• Journal of Electrical Engineering and Technology
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• 제12권2호
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• pp.880-885
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• 2017

Radiation from a cavity-backed circular aperture surrounded by concentric corrugations is studied. An electromagnetic boundary-value problem of the cavity-backed circular aperture surrounded by concentric corrugations is solved by using the Green's function, Hankel transform, and mode matching method. The radiated fields are computed in terms of corrugation geometry to illustrate radiation behaviors and measured to validate our computation. The effects of the corrugation geometries on the radiation are discussed.

• Journal of the Optical Society of Korea
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• 제10권1호
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• pp.23-27
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• 2006

We are studying the application of an adaptive optics system to upgrade the beam quality of a laser. The adaptive optics (AO) system consists of a bimorph deformable mirror, a Shack-Hartmann sensor and a control system. In most AO applications, the beam aperture is considered to be circular. However, in some cases such as laser beams from unstable resonators, the beam apertures are annulus or a holed-rectangle. In this paper, we investigate how well a bimorph deformable mirror of ${\Phi}120\;mm$ clear aperture can compensate phase distortions for three different beam configurations; 1) ${\Phi}120\;mm$ circular aperture, 2) ${\Phi}100\;mm$ annulus aperture with a ${\Phi}20\;mm$ hole and 3) $70\;mm{\times}70\;mm$ square aperture with a hole of $30\;mm{\times}30\;mm$. This study concludes that the bimorph mirror, which might be considered as a modal controller, can compensate tilt, defocus, coma and astigmatism, and spherical aberration for all three beams.

• Journal of electromagnetic engineering and science
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• 제1권2호
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• pp.173-175
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• 2001

A polarizability fur a circular aperture near a conducting plane is derived. The Mantel-transform and mode-matching is used to obtain a simple series solution. The presented series solution is fast convergent so that it is very efficient fur numerical computations.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• 제22권6호
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• pp.654-660
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• 2011

In this paper, the electromagnetic wave transmission through a ridge-loaded small circular aperture is considered. The transmission problem when a plane wave is normally incident on the aperture in an infinite conducting plane is solved by a method of moments(MoM). From the results for the transmitted power and the patterns of radiation from the aperture, the transmission characteristics of a small sub-wavelength circular aperture, a ridge-loaded circular aperture, and a half wavelength slot are compared. In addition, the theoretical study is verified through the experiments for the apertures fabricated on an Flexible Printed Circuit Board(FPCB), which shows fairly good agreements with the simulated results.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• 제16권10호
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• pp.982-988
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• 2005

An analytic solution of circular aperture antenna with a feed transition is presented using a hybrid method of generalized scattering matrices and integral transform. The method can give an analytic solution to antennas with integrated filters or mode converters, etc. Scattering matrices and integral transform techniques are combined to accommodate discontinuities connected between an aperture and a feed waveguide, and radiated field from the aperture. The method gives radiation fields as well as return losses of the antenna.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• 제24권5호
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• pp.502-507
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• 2013

In this paper, a circular dual mode horn with modified aperture is proposed to improve a E/H-plane radiation pattern symmetry of a conventional oversized circular dual mode horn. The proposed antenna consists of a feeding section, a mode generation section and a phase matching section which has aperture shape transition from circle to ellipse or rectangle to improve a E/H-plane radiation pattern symmetry. To compare the performances between the proposed antenna and the convenional circular dual mode horn, the conventional circular dual mode horn and the proposed circular dual mode horn with rectangular aperture are fabricated and researched at 15 GHz. The measured results show that the conventional circular dual mode horn has 3.394 dB difference while the proposed antenna has only 0.539 dB difference between E and H-plane radiation patterns within the -11 dB beamwidth($53^{\circ}$) which is required beamwidth of the feed horn for the maximum aperture efficiency where f/d ratio of reflector antenna is 1.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제40권7호
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• pp.1363-1368
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• 2015

Aperture-coupled circular polarization microstrip array antenna is proposed in this paper. The proposed antenna is useful for 2.4GHz ISM band and its aperture shape is a modified H-slot. The optimal design parameters for the antenna structure is found by using electromagnetic analysis tool HFSS repeatedly. The HFSS simulation results, such as return loss, axial ratio, radiation pattern and gain of the proposed array antenna are compared with results of the single antenna. It is able to verify that the proposed array antenna is valuable enough to be used in various applications as well as 2.4GHz ISM band.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• 제25권11호
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• pp.1113-1120
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• 2014

In this paper, general methods for enhancing the transmission efficiency through the small subwavelength aperture in an infinite conducting plane are considered first by use of the transmission-resonant aperture like the ridged circular aperture structure, second by employing the transmission-resonant cavity structure. In particular, the maximum transmission cross section is found to be $\frac{2G{\lambda}^2}{4{\pi}}[m^2]$ for the two structures, where G is the gain of the aperture in the output half space. As experimental works, the impedance matching characteristics are investigated for the cases that above two structures are incorporated as a potential near field microscopic probe in the waveguide end. As a complementary problem to the above transmission-resonant aperture problem, some discussions are also given on the scattering resonance by the scattering object much smaller than the wavelength. This discussion may provide a good understanding of the physics for the phenomena that the maximum scattering cross section is much larger than the physical size of the atom in atomic physics area.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• 제25권2호
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• pp.156-163
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• 2014

In this paper, a compact circularly polarized metamaterial patch antenna using cross aperture-coupled feed is proposed. The CP antenna utilizes the -1 mode that is induced by the composit right-left handed(CRLH) transmission line. Since the -1 mode has the same properties with the $TM_{010}$ mode of the conventional patch antenna, the circular polarization(CP) can be realized. If two orthogonal modes are excited with $90^{\circ}$ phase difference, the CP property can be obtained. In order to obtain two orthogonal modes and $90^{\circ}$ phase difference, 4 mushroom structures having the shape of square are employed. The width and length of the cross aperture are optimized through the design algorithm. The fabricated antenna is based on RT/duroid5880 substrate and the total area of the 4 mushroom is $0.25{\lambda}_0{\times}0.25{\lambda}_0$. The center frequency of the LHCP(Left-Handed Circular Polarization) antenna is measured as 1.622 GHz and circular polarization bandwidth(3 dB) is measured as 3 MHz. The center frequency of the RHCP(Right-Handed Circular Polarization) antenna is measured as 1.609 GHz and circular polarization bandwidth (3 dB) is measured as 3 MHz, respectively. The measured radiation efficiency of LHCP antenna is 61.1 % and the measured radiation efficiency of RHCP antenna is 54.5 %.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• 제13권4호
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• pp.393-400
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• 2002

In this paper, a novel series feeding cross-aperture coupled microstrip antenna with the effect of hybrid feeding is proposed and demonstrated experimentally to improve narrow axial ratio bandwidth of cross-aperture coupled antenna with single feeding among the various methods for generating circular polarization. The validity of a proposed series feeding cross-aperture coupled microstrip antenna is shown by comparing experimental results between the reported and the proposed microstrip antenna, and 2${\times}$2 array microstrip antenna based on the proposed single microstrip antenna used sequential rotation technique to accomplish broader axial ratio bandwidth. In the proposed single and 2${\times}$2 array microstrip antenna, the measured axial ratio bandwidths are 110 ㎒(4.6%) and 420 ㎒(17.5%), maximum gains are 8.2 ㏈i and 12.5 ㏈i, 3 dB gain bandwidths are above 400 ㎒(16.7%), and impedance bandwidths for the VSWR<1.5 are 240 ㎒(10%) and 500 ㎒(20.8%), respectively.