Sangwook Nam

Seoul National University, Sŏul, Seoul, South Korea

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Publications (158)126.61 Total impact

  • Hee-Ran Ahn, Sangwook Nam
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    ABSTRACT: Wideband coupled-line ring hybrids are presented for high power-division ratios. For this, an equivalent circuit to make the characteristic impedance of a transmission-line section lower is firstly investigated, based on a Π-type lumped-element equivalent circuits. Design formulas of four types of equivalent circuits (LΠ-, LT-, LS2-, and LS1-types) are then derived, and N is introduced for more design flexibility and wideband performance. The LS2-type with N=1 is composed of one transmission-line section and two identical series inductances at both ends, which cannot be used for the ring hybrids with the high power-division ratios. To avoid the problem, modified LS2-type (MLS2-type) with N is additionally suggested, and that with N=1 is intensively discussed. Using two of those, LS1-type with N=2 and MLS2-type with N=1, the coupled-line ring hybrids with 13- and 11-dB power-division ratios are fabricated. The measured results show good agreement with those predicted.
    IEEE Transactions on Microwave Theory and Techniques 05/2013; 61(5):1768-1780. · 2.23 Impact Factor
  • Hee-Ran Ahn, Sangwook Nam
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    ABSTRACT: New symmetric equivalent circuits are suggested for 90° and 270° transmission-line sections, with which compact coupled-line ring and branch-line hybrids can be designed and fabricated. For this purpose, firstly stepped-impedance transmission-line (SITL) sections, being equivalent to a uniform transmission-line section with arbitrary electrical lengths, are synthesized, and design formulas for the SITL sections are derived. Secondly, three types of equivalent circuits are introduced by combining the SITL sections with coupled-line Π-, modified Π-, or T-type, and are called stepped-impedance coupled-line Π-type (SCΠ ), stepped-impedance modified T-type (SMT), and stepped-impedance modified Π-type (SMΠ). The SCΠs are for 270° transmission-line sections, while both SMTs and SMΠs are for 90° transmission-line sections. Based on the suggested equivalent circuits, compact coupled-line ring and branch-line hybrids designed at 1 GHz are fabricated, and the measured bandwidth of the ring hybrid is 50% with 15-dB return loss. The measured results may be considered as excellent, reflecting their total transmission-line lengths of 183° and 111° for the ring and branch-line hybrids, respectively.
    IEEE Transactions on Microwave Theory and Techniques 03/2013; 61(3):1067-1078. · 2.23 Impact Factor
  • Sumin Yun, Sangwook Nam
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    ABSTRACT: A technique for miniaturization of a cavity-backed crossed-slot antenna is presented. A conventional cavity-backed crossed-slot antenna is a square half guided-wavelength on a side. The proposed technique reduces the size of the cavity by folding each side. By folding the cavity, the guided length inside the cavity can be increased. The size of a cavity-backed crossed-slot antenna using proposed technique operating at 2.45 GHz is 26 mm × 26 mm. Compared to the conventional cavity-backed slot antenna, which has a size of 60 × 60 mm, more than 81.2 % size reduction is achieved with proposed technique.
    Antennas and Propagation (EuCAP), 2013 7th European Conference on; 01/2013
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    ABSTRACT: A fully-integrated low power 77 GHz radar transceiver in 65 nm CMOS process is presented. It consists of a low-noise amplifier (LNA), a down-conversion mixer, a power amplifier (PA), and a frequency synthesizer based on a tripler. The receiver front-end provides a conversion gain of 21 dB, and the PA has an output power over 10 dBm. The phase noise of VCO is -75 dBc/Hz at 1-MHz offset. The total dc power dissipation of the transceiver is 217 mW and the size of the chip is 0.8 × 1.1 mm2.
    Microwave Conference Proceedings (APMC), 2013 Asia-Pacific; 01/2013
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    ABSTRACT: A digital RF receiver front-end employing a FIR(Finite Impulse Response) filter is proposed for SAW-less receiver architecture, where the large out-of-band interferer can be rejected selectively by using a scalable frequency response property of FIR filter. The FIR filter, followed by the transconductor stage and current-commutating passive mixer, operates in current domain to improve the linearity. Also, the clock generator circuit can be simplified by making the FIR filter operate with 8-phase clock signal. The designed receiver front-end is fabricated using UMC 0.13 μm CMOS process. The chip shows unwanted blocker rejection over 80 dB, with good linearity of +3.94 dB IIP3.
    Microwave Conference Proceedings (APMC), 2013 Asia-Pacific; 01/2013
  • Source
    Yoon Goo Kim, Jongmin Park, Sangwook Nam
