Ikmo Park

Highly efficient photonic crystal-based multichannel drop filters of three-port system with reflection feedback

We have derived the general condition to achieve 100% drop efficiency in the resonant tunneling-based channel drop filters of a threeport system with reflection feedback. According to our theoretical modeling based on the coupled mode theory in time, the condition is that the Q-factor due to coupling to a bus port should be twice as large as the Q-factor due to coupling to a drop port and the phase retardation occurring in the round trip between a resonator and a reflector should be a multiple of 2pi. The theoretical modeling also shows that the reflection feedback in the threeport channel drop filters brings about relaxed sensitivity to the design parameters, such as the ratio between those two Q-factors and the phase retardation in the reflection path. Based on the theoretical modeling, a fivechannel drop filter has been designed in a two-dimensional photonic crystal, in which only a single reflector is placed at the end of the bus waveguide. The performance of the designed filter has been numerically calculated using the finite-difference time domain method. In the designed filter, drop efficiencies larger than 96% in all channels have been achieved.

Electromagnetically coupled small broadband monopole antenna

The paper presents a small broadband monopole antenna. The proposed structure consists of a circular disk-loaded monopole and a probe with a circular spiral strip line monopole. Broad bandwidth can be achieved through electromagnetic coupling between these two monopoles that generate two resonances closely spaced in frequency. The antenna occupies a cylindrical volume with a radius of /spl rho/ /spl cong/ 0.04/spl lambda//sub o/ (5.5 mm) and a height of h /spl cong/ 0.08/spl lambda//sub o/ (11 mm) and has 430 MHz of impedance bandwidth for VSWR<2 with a center frequency at 2.185 GHz, which is fractional bandwidth of approximately 19.7%. The gain of the antenna is more than 1.7 dBi within the entire bandwidth with good omnidirectional radiation characteristics.

Multi-Band, Wide-Beam, Circularly Polarized, Crossed, Asymmetrically Barbed Dipole Antennas for GPS Applications

This communication presents a multi-band, circularly polarized (CP), wide beamwidth, highly efficient antenna for use in global positioning systems (GPS). The primary radiating elements are two crossed printed dipoles, which incorporate a 90° phase delay line realized with a vacant-quarter printed ring to produce the CP radiation and broadband impedance matching. To achieve multiple resonances, each dipole arm is divided into four branches with different lengths, and a printed inductor with a barbed end is inserted in each branch to reduce the radiator size. An inverted, pyramidal, cavity-backed reflector is incorporated with the crossed dipoles to produce a unidirectional radiation pattern with a wide 3-dB axial ratio (AR) beamwidth and a high front-to-back ratio. The multi-band antennas have broad impedance matching and 3-dB AR bandwidths, which cover the GPS L1-L5 bands.

A T-shaped microstrip-line-fed wide slot antenna

We propose a simple feed structure for the wide rectangular slot antenna that can achieve a good impedance match over a wide frequency range. The feed structure is composed of a horizontal strip conductor connected at the end of the microstrip feed line. The proposed antenna is analyzed by using the finite difference time domain (FDTD) method. The measured result for the return loss of the antenna is also presented.

A novel wireless, passive CO2 sensor incorporating a surface acoustic wave reflective delay line

A 440 MHz wireless and passive surface acoustic wave (SAW) chemical sensor was developed for CO2 detection. The developed SAW gas sensor is composed of single phase unidirectional transducers (SPUDTs), three shorted grating reflectors, and CO2-sensitive polymer film on 41° YX LiNbO3 substrate. Coupling of modes (COM) modeling was used to find optimal design parameters. Using the extracted design parameters, the SAW device was fabricated. Teflon AF 2400 was used as the sensitive film because it provides high CO2 solubility, permeability and selectivity. In wireless device testing using a network analyzer, four sharp reflection peaks with high signal-to-noise (S/N) ratio, small signal attenuation, and few spurious peaks were observed in the time domain. The time positions of the reflection peaks were well matched with the predicted values from the simulation. Infusion of CO2 into the chamber induced large phase shifts of the reflection peaks. Good linearity and repeatability were observed for a CO2 concentration of 0–450 ppm. The obtained sensitivity was 1.98° ppm−1. Temperature and humidity effects were also investigated during the sensitivity evaluation process.

