• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.3
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• pp.1-11
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• 1999

It is now common practice to utilize the quadrature RF coils to improve the signal-to-noise ratio (SNR) in the Magnetic Resonance Imaging (MRI) System. In addition, to make such an available SNR improvement, it is mandatory to use a well-designed quadrature coupler, which facilitates a perfect 3-dB coupling and quadrature-phase shift. However, the four ports matching condition has to be well considered during the RF excitation and the signal detection period. This work investigates the effects of such a mismatching condition (especially, due to patient) from the analysis, simulation, and real implementation and firstly proposes dynamic loading technique for a quadrature coupler and transmitting/receiving switch module to minimize a patient mismatching and enhance a system reliability. Also, we designed and implemented the quadrature coupler and transmitting/receiving switch module using microstrip. As a result, the SNR of our MRI system using the microstrip quadrature coupler and transmitting/receiving switch module with dynamic load increases 3 dB compared with the old one using USA quadrature switch. Also, the power capability of quadrature coupler and transmitting/receiving switch module is 5-kw peak power. Considering power loss and reduction of size, we used a RT/duroid 6010 substrate with high permittivity and for simulation we use Compact Software.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.1
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• pp.94-100
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• 2002

In this paper, we proposed a 3 dB coupler using N-section parallel-coupled lines and designed a very compact one based on the analysis results. The coupled line has been analyzed by spectral domain method. After we obtain the s-parameters of N-section parallel-coupled lines by using port reduction method 4-port s-parameters are derived. The 3 dB couplers, which were fabricated, are not necessary to implement high impedance lines and tight coupling gaps as Lange Couplers because loose coupling is used. To realize a minimum section, we used the PCB that has high a dielectric constant and a thickness. The experimental results show that it has wide bandwidth of about 42 %(0.5 dB unbalance) from 3.6 GHz to 5.5 GHz and phase difference within 1 degree. Also, The isolation characteristics about 15 dB at its pass-band are obtained.

• Journal of IKEEE
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• v.18 no.4
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• pp.559-565
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• 2014

A 3 dB coupler has been designed and implemented using the most commonly used double-sided FR4 boards. The coupling and the bandwidth of the coupler are enhanced with the enlarged overlapped area of the coupler. Major design parameters are plotted as a design guide and the parameters are verified by simulation and measurement. The size of the manufactured coupler is $30{\times}14mm^2$. Its measured insertion loss and phase difference are 0.6 dB and $90.5^{\circ}$ at center frequency of 2.5 GHz, respectively. The operating frequency range is 1.72 GHz to 3.08 GHz for $3.6{\pm}0.5dB$ insertion loss. The coupler has the performance similar to that of conventional Lange coupler, and implementation of the coupler is easy and cheap with wide metal width and spacing and no additional wire bonding process.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2001.11a
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• pp.180-183
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• 2001

본 논문에서는 N개의 평행 결합선로를 이용한 3dB 결합기를 해석하였으며, 유도된 식에 의하여 최소의 단수와 크기로 3dB 결합기를 설계하였다. 기존의 Spectral Domain상에서 N단 평행 결합선로의 복잡한 관계식 유도를 S 파라미터 관계식으로 간단히 유도 하였으며, 유도된 식의 타당성을 위해 실제 제작 검증하였다. 제작된 결합기는 Loose coupling의 평행 결합 선로의 광대역 특성을 그대로 이용하기 때문에 Lange Coupler와 같은 높은 임피던스와 Tight coupling을 구현 할 필요가 없으며, wire bonding도 용이하게 된다. 최소의 단수로 구현하기 위해 RT/Duroid의 R06006과 같은 높은 유전율과 두꺼운 기판을 사용하여 2단으로 3dB 구현이 가능하게 하였다. 제작결과 3.6GHz에서5.5GHz로 대략 42%(0.5dB imbalance) 정도의 광대역특성을 가지고 위상오차도 1$^{\circ}$내외의 결합기를 구현할 수 있었고 격리도 특성 또한 대역 내에서 15dB 내외의 특성을 보였다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.4
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• pp.575-581
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• 2000

