• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.8
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• pp.641-651
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• 2020

This paper implements an antenna selection logic that automatically selects omni-directional antennas mounted on the top and bottom of an unmanned helicopter to maintain the link margin of the data link at 0dB or higher during flight. The selection criteria were derived by simulating and analyzing the radiation pattern. In addition, it is implemented to select the optimal antenna in real time during the flight by deriving the directivity angle function.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.5
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• pp.857-871
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• 1994

In this paper, six kinds of spiral antenna, a combination of two types of spiral arm-width and three types of spiral curvature are analyzed by using moment method. Dividing spiral arms into N sections, the current distribution is calculated by Galerkin`s method. The radiation pattern and the antenna gain are derived from antenna currents. All os the six spiral antenna have amni-dirctional and wide-band characteristics, although the antenna gain changes within +_ 5dB bound for operating range(600MHz-2GHz). The variation of antenna`s gain is caused by the return loss in connection the Balun to the antenna. Simulation and experimental results on the radiation pattern also show spiral antennas have omni-directional and wide-band characteristics.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.5
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• pp.515-522
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• 2008

In this paper, a slot antenna with built-in Bazooka balun aimed for a WiBro repeater was designed and fabricated. The return loss and radiation pattern of the slot antenna were improved due to the introduced Bazooka balun. This balun brings about even radiation pattern and keeps the stabilized coverage of repeater And it is easy to unite this balun with the antenna body by providing the terminal of Bazooka balun with screw shape. H-type slot was used to reduce the size of the antenna, and the slot antenna was fabricated in the structural symmetry with respect to a feeding point to afford the omni-directional radiation pattern. The simulated results were obtained by MWS(Microwave Studio Simulator) of CST company, and the measurement on the proposed antenna was conducted in an anechoic chamber equipped with a network analyzer and a far field measurement system. The measured peak gain shows 5.75 dBi and the average gain is above -0.8 dBi. The return loss remains below -12.35 dB for all frequency bands in WiBro regarded as a good performance.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2005.11a
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• pp.245-248
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• 2005

In this paper, small sized half-wavelength circular loop antenna which attached beneath a visor of helmet is designed and fabricated at the resonant frequency of 449MHz. To reduce the size of the antenna, double series-shorted stubs are inserted inside the loop for practical use of a vacant space of loop inside. Also, It is designed for the printed type to install the helmet easily. The size of antenna on helmet is reduced to 87.75%(diameter : 70mm, height :.36mm) compare with general type antenna(diameter : 200mm height 101mm). The return loss, -10dB bandwidth and gain are -13.2dB, 17.6MHz(3.9%), and -1.78dBd. And, radiation pattern is omni-directional pattern at H-plane. Therefore, it can be seen that the half-wavelength circular loop antenna using double series-shorted stubs is proper structure for the miniaturization and the installed antenna of the helmet.

• Progress in Superconductivity
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• v.2 no.1
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• pp.51-55
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• 2000

A $Y_1Ba_2Cu_3O_{7-\delta}$ square spiral microstrip antenna (YBCO antenna) was epitaxially grown on a $LaAlO_3$ substrate by laser ablation. Also fabricated was a gold square spiral microstrip antenna (gold antenna) having the same structure as that of the YBCO antenna in order to compare the properties of both antennas. Both the YBCO antenna and the gold antenna were operated in Ku (12-18 GHz) band, and their properties such as the return loss, SWR, power gain, and radiation patterns were investigated at 77 K. The return loss below -10 dB was obtained in two frequency ranges, i.e., 14.05-14.90 GHz, and 16-18 GHz for the YBCO antenna at 77 K (YBCO superconducting antenna), and in the frequency range of 15.05-17.60 GHz for the gold antenna at 77 K. The SWR bandwidths are 0.85 GHz and 2 GHz for the YBCO superconducting antenna, and 2.55 GHz for the gold antenna at 77 K. The gain improvement of the superconducting YBCO antenna over the gold antenna at 77 K was about 10 dB in the frequency range of 16 GHz to 18 GHz. The radiation patterns show the YBCO superconducting antenna has the omni-directional property of a spiral antenna.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.4
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• pp.386-392
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• 2002