Higher order optical resonant filters based on coupled defect resonators in photonic crystals

In this paper, a general methodology for the design of higher order coupled resonator filters in photonic crystals (PCs) is presented. In the proposed approach, the coupling between resonators is treated as though it occurs through a waveguide with an arbitrary phase shift. The coupling through the waveguide is analyzed theoretically, based on the coupled-mode theory in time. The derived theoretical model suggests a way to extend an equivalent circuit approach, previously demonstrated with a certain value of a phase shift, to the higher order filter design with an arbitrary phase shift. The validity of the proposed approach is confirmed by the design of a third-order Chebyshev filter having a center frequency of 193.55 THz, a flat bandwidth of 50 GHz, and ripples of 0.3 dB in the passband. The characteristics of the designed filter are suitable for wavelength-division-multiplexed (WDM) optical communication systems with a 100-GHz channel spacing. The performance of the designed filter is numerically calculated using the two-dimensional (2-D) finite-difference time-domain (FDTD) method.

Design of a Circularly Polarized Tag Antenna for Increased Reading Range

We introduce a novel circularly polarized tag antenna, consisting of a truncated patch, a shorting plate, and a ground plane, to increase the reading range while remaining in compliance with EIRP regulations. The reading range of the proposed tag is twice that of linearly polarized tags, due to the decreased polarization mismatch between the reader and tag antennas. An additional parasitic patch is loaded onto the structure to boost the reading range in the UHF RFID band. As a result, an average reading range of 8 m is achieved between 860 MHz and 960 MHz, compared to a range of about 3 m with conventional dipole tags.

Compact Circularly Polarized Composite Cavity-Backed Crossed Dipole for GPS Applications

In this paper, we present a circularly polarized (CP) composite cavity-backed crossed dipole antenna for global positioning system (GPS) applications. We produce the CP radiation by crossing two dipoles through a 90° phase delay line of a vacant-quarter printed ring, which also has a broadband impedance matching characteristic. Two techniques, insertion of meander lines in the dipole arm and arrowhead-shaped trace at its end, are employed to reduce the sizes of the primary radiation element. The compact radiator is backed by a cavity reflector to achieve a wide CP radiation beamwidth. The proposed antenna exhibits a measured bandwidth of 1.450～1.656 GHz for a voltage standing wave ratio (VSWR) < 2 and 1.555～1.605 GHz for AR < 3-dB. At 1.575 GHz, the antenna has a gain of 7 dBic, a frontto-back ratio of 27 dB, AR of 1.18 dB, and 3-dB AR beamwidths of 130° and 132° in the x-z and y-z planes, respectively.

Crossed Dipole Loaded With Magneto-Electric Dipole for Wideband and Wide-Beam Circularly Polarized Radiation

A crossed dipole that is loaded with a magneto-electric dipole to produce the wideband and wide-beam circularly polarized radiation characteristics is proposed. The crossed dipole is incorporated with double-printed vacant-quarter rings to feed the antenna. The antenna is backed by a metallic cavity to provide a unidirectional radiation pattern with a wide axial-ratio (AR) beamwidth and a high front-to-back ratio. Experimental results showed that the prototype with an overall size of 120×120×30.5 mm3 has a |S11|<;-10 dB bandwidth of 1.274-2.360 GHz and a 3-dB AR bandwidth of 1.39-1.82 GHz. The antenna showed a right-hand circular polarization (CP) radiation with a very wide 3-dB AR beamwidth (>165°) and a high radiation efficiency (>94%) within the operational bandwidth.

Circularly Polarized Crossed Dipole on an HIS for 2.4/5.2/5.8-GHz WLAN Applications

A triband circularly polarized (CP) crossed-dipole antenna is introduced for 2.4/5.2/5.8-GHz wireless local area network (WLAN) applications. It employs a single feed and only two crossed trident-shaped dipoles as the primary radiating elements. To achieve a compact radiator size, two techniques are utilized, namely, insertion of a meander-line segment in the middle branch of the tridents and termination of all trident arms with arrowhead-shaped tips. The crossed trident-shaped dipoles are backed by a high impedance surface (HIS) to achieve a broadband characteristic and unidirectional radiation pattern at three bands. The measured impedance bandwidths, based on the -10-dB reflection coefficient values, are 2.21-2.62 GHz (410 MHz), 5.02-5.44 GHz (420 MHz), and 5.62-5.96 GHz (340 MHz), and the measured 3-dB axial-ratio bandwidths are 2.34-2.58 GHz (240 MHz), 5.14-5.38 GHz (240 MHz), and 5.72-5.88 GHz (160 MHz). The proposed antenna exhibits right-hand circular-polarized radiation with high gain.