In this paper, a new active phase shifter is proposed using a vector sum method, and a unique digital phase control method of the circuit is suggested. The proposed scheme was designed and implemented using a Wilkinson power combiner/divider, a branch line 3 dB quadrature hybrid coupler and variable gain amplifiers (VGAs) using gate FETs(DGFETs). Furthermore, it was also shown that the proposed scheme is more efficient and works properly with the digital phase control method.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.5
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• pp.10-16
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• 2000

This paper presents new double-sided 3-dB branch-line coupler using CPW-to-Microstrip via-hole transitions for the multi-layer applications. The characteristic impedance is obtained using the even-odd mode method, and the circuit performance Is accurately estimated by the Finite Difference Time Domain(FDTD) method. The fabricated double-sided 3-dB branch-line coupler has less than 0.3 dB power dividing imbalance and 1。 phase imbalance, greater than 30 dB isolation, and 25 dB return loss over a 20% bandwidth centered at 2 GHz. Calculated and fabricated results show that this coupler provides better performance as compared to the conventional microstrip branch-line couplers.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.5
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• pp.383-388
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• 2018

This paper presents a 1.8 GHz six-port-based impedance modulator using CMOS technology, which can select an arbitrary load impedance with switch control. The proposed 1.8-GHz impedance modulator comprises a Wilkinson power divider, three quadrature hybrid couplers, and four SP3T switches for each load impedance selection. The measured insertion loss of -13 dB and the input/output return losses of >10 dB are achieved in the range of 1.4~2.2 GHz. The low drop output regulator for a stable 3.3 V DC power and the serial peripheral interface(SPI) for an easy digital control are integrated. The chip size, including the pads, is $1.7{\times}1.8mm^2$.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.3 s.357
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• pp.7-17
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• 2007

An analysis and design theory of an aperture-coupled cavity-fed back-to-back microstrip directional coupler is presented for the efficient and optimized design. For this purpose, an equivalent network is developed, and simple but accurate calculations of circuit element values are described. Design equations of the coupler are derived based on the equivalent circuit. In order to determine various structural design parameters, the evolutionary hybrid optimization method based on the genetic algorithm and Nelder-Mead method is invoked. As a validation check of the proposed theory and optimized design method, a 10 dB directional coupler was designed and fabricated. The measured coupling was 10.3 dB at 3 GHz, and the return loss and isolation were 31.8 dB and 30.5 dB, respectively. The directional coupler also showed very good quadrature phase characteristics. Good agreements between the measured and the design specifications fully validate the proposed network analysis and design procedure.

• Journal of IKEEE
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• v.17 no.3
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• pp.385-392
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• 2013

In this paper, microstrip antenna to enhance the isolation between transmitting port and receiving port under the proximity objects is proposed, and applied to the Doppler radar sensor working at 5.8GHz ISM band which detects vital signals of a human body. Two 3dB quadrature hybrids are placed around radiation patch to form a balanced structure between transmitting port and receiving port, such that it consistently provides enhanced Tx/Rx isolation and excellent return loss over nearby objects. It is theoretically analyzed and simulated to verify the validity of the proposed application. The fabricated antenna that is 2mm away from the human body, has more than 16 dB return loss and at least 30dB isolation over ISM frequency band of 5.8GHz.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.12 s.115
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• pp.1156-1163
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• 2006

This paper presents an ultra wideband(UWB) direct conversion mixer for IEEE 802.15.3a applications with simulation and measurement results. Since the direct conversion mixing causes dc-offset and even-order distortion, the proposed mixer adopts an anti-parallel diode pairs(APDPs) to solve these problems. The proposed mixer consists of an in-phase wilkinson power divider over $3.1{\sim}4.8GHz$, a wideband $45^{\circ}$ power divider over $1.5{\sim}2.4GHz$, and miniatured band pass filters(BPFs) for RF-LO isolations. The conversion loss is optimized with impedance matchings between APDPs and wideband components. The measured mixer shows the conversion loss of 13.5 dB, input third-order intercept-point($IIP_3$) of 7 dBm, and 1-dB gam compression point($P_{1dB}$) of -4 dBm. Quadrature(I/Q) outputs have the magnitude difference of about 1 dB and phase difference of ${\pm}3^{\circ}$.