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    ABSTRACT: We derive the Z-parameters for the two coupled antennas used for wireless power transfer under the assumption that the antennas are canonical minimum scattering antennas. Using the Z-parameter and the maximum power transfer efficiency formula, we determine the maximum power transfer efficiency of wireless power transfer systems. The results showed that the maximum power transfer efficiency increases as the mode number or the radiation efficiency increases. To verify the theory, we fabricate and measure two different power transfer systems: one comprises two antennas generating mode; the other comprises two antennas generating mode. When the distance between the centers of the antennas was 30 cm, the maximum power transfer efficiency of the antennas generating the mode increased by 62 % compared to that of the antennas generating the mode.
    Journal of electromagnetic engineering and science. 01/2013; 13(1).
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    Hyun-Jin Shim, Jong-Min Park, Sangwook Nam
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    ABSTRACT: The effective way of estimation and analysis of EMI(Electromagnetic Interference) in Wireless Power Transfer System operating at 13.56 MHz is proposed. In this paper methodology of driving magnetic field strength and electric loop current of two antennas which are in free space and on PEC plane using image theory and duality is proposed. Perfect electric conductor(PEC) is planar, infinite in extent, and perfectly conducting plane. And we will refer it as PEC plane. A equivalent circuit model is used to analyze. Using this theoretical analysis, we can derive maximum magnetic field strength of the far-field region numerically using measured data of near-field maximum magnetic field strength. The experimental results using commercial numerical simulation tool are in agreement with the theoretical results. Also, using the derivation of maximum magnetic field strength in the far-field region, we can easily estimate the maximum allowable power dissipation that meets EMI regulations.
    The Journal of Korean Institute of Electromagnetic Engineering and Science. 01/2013; 24(9).
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    Dong-Yeon Kim, Sangwook Nam
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    ABSTRACT: The 4 by 4 series slot sub-array antenna is proposed using substrate integrated waveguide(SIW) technology for 35 GHz of Ka band application. The proposed antenna is realized with multi-layered structure for compact size and easy integration features. 4 by 4 radiating slots are arrayed on top PCB with equal spacing and the feeding SIWs are arranged on middle and bottom PCBs for uniform power distribution. The multi-layered antenna is realized using RT/Duroid 5880 that has dielectric constant of 2.2 and the total antenna size is . The individual parts such as radiators and feeding networks are simulated using full-wave simulator CST MWS. Furthermore, the total sub-array antenna also fabricated and measured the electrical performances such as impedance bandwidth under the criteria of -10 dB(490 MHz), maximum gain(18.02 dBi), sidelobe level(SLL)(-11.0 dB), and cross polarization discrimination (XPD)(-20.16 dB).
    The Journal of Korean Institute of Electromagnetic Engineering and Science. 01/2013; 24(4).
  • Hee-Ran Ahn, Sangwook Nam
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    ABSTRACT: A 3-dB power divider (PD) terminated in equal complex impedances is presented. It consists of two identical 90 ° transmission-line sections and an isolation circuit, being composed of resistance and capacitance, or resistance and inductance, depending on the termination impedances. If the termination impedance has capacitance, the isolation impedance should consist of inductance, and therefore, the isolation circuit should be implemented with a chip inductor. However, the chip inductor contains additional stray capacitance and resistance, which lead to undesired frequency performance. To avoid the usage of the chip inductors, even with arbitrary termination impedances, three design methods by adding transmission-line sections, adding open stubs, and adding short stubs are introduced. The PDs designed by the three methods can have not only desired isolation impedances, but also the total size of the PDs can be reduced. To verify the suggested theory, three PDs are measured. For one PD with adding transmission-line sections, the measured reflection coefficients at all ports are -43.29, -41.55, and -51.69 dB, the isolation is 56.7 dB, and the power division is -3.042 dB at a design center frequency of 1 GHz, which agree quite well with those predicted.
    IEEE Transactions on Microwave Theory and Techniques 01/2013; 61(11):3872-3883. · 2.23 Impact Factor
  • Yoon Goo Kim, Sangwook Nam
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    ABSTRACT: A method to determine the generalized scattering matrix of an antenna using characteristic modes is presented. When the characteristic currents flowing at a feed point, the radiation patterns of the characteristic currents, and the eigenvalues are known, the generalized scattering matrix can be calculated. It is shown that an antenna whose behavior is dominated by a single characteristic mode becomes a minimum scattering antenna. The formula is verified using a two wavelength dipole antenna and a bow-tie antenna.
    IEEE Transactions on Antennas and Propagation 01/2013; 61(9):4848-4852. · 2.33 Impact Factor
  • Yoon Goo Kim, Sangwook Nam
