Yongchae Jeong

Chonbuk National University, Sŏul, Seoul, South Korea

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Publications (63)60.47 Total impact

  • Yongchae Jeong, Girdhari Chaudhary
    IET Microwaves Antennas & Propagation 01/2015; · 0.97 Impact Factor
  • Phirun Kim, Girdhari Chaudhary, Yongchae Jeong
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    ABSTRACT: This article presents the design of a wideband impedance transformer with out-of-band suppression characteristics. The out-of-band suppression characteristics are obtained by loading several transmission zeros at both the lower and upper stop-bands. For experimental validation, a 50-to-25 Ω transformer has been implemented at a center frequency (f0) of 2.6 GHz. The measured results were in good agreement with simulations, showing a return loss better than 20 dB over 0.92 GHz (2.1–3.02 GHz) and an out-of-band suppression better than 18 dB over DC to 1.42 and 3.8 to 6.65 GHz. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2612–2616, 2014
    Microwave and Optical Technology Letters 11/2014; 56(11). · 0.59 Impact Factor
  • Girdhari Chaudhary, Yongchae Jeong
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    ABSTRACT: This article presents a novel approach to the design of a compact wideband negative group delay (NGD) network using cross coupling between open stubs. The NGD time can be controlled by external series resistors, whereas the NGD bandwidth can be controlled by the coupling coefficient between open stubs. To verify the design concept, the NGD network operating at center frequency of 1.96 GHz was designed and fabricated. From the measurement results, a maximum achievable NGD time of −1.1 ± 0.2 ns was obtained over a 410 MHz BW with a maximum signal attenuation of 29.23 dB. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2495–2497, 2014
    Microwave and Optical Technology Letters 11/2014; 56(11). · 0.59 Impact Factor
  • Girdhari Chaudhary, Yongchae Jeong
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    ABSTRACT: This paper presents the design and analysis of novel topologies of reflective-type negative-group-delay (NGD) networks with very small signal attenuation (SA). The proposed topologies are based on short-circuited coupled lines. Theoretical analysis shows that predefined group-delay (GD) time with very small SA can be obtained due to the high characteristic impedance of a coupled line and the small coupling coefficient. Due to the very low SA characteristics of the proposed networks, the burden of compensating general-purpose gain amplifiers can be reduced and provide stable operations while integrated to RF systems. This paper also analyses performance degradation of the GD time and SA of the proposed NGD networks according to the temperature-dependent resistance variation. For an experimental validation of the proposed topologies, distributed microstrip line NGD networks (type-I and type-II) are designed, simulated, and measured for a wideband code division multiple access (WCDMA) downlink frequency operating at a center frequency of 2.14 GHz. These results show a GD time of $-{hbox {7.27 ns}}$ with an SA of 7.43 dB for the type-I NGD network, and $-{hbox{6.3}}$ and 9.23 dB for the type II- NGD network at the center frequency, and agree closely with the simulations. To enhance the NGD bandwidth, two NGD networks with slightly different center frequencies are connected in parallel, which provides wider bandwidth than the single stage case and shows practical applicability.
    IEEE Transactions on Microwave Theory and Techniques 10/2014; 62(10):2316-2324. · 2.94 Impact Factor
  • Girdhari Chaudhary, Yongchae Jeong, Jongsik Lim
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    ABSTRACT: In this letter, a design for a dual-band negative group delay circuit (NGDC) using dual-plane U-shaped defected structures is presented. The center frequency and group delay (GD) time of each band are separately controlled by a defected microstrip structure (DMS) and a defected ground structure (DGS) with resistors connected across the DMS and DGS slots. To verify the design concept, the NGDC is designed, fabricated, and compared with the circuit simulation. To get a wideband bandwidth, two NGDCs with different center frequencies are connected in a cascade design. From the measurements, the GD times of $-4.54 pm 0.6~{rm ns}$ and $-4.20 pm 0.5~{rm ns}$ are obtained at 3.46–3.58 GHz and 5.10–5.20 GHz, respectively.
    IEEE Microwave and Wireless Components Letters 08/2014; 24(8):521-523. · 2.24 Impact Factor
  • Namsik Ryu, Seunghyun Jang, K.C. Lee, Yongchae Jeong
