• Journal of the Korean Institute of Telematics and Electronics
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• v.11 no.6
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• pp.33-37
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• 1974

In this paper, the radiation characteristics for the array of a circular loop antenna is studied in moving media. The medium is assumed to be homogeneous, isotropic, and to move with a constant velocity much less than the speed of light. The integral equation for the current distribution is derived and the current functions is found by means of courier Series as a solution of the integral equation. The electric field is derived from the current on circular loop antenna and the Dyadic Green's Function in moving media. The numerical calculation of the electric field concerning to the two element antenna array,, in which one element is parasitic, is carried out. The field patterns are plotted from the computed values. As a result, the field patterns in moving media, compared with the patterns in stationary media, are found to decrease in the direction of media velocity and increase in the opposite direction, and the maximum directivity is shifted.

• 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.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.3
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• pp.361-374
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• 1996

In general, a cooling tower has two major noise sources, one is the fan and the other is the falling water. The fan noise is produced by passage of its blades through the air and radiates from the fan stack. Noises from the falling water are caused by splashing and dropping of water cascading over the internal filler of the cooling tower and into the basin and radiate from the louvered face. In this paper, the noise measurements and its frequency analysis are carried out for the locations facing the louvered side and near the fan stack referring the related code and standards in order to study the noise characteristics of the induced-draft cooling tower, especially for the buildings. As a result, it is found that for every doubling of distance from the noise source the noise level decreases by 2~4dBA in the near field with reflect surfaces and decreases by about 6dBA also in the far field without reflect surfaces. As a supplement to the noise measurements, a computer program with simple algorithm is developed in order to estimate the noise level at a distance from the cooling tower, so that the user could apply and modify it for the particular boundary conditions easily.

• Journal of IKEEE
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• v.12 no.4
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• pp.185-195
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• 2008

In this paper, PIFA(Planar Inverted F Antenna) which operates in PCS(Personal Communication System) band is designed and characteristics are investigated. Designed PIFA was installed in three types of handsets, folder, bar, slide, and the performance was evaluated. Head and hand phantom were added to make the most similar environment to real condition of mobile phone use, and influences on antenna performance were analyzed. The simulation results confirm radiation patterns are greatly changed and antenna efficiency is decreased by the effect of human body. Performance variation of the mobile handset antenna was observed as changing the angle between mobile handset and head phantom from $0^{\circ}$ to $2^{\circ},\;4^{\circ}$ to confirm the variation caused by the relative position of mobile handset and head phantom. Directivity was decreased gradually as the antenna goes away from head phantom, and showed the trend of increasing efficiency. But in the case of bar type, where the position of antenna is relatively close to head phantom, that trend didn't show. It was confirmed that the shape of handset has a great effect on the performance.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.27 no.2
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• pp.234-242
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• 2017

This study investigates vibro-acoustic characteristics of a short, thick cylinder containing a slot given a pined-free boundaries. Using the finite element analysis results, structural modes of the asymmetric cylinder (with a slot) are expressed as the linear combinations of modes of the symmetric cylinder made of same material with identical geometry except the slot. Based on synthesized modal vibrations, acoustic modes of the asymmetric cylinder are obtained with two approaches, i.e., Rayleigh integral calculation and modal expansion of the acoustic modes of the symmetric cylinder. Also, acoustic powers, max. sound pressure and directivity pattern are obtained from acoustic modes and verified with the boundary element analyses. Based on these results, the accuracy of proposed approaches in calculating the vibro-acoustic properties of a short, thick, asymmetric cylinder has been confirmed. The procedure can be applied to the similar cylinders with other boundaries or asymmetric properties. Also, attenuation of vibration and/or sound radiation of the cylinder type practical components can be studied using these approaches.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.2
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• pp.197-205
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• 2017

