• Journal of the Korean Ceramic Society
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• v.56 no.4
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• pp.399-402
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• 2019

The phase evolution, microstructure, and microwave dielectric properties of (Ba_1-xNa_x)(Mg_0.5-2xY_2xW_0.5-xTa_x)O₃ (0 ≤ x ≤ 0.05) ceramics were investigated. All compositions exhibited a 1:1 ordered perovskite structure. As the value of x increased, the dielectric constant (ε_r) exhibited a tendency to increase slightly. The quality factor reached the maximum value at x = 0.01. The temperature coefficient of resonant frequency (τ_f) increased from -19.32 ppm/℃ to -5.64 ppm/℃ in the positive direction as x increased. The dielectric constant (ε_r), quality factor (Q × f₀), and temperature coefficient of resonant frequency (τ_f) of the composition x = 0.05, i.e., (Ba_0.95Na_0.05)(Mg_0.4Y_0.1W_0.45Ta_0.05)O₃ were 19.9, 128,553 GHz, and -5.6 ppm/℃, respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.9
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• pp.919-925
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• 2011

In this paper, we designed and analyzed a 3D isotropic bulk structure consisting of thin wires and SRR's(Split Ring Resonator) with which the permittivity and permeability can be controlled at the same time. For the 3D isotropic bulk structure, first of all, the geometry seen by three main axes must look alike. Thus, we adopted the orthogonal thin wires and symmetrical SRR's. As a result, we constructed metamaterial bulk structures of which effective relative permittivity and permiability are about -0.6 and -1.5, respectively. Its refractive index is about -0.95 in each direction(x, y and z direction). The computed Brillouin dispersion diagram also showed that the proposed structure is almost near isotropic.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.4
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• pp.470-480
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• 2011

Analog ferrite phase shifters based on rectangular waveguides which are used as component of passive phased array system have high power handling capability, but it is heavy and has high cost to fabricate. In this paper, we propose an analog ferrite phase shifter using substrate integrated waveguide(SIW), which has low cost and is easy to fabricate because it uses printed circuit board(PCB) process. The proposed structure is fabricated by using centeral dielectric material removal for inserting a ferrite bar. The measured results show that the proposed structure has not only $5.1^{\circ}$/mm phase variation but also return loss variation under 12.9 dB. Therefore, it is expected that the proposed phase shifter can plays an role to reduce weight and to has low cost on the phased array system.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.9
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• pp.1077-1082
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• 2007

This paper presents the analysis of the potential ultra-wideband(UWB) interference to WiMAX at 3.5 GHz bands and the mitigation method using transmit power control(TPC) of UWB system. UWB interference effect is evaluated with WiMax's outage probability over UWB density when multiple UWB systems and single WiMAX receiver distribute in unit area of 1$km^2$, When UWB distribution density is 20$devices/km^2$ and the dynamic range of TPC is 30 dB, UWB interference effect with TPC is decreased by 42 % rather than that without mitigation scheme. Finally, we describe that the proposed TPC is an effective method to mitigate UWB interference to WiMAX.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.10
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• pp.983-994
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• 2014

In this paper, we analyze the telecom services and their socio-economic effect of using open spectrum, which is to access sharing spectrum. For this, we suggest a concept and a classification of open spectrum as spectrum access model and make a survey for analyzing the socio-economic effect of spectrum, 2,605 MHz which is candidated for sharing between 2.9~5.925 Hz in Korea. From survey results, we propose Mobile Telecommunications Assist Service and WiFi as the most effective services and Smart Car Service and M2M, IoT, and RFID/USN Service as the effective services to open spectrum.

• The Journal of Korean Institute of Information Technology
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• v.17 no.3
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• pp.43-50
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• 2019

In this paper, we propose a S-band oscillator with a reduced electrical size by applying a vertical split ring resonator(VSRR). The VSRR is a type of split ring resonator that operates as a resonator by the capacitance and inductance generated between the microstrip lines arranged on the top and bottom of the dielectric substrate and it has an advantage that the electrical size of the resonance circuit can be reduced as compared with the conventional ring resonator. In this paper, we design a VSRR operating over S-band and an oscillator using the VSRR as the resonant circuit. The proposed oscillator showed the output of 5.9dBm at 2.4HGz and showed the phase noise characteristics of -112.58dBc at 100KHz offset frequency and -117.85dBc at 1MHz offset.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.1
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• pp.53-61
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• 2014

In this paper, we present the design, fabrication and measurement of high efficiency GaN HEMT power amplifier using harmonic matching technique. In order to achieve high efficiency, harmonic load-pull simulation is performed, that is, the optimum load impedances are determined at $2^{nd}$ and $3^{rd}$ harmonic frequencies as well as at the fundamental. Then, the output matching circuit is designed based on harmonic load-pull simulation. The measurement of the fabricated power amplifier shows the linear gain of 20 dB and $P_{1dB}$(1 dB gain compression point) of 33.7 dBm at 1.85 GHz. The maximum power added efficiency(PAE) of 80.9 % is achieved at the output power of 38.6 dBm, which belongs to best efficiency performance among the reported high efficiency power amplifiers. For W-CDMA input signal, the power amplifier shows a PAE of 27.8 % at the average output power of 28.4 dBm, where an ACLR (Adjacent Channel Leakage Ratio) is measured to be -38.8 dBc. Digital predistortion using polynomial fitting was implemented to linearize the power amplifiers, which allowed about 6.2 dB improvement of an ACLR performance.