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    ABSTRACT: This paper presents a novel CMOS Doherty power amplifier (PA) with an impedance inverter using a variable balun transformer (VBT) and adaptive bias control of an auxiliary amplifier. Unlike a conventional quarter-wavelength $(lambda /4)$ transmission line impedance inverter of a Doherty PA, the proposed VBT impedance inverter can achieve load modulation without any phase delay circuit. As a result, a $lambda /4$ phase compensation circuit at the input path of the auxiliary amplifier can be removed, and the total size of the Doherty PA can be reduced. Additionally, an enhancement of the power efficiency at backed-off power levels can successfully be achieved with an adaptive gate bias in a common gate stage of the auxiliary amplifier. The PA, fabricated with 0.13-µm CMOS technology, achieved a 1-dB compression point (P1 dB) of 31.9 dBm and a power-added efficiency (PAE) at P1 dB of 51%. When the PA is tested with 802.11g WLAN orthogonal frequency division multiplexing (OFDM) signal of 54 Mb/s, a 25-dB error vector magnitude (EVM) compliant output power of 22.8 dBm and a PAE of 30.1% are obtained, respectively.
    IEEE Journal of Solid-State Circuits 06/2014; 49(6):1356-1365. · 3.11 Impact Factor
  • Girdhari Chaudhary, Yongchae Jeong, Jongsik Lim
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    ABSTRACT: This paper presents a novel approach to the design and implementation of a distributed transmission line negative group delay filter (NGDF) with a predefined negative group delay (NGD) time. The newly proposed filter is based on a simple frequency transformation from a low-pass filter to a bandstop filter. The NGD time can be purely controlled by the resistors inserted into the resonators. The performance degradation of the NGD time and signal attenuation (SA) of the proposed NGDF according to the temperature dependent resistance variation is also analyzed. From this analysis, it is shown that the NGD time and SA variations are less sensitive to the resistance variation compared to those of the conventional NGD circuit. For an experimental validation of the proposed NGDF, a two-stage distributed microstrip line NGDF is designed, simulated, and measured at an operating center frequency of 1.962 GHz. These results show a group delay time of $-{hbox {7.3 ns}}$ with an SA of 22.65 dB at the center frequency and have good agreement with the simulations. The cascaded response of two NGDFs operating at different center frequencies is also presented in order to obtain broader NGD bandwidth. NGDFs with good reflection characteristics at the operating frequencies are also designed and experimentally verified.
    IEEE Transactions on Microwave Theory and Techniques 02/2014; 62(2):234-243. · 2.94 Impact Factor
  • Girdhari Chaudhary, Yongchae Jeong
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    ABSTRACT: In this letter, a novel design and implementation of a distributed negative group delay circuit (NGDC) with reduced signal attenuation is demonstrated. By inserting an additional transmission line Z2 into the conventional NGDC, the proposed NGDC provides further design parameters in order to obtain the required differential-phase group delay (GD) time and help to reduce the signal attenuation. As a result, the number of gain compensating amplifiers can be reduced, which can contribute to the efficiency enhancement as well as the stable operation when integrated into the RF system. Both theory and experiment are provided to validate the proposed structure. From the experiment, for the same GD time of -7.9 ns, the signal attenuation of the proposed circuit is 16.5 dB, an improvement signal attenuation of the conventional circuit of 19.2 dB.
    IEEE Microwave and Wireless Components Letters 01/2014; 24(1):20-22. · 2.24 Impact Factor
  • Girdhari Chaudhary, Yongchae Jeong
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    ABSTRACT: This letter presents a novel design and implementation of a transmission-line negative group delay (NGD) network with improved signal attenuation (SA). Theoretical analysis shows that the NGD time can be controlled by characteristic impedance of the coupled line, coupling coefficients, and resistor, respectively. The low SA characteristic in the proposed structure is obtained due to high characteristic impedance of the coupled line. To validate the proposed structure, the transmission-line NGD networks are fabricated and measured at 2.14 GHz. From the experiment, the differential-phase group delay (GD) time and SA for a single stage are ${-}$ 6.16 ns and 8.65 dB over bandwidth of 15 MHz, respectively. For bandwidth enhancement, two-stage NGD networks with slightly different center frequencies are designed and fabricated, where GD of ${-}7.48 pm 0.84~$ns and SA of 17.45 dB were obtained over a bandwidth of 28 MHz.
    IEEE Antennas and Wireless Propagation Letters 01/2014; 13:1039-1042. · 1.95 Impact Factor
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    ABSTRACT: A new defected ground structure (DGS) microstrip line that is free from the ground contact problem is described together with its application example. The proposed DGS microstrip line adopts a double-layered substrate. The first layer contains the microstrip line and DGS patterns on the top and bottom planes as with the conventional DGS line. The second substrate, of which upper metal plane has already been removed, is attached to the bottom ground plane of the first layer. This structure prevents the ground plane of the first substrate with DGS patterns from making contact with the metal housing. The proposed DGS microstrip line has advantageous transmission and rejection characteristics, without the ground contact problem of DGS patterns, which has been a critical problem of previous DGS lines. A 10 dB branch line hybrid coupler is designed and measured, as an example of application of the proposed DGS microstrip line.
