• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.2
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• pp.178-182
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• 2004

In this paper, a 90$^{\circ}$ hybrid coupler with both power division and harmonic rejection characteristics is presented by applying a LPF characteristic to a conventional 90$^{\circ}$ hybrid. Since a conventional 90$^{\circ}$ hybrid coupler operates as a power divider/combiner using phase difference, it does not suppress higher order harmonics when it is incorporated with nonlinear amplifier. This requires an additional filter to take into account of the harmonics. The proposed 90$^{\circ}$hybrid coupler power provides the division capability and proper phase difference, as well as harmonic suppression characteristic by integrating LPF characteristic.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2016.10a
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• pp.85-88
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• 2016

Two output ports of $90^{\circ}$ hybrid-coupler are generally the same output power with $90^{\circ}$ phase difference. But, Two output ports of $90^{\circ}$ hybrid-coupler must be the different output slope characteristic about frequency because of the different electrical length. In $90^{\circ}$ hybrid-coupler being the same power distribution, 3-dB power distribution at two output ports only exists near the center frequency. And, the output power difference between two output ports increases in accordance with the further away from the center frequency. This paper proposes $90^{\circ}$ hybrid-coupler being the similar output slope characteristic of two output ports in wideband to modify the ${\lambda}/4$ transmission line of $35-{\Omega}$ characteristic impedance between input port and output port near input port. The power difference between two output ports of the proposed circuit is below 0.2dB over 20% bandwidth of the center frequency in ADS(advanced Design System).

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.2
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• pp.191-196
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• 2010

Hybrid heat pumps, which combine the vapor compression and absorption heat pump cycle, can efficiently produce hot water of $80^{\circ}-90^{\circ}C$ from the low temperature of ${\sim}50^{\circ}C$. In this study, the performance of a two-stage hybrid heat pump (HHP) was compared with a single-stage hybrid heat pump using EES (Engineering Equation Solver). For the same operating conditions, the two-stage HHP showed a slightly higher COP (Coefficient Of Performance) and more stable operating conditions than the single-stage HHP. Moreover, the maximum working fluid temperature of the two-stage HHP was found to be lower than that of the single-stage HHP by about 40 K, which makes the working conditions of the lubricating oil safer. The COPs of both systems decreased with increasing UA-values. However, the heat output of the HHP was increased at the same time.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.17 no.5
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• pp.128-134
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• 2018

In this paper, two ports feeding a microstrip patch antenna using a quadrature hybrid circuit was proposed to enhance the bandwidth for the global positioning system(GPS). The square patch was designed, and the probe feeding was applied. The quadrature hybrid chip circuit for two-port feeding was designed, and output ports that have a 90-degree phase difference feed to the patch antenna. The designed patch and quadrature hybrid circuit were implemented on an FR4 board, and were combined. The measurement of the bandwidth within a voltage standing wave ratio(VSWR) of 2:1 and axial ratio(AR) in 3dB were wide band as 29% BW (1,230~1,700 MHz) and 15.87% BW (1,400~1,650 MHz), respectively. Antenna gain were measured 2.75dBi at the center frequency.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.7 s.98
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• pp.661-670
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• 2005

In this paper, the microstrip $90^{\circ}$ hybrid to provide -3dB coupling and $90^{\circ}$ phase difference at broadband frequency range of 2 to 6 GHz is designed. This proposed hybrid is composed of 3-section. The two outside section are realized by symmetrical edge coupled lines, but on the other hand the middle section consists of VIP(Vertically Installed Planar) circuit. The ground part of VIP circuit is partially removed to get tight coupling, particularly. This hybrid is easy to realize due to microstrip structure and has good holing flexibility by taking advantage of VIP circuit as a control point of optimization. The proposed hybrid provide satisfactory performance as compared with simplicity of structure and fabrication first of all.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2003.11a
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• pp.357-360
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• 2003

본 논문에서는 $90^{\circ}$ 하이브리드 결합기에 여파기 특성을 결합하여 전력분배와 하모닉 저지특성효과를 보여주고 있다. 일반적인 $90^{\circ}$ 하이브리드 결합기는 위상차를 갖고 전력을 분배, 합성하는 데에만 쓰이고 있기 때문에 비선형 소자와 결합함으로써 생기는 하모닉 성분을 억제하려면 여파기를 따로 설계해야 하는 단점이 있다. 그래서 본 논문에서는 하이브리드에 저역통과 여파기 특성을 결합함으로써 위상차와 전력분배는 물론 여파기 특성인 감쇠효과를 이용하여 하모닉 성분을 크게 감소시킬 수 있는 구조를 연구하였다.

