• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.12
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• pp.1470-1481
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• 2008

A demand for spectrum resources, especially in the low frequency bands, is ever increasing with the development of mobile telecommunications and so is their economic value as other national resources. Also, development in mobile broadband require more bandwidth with excellent propagation characteristics, such as those frequencies in the 700/800/900 MHz bands. As a way to enhance the economic efficiency of using spectrum resources, many countries including the U.S., the U.K. and Japan, have recently focused on the refarming plan of the low frequency bands according to the transition from analogue to digital TV. By the way, as a result of WRC-07, those parts of the band $698{\sim}960\;MHz$ in Region 2 and the band $790{\sim}960\;MHz$ in Regions 1 and 3 which are allocated to the mobile service on a primary basis are identified for use by administrations wishing to implement International Mobile Telecommunications (IMT). Therefore, after analogue to digital television switchover, some administrations may decide to use all or parts of the band $698{\sim}806/862\;MHz$ for other services to which the band is allocated on a primary basis, in particular the mobile service for the implementation of IMT, while in other countries the broadcasting service will continue to operate in that band. And to conclude, bands already identified for IMT-2000 will also be able to be used for IMT. This work will help establish a policy direction for spectrum refarming in the low frequency bands in Korea(Rep. of).

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.12
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• pp.1339-1349
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• 2008

In this paper, a nonlinear relationship between an input complex envelope and an output complex envelope of m-th harmonic zone is theoretically analyzed, and AM/$AM_m$ and AM/$PM_m$ are defined. A scheme to extract these characteristics from measured in-phase and quadrature-phase data is suggested. The proposed analysis is verified with a fundamental-fundamental and fundamental-third harmonic measurements for a InGaP power amplifier(PA). Based on the harmonic-band nonlinear analysis and extraction scheme, a new technique to send a signal in m-th harmonic band with a harmonic signal Linearization Digital Predistortion(DPD) scheme is presented. A numerical analysis and a Look-Up Table(LUT) based DPD algorithms to linearize output signal on m-th harmonic zone are developed. For a 16- and a 64-QAM input signals, a DPD for third harmonic signal linearization is implemented, and output spectrum and signal constellation are measured. The wholly distorted signals are linearized, and thus the measured Error Vector Magnitudes (EVM) are 6.4 % and 6.5 % respectively. The results show that a proposed scheme linearizes a nonlinearly distorted harmonic band signals. The proposed nonlinear analysis and predistortion scheme can be applied to multiband transmitter in next generation software defined radio(SDR)/cognitive radio(CR) wireless system.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.8
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• pp.844-853
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• 2008

This paper describes the design of a FEM(Front End Module) having power detection function for mobile handset application. The designed FEM consists of a MMIC(Monolithic Microwave Integrated Circuits) power amplifier chip, SAW Tx filter and duplexer, diode power detector and stripline matching circuit. An LTCC(Low Temperature Co-fired Ceramics) technology is adopted for miniaturized FEM. The frequency band is $824{\sim}869$ MHz which is the uplink Tx band of the CDMA mobile system. The size of designed FEM is $7.0{\times}5.5{\times}1.5\;mm^3$, which is an ultra-small size even though the power detector circuit is included. All sub-components of FEM have been developed and measured in advance before being integrated into FEM. The measured output power and gain are 27 dBm and 27 dB, respectively. In addition, the measured ACPR characteristics are 46.59 dBc and 55.5 dBc at 885 kHz and 1.98 MHz offset, respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.11
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• pp.1183-1189
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• 2014

The accuracy of the resistive-sheet technique in calculating the RCS(Radar Cross Section) of a deciduous leaf is examined in this paper for various thicknesses and dielectric constants, and a range of thicknesses for the resistive sheet technique is proposed. At first, a leaf was assumed to be a lossy dielectric disk, and the dielectric disk was again assumed to be a resistive sheet with an appropriate resistivity for a given thickness, a dielectric constant, and a frequency. Then, the RCS of the leaf was computed using the physical optics(PO) method, and was compared with the calculation results of a numerical analysis: i.e., a commercial tool based on the FEM (Finite Element Method) technique. It was shown that the error increases as the thickness increases. The error was 0.1 dB, for example, when the thickness is 1.2 mm and 3.7 dB when the thickness is 3 mm with a dielectric constant of(21.4, 9.7) at 9.6 GHz. It was also found that the error decreases as the dielectric constant increases. This study will be very useful for calculating the scattering characteristics of numerous leaves in a vegetation canopy for estimating its radar backscatter using scattering model.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.8
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• pp.745-753
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• 2011

In this paper, the planar monopole antenna for multi-band service is proposed. The proposed antenna, which is a rectangular patch antenna with a U-shaped slit based on a monopole antenna for wide bandwidth characteristic, is designed and analyzed. The antenna size has been miniaturized by using the U-shaped slit. The frequency characteristics are modified and optimized by varying specific parameters. To obtain desired frequency bands, the U-shaped slit and patch lines have been applied. Whole antenna dimensions including the ground plane are $35{\times}50{\times}1\;mm^3$, and the antenna part size is $35{\times}27\;mm^2$. It is fabricated on the FR-4 substrate(${\epsilon}_r=4.4$) using a microstrip line of $50{\Omega}$ for impedance matching. For the measured results, the impedance bandwidth below a VSWR of 2 is 790~916 MHz, 1.74~2.14 GHz, and 2.36~3.13 GHz. The fabricated antenna is satisfied with the aimed impedance bandwidth in GSM/DCS/US-PCS/UMTS/Bluetooth/S-DMB applications.