• International Journal of Highway Engineering
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• v.17 no.6
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• pp.1-9
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• 2015

PURPOSES : The objective of this study is to propose a quality control and quality assurance method for use during asphalt pavement construction using non-destructive methods, such as ground penetrating radar (GPR) and an infrared (IR) camera. METHODS : A 1.0 GHz air-coupled GPR system was used to measure the thickness and in situ density of asphalt concrete overlay during the placement and compaction of the asphalt layer in two test construction sections. The in situ density of the asphalt layer was estimated based on the dielectric constant of the asphalt concrete, which was measured as the ratio of the amplitude of the surface reflection of the asphalt mat to that of a metal plate. In addition, an IR camera was used to monitor the surface temperature of the asphalt mat to ensure its uniformity, for both conventional asphalt concrete and fiber-reinforced asphalt (FRA) concrete. RESULTS : From the GPR test, the measured in situ air void of the asphalt concrete overlay gradually decreased from 12.6% at placement to 8.1% after five roller passes for conventional asphalt concrete, and from 10.7% to 5.9% for the FRA concrete. The thickness of the asphalt concrete overlay was reduced from 7.0 cm to 6.0 cm for the conventional material, and from 9.2 cm to 6.4 cm for the FRA concrete. From the IR camera measurements, the temperature differences in the asphalt mat ranged from $10^{\circ}C$ to $30^{\circ}C$ in the two test sections. CONCLUSIONS : During asphalt concrete construction, GPR and IR tests can be applicable for monitoring the changes in in situ density, thickness, and temperature differences of the overlay, which are the most important factors for quality control. For easier and more reliable quality control of asphalt overlay construction, it is better to use the thickness measurement from the GPR.

• Journal of The Korean Astronomical Society
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• v.38 no.4
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• pp.437-443
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• 2005

The Solar Radio Burst Locator (SRBL) is a spectrometer that can observe solar microwave bursts over a wide band (0.1-18 GHz) as well as detect the burst locations without interferometry or mechanical scanning. Its prototype has been operated at Owens Valley Radio Observatory (OVRO) since 1998. In this study, we have evaluated the capability of the SRBL system in flux and radio burst location measurements. For this, we consider 130 microwave bursts from 2000 to 2002. The SRBL radio fluxes of 53 events were compared with the fluxes from USAF/RSTN and the burst locations of 25 events were compared with the optical flare locations. From this study, we found: (1) there is a relatively good correlation (r = 0.9) between SRBL flux and RSTN flux; (2) the mean location error is about 8.4 arcmin and the location error (4.7 arcmin) of single source events is much smaller than that (14.9 arcmin) of multiple source events; (3) the minimum location error usually occurred just after the starting time of burst, mostly within 10 seconds; (4) there is a possible anti-correlation (r = -0.4) between the pointing error of SRBL antenna and the location error. The anti-correlation becomes more evident (r=-0.9) for 6 strong single source events associated with X-class flares. Our results show that the flux measurement of SRBL is consistent with that of RSTN, and the mean location error of SRBL is estimated to be about 5 arcmin for single source events.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.232-232
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• 2021

수재해 저감과 예방을 위해서는 공간적 변동성을 반영한 정확한 면적 강우량의 측정은 필수적이다. 이러한 요구에 부응하기 위해 24 GHz 이중편파 전자파를 기반으로 소규모 공간 범위에 대해 저고도의 지상 강우를 30 m의 거리해상도로 관측할 수 있는 전파강수계가 개발되었다. 전파강수계는 시제품이 개발된 이래로 한국건설기술연구원 연천센터와 국내 여러 현장과 인도네시아 등에서 시험을 실시하였다. 임상훈 등(2020)은 전파강수계의 반사도와 비차등위상차를 이용한 강우 추정식을 개발하여 연천 및 거제 관측 자료에 적용한 바 있다. 본 논문에서는 연천센터에 분산 배치한 우량계 자료를 이용하여 전파강수계의 강우 공간분포 측정 성능을 평가하였다. 공간우량계는 15대 중 음영구역 바깥에서 정상 작동한 7개의 0.5mm급 우량계 자료와 핏게이지에 있는 0.2mm급 우량계 2대가 비교에 사용되었다. 전파강수계 강우강도는 비교 위치에 해당하는 점 주변의 레이 방향 5개(37.5 m에 해당) 및 방위각 방향 5개 게이트 등 총 25개의 복셀에서 산출된 강우 정보를 평균하여 비교하였다. 정확도는 지상우량계를 참값으로 보고 MAE(Mean absolute error)로 평가하였다. 그 결과 평균 4.2%의 오차를 보였으며, 우량계의 오차를 ±5%로 가정할 경우 3.3~7.9%로 나타났다. 전파강수계의 누적 강우량 값은 강우계에 비해 작은데, 이는 지속적인 관측을 통해 강우 산정의 정확도를 개선하는 것이 필요함을 의미한다.