Yongchae Jeong

Chonbuk National University, Sŏul, Seoul, South Korea

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Publications (56)25.25 Total impact

  • 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
  • G. 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. · 1.78 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. · 0.68 Impact Factor
  • Source
    G. 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. · 2.23 Impact Factor
  • [Show abstract] [Hide abstract]
    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
  • 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
  • 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 01/2013; 62(5).
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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
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    ABSTRACT: In this paper, a design of tunable microstrip transmission line negative group delay circuit (NGDC) using p-i-n diodes is proposed. The design was based on reflective parallel R-L-C circuit and group delay (GD) can be varied with help of variable resistance. To get the variable resistance, the transmission line (TL) terminated with p-i-n diode is used. The GD is varied with help of bias voltages of p-i-n diodes. Both design equations and design procedures are presented. The measured GD time variation range is 0 ~ -20 ns and well agreed with simulation results.
    Radio-Frequency Integration Technology (RFIT), 2012 IEEE International Symposium on; 01/2012
  • G. Chaudhary, Phirun Kim, Yongchae Jeong, Jongsik Lim
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    ABSTRACT: This paper presents a compact dual-mode tunable bandpass filter (BPF) with independently tunable center frequencies and bandwidths based on varactor loaded transmission line dual-mode resonator. The center frequency can be controlled by tuning the even-mode and odd-mode resonant frequencies of the dual-mode resonator. The bandwidth of passband can be tuned by fixing the odd-mode and changing the even-mode resonant frequency. To validate the proposed structure, two-pole microstrip tunable BPF is presented and experimentally verified.
    Radio-Frequency Integration Technology (RFIT), 2012 IEEE International Symposium on; 01/2012
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    ABSTRACT: A design of dual band amplifier using composite right/left handed (CRLH) transmission line structure is described. First, two single-band matching networks are designed for two frequencies, and they are synthesized into one dual band matching network. It is shown that CRLH transmission lines with arbitrary dual frequencies and dual electrical lengths can be designed. The CRLH transmission line section for the dual band matching network is implemented by lumped inductors and capacitors as the left handed (LH) section, and normal transmission line elements as the right handed (RH) section. As an example, a dual band amplifier for 1800MHz and 2300MHz is designed and measured. The simulated and measured performances well verify the proposed design by showing good matching and gain responses at the desired frequencies.
    IEICE Transactions on Electronics. 01/2012; E95.C(5):964-967.
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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 01/2012; 54(10). · 0.59 Impact Factor
  • Progress In Electromagnetics Research 01/2012; 124:17-34. · 5.30 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 01/2012; 60(7):2115-2123. · 2.23 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). · 0.74 Impact Factor
  • Source
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    ABSTRACT: In this letter, the application of a variable character- istic impedance transmission line that can be used to design a dual- band bandpass filter (BPF) is presented. The proposed filter of- fers a fixed first passband and a controllable second passband. The tuning of the second passband is achieved by varying the charac- teristic impedance of the shunt open stub of stub loaded resonator (SLR) with the help of a defected ground structure (DGS) trans- mission line and varactor diodes. In order to validate the theoret- ical predictions and simulated results, a two stage dual-band BPF with three transmission zeros was implemented and experimen- tally verified.
    IEEE Microwave and Wireless Components Letters 11/2011; 21(11):589-591. · 1.78 Impact Factor
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    ABSTRACT: In this paper, we propose a novel composite negative group delay circuit to reduce the signal attenuation required to obtain negative group delay. It is already known that negative group delay can be obtained in a specific frequency of signal attenuation. For the same negative group delay of -6 ns, the signal attenuation of the conventional circuit is 31.25 dB, while the proposed composite circuit involves signal attenuation of only 13.9 dB. As a result, the number of gain compensating amplifiers can be reduced. This contributes to the efficiency enhancement as well as out-of-band noise reduction and stable operation when integrated into the power amplifier linearization system.
    Microwave Symposium Digest (MTT), 2011 IEEE MTT-S International; 07/2011
  • Source
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    ABSTRACT: In this letter, a novel design for a dual-band negative group delay circuit (NGDC) is proposed. Based on the topology of a single-band reflection type NGDC, composite right/left handed λ/4 short stubs are employed to obtain a negative group delay (NGD) at two separate frequency bands simultaneously. In order to achieve a bandwidth extension, the proposed structure consists of a two-stage dual-band NGDC with different center frequencies connected in a cascade. According to the measurements performed for wide-band code division multiple access and worldwide interoperability for microwave access, an NGD of -3.0 ± 0.4 ns and -3.1 ± 0.5 ns are obtained at 2.12-2.16 GHz and 3.46-3.54 GHz, respectively.
    IEEE Microwave and Wireless Components Letters 02/2011; · 1.78 Impact Factor

Publication Stats

108 Citations
25.25 Total Impact Points

Institutions

  • 2007–2013
    • Chonbuk National University
      • Department of Electronic Engineering
      Sŏul, Seoul, South Korea
  • 2007–2010
    • Soonchunhyang University
      • Department of Electrical and Communication Engineering
      Asan, South Chungcheong, South Korea
  • 2008
    • Georgia Institute of Technology
      • School of Electrical & Computer Engineering
      Atlanta, Georgia, United States