Chean Khan Goh

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

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.

A Broadband UHF Near-Field RFID Antenna

A broadband segmented loop antenna is presented for ultra high frequency (UHF) near-field radio frequency identification (RFID) applications. Using a segmented line, the current distribution along the loop is kept in phase even though the perimeter of the loop is more than two operating wavelengths so that the proposed antenna generates strong and even magnetic field distribution in the near-field zone of the antenna. The antenna prototype, printed onto a piece of FR4 substrate, with an overall size of , achieves a large interrogation zone of with good impedance matching and uniform magnetic field distribution over the entire UHF RFID band of 840-960 MHz.

Electrically Large Dual-Loop Antenna for UHF Near-Field RFID Reader

An electrically large dual-loop antenna is proposed for ultra high frequency (UHF) near-field radio frequency identification (RFID) readers. The proposed antenna is composed of a main loop and a parasitic loop wherein the loops are constructed using segmented lines with distributed capacitors. The parasitic loop enhances and uniforms the magnetic field distribution in the central portion of the larger main loop so that the perimeter of interrogation zone of the dual-loop antenna can be extended up to three operating wavelengths. The measurement shows that a dual-loop antenna prototype printed onto a piece of FR4 printed circuit board (PCB) achieves good impedance matching over the frequency range of 845-928 MHz and produces strong and uniform magnetic field distribution with an interrogation zone of 250 mm 250 mm. A parametric study is carried out to provide the guidelines for the antenna design.

A segmented loop antenna for UHF near-field RFID

Radio frequency identification (RFID) is a technology that provides wireless identification and tracking capability and it is more robust than the bar code system [1]. A typical RFID system consists of at least a reader, a reader antenna, a host computer, a software system, and the tag (transponder) attached items. The reader communicates with the tag through the reader antenna. Radio signal emitted from the reader antenna is used to activate the tag. Data is encoded in the tag and it will be decoded once the tag passes through the electromagnetic zone. The signal coming from the reader must have enough power to power-up the tag for data processing. The data or information will be processed by the host computer with the software available in the computer.

Platform effect on RFID tag antennas and co-design considerations

In this paper, an UHF tag antenna is demonstrated to be co-designed with a plastic Sushi plate to achieve the conjugate impedance matching between the antenna and the ASIC. The reading range of the RFID system using such co-designed tag is greatly enhanced.

Measurement of UHF RFID tag antenna impedance

A methodology to measure UHF RFID tag antenna impedance using network approach is presented. The balanced UHF RFID tag antenna is considered as a two-port network and the impedance of the antenna is characterized by network parameters. In the measurement, the balanced antenna is connected to the two ports of a two-port vector network analyzer (VNA) through a test fixture. The influence of the test fixture is de-embedded by using a portextension technique and then the antenna impedance is extracted directly from the measured S-parameters. The proposed method is validated by comparing the measured and the simulated impedance of an asymmetrical dipole antenna and a symmetrical meander line dipole antenna both for UHF RFID tags.

A UHF near-field/far-field RFID metamaterial-inspired loop antenna

A metal-plate backed metamaterial-inspired loop antenna is proposed for both near-field and far-field radio frequency identification (RFID) applications at ultra high frequency (UHF). The antenna is composed of a distributed capacitor loaded segmented loop and a backed metallic plate. The antenna prototype printed onto an FR4 printed circuit board (PCB) with an overall size of 250 mm × 250 mm × 25 mm shows desirable performance for both near-field and far-field applications over the frequency range of 900-960 MHz. Hence, it is very promising for UHF RFID reader applications.

UHF near-field RFID reader antenna

A segmented loop antenna is presented for ultra high frequency (UHF) near-field radio frequency identification (RFID) applications. Even though the perimeter of the loop is comparable to the operating wavelength, the proposed segmented line configuration allows current along the loop to remain in phase so that a strong and uniform magnetic field is generated in the region surrounding the antenna. The antenna is printed on an FR4 printed circuit board (PCB) with an overall size of 160 mm × 180 mm × 0.5 mm. It achieves good impedance matching and uniform magnetic field distribution over an operating bandwidth of 800 - 1040 MHz which is desirable for UHF near-field RFID reader applications.

RF transmission in/through the human body at 915 MHz

The Medical Implant Communication Service (MICS), which was allocated by the Federal Communication Committee (FCC) on a shared, secondary basis in 1999, refers to a specification for using a frequency band between 402 to 405 MHz in communication with medical implants [1, 2]. It allows bi-directional radio communication with a pacemaker or other electronic implants. The maximum transmit power is limited to 25 µW, or −16 dBm, in order to reduce the risk of interfering with other users within the same band. The maximum usable bandwidth at any instant is 300 kHz, which makes it a low data rate system compared with WiFi (5.8GHz) or Bluetooth (2.4GHz). Other frequencies considered for implant communication include 915 MHz, 1.5 GHz, and 3.1–10.6 GHz ultra-wideband (UWB). The frequency band of 902–928 MHz is one of the Industrial, Scientific, and Medical (ISM) bands, commonly abbreviated as the 915 MHz ISM band. In this band, there are no restrictions to the application or the duty cycle. Furthermore, the allowed power output is considerably higher. Due to the lack of restrictions and higher allowed power, this band is very popular for unlicensed short range applications including audio and video transmissions. The FCC section 15.249 allows 50 mV/m of electrical field strength at a distance of 3 meters within the frequency band of 902–928 MHz. This corresponds to an EIRP of −1.23 dBm. A higher output power of up to 30 dBm is permitted if the system employs some form of spread spectrum such as frequency hopping or direct sequence spread spectrum since they are less likely to interfere with other systems and are also immune to interference from other systems.

RF transmission characteristics in/through the human body

In this paper, the RF transmission characteristics in/through human body are investigated experimentally and numerically. An experimental methodology to characterize the RF transmission of human body is presented. The proposed method addresses the challenge to characterize the RF transmission accurately and reliably without the body tissue effect on the antennas under test. The proposed methodology of using tissue-embedded antennas is validated at 403 MHz band (Medical Implant Communication Service, MICS).