    International Journal of Antennas and Propagation 07/2013; 2013. · 0.83 Impact Factor
  • Source
    Girdhari Chaudhary, Yongchae Jeong, Jongsik Lim
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    ABSTRACT: This paper presents a novel approach to the design of tunable dual-band bandpass filter (BPF) with independently tunable passband center frequencies and bandwidths. The newly proposed dual-band filter principally comprises two dual-mode single band filters using common input/output lines. Each single BPF is realized using a varactor-loaded transmission-line dual-mode resonator. The proposed filter also offers switchable characteristics to select either of the passbands (either the first or the second passband only). To suppress the harmonics over a broad bandwidth, defected ground structures are used at input/output feeding lines without degrading the passbands characteristics. From the experimental results, it was found that the proposed filter exhibited the first passband center frequency tunable range from 1.48 to 1.8 GHz with a 3-dB fractional bandwidth (FBW) variation from 5.76% to 8.55% and the second passband center frequency tunable range from 2.40 to 2.88 GHz with the 3-dB FBW variation from 8.28% to 12.42%. The measured harmonic results of the proposed filters showed a rejection level of 19 dB, which is up to more than ten times of the highest center frequency of the first passband without degradation of the passbands.
    IEEE Transactions on Microwave Theory and Techniques 06/2013; 61(1):107-116. · 2.94 Impact Factor
  • Source
    Kyunghoon Kwon, Jongsik Lim, Yongchae Jeong, Dal Ahn
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    ABSTRACT: A size-reduced high frequency mixer designed by adopting artificial dielectric substrate is described in this work. The artificial dielectric substrate is composed by stacking the lower substrate in which a lot of metalized via-holes exist, and upper substrate on which microstrip lines are realized. The effective dielectric constant increases due to the inserted lots of via-holes, and this may be applied to size-reduction of high frequency circuits. In this work, in order to present an application example of size-reduction for active high frequency circuits using the artificial dielectric substrate, a 8GHz single gate mixer is miniaturized and measured. It is described that the basic circuit elements for mixers such as hybrid, low pass filter, and matching networks can be replaced by the artificial dielectric substrate for size-reduction. The final mixer has 55% of size compared to the normal one. The measured average conversion gain is around 3dB which is almost similar result as the normal circuit.
    Transactions of the Korean Institute of Electrical Engineers 05/2013; 62(5).
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    ABSTRACT: In this paper, a design of negative group delay circuit (NGDC) with independently tunable center frequency and group delay (GD) is presented. Since the proposed structure consists of a parallel RLC resonance circuit, it is possible to obtain a variable negative GD by using a variable resistor and an adjustment of center frequency of GD is possible due to a variable inductor. To get the pure variable resistor, the transmission line (TL) terminated with the PIN diode is used. Similarly, the variable inductor is realized by TL terminated with the varactor diode. To show the effectiveness of the proposed NGDC, it is designed at 2.14 GHz of WCDMA downlink band. The measured negative GD time is -2 ~ -20ns, and are able to change the center frequencies of negative GD in the range of 2.04 ~ 2.24 GHz.
    Microwave Conference Proceedings (APMC), 2013 Asia-Pacific; 01/2013
  • Phirun Kim, Girdhari Chaudhary, Yongchae Jeong
    Progress In Electromagnetics Research 01/2013; 141:443-461. · 5.30 Impact Factor
  • Girdhari Chaudhary, Yongchae Jeong, Jongsik Lim
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    ABSTRACT: In this paper, a design of miniaturized negative group delay circuit (NGDC) using U-shaped defected microstrip structure (DMS) and lumped elements is presented. The resonant center frequency and group delay (GD) time are controlled by an external capacitor and resistor connected across the DMS slot. To verify the design concept, a single stage NGDC is designed, fabricated and compared with the circuit simulation. To get wideband bandwidth of GD, two stages NGDC is also demonstrated and the GD of −7 ns with the maximum insertion loss of 34 dB was obtained over 60 MHz bandwidth.
    Microwave Symposium Digest (IMS), 2013 IEEE MTT-S International; 01/2013
