Youn-Kwon Jung

Dual-Band Circularly Polarized Microstrip RFID Reader Antenna Using Metamaterial Branch-Line Coupler

A dual-band circularly polarized aperture coupled microstrip RFID reader antenna using a metamaterial (MTM) branch-line coupler has been designed, fabricated, and measured. The proposed antenna is fabricated on a FR-4 substrate with relative permittivity of 4.6 and thickness of 1.6 mm. The MTM coupler is designed employing the provided explicit closed-form formulas. The dual-band (UHF and ISM) circularly-polarized RFID reader antenna with separate Tx and Rx ports is connected to the designed metamaterial (MTM) branch-line coupler. The maximum measured LHCP antenna gain is 6.6 dBic at 920 MHz (UHF) and RHCP gain is 7.9 dBic at 2.45 GHz (ISM). The cross-polar CP gains near broadside of the RFID reader antenna are approximately less than - 20 dB compared with the mentioned co-polar CP gains in both bands. The isolations between the two ports are about 25 dB and 38 dB, at 920 MHz and 2.45 GHz, respectively. The measured axial ratios are less than 0.7 dB in the UHF band (917-923 MHz) and 1.5 dB in the ISM band (2.4-2.48 GHz).

Metamaterial-inspired loop antennas for wireless power transmission

The concept of wireless power transmission (WPT) was initiated by N. Tesla in 1914[1]. The efficient non-radiative power transfer was demonstrated by the experiment [2]. This article shows that the efficiency of the power transfer is about 40 % in 2meters (V15) at 9.9MHz employing two single loops and two helical coils for resonance. In this paper, we provide a thin WPT system mountable on any flat objects. Two metamaterial-inspired [3–6] loop antennas compose the WPT system. The metamaterial-inspired antenna is for a uniform current distribution using capacitive loadings [7], which significantly increases the magnetic field intensity in the loop. The performance of the proposed WPT system is evaluated in various environments to investigate its usefulness for short range power transmission.

Wireless Power Transmission between Two Metamaterial-Inspired Loops at 300 MHz

Based on a provided closed-form wireless power transmission (WPT) efficiency formula, which may be used for any value of load, we have analyzed the WPT efficiencies between two metamaterial-inspired loop antennas in various aspects. Due to the modeling based on low frequency circuit theory, the provided formula at the center resonant frequency has been found to be accurate until when the distance between the two loop antennas increases to 15 cm (about λ0/6 at 300 MHz). When the two loops get closer, the resonant frequency has been found to split into two in theory, simulations, and measurements. The EM-simulated and measured efficiencies at new resonant frequencies are 60.9 % and 46.3 %, respectively, at d=15 cm. With two extra rings around the loops, the maximum efficiency is enhanced to 93.7 % at d=15 cm. The effect of the additional two rings is about 30 %.

Design of adaptive optimal load circuit for maximum wireless power transfer efficiency

An adaptive optimal load circuit (ALC) for the maximum wireless power transfer (WPT) efficiency is presented for a magnetically coupled resonant WPT system at 13.56 MHz. The ALC is based on the lumped-element matching circuit. The series part is composed of a series capacitor block and an inductor. The shunt part is composed of a varactor and a capacitor block with switches. The tunable range of the optimal load impedance is from 0.2 to 50 Ω. The provided examples demonstrate the usefulness and effectiveness of the ALC to achieve the maximum efficiency.

Beam scannable patch array antenna employing tunable metamaterial phase shifter

A beam scannable 4-patch array antenna using three tunable metamaterial (MTM) phase shifter has been designed and simulated. For this work, a shunt inductor required for a MTM unit cell is realized by a chip varactor and a quarter wave impedance transformer. The proposed phase shifter consists of four meta-unit cells. The phase shifting range of the tunable MTM phase shifter is about 140 °. The 10 dB bandwidth and the maximum gain of the antenna are 14 MHz and 12.7 dBi, respectively. The scanning range of the antenna is about 43 °.

Compact Metamaterial-Based Tunable Zeroth-Order Resonant Antenna with Chip Variable Capacitor

This letter presents a compact metamaterial-based tunable zeroth-order resonant antenna. It is based on the double-negative unit cell with a function of tunable inductance realized by a varactor and impedance convertor in the shunt branch. The resonant frequency of the designed antenna ranges from 2.31 to 3.08 GHz, depending on the capacitance of the used varactor. Its size is very compact (0.05 λ0×0.2 λ0) with a relatively wide tunable range of 29.1%. The impedance bandwidth of the antenna is from 20 to 50 MHz for the resonant center frequency. The measured maximum total realized gain is from 0.68 dBi (2.43 GHz) to 1.69 dBi (2.97 GHz). The EM-simulated and measured results are in good agreement.

Capacitively loaded loop antenna fed by wideband metamaterial balun

A capacitively loaded loop antenna fed by a wideband balun has been designed for a possible use as a near field RFID UHF reader. The balun bandwidth is about 88 % based on phase balance and the loop antenna bandwidth is approximately 6.5 %. The simulated current distribution on the capacitively loaded loop antenna is quite uniform to ensure high magnetic field intensity at the loop center.

Compact Metamaterial-Based Tunable Phase Shifter at 2.4 GHz

A compact metamaterial (MTM)-based tunable phase shifter consisting of four unit cells with a simple DC bias circuit has been designed at 2.4 GHz. The variable series capacitors and shunt inductors that are required to be loaded periodically onto a host transmission line are realized employing only chip variable capacitors (varactors). In addition, the proposed phase shifter requires only one DC bias source to control the varactors, with the matching condition of the MTM line automatically satisfied. The measured phase shifting range is 285.2° (from —74.2° to 211°). The measured insertion loss is approximately 1.5 dB. The circuit/electromagnetic-simulated and measured results are in good agreement.

Capacitively Loaded Loop Antenna Fed with Metamaterial Balun

This paper presents a balun consisting of a T-junction, a Right/Left Handed Transmission line(RLH-TL), and a conventional Right Handed(RH) line. It is assumed that the RLH-TL consists of N unit-cells. We provide closed-form solutions and design a very compact wideband(80 %) balun using CPW lines based on the obtained solutions. Then, we propose a capacitively loaded loop antenna designed for a uniform current distribution. The antenna resistance of the proposed antenna at resonance is about 204 ohms. The length of the unit cell is about (total length: ). The magnetic field generated from the proposed antenna is stronger than that of the conventional one by as much as 20 dB. We used a coplanar strip line(CPS) to combine the loop antenna and balun. The proposed antenna may be used as a near field UHF RFID reader antenna.