This paper presents a basic characteristics of 4-element circular array dipole antennas for 4-sector beam steering. The coupled integral equations for the unknown current distributions on dipole elements are derived and solved by applying Galerkin's method of moments. The parasitic elements have been used to increase the directional gain and the beam is steered electronically either by sswitching between the parasitic elements or switching the position of the active element. The parasitic elements are switched short-circuited or open-circuited as required to steer a directional beam. In order to verify the theoretical analysis, the radiation pattern was compared with experiments.

• Journal of Satellite, Information and Communications
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• v.8 no.4
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• pp.30-36
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• 2013

Recently the globalization of the media content industry, various activities have been made in the field of art and the speaker system is very important in the sound industry which is one of the arts. The directional characteristics of a loudspeaker refer to the radiation of sound in certain directions and are among the most important features of a loudspeaker. Designing a loudspeaker that can keep all of its constant directivity at all frequencies is difficult due to the wavelengths of audio frequencies and the size of horns and transducers. This study proposed gradient array methods to improve low frequency pattern control of full-range speakers to maximize Direct to Reverberant Ratios at the listeners.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.3 s.118
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• pp.233-240
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• 2007

In this paper, the broadband cross monopole antenna is presented and the radiation characteristics are investigated. The presented broadband cross monopole antenna is composed of the cross monopole element and the folded short stub, which has a excellent band characteristics more than the existing cross monopole antenna. To conform the broadband characteristics of the presented antenna, the experimental antenna is designed, fabricated, and its radiation characteristics are measured in $1.75\sim2.655\;GHz$. It is shown that the designed antenna has the nondirectional pattern in the horizontal plane, the directional pattern in the vertical plane, VSWR less than 1.5, and gain in $2.17\sim4.87\;dBi$. From these results, the presented antenna is conformed as a broadband indoor antenna which can be used for PCS, WCDMA, Wibro, and satellite DMB band.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.12
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• pp.1327-1336
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• 2007

In this paper, we propose a reconfigurable antenna which operates as a disk-loaded dipole antenna and a folded dipole antenna alternatively using RF on/off switches. The antenna can change its effective length to achieve dual-band operation; operates as the folded dipole antenna for stepping up the radiation resistance in low frequency band of $20{\sim}300$ MHz, and as the disk-loaded dipole antenna for an omni-directional radiation pattern (horizontal plane) and a donut-shaped radiation pattern (vertical plane) in high frequency band of $300{\sim}1.3$ GHz. In the low band, the proposed antenna shows higher gain than a conventional dipole antenna with a reduced antenna size. In the high band, the antenna maintains a broad beamwidth of about $80^{\circ}$, thus the antenna can be applicable to antennas for direction finding applications.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.1
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• pp.286-290
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• 2017

In this paper, we have proposed a hexagonal patch UWB antenna with a band notch characteristic where the notch band of 5.15 ~ 5.85 GHz band of WLAN was induced by inserting a circular slit in the patch. The impedance bandwidth of the proposed antenna meet the band width criteria of UWB communication system where is mentioned as frequencies range form 3.1 ~ 11.8 GHz. The characteristic band at 5.2 ~ 5.8 GHz notch band was observed. The radiation pattern of the antenna shows a directinal radiation pattern at $0^{\circ}$ and $180^{\circ}$ in XZ-plane and YZ-plane is an omni-directional pattern, respectively. In addition, it is observed that increase in frequency results in increases of the antenna gain whereas the notch band section is decreased. The proposed antenna was designed TRF-45 substrate with thickness of 1.62 mm, a loss tangent of 0.0035, a relative permittivity of 4.5 and designed were used Ansys Inc. HFSS.