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    ABSTRACT: To investigate the wireless power transfer, we need to analyze the antenna coupling. We derive a Z-parameter between two antennas using spherical modes and the addition theorem. We present formulas that calculate the maximum power transfer efficiency and the optimum load impedance for the antennas generating arbitrary modes. To simplify the formula, we assume that the antennas are canonical minimum scattering antennas. We find from the formula presented in this paper that the power transfer efficiency increases as the mode number and the radiation efficiency increase.
    01/2012;
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    ABSTRACT: According to the MIMO theory, the capacity of a channel can be increased by using multiple antennas at each transmitting and receiving end. In order to construct a near-field 2×2 MIMO system, an antenna array, which is composed of short electric dipoles with different polarizations, can be used. When small antennas are used, the characteristics of the channel matrix can be analyzed based on the addition theorem, and thus the capacity can also be easily estimated.
    Antenna Technology and Applied Electromagnetics (ANTEM), 2012 15th International Symposium on; 01/2012
  • Source
    Youndo Tak, Sangwook Nam
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    ABSTRACT: An extended mode-based analysis for near-field coupled antennas is proposed. Based on this analysis, a method for estimating 3 dB bandwidth of near-field communication (NFC) systems with non-identical electrically small antennas is also proposed. The estimated results are in good agreement with the results from a full EM simulation.
    IEEE Transactions on Antennas and Propagation 01/2012; 60(1):421-424. · 2.33 Impact Factor
  • Sumin Yun, Sangwook Nam
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    ABSTRACT: The optimum thickness distribution for the antenna efficiency enhancement of a resonant line antenna is proposed. Unlike a standard printed circuit board process, which removes the unwanted metal from the substrate, inkjet-printing technology is a additive process. By using the inkjet-printing technology, the thickness of a line can be controlled. The calculated loss along the antenna showed that the power loss along the line antenna is minimum when thickness and current has a same distribution. For the demonstration, the continuous sinusoidal distribution is replaced by the 5-layered dipole antenna. The simulated results show that the proposed distribution has a 2 %p higher antenna efficiency and 0.12 dBi higher gain compared to the those of the flat dipole antenna with a same volume. The proposed thickness distribution can be used to enhance the antenna efficiency of a resonant line antenna with the known current distribution.
    Antennas and Propagation (ISAP), 2012 International Symposium on; 01/2012
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    ABSTRACT: We found the optimal conditions for an efficient wireless power transfer system (WPTS).In addition, we found that a class‐D power amplifier (PA) has an advantage as a source when the input resistance changes with the position of the receiving antenna. Finally, the proposed WPTS was verified through the experimental results. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27062
    Microwave and Optical Technology Letters 01/2012; 54(10). · 0.59 Impact Factor
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    Hee-Ran Ahn, Sangwook Nam
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    ABSTRACT: A design method for the bandpass filters with even number of resonators is presented for compacter size and wider bandwidth. The design method is based on the conventional filters with two resonators defined as a scattering parameter at a given frequency and a characteristic impedance of a 0$^{\circ}$ lumped-element equivalent circuit. The filter designed in this paper can be terminated in equal impedances and may have ripple responses at the same time for the wider bandwidths. Since the filter suggested in this paper has advantages that both Butterworth and Chebyshev filters possess, it is called a Butter–Cheby filter to distinguish from conventional filters. For better performance of the Butter–Cheby filter, a way to make transmission zeros is also discussed. To verify the design method, a Butter–Cheby filter with four resonators having 0.01-dB ripple is fabricated with distributed and lumped elements and measured at a design center frequency of 1 GHz. The measured results are in good agreement with the prediction, achieving less than 0.4-dB insertion loss, more than 20-dB return loss, and a transmission zero of 2 GHz.
    IEEE Transactions on Microwave Theory and Techniques 01/2012; 60(6):1549-1559. · 2.23 Impact Factor