We investigate the slat noise generation mechanism by using large-eddy simulation (LES) and simple source modeling based on linearized Euler equations. An incompressible LES of an MD 30P30N three-element airfoil in the high-lift configuration is conducted at $Re_c=1.7{\times}10^6$. Using the total derivative of the hydrodynamic pressure (DP/Dt) acquired from the incompressible LES, representative noise sources in the slat cove region are characterized in terms of simple sources such as frequency-specific monopoles and dipoles. Acoustic radiation around the 30P30N multi-element airfoil is effectively computed using the Brinkman penalization method incorporated with the linearized Euler equation. The directivity pattern of $p^{\prime}_{rms}$ at $r=20c_{slat}$ in the multiple sources is closely compared to that obtained by the application of the LES/Ffowcs-Williams and Hawking's methods to the entire flow field. The power spectrum of p' at ${\theta}=290^{\circ}$ is in good agreement with the data reported in BANC-III, especially the broadband part of the spectrum with a decaying slope ${\propto}f^{-3}$.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.7
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• pp.1541-1547
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• 2005

In this paper, Dualband internal antenna for GSM/DSC handset is proposed. The antenna has a size of about $38mm{\times}90mm{\times}1mm$, giving a total mobile phone PCB for support and fold type patch of about $30mm{\times}8mm{\times}3.2mm$. This antenna characteriatic facilitates the fine-tuning of the two operating frequencies of 909MHz and 1762MHz in the dualband design. The measured radiation pattern in the E-plane and H-plane for operating frequencies of 909MHz and 1762MHz is compared and analyzed. The designed and fabricated two band internal antenna for GSM/DSC handset have a gain between 0dBi and 2.0dBi at all bands. Also, the electric firld distribution and directivity on human head caused by portable phone is analyzed. An analysis model is composed of a human head model and the antenna mounted on the same ground plane as portable telephone size.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.5A
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• pp.696-701
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• 2000

Electronic Toll Collection (ETC) System makes the telecommunication possible between the Beacon and the On Board Unit(OBU) for automatic toll collection. In this paper, the propagation path of microwave is modelled and the induced voltage of receiving antenna is analyzed numerically according to multi-path fading effect. In our modelling, we consider frequency, weather condition, polarization and antenna radiation pattern. Also, we suggest the diversity technique in order to reduce the fading effect. In the resuts, the fading effect is reduced significantly in case of the vertical polarization at the rain condition. In general the circular polarization is the most desirable in this application. The antenna which has the high directivity, is also desirable. Using the space and frequency diversity technique at the Beacon, the fading effect is reduced effectively. These results are compared with our experimental data.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.4 s.107
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• pp.351-357
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• 2006

In this paper, a direct $TM_{01}-TE_{11}$ mode converter of circular waveguide which is used the approximated design method of mode conversion between $TM_{01}$ and $TE_{11}$ modes is designed for radiation with the maximum directivity of high power energy into air (rom high power microwave antenna system. The proposed direct $TM_{01}-TE_{11}$ mode converter is calculated and designed with an approximated method for non-linear function about an extended non-constant serpentine type of circular waveguide. Then, the designed mode converter is optimized by length of 200 mm and efficiency above 95% by FIM simulation and achieved short length and high efficiency of the antenna by results of fabricated and measured characteristics.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.9
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• pp.1019-1024
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• 2012

In this paper, a UWB antenna using a SIR(Step Impedance Resonator) that eliminate signal interference at 5 GHz WLAN as the first rejection band and adjust the second rejection band is proposed. Unlike the unit impedance resonator, the second harmonic of SIR is decided according to step impedance. Therefore, To adjust the second rejection band, SIR is applied to UWB antenna. Also, the equivalent circuit of the antenna at first rejection band is presented and the equivalent modeling values of the SIR and the coupling value is obtained. The proposed antenna is satisfied to cover full UWB band with return losses less than -10 dB and has band rejection characteristic in 5 GHz WLAN band. The radiation patterns show +y directivity characteristics in H-plane and the group delay variations are within 1.0 ns.