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    ABSTRACT: A novel design of compact negative group delay circuit (NGDC) using U-shaped defected ground structure (DGS) is presented in this paper. The required group delay (GD) time can be controlled by an external resistor connected across the DGS slot. For experimental verification, a single stage NGDC is designed, fabricated, and compared with a circuit simulation. To enhance NGD bandwidth, two stages NGDC with the different center frequencies in cascade are demonstrated and GD of -3.8 ns with maximum signal attenuation of 37.10 dB was obtained on 3.45-3.55 GHz.
    Microwave Conference Proceedings (APMC), 2013 Asia-Pacific; 01/2013
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    ABSTRACT: In this letter, a high efficiency RF‐DC conversion circuit for RF energy harvesting system (EHS) is proposed.The proposed circuit consists of Villard voltage doubler, the input and output termination networks which can suppress the unwanted RF signals produced by Schottky diodes. The fabricated circuit operating at 2.45 GHz has a maximum RF‐DC conversion efficiency of 83.37% and output voltage of 11.30 V at an input RF power of 140 mW. The proposed circuit has an advantage of simple design which helps to reduce the design cost of EHSs. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:2330–2335, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27087
    Microwave and Optical Technology Letters 10/2012; 54(10). · 0.62 Impact Factor
  • Source
    Girdhari Chaudhary, Yongchae Jeong, Jongsik Lim
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    ABSTRACT: This paper presents a novel approach to the design of tunable dual-band bandpass filter with broadband harmonic suppression characteristics. The proposed filter structure offers the possibility of two tunable passbands, as well as a fixed first passband and controllable second passband. The tunable passband frequency usually causes a shift of the harmonics, which need to be suppressed to improve out-of the passband characteristics. In order to suppress the harmonics over a broad bandwidth, defected ground structures are used at input and output feeding lines without degrading the passbands characteristics. Both theory and experiment are provided to validate the proposed filter. From the experimental results, it is found that the proposed filter exhibits a first passband center frequency tunable range of 34.14% from 0.85 to 1.2 GHz with the almost constant 3-dB fractional bandwidth (FBW) of 13% and second passband center frequency tunable range of 41.81% from 1.40 to 2.14 GHz with the 3-dB FBW of 11%. The measured results of the proposed filters show a rejection level of 20 dB up to more than ten times of second passband frequency can be obtained, thereby ensuring broad harmonics rejection characteristics without degradation of passbands. The measurement data have good agreement with the simulation.
    IEEE Transactions on Microwave Theory and Techniques 07/2012; 60(7):2115-2123. · 2.94 Impact Factor
  • Source
    Namsik Ryu, Jae-Ho Jung, Yongchae Jeong
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    ABSTRACT: This paper proposes a high-efficiency power amplifier (PA) with uneven bias. The proposed amplifier consists of a driver amplifier, power stages of the main amplifier with class AB bias, and an auxiliary amplifier with class C bias. Unlike other CMOS PAs, the amplifier adopts a current-mode transformer-based combiner to reduce the output stage loss and size. As a result, the amplifier can improve the efficiency and reduce the quiescent current. The fully integrated CMOS PA is implemented using the commercial Taiwan Semiconductor Manufacturing Company 0.18- RF-CMOS process with a supply voltage of 3.3 V. The measured gain, , and efficiency at are 29 dB, 28.1 dBm, and 37.9%, respectively. When the PA is tested with 54 Mbps of an 802.11g WLAN orthogonal frequency division multiplexing signal, a 25-dB error vector magnitude compliant output power of 22 dBm and a 21.5% efficiency can be obtained.
    Etri Journal 01/2012; 34(6). · 0.95 Impact Factor
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    ABSTRACT: A design of size-reduced 90° branch line coupler (BLC) is described in this work. A common defected ground structure (CDGS) is adopted to design the coupler. Common DGS patterns are realized on the common ground plane of double-sided microstrip lines of which ground planes are attached to each other back-to-back. The CDGS patterns play a great role in size-reduction of microwave circuits. As an example, a BLC is designed, fabricated and measured at 1GHz for the verification of the size-reduction using CDGS. The size of the fabricated coupler is less than 50% of the normal one without any critical degradation in performances. The measured S-parameters well agree with the simulation results.
    Antennas and Propagation Society International Symposium (APSURSI), 2012 IEEE; 01/2012

Publication Stats

183 Citations
60.47 Total Impact Points

Institutions

  • 2007–2013
    • Chonbuk National University
      • Department of Electronic Engineering
      Sŏul, Seoul, South Korea
    • Soonchunhyang University
      • Department of Electrical and Communication Engineering
      Onyang, Chungcheongnam-do, South Korea
  • 2008
    • Georgia Institute of Technology
      • School of Electrical & Computer Engineering
      Atlanta, Georgia, United States