• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.3
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• pp.217-224
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• 2020

The use of a high gain flight control system to achieve high bandwidth performance increase the instability of a helicopter. To investigate these phenomena numerically, high fidelity EC155B1 helicopter model and simplified flight control system that include actuator, digital processor and noise rejection filter was developed. A study conducts an analytical investigation of roll axis stability of the helicopter model as feedback gain increases. And this study analyzes roll-rate and roll-attitude feedback gains limited by rotor flap mode. The results indicate that the phase delays caused by the filter can severely limit the usable values of the roll-rate and roll-attitude feedback gains.

• Journal of the Optical Society of Korea
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• v.18 no.6
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• pp.657-662
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• 2014

We demonstrate a simulation of a parallel hybrid fiber amplifier in the C+L-band with a gain controlling technique. A variable optical coupler is used to control the input signal power for both EDFA and RFA branches. The gain spectra of the C+L-band are flattened by optimizing the coupling ratio of the input signal power. In order to enhance the pump conversion efficiency, the EDFA branch was pumped by the residual Raman pump power. A gain bandwidth of 60 nm from 1530 nm to 1590 nm is obtained with large input signal power less than -5 dBm. The gain variation is about 1.06 dB at a small input signal power of -30 dBm, and it is reduced to 0.77 dB at the large input signal power of -5 dBm. The experimental results show close agreement with the simulation results.

• Journal of Satellite, Information and Communications
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• v.1 no.1
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• pp.12-19
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• 2006

In this paper, we propose the bandwidth borrowing scheme which improves the performance of the cal admission control of the integrated GEO satellite networks. In general, target transmission rates of communications and streaming services are fixed, but data services do not have the target transmission rates. Therefore, we can control the transmission rates for data services flexibly according to the system loading situation. When the available bandwidth of the system is insufficient, the bandwidth borrowing scheme gives the bandwidth to request real time services by the transmission rates control of data services through packet scheduler. We make the queueing model for our system model and demonstrate the results through simulations. The simulation results show that there is a 8.7-35.2 dB gain at the total blocking probability according to the use of bandwidth borrowing scheme.

• Journal of the Korea Institute of Military Science and Technology
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• v.7 no.4 s.19
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• pp.20-25
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• 2004

The existing antenna that equipped with Micro Aerial Vehicle, microstrip antenna only can send and receive image signal because of limited bandwidth. But, proposed antenna that equipped with Micro Aerial Vehicle flight introduces tapered type patch antenna, also improves bandwidth then can transfer present location, altitude, movement speed. Furthermore, as a result of introduce stacked type, it transfers more quality of image signal, and represents most suitable performance in Korean peninsula that has many mountain peaks. In this paper, to transmit and receive the wideband signals with a antenna system, the wideband microstrip antenna is proposed and designed. This antenna operates at 2.4GHz. In this thesis, the resonance frequency of 2.4GHz and the reflective loss of the antenna of -22dB were calculated by measuring the fabricated Tapered Microstrip Patch Antenna which was designed with the resonance of 2.4GHz. The calculated gain and efficiency of antenna were 6.7dB and $60\%$ respectively. The characteristic of the bandwidth shows with $50\~60MHz$ which is $6.02\%$ at the basis of -l5dB reflective loss. The experimental results can be used in the characteristic of the resonators and this antenna produces a greatly enhanced bandwidth.

• The Journal of the Acoustical Society of Korea
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• v.23 no.6
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• pp.481-487
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• 2004

In this paper. the structure of bandwidth scalable wideband speech codec and its high-band codec are proposed. In the high-band codec. the signal is divided into frequency bands. and each band is quantized in DCT domain. The DCT coefficients are splitted into magnitude and sign, and each is quantized independently by a specialized method based on its characteristics. In addition. the quantized gain parameter in the low-band codec is utilized in the high-band codec for an enhanced performance. The bandwidth scalable wideband speech codec using G.729E for low-band and the proposed codec for high-band is developed, and it is confirmed that the proposed codec has better subjective performance than 24kbps G.722.1.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.43 no.10 s.352
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• pp.1-9
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• 2006

In this paper, a couple of 10Gb/s transimpedance amplifiers are realized in a 0.18um standard CMOS technology for optical communication applications. First, the voltage-mode inverter TIA(I-TIA) exploits inverter input configuration to achieve larger effective gm, thus reducing the input impedance and increasing the bandwidth. I-TIA demonstrates $56dB{\Omega}$ transimpedance gain, 14GHz bandwidth for 0.25pF photodiode capacitance, and -16.5dBm optical sensitivity for 0.5A/W responsivity, 9dB extinction ration and $10^{-12}$ BER. However, both its inherent parasitic capacitance and the package parasitics deteriorate the bandwidth significantly, thus mandating very judicious circuit design. Meanwhile, the current-mode RGC TIA incorporates the regulated cascade input configuration, and thus isolates the large input parasitic capacitance from the bandwidth determination more effectively than the voltage-mode TIA. Also, the parasitic components give much less impact on its bandwidth. RGC TIA provides $60dB{\Omega}$ transimpedance gain, 10GHz bandwidth for 0.25pF photodiode capacitance, and -15.7dBm optical sensitivity for 0.5A/W responsivity, 9dB extinction ration and $10^{-12}$ BER. Main drawback is the power dissipation which is 4.5 times larger than the I-TIA.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.10
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• pp.2395-2402
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• 2013