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    ABSTRACT: The design method for a standing-wave series slot array antenna with 45$^{\circ}$ -inclined linear polarization in the Ka-band is presented. The proposed 16$\,\times\,$8 planar slot array antenna consisted of arrays with alternating reactance slot pairs that could achieve impedance matching and uniform field excitation, simultaneously. Furthermore, the grating lobes were effectively suppressed with the help of these radiating units due to the one-half guided wavelength slot spacing. An equivalent circuit analysis was done to evaluate the input impedances of the radiating and feeding lines with the impedance recursive formulas as well as the mode voltages of the radiating slot elements. In addition, a wideband transition with a 30.13% bandwidth under the criteria of less than VSWR 1.5:1 was presented to provide the necessary power with the minimal reflection and to prevent the distortion of the radiation patterns. The proposed planar slot array antenna occupied an aperture area of 57.4 $\,\times\,$51.6 mm. The measured bandwidth, gain, and efficiency were 990 MHz (2.88%), 24.3 dBi, and 53.7%, respectively. Furthermore, the side lobe levels (SLLs) were verified for each cutting plane with ${- 13.57}~{\rm dB}$ and ${-}{13.17}~{\rm dB}$, respectively. The proposed antenna structure was achieved with a substrate integrated waveguide (SIW) with the low costs and lightweight features.
    IEEE Transactions on Antennas and Propagation 01/2012; 60(4):1785-1795. · 2.33 Impact Factor
  • Sumin Yun, Dong-Yeon Kim, Sangwook Nam
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    ABSTRACT: A novel technique for the bandwidth enhancement of a cavity-backed slot antenna is presented. A via-hole located above the slot creates an additional resonance at a higher frequency by shortening the effective length of the slot. The location of the via-hole can be changed to determine the second resonance frequency of the antenna. With proper placement of the via-hole, the bandwidth of cavity-backed slot antenna can be increased. The fabricated antenna has a 60% wider bandwidth than a cavity-backed slot antenna without a via-hole. The proposed antenna maintains high radiation efficiency and gain, which are characteristics of a conventional cavity-backed slot antenna. The proposed technique is especially useful for enhancing the bandwidth of a cavity-backed slot antenna in a limited area.
    IEEE Antennas and Wireless Propagation Letters 01/2012; · 1.67 Impact Factor
  • Sumin Yun, Dong-Yeon Kim, Sangwook Nam
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    ABSTRACT: A technique for enhancement of bandwidth and efficiency of a cavity-backed slot antenna is proposed. The bandwidth of the cavity-backed slot antenna depends on the Q of the slot and the cavity. The proposed technique removes the substrate under the slot to decrease the capacitance of the slot. Because a half-wavelength slot is considered a parallel resonant circuit at resonant frequency, lowered capacitance increases the bandwidth of the antenna. Antenna efficiency also can be enhanced by the proposed technique. The dielectric loss, which is produced by the E-field across the slot, is effectively decreased by removing the substrate under the slot. Various simulation results of demonstration of the proposed technique are given. The proposed antenna, which was fabricated on a 2-mm-height FR-4 substrate, shows 6.2% higher antenna efficiency and 24% wider bandwidth compared to the conventional cavity-backed slot antenna, which has a whole substrate. The proposed technique is effective in enhancing the efficiency and bandwidth of a cavity-backed slot antenna.
    IEEE Antennas and Wireless Propagation Letters 01/2012; · 1.67 Impact Factor
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    ABSTRACT: This paper presents a high-speed and high-efficiency capsule endoscopy system. Both a transmitter and a receiver were optimized for its application through an analysis of the human body channel. ON-OFF keying modulation is utilized to achieve low power consumption of the in-body transmitter. A low drop output regulator is adopted to prevent performance degradation in the event of a voltage drop in the battery. The receiver adopts superheterodyne structure to obtain high sensitivity, considering the link budget from the previous analysis. The receiver and transmitter were fabricated using the CMOS 0.13-μm process. The output power of the transmitter is -1.6 dB·m and its efficiency is 27.7%. The minimum sensitivity of the receiver is -80 dB·m at a bit error ratio (BER) of 3 × 10 (-6). An outer wall loop antenna is adopted for the capsule system to ensure a small size. The integrated system is evaluated using a liquid human phantom and a living pig, resulting in clean captured images.
    IEEE transactions on bio-medical engineering 12/2011; 59(4):1005-11. · 2.15 Impact Factor

Publication Stats

1k Citations
126.61 Total Impact Points

Institutions

  • 1995–2012
    • Seoul National University
      • • Department of Electrical and Computer Engineering
      • • School of Computer Science and Engineering
      Sŏul, Seoul, South Korea
  • 2011
    • Yonsei University
      • Department of Electrical and Electronic Engineering
      Seoul, Seoul, South Korea
  • 2008–2009
    • Sungkyunkwan University
      Sŏul, Seoul, South Korea
    • Samsung Thales
      Sŏul, Seoul, South Korea
  • 2007
    • Chung-Ang University
      • School of Electrical and Electronics Engineering
      Seoul, Seoul, South Korea
  • 2004
    • Chonbuk National University
      • Department of Electronic Engineering
      Seoul, Seoul, South Korea
  • 2000
    • Soonchunhyang University
      Onyang, South Chungcheong, South Korea