• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.8
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• pp.87-92
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• 2004

In this paper, a microstrip slot antenna with a fork-shaped feedline is designed and fabricated. To obtain a broadband characteristic of a wide slot antenna a feedline is transformed into a shape of a fork, and a size of the slot and offset - length is varied. As the characteristics of the slot antenna as the function of design parameters are analyzed, a broadband microstrip slot antenna is designed. The microstrip slot antenna with a fork-shaped feedline is fabricated and its measured bandwidth is from 1.65 GHz to 6.20 GHz for VSWR$\leq$2.

• Current Optics and Photonics
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• v.8 no.1
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• pp.65-71
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• 2024

We present a Yb-doped narrow-linewidth polarization-maintaining all-fiber amplifier that achieves a high mode-instability (MI) threshold, high output power, and 9.7-GHz spectral linewidth. Six wavelength-multiplexed laser diodes are used to pump this amplifier. First, we construct a high-power fiber amplifier based on a master oscillator-power amplifier configuration for experiments. Subsequently, we examine the MI threshold by individually pumping the amplifier with wavelengths of 976, 974, 981, 974, and 981 nm respectively. The experimental results demonstrate that the amplifier exhibits a high MI threshold (>3.5 kW) when pumped with a combination of wavelengths at 974 and 981 nm. Afterward, we inject an optimized phase-modulated seed with a nearly flat-top spectrum into this amplifier. Ultimately, laser output of 3.2 kW and 9.7 GHz are obtained.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.7
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• pp.65-70
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• 2012

In this paper, a compact UWB (Ultra Wideband) BPF(Band-Pass Filter) with dual notched bands is proposed using a hybrid Composited Right-Left Handed (CRLH) and Defected Ground Structure (DGS). To avoid the interferences such as Wireless LAN (Center frequency: 2.4GHz and 5.8GHz), the CRLH is employed to obtain the dual notched bands and the DGS is used to obtain the wide stop-band above the pass-band. The fabricated filter has good performance and has more than 30dB rejection at the center frequency of 2.4 GHz and 5.8GHz. The dual notched bands are easily movable by changing the CRLH parameter. Also the insertion loss is less than 0.4dB in the lower pass-band and 0.7dB in the upper pass-band, and it has small group delay variation less than 0.6ns. The size of the fabricated filter is very compact (17mm*17mm).

• Journal of The Korean Astronomical Society
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• v.46 no.2
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• pp.65-74
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• 2013

We probe the feasibility of high-frequency radio observations of very rapid flux variations in compact active galactic nuclei (AGN). Our study assumes observations at 230GHz with a small 6-meter class observatory, using the SNU Radio Astronomical Observatory (SRAO) as an example. We find that 33 radio-bright sources are observable with signal-to-noise ratios larger than ten. We derive statistical detection limits via exhaustive Monte Carlo simulations assuming (a) periodic, and (b) episodic flaring flux variations on time-scales as small as tens of minutes. We conclude that a wide range of flux variations is observable. This makes high-frequency radio observations-even with small observatories-a powerful probe of AGN intra-day variability; especially, those which complement observations at lower radio frequencies with larger observatories like the Korean VLBI Network (KVN).

• JSTS:Journal of Semiconductor Technology and Science
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• v.16 no.4
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• pp.415-424
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• 2016

This paper describes a high data rate proximity transmitter design for high resolution smartphone-mirrored display applications. A 2 Gb/s transmitter is designed with a low transmission power of -70 dBm/MHz and a wide bandwidth of nearly 3 GHz. A digital pre-correction method is employed in the transmitter to mitigate the inter-symbol interference problem. A carrier-based digital pulse shaping and a reconfigurable digital envelope generation methods are employed for robust operation by utilizing 20 phases from a 2 GHz phase-locked loop. A 6.5-9.5 GHz transmitter implemented in 65 nm CMOS achieves the maximum data rate of 2 Gb/s, consuming only 7.6 mW from a 1 V supply.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.2A
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• pp.195-201
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• 2004