An active-RC channel selection filter (CSF) with the bandwidth of 40MHz and the improved linearity is proposed in this paper. The proposed CSF is the fifth butterworth filter which consists of a first order low pass filter, two second order low pass filters of a biquad architecture, and DC feedback circuit for cancellation of DC offset. To improve the linearity of the CSF, a body node of a MOSFET for a switch is connected to its source node. The bandwidth of the designed CSF is selected to be 10MHz, 20MHz and 40MHz and its voltage gain is controlled by 6 dB from 0 dB to 24 dB. The proposed CSF is designed by using 40nm 1-poly 8-metal CMOS process with a 1.2V. When the designed CSF operates at the bandwidth of 40 MHz and voltage gain of 0 dB, the simulation results of OIP3, in-band ripple, and IRN are 31.33dBm, 1.046dB, and 39.81nV/sqrt(Hz), respectively. The power consumption and layout area are $450{\times}210{\mu}m^2$ and 6.71mW.

• Journal of IKEEE
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• v.22 no.1
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• pp.127-135
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• 2018

This paper was studied the tri-band folded monopole antenna design with Mu-negative metamaterial unit cell, which operates at 700 MHz UHD broadcast band and 2.45 GHz/5 GHz WiFi band. The MNR metamaterial is fabricated by forming a capacitor on the backside of the antenna substrate and connecting it to the ground plane through a strip line and a via hole so that a single cell can operate in the MZR (Mu zero resonator). Through this, the resonance point can be controlled to resonate in the zero mode in 700 MHz band, and the bandwidth is improved. Experimental results show that the 10dB bandwidth and gain are 309 MHz (41.2%) and 5.298 dB at the first resonance point, and the 10dB bandwidth and gain at the second resonance point are 821.9 MHz (33.5%) and 2.7840 dB respectively. At the third resonance point, the gain and bandwidth were 1.1314 GHz (20.6%) and 2.9484 dB respectively. We confirmed that the resonance point with theoretical value is in agreement with experimental value. And the radiation pattern is generally omnidirectional, and it has been confirmed that the radiation pattern is good in both forward and backward directions at 0.75 GHz and 2.45 GHz, and has a radiation pattern with multiple lobes at 5.5 GHz.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.2 s.117
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• pp.158-165
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• 2007

In this paper, the circularly polarized $4{\times}4$ array antenna is proposed for the X-band. A single antenna consists of square patch and unequal cross-aperture coupled feeding. The RHCP(Right Handed Circularly Polarization) is generated by unequal cross-aperture coupled feeding. By reducing space among elements of way antenna from 0.8 ${\lambda}_0$ to 0.45 ${\lambda}_0$, the mounting area of array antenna is miniaturized. The $2{\times}2$ array antenna is designed using sequential rotation feeding network. The good level of gain, axial ratio, and impedance bandwidth are achieved. The $4{\times}4$ array antenna is extended by ${\lambda}/4$ transformer and T-junction power divider. The simulated maximum radiation gain is 15.09 dBi at 10 GHz. The simulated 3 dB Axial Ratio bandwidth is from 9.05 to 10.4 GHz(13.5%). Also the measured impedance bandwidth($VSWR{\leq}2$) of manufactured $4{\times}4$ array antenna is from 8.45 to 11.84 GHz(33.9%). The measured maximum radiation gain is 11.10 dBi at 10 GHz. The measured 3 dB Axial Ratio bandwidth is from 9.42 to 10.47 GHz(10.5%).

• ETRI Journal
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• v.27 no.5
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• pp.569-578
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• 2005

The purpose of this paper is to describe the implementation of monolithically matching circuits, interface circuits, and RF core circuits to the same substrate. We designed and fabricated on-chip 1 to 6 GHz up-conversion and 1 to 8 GHz down-conversion mixers using a 0.8 mm SiGe hetero-junction bipolar transistor (HBT) process technology. To fabricate a SiGe HBT, we used a reduced pressure chemical vapor deposition (RPCVD) system to grow a base epitaxial layer, and we adopted local oxidation of silicon (LOCOS) isolation to separate the device terminals. An up-conversion mixer was implemented on-chip using an intermediate frequency (IF) matching circuit, local oscillator (LO)/radio frequency (RF) wideband matching circuits, LO/IF input balun circuits, and an RF output balun circuit. The measured results of the fabricated up-conversion mixer show a positive power conversion gain from 1 to 6 GHz and a bandwidth of about 4.5 GHz. Also, the down-conversion mixer was implemented on-chip using LO/RF wideband matching circuits, LO/RF input balun circuits, and an IF output balun circuit. The measured results of the fabricated down-conversion mixer show a positive power conversion gain from 1 to 8 GHz and a bandwidth of about 4.5 GHz.