Jun-Seok Park

Effects of reader interference on the RFID interrogation range

In this paper, the effects of radio frequency identification (RFID) reader interference are investigated in terms of the interrogation range. In order to evaluate RFID interference quantitatively, the signal-to-interference ratio (SIR) equation is initially derived, and the interrogation-reduction range ratio (IRRR) defined. IRRR is a function of the distance between a desired reader and an interfering reader. Co-channel interference (CCI) and adjacent-channel interference (ACI) instances of IRRR are simulated. Simulation results show that reader-reader distances achieving 0 % IRRR, indicating no interference between the two readers, are 1200 m and 35 m for the CCI and ACI cases, respectively. The IRRR factor is inversely proportional to the reader-reader distance in both cases. The simulation results were also verified by measurement results using an ETRI UHF RFID system. Measurement results were found to be in good agreement with the simulation results. It can be concluded that the present simulation results are reliable and applicable in analyses of more complex interfering problems in actual RFID system deployment instances.

A Passive Circulator with High Isolation using a Directional Coupler for RFID

In radio-frequency identification (RFID) system, a directional coupler has been used to isolate RX from TX due to its simplicity and low cost compared with a circulator. Nevertheless, a conventional microstrip directional coupler has inherent drawback of poor isolation due to unequal phase velocity between even and odd mode. In this paper, a newly proposed circulator using a microstrip directional coupler is proposed to achieve good isolation between TX and RX. The proposed circulator is used for UHF band RFID reader with a single antenna, of which the operating frequency band is 860 MHz-960 MHz. The measurement of the fabricated circulator using a modified directional coupler exhibits excellent isolation of 64 dB and directivity of 49 dB in its frequency band. The validity of the proposed circulator is demonstrated by comparing the TX leakage at the RX port of RFID reader system with that of a conventional directional coupler

A novel defected ground structure for an active device mounting and its application to a microwave oscillator

This letter is to present a new defected ground structure (DGS), which is useful for mounting an active device, and its application to a microwave oscillator. The newly proposed DGS circuit is useful for mounting a transistor such as a BJT or field effect transistor (FET) on ground plane. In order to bias dc to a transistor, it is necessary to implement the dc isolated circuit in a practically applied active device with a DGS. For dc isolation, each branch of DGS should be isolated from ground. However, the proposed DGS structure with dc isolations introduces a degradation of gain performance for a transistor and changes the matching point. In order to overcome these limits, we have investigated a coupling method by using the simple coupling capacitor without degradations in RF performances. This letter displays the comparison of several measurements for the fabricated DGS circuits including the case that compensates the degradations due to the dc isolation. Furthermore, a design example of a microwave oscillator with the proposed DGS is demonstrated to show the validity of this letter.

Extending the Interrogation Range of a Passive UHF RFID System With an External Continuous Wave Transmitter

This paper introduces an interrogation enhancer (IE) as an external system that boosts a reader continuous wave (CW) with its auxiliary CW. The boosted reader CW powers the backscatters from a passive ultrahigh frequency radio frequency identification (UHF RFID) tag to reach the reader in extended range. The system performance is verified according to the measured ranges in practical tests. The IE permits the reader to successfully interrogate the tag in tripled or doubled range (e.g., 80-290 and 182-370 cm). The measurement results imply that the IE can be used for readers that may not transmit enough CW due to the local regulation or its limited battery capacity.

An advance design approach for circular polarization of the microstrip antenna with unbalance DGS feedlines

A novel design approach is offered to attain circular polarization of the microstrip antenna fed by unbalanced vertical feedlines. Usually, diagonally balanced-line feeds with hybrid couplers are used to attain circular polarization. Here, defected ground structures (DGSs) have been implemented under the unbalanced feedlines to achieve circular polarization. Adopting DGSs make it easy to tune antennas for circular polarization by varying the impedance of the feedlines.

TX Leakage Cancellation via a Micro Controller and High TX-to-RX Isolations Covering an UHF RFID Frequency Band of 908–914 MHz

A transmitter (TX) leakage cancellation scheme using a micro controller (MCU) is introduced. This letter highlights an adaptive anti-leakage signal generation via an MCU, which plays the key role in reducing the TX leakage signal level. High transmitter-to-receiver (TX-to-RX) isolation is verified with measurement results.

Robust design of dual band/polarization patch antenna using sensitivity analysis and Taguchi's method

In this paper, sensitivity analysis and Taguchis method are applied to the design of dual band patch antenna using gap coupling. The proposed structure uses T-slotted aperture coupling between patch and feed line of ground plane. Using sensitivity analysis, optimum dimensions of patch and coplanar waveguide (CPW) feed line are first sought. Then the optimized values are modified by Taguchis method in order to obtain robustness against the change of material constant and gap between patch and feed line. Moreover, the validity of the robust design has been tested with two antennas manufactured according to the final design. From the numerical and experimental results, it is confirmed that the final design is insensitive to noise factors.

A Passive Circulator for RFID Application with High Isolation using a Directional Coupler

In this paper, a newly invented circulator for T/R switch of UHF radio-frequency identification (RFID) application is proposed to overcome TX-to-RX leakage problem. A microstrip coupled-line directional coupler is used for this passive circulator and the isolation characteristic is drastically improved not by complex method such as compensating phase velocity, but by considering both directional coupler itself and imperfect input impedance of the employed antenna. The measurement result of the proposed circulator using modified microstrip coupled-line directional coupler with employed antenna shows excellent TX-to-RX leakage suppression in the 860 MHz - 960 MHz, more than 45 dB enhancement at the center frequency compared to the conventional coupler. Experimental verification using RFID system is also performed to prove the validity of the proposed circulator

A 900-MHz Direct-Conversion Transceiver for Mobile RFID Systems

A fully integrated 900-MHz direct-conversion transceiver for mobile RFID system is presented. The transceiver consists of a low noise amplifier, a down-conversion mixer, a band pass filter, and programmable gain amplifier (PGA) for RX path; and a power amplifier, an up-conversion mixer, a low-pass filter, and a PGA for TX path. In addition, the fractional N PLL is integrated to cover different frequency standards for different nations. The transceiver meets the dense reader environment specifications.

A novel modeling method for defected ground structure using adaptive frequency sampling and its application to microwave oscillator design

This paper demonstrates new systematic approaches to equivalent circuit model extraction for defected ground structure (DGS) directly from full-wave frequency domain simulation. The DGS circuits being modeled may be either lossy or lossless. Adaptive frequency sampling (AFS) is used to minimize the computational effort of electromagnetic (EM) simulation while critically assisting in determining the cutoff frequency and attenuation pole location of the DGS circuits. A simple circuit model for lossy DGS circuits without any optimization of lumped element component values is presented. Furthermore, lossless circuit model relative complex along with a determined starting point of optimization of lumped element values is also presented in detail. The overall results are an efficient and accurate means to produce the complete equivalent models of DGS circuit for the design of various RF and microwave circuits such as oscillators that may require the high accurate nonlinear design procedures.