In this paper, U-Shaped slot Bow-Tie antenna for 5.15㎓∼5.35㎓ is designed, fabricated, and measured. The prototype consist of U-Shaped slot. To obtain suitable bandwidth, the form layer is inserted between ground plane and substrate. Important parameters in the design are U-slot length, width, position, air-gap height, and feed point position. From these parameters optimized, a U-shaped slot Bow-Tie antenna is fabricated and measured. The measured results of the antenna are obtained as follows results. The resonant frequency of the Fabrication U-shaped slot Bow-Tie antenna is 5.28㎓, bandwidth for approximately 7.76％(VSWR<1.2) and the gain is 4∼7dBi. The experimental far-field patterns are stable across the pass band. The 3dB bandwidth in Elevation and Azimuth are 73.63$^{\circ}$and 65.08$^{\circ}$, respectively.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.10
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• pp.1261-1268
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• 2019

In this paper, we present the analysis of a novel monopole antenna with a reflector. The proposed monopole antenna is printed on a TRF-45 substrate, and the reflector, which is positioned near the base of the antenna, is printed on the FR-4 substrate. Positioning the reflector near the base of the antenna was found to suppress current radiation toward the back of the monopole antenna. Comparative analysis of the proposed monopole antenna and a conventional monopole antenna without a reflector revealed that the bandwidths of the antenna with and without a reflector were 2.65 GHz and 2.88 GHz, respectively. Additionally, the antenna without a reflector was observed to have a bi-directional radiation pattern in the E-plane, and an omni-directional radiation pattern in the H-plane. However, only the antenna with a reflector was found to suppress back radiation, and provide non-uniform directional radiation in the E-plane and H-plane.

• ETRI Journal
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• v.25 no.1
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• pp.19-24
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• 2003

This paper describes the performance of a Ku-band 5-bit monolithic phase shifter with metal semiconductor field effect transistor (MESFET) switches and the implementation of a ceramic packaged phase shifter for phase array antennas. Using compensation resistors reduced the insertion loss variation of the phase shifter. Measurement of the 5-bit phase shifter with a monolithic microwave integrated circuit demonstrated a phase error of less than $7.5{\circ}$ root-mean-square (RMS) and an insertion loss variation of less than 0.9 dB RMS for 13 to 15 GHz. For all 32 states of the developed 5-bit phase shifter, the insertion losses were $8.2{\pm}1.4$dB, the input return losses were higher than 7.7 dB, and the output return losses were higher than 6.8 dB for 13 to 15 GHz. The chip size of the 5- bit monolithic phase shifter with a digital circuit for controlling all five bits was 2.35 mm ${\times}$1.65 mm. The packaged phase shifter demonstrated a phase error of less than $11.3{\circ}$ RMS, measured insertion losses of 12.2 ${\pm}$2.2 dB, and an insertion loss variation of 1.0 dB RMS for 13 to 15 GHz. For all 32 states, the input return losses were higher than 5.0 dB and the output return losses were higher than 6.2 dB for 13 to 15 GHz. The size of the packaged phase shifter was 7.20 mm${\times}$ 6.20 mm.

• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.4
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• pp.484-494
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• 2014

We describe a digitally controlled oscillator (DCO) which compensates the frequency variations for process, voltage, and temperature (PVT) variations with an accuracy of ${\pm}2.6%$ at 2.5 GHz. The DCO includes an 8 phase current-controlled ring oscillator, a digitally controlled current source (DCCS), a process and temperature (PT)-counteracting voltage regulator, and a bias current generator. The DCO operates at a center frequency of 2.5 GHz with a wide tuning range of 2.2 GHz to 3.0 GHz. At 2.8 GHz, the DCO achieves a phase noise of -112 dBc/Hz at 10 MHz offset. When it is implemented in an all-digital phase-locked loop (ADPLL), the ADPLL exhibits an RMS jitter of 8.9 ps and a peak to peak jitter of 77.5 ps. The proposed DCO and ADPLL are fabricated in 65 nm CMOS technology with supply voltages of 2.5 V and 1.0 V, respectively.

• Journal of electromagnetic engineering and science
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• v.2 no.1
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• pp.56-58
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• 2002

In this paper, the double conversion gate mixer using a half-LO frequency is described at 25 GHz band. The proposed mixer uses two HEMTs excited by a single LO signal of half-LO frequency in order to generate the second IF signal. That is, the LO signal having the half-LO frequency is only fed into the gate of the first HEMT mixer as a normal gate mixer. The LO signal through the first mixer is find into the second mixer The proposed miler requires not only half of the normal LO frequency, but also lower LO power than the conventional subharmonically pumped milers. Over the bandwidth of 500 MHz at 24.5 GHz, the conversion gain is 2.5 dB, the noise figure is 9 dB, and the isolation between RF and LO port is 32 dB when the LO poller is 0 dBm at 12.65 GHz.