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Ikmo Park,Huy Hung Tran,Son Xuat Ta 한국전자파학회JEES 2014 Journal of Electromagnetic Engineering and Science Vol.14 No.3
A wideband circularly polarized (CP) antenna with a single feed is proposed for use in global navigation satellite systems. Its primary radiation elements are composed of two orthogonal bowtie dipoles, which are equipped with double-printed vacant-quarter rings to allow direct matching of the antenna to a single 50-Ω coaxial line and to produce CP radiation. The crossed bowtie dipole is appropriately incorporated with a planar metallic reflector to produce the desired unidirectional radiation pattern as well as to achieve a wideband characteristic in terms of impedance matching and axial ratio (AR) bandwidths. The designed antenna was fabricated and measured. The prototype antenna with an overall 1.2-GHz frequency size of 0.48 λo×0.48 λo×0.25 λo produced a measured |S11|<-10 dB bandwidth of 1.05-1.79 GHz and a measured 3-dB AR bandwidth of 1.12-1.64 GHz. It also showed right-hand CP radiation with a small gain variation (±0.3 dB) and high radiation efficiency (>93%) over the operational bandwidth.
Aperture-Coupled Quarter-Wavelength Microstrip Antenna
Ikmo Park 한국정보과학회 1999 Journal of Electrical Engineering and Information Vol.4 No.1
The aperture-coupled quarter-wavelength microstrip antenna is described in this paper. The antenna is formed on a substrate above the ground plane by short-circuiting the microstrip radiating element with a shorting pin to the ground plane. The antenna is fed by microstrip feedline through an electrically small aperture. With this structure, the size of the antenna can be significantly reduced and it enables ease of manufacturing of the antenna. Measured return loss and radiation pattern as well as the computed results using the FDTD method are presented and discussed.
Single-Feed Composite Cavity-Backed Four-Arm Curl Antenna
Ikmo Park,Son Xuat Ta 한국전자파학회JEES 2014 Journal of Electromagnetic Engineering and Science Vol.14 No.4
A single-feed composite cavity-backed four-arm curl antenna is presented for use in global positioning system (GPS). Its primary radiating element is fed by a vacant-quarter printed ring, which helps the antenna directly match to a 50- Ω coaxial line and produce a good circular polarization (CP). The cavity-backed reflector is employed to improve the CP radiation characteristics in terms of 3-dB axial ratio (AR) beamwidth and minimum AR value. The optimized design with an overall size of 90 x 90 x 25㎣ (0.4725 λ? x 0.4725 λ? x 0.13 λ? at 1.575 MHz). results in a |Su|〈-10 dB bandwidth of 8.66%(1,514-1,651 MHz) and a 3-dB AR bandwidth of 2.23% (1,555-1,590 MHz). The antenna radiates a widebeam right-hand circular polarization and operates with a measured radiation efficiency greater than 90% within its impedance matching bandwidth.
Higher order optical resonant filters based on coupled defect resonators in photonic crystals
Park, Dongsoo,Kim, Sangin,Park, Ikmo,Lim, Hanjo IEEE 2005 Journal of Lightwave Technology Vol.23 No.5
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.
Broadband electrically small antenna using two electromagnetically coupled radiators
Cho, Chihyun,Park, Ikmo,Choo, Hosung Wiley Subscription Services, Inc., A Wiley Company 2010 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS Vol.52 No.6
<P>We propose an electrically small antenna that achieves broad bandwidth with small antenna size. This antenna is composed of a hemispherical disk-loaded monopole and a hemispherically wound helix to maximize the disk loading effect and the electromagnetic coupling between the two radiating elements in a given space. The fabricated antenna is 10.7 cm in size (kr = 0.449) and exhibits a measured −3 dB bandwidth of about 30% for a center frequency of 200 MHz. The antenna also achieves a radiation efficiency of over 85% and a transmission loss similar to that of a conventional λ/4 monopole, despite the fact that size of the antenna is about 30% that of the λ/4 monopole. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1369–1372, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25164</P>
Characteristics of the Angled Printed Dipole Array Antenna with Different Numbers of Dipole Elements
Heesu Wang,Ikmo Park 한국전자파학회JEES 2020 Journal of Electromagnetic Engineering and Science Vol.20 No.3
This paper investigated the characteristics of series-fed angled dipole antennas as the number of dipoles increased from one to two, four, and eight. A parallel strip line printed on both sides of the substrate was used to connect angled printed dipoles of the same size in a series with equal spacing. As expected, although the gain increased as the number of dipoles increased, the impedance and gain bandwidths decreased. In addition, as the number of dipoles increased, the half-power beamwidth (HPBW) differences between the xz- and yzplanes decreased and the radiation pattern of the xz-plane became more symmetric. Antennas with one, two, four, and eight-dipole elements in a series were designed, and their peak gains were 5.0 dBi, 7.2 dBi, 9.4 dBi, and 10.4 dBi, respectively. The differences between the xz- and yz-plane HPBWs of the four antennas were 160.4°, 41.7°, 14.2°, and 5.3°, respectively. As the number of dipoles in the antenna increased, the differences between the HPBWs in the xz- and yz-planes decreased.