3 (27 mm × 14 mm × 1.27 mm). The simulated and measured bandwidths are 7.3% and 7.9% at the first resonant frequency, 5.4% and 6.4% at the second resonant frequency. The specific absorption rate (SAR) distribution induced by the implantable antenna inside a tissue-mimicking solution is evaluated. The performance of the communication link between the implanted antenna and external half-wavelength dual-band dipole is also examined.

Differentially Fed Dual-Band Implantable Antenna for Biomedical Applications

This paper presents a method of antenna impedance measurement for RFID tag antenna based on a differential probe. The importance of accurate impedance measurement in optimal design of tag antenna, especially for the metal tags, is first addressed. Afterwards, an overview of the existing methods based on the single- ended probe and the balun probe is presented. The proposed method using the differential probe is explained based the well-known two port network model. Experiments for both balanced and unbalanced tag antenna measurement demonstrate the differential probe can provided better agreement with simulated results.

/pdf/an-accurate-method-for-impedance-measurement-of-rfid-tag-82digvz0f2.pdf

An accurate method for impedance measurement of rfid tag antenna

This paper presents a simple broadband network analyzer technique for measuring balanced loads, such as antennas, without a balun. The technique uses the normal two-port calibration of the network analyzer, which is extended by the addition of two short lengths of cable. From the measured data, a circuit model of the antenna impedances can be found, and both the balanced and unbalanced impedances are readily extracted. Measured and computed data are presented and compared.

/pdf/simple-broadband-measurements-of-balanced-loads-using-a-5e2f41t6ip.pdf

K.D. Palmer

Papers

Simple broadband measurements of balanced loads using a network analyzer