• Journal of Biomedical Engineering Research
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• v.23 no.3
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• pp.217-225
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• 2002

The implantable middle ear(IME) system, which has good sound quality. superior sound intelligibility and wide frequency characteristics. can resolve the sound distortion and ringing effect by sound feedback at high gain operation those are the major problems of conventional hearing aid. In this paper, we have manufactured the IME system using differential electromagnetic transducer(DET) and verified the performance of the system by carrying out vibration and animal implanting experiment. The DET was manufactured using micro-machining technology and vibration experiment of the transducer was performed to inspect whether the transducer could vibrate in accordance with the applied sound signal or not. And the result of the loaded experiment using temporal bone sampled from cadaver showed that the transducer can drive the middle ear bone and transmit the signal to inner ear After the internal unit of IME system was implanted in a dog. the auditory brainstem response (ABR) test was carried out. The result of the test indicated the Proper behavior of the IME system in the living body From the results of the experiments, it is verified that the manufactured system ewll work well when it is applied to human and a basis of clinical experiment of IME system to real human hearing impaired was be arranged.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.6
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• pp.1006-1014
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• 2000

Hemisphere type Luneberg lens antenna with a reflector(frequency : 9.375 GHz, -3 dB beam width 6$^{\circ}$, diameter 30.3 cm(about 10 A), which is miniaturized and lightweightized by attaching a reflector on a section of half the Luneberg lens antenna, is designed and fabricated on the basis of Luneberg lens antenna from which easy beam pointing is acquired only by movement of 1st radiator. Measurement shows -3dB beamwidth is 6.1$^{\circ}$ in case of E-plane and 5.5$^{\circ}$ in case of H-plane. These are good agreements with expected value. Gain of this antenna is 26dBi(Aperture efficiency for uniform distribution : $\pi$ = 44.97%) which is greater than that of 1st radiator(Rectangular microstrip antenna) by 20.4 dB. And, after calculating the approximated pattern of the 1st radiator, far-field pattern, whose source is the second aperture source farmed from the approximated pattern of the 1st radiator is computed. Comparing this far-field pattern with the expected pattern, a (relatively) good agreement is observed. Circular polarization Luneberg lens antenna is also manufactured by making 1st radiator so that it has the characteristics of LHCP and RHCP radiation. The results are as followings : -3 dB beamwidth 5.8$^{\circ}$ , side lobe level -15.3 dB, isolation between LHCP and RHCP radiation 2543, axial ratio 2 dB bandwidth about 1.4 GHz(14.9%).

• 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.334-340
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• 2007

The prediction for vegetation attenuation using the RET model recommended in the ITU-R requires six RET input parameters. Among these, 4 parameters are related to the scattering characteristics of vegetation. To extract these parameters, two methods can be used. One is to extract the parameters by curve fitting of the measured vegetation-attenuation curve with the RET prediction model, and the other is to use the additional phase function measurement data. In the former method, fitting is quite complex and it does not result in the unique results in some cases. In addition, the extracted parameters lack the physical meaning as well. Thus, in this paper, the measurement method of phase function, and the method of extracting the RET model parameters which lead to more accurate and physically more meaningful results are presented. The extracted RET model parameters are also presented. The RET modeling method, measurement data, and the extracted RET model parameters presented in this paper were submitted to the ITU-R meeting in 2006, and adapted for ITU-R report and recommendation P.833.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.1
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• pp.101-112
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• 2015

II~VI compound semiconductors, $Zn_xCd_{1-x}S$ thin films have been synthesized onto indium-tin-oxide(ITO) coated glass substrates using thermal evaporation technique. The composition ratio x($0{\leq}x{\leq}1$) was varied to fabricate different kinds of $Zn_xCd_{1-x}S$ thin films including CdS(x=0) and ZnS(x=1) thin films. Then, the deposited thin films were thermally annealed at $400^{\circ}C$ to enhance their crystallinity. The chemical composition and electronic structure of films were investigated by using X-ray photoelectron spectroscopy(XPS). The optical energy gaps of the samples were determined by ultra violet-visible-near infrared(UV-Vis-NIR) spectroscopy and were found to vary in the range of 2.44 to 3.98 eV when x changes from 0 to 1. Finally, we measured the THz characteristics of the $Zn_xCd_{1-x}S$ thin films using THz-TDS(time domain spectroscopy) system to identify the capability for electronic and optical devices in THz region.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.9
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• pp.1039-1046
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• 2007

In this paper, a coupled-defected ground structure(C-DGS) using negative inductive coupling is proposed and a bandstop filter(BSF) using C-DGS is designed and fabricated. The proposed C-DGS is the closely-located DGS cells for the negative coupling, the negative coupling of ground currents between adjacent DGS cells greatly improves the stopband characteristics. The proposed BSF utilizing the sharp cutoff response of the C-DGS has a -10 dB rejection band from 4 GHz to 11.3 GHz. A maximum attenuation rate is -64.3 dB/GHz in 3 cell structure, -108 dB/GHz in 5 cell structure. The C-DGS BSF shows the improved attenuation rate 3.8 times in 3 cell structure, 2.4 times in 5 cell structure, Also, the C-DGS BSF is reduced to 35.2 % and 40 % of the DGS BSF, respectively, due to the closely-located DGS cells. We fabricated the single gate mixer using C-DGS BSF. The single gate mixer has 6.6 dB conversion gain.