• Journal of the Korean Ceramic Society
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• v.39 no.7
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• pp.669-674
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• 2002

Ni-Zn ferrite was sintered by microwave hybrid sintering method using microwave energy of 2.45 GHz, 700 W in the temperature range of 900$^{\circ}C$ ∼ 1070$^{\circ}C$. A high density (98%TD) Ni-Zn ferrite, added Bi$_2$O$_3$ and CuO, with a single phase was obtained by microwave sintering at 970$^{\circ}C$ for 15 min. All the sintered samples showed sintered density over 90% of TD. These results indicate that the processing time and energy consumption can be reduced significantly by microwave hybrid sintering method.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.11
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• pp.1279-1290
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• 2007

In this paper, a cylindrical hybrid antenna which is spatially fed by an off-set linear feed array is described to form complex beam patterns. The linear feed array consists of twelve micro-strip patch elements and forms a flat-topped beam pattern with a beam-width of $90^{\circ}$ in the horizontal plane. The vertical curve on the cylindrical reflector with the linear feed array is shaped in order to form a cosecant beam pattern within the range of $-5^{\circ}$ to $-25^{\circ}$ in the vertical plane. To form complex beam patterns, the hybrid antenna with cylindrical reflector aperture of $140{\times}50\;cm$ was designed and fabricated to be operated within the IMT 2000 service band, and also electrical performances of the antenna were measured and analyzed.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.9
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• pp.786-790
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• 2016

This paper discusses numerically explored orientation effects on the thermal performance of hollow hybrid fin heat sinks (HHFHSs) under natural convection. A HHFHS consists of an array of hollow pin fins concatenated with plate fins and having perforations near the fin bases. Orientation effects on the footprint-based and mass-based thermal performance of the HHFHS were numerically studied for orientation angles ranging from $0^{\circ}$ to $180^{\circ}$. The performance of the HHFHS was compared with that of a pin fin heat sink (PFHS) having similar physical parameters. The results show that the thermal resistance of the HHFHS did not vary considerably from $0^{\circ}$ to $45^{\circ}$. The thermal resistance increased from $45^{\circ}$ to $90^{\circ}$, reached its maximum at $90^{\circ}$, and decreased consistently from $90^{\circ}$ to $180^{\circ}$. Dissimilar behaviors of the thermal resistance of the HHFHS vs. the PFHS resulted mainly from the effect of heat pumping induced by the internal flows of the hollow fins. Despite various orientations, the mass-based thermal resistance of the HHFHS was found to be nearly 30% smaller than that of the PFHS. This result shows the feasibility of the HHFHS for the lightweight thermal management of electronics under natural convection.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.1
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• pp.39-46
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• 2015

In this paper, a gas sensor using a modified $90^{\circ}$ hybrid coupler structure with conducting polymer which operates at 2.4 GHz is represented. Conducting polymers are used to the gas sensing material in proposed sensors. The conducting polymer varies its electrical property, such as work function and conductivity corresponding to the certain gas. To verify this variation of electrical property of conducting polymer at microwave frequencies, the conducting polymer is incorporated with the $90^{\circ}$ hybrid coupler structure, and this proposed sensor operates as reflection type variable attenuator and variable phase shifter. The conducting polymer is employed as impedence-variable transmission lines that cause a impedance mismatching between the general transmission line and conducting polymer. The experiment was conducted with 100 ppm ethanol gas at temperature of $28^{\circ}C$ and relative humidity of 85 %. As a result, the amplitude deviation of $S_{21}$ is 0.13 dB and the frequency satisfying ${\angle}S_{21}=360^{\circ}$ is shifted about 2.875 MHz.