• Journal of Communications and Networks
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• v.16 no.2
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• pp.140-145
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• 2014

In this paper, we propose an anti-interference cooperative spectrum sharing strategy for cognitive system, in which a secondary system can operate on the same spectrum of a primary system. Specifically, the primary system leases a fraction of its transmission time to the secondary system in exchange for cooperation to achieve the target rate. To gain access to the spectrum of the primary system, the secondary system needs to allocate a fraction of bandwidth to help forward the primary signal. As a reward, the secondary system can use the remaining bandwidth to transmit its own signal. The secondary system uses different bandwidth to transmit the primary and its own signal. Thus, there will be no interference felt at primary and secondary systems. We study the joint optimization of time and bandwidth allocation such that the transmission rate of the secondary system is maximized, while guaranteeing the primary system, as a higher priority, to achieve its target transmission rate. Numerical results show that the secondary system can gain significant improvement with the proposed strategy.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.5
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• pp.748-754
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• 2000

A novel single feed wide band CP stacked microstrip antenna using crossed slots has been designed, fabricated and measured. For the single rediating element the designed 10dB return loss bandwidth is 34.5%99.45~13.54 GHz), 3dB axial ratio bandwidth is 18.7%(11.17~13.39GHz), and 6 dB gain bandwidth is 29%(10.21~13.64GHz). For the 2$\times$2 array designed using a sequential rotation method, the 10dB return loss bandwidth is 35.9%(9.69~13.94GHz), 3dB axial ratio bandwidth is 34.6GHz (9.93~14.03GHz), and 6dB gain bandwidth is 27.4%(10.35~13.6GHz). For the fabricated 8$\times$8 array antenna, the 10dB return loss bandwidth is 27.3%(10.17~13.41GHz), 3dB axial ratio bandwidth is 27.9GHz(10.1~13.4GHz), and the radiation pattern is good agreement with theory. This antenna can be used for broadband applications for communications or broadcasting in Ku band.

• Smart Media Journal
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• v.4 no.2
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• pp.55-61
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• 2015

A bandwidth-enhanced ultra-wide band (UWB) CMOS balun-LNA is implemented as a part of a software defined radio (SDR) receiver which supports multi-band and multi-standard. The proposed balun-LNA is composed of a single-to-differential converter, a differential-to-single voltage summer with inductive shunt peaking, a negative feedback network, and a differential output buffer with composite common-drain (CD) and common-source (CS) amplifiers. By feeding the single-ended output of the voltage summer to the input of the LNA through a feedback network, a wideband balun-LNA exploiting negative feedback is implemented. By adopting a source follower-based inductive shunt peaking, the proposed balun-LNA achieves a wider gain bandwidth. Two LNA design examples are presented to demonstrate the usefulness of the proposed approach. The LNA I adopts the CS amplifier with a common gate common source (CGCS) balun load as the S-to-D converter for high gain and low noise figure (NF) and the LNA II uses the differential amplifier with the ac-grounded second input terminal as the S-to-D converter for high second-order input-referred intercept point (IIP2). The 3 dB gain bandwidth of the proposed balun-LNA (LNA I) is above 5 GHz and the NF is below 4 dB from 100 MHz to 5 GHz. An average power gain of 18 dB and an IIP3 of -8 ~ -2 dBm are obtained. In simulation, IIP2 of the LNA II is at least 5 dB higher than that of the LNA I with same power consumption.

• International Journal of Computer Science & Network Security
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• v.22 no.12
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• pp.245-251
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• 2022

In this paper, a high gain, broadband planar vivaldi antenna (PVA) by utilizing a broadband stripline feed is developed for wireless communication for IoT systems. The suggested antenna is designed by attaching a tapered-slot construction to a typical vivaldi antenna, which improves the antenna's radiation properties. The PVA is constructed on a low-cost FR4 substrate. The dimensions of the patch are 1.886λ₀×1.42λ₀×0.026λ₀, dielectric constant Ɛ_r=4.4, and loss tangent δ=0.02. The width of the feed line is reduced to improve the impedance bandwidth of the antenna. The computed reflection coefficient findings show that the suggested antenna has a 46.2% wider relative bandwidth calculated at a 10 dB return loss. At the resonance frequencies of 6.5 GHz, the studied results show an optimal gain of 5.82 dBi and 85% optimal radiation efficiency at the operable band. The optometric analysis of the proposed structure shows that the proposed antenna can achieve wide enough bandwidth at the desired frequency and hence make the designed antenna appropriate to work in satellite communication and medical internet of things (M-IoT) healthcare applications.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.7
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• pp.52-60
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• 2009

In this pater, a CP-DRA(Circularly Polarized Dielectric Resonator Antenna) using cross-slot-feed is studied to enhance the gain and axial ratio bandwidth. First, a single layer CP-DRA is studied as a reference for comparison. Then a new type of multilayer CP-DRA is proposed to enhance the gain and axial ratio bandwidth. In consideration of the antenna gain enhancement, the spacing between the elements of the multilayer CP-DRA is examined through analysis of the radiation performance of a 2$\times$2 planar amy of DRAs with a spacing of 0.7$\lambda_0$ and 1.2$\lambda_0$ using CST Microwave Studio. The measured result shows that the gain and bandwidth of the multilayer structure is approximately twice that of the single layer one. In the case of the array antenna in which the spacing between multilayer CP-DRA element is 1.2$\lambda_0$, a grating lobe is reduced, in contrast to what we can expect from a conventional antenna array. The gain is 13.4dBi and axial ratio bandwidth is 0.8GHz.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.2A
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• pp.110-118
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• 2006

In part-I of the paper, two sub-channel structures, either contiguous or distributed, were considered. Modeling the SNR distribution over a sub-channel as Ricean in general, the statistical chracteristics were investigated. In this part of the paper, we develop a generalized two step channel/resource allocation algorithm, which incorporates the two statistical measurements, and analyze the spectral efficiency of OFDMA in terms of average frequency utilization for the two sub-channel structures. In OFDMA with distributed structure, the key design parameter would be the sub-channel bandwidth. To give an insight into the impact on this parameter, we show in the numerical results the frequency utilization as a function of sub-channel bandwidth normalized to coherence bandwidth. As confirmed by numerical results, for contiguous sub-channel structure, we obtain the nominal multiuser diversity gain when the sub-channel bandwidth is smaller than the coherence bandwidth and lose the gain as it is getting larger.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.8
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• pp.1455-1461
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• 2000

There are many researches to increase bandwidth of the microstrip patch antenna for wireless LAN. In spite of broad bandwidth, Bow-Tie antenna has disadvantages that are low gain and big size. In this paper, stacked Bow-Tie microstrip patch antenna for wireless LAN is designed in 5.725 ~5.825 GHz band. This antenna has characteristics that are broadband bandwidth, high gain and small size compared with microstrip patch antenna. In simulated results, the return loss is -34.2 dB at 5.78 GHz and bandwidth is 11.345% for VSWR 2:1 and 7.75%for VSWR 1.5:1. In measured results, the return loss is -38.45 dB at 5.78 GHz and bandwidth is 13% for VSWR 2:1 and 5.6% for VSWR 1.5:1. It has 73.16$^{\circ}$ -3dB beam width and 6.5dB gain.

• ETRI Journal
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• v.37 no.1
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• pp.26-31
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• 2015

Axial-ratio (AR) bandwidth enhancement is achieved for a circularly polarized (CP) cylindrical dielectric resonator antenna (DRA) using a wideband hybrid coupler (WHC) combined with dual probe feed. The presented WHC, comprised of a Wilkinson power divider and a wideband $90^{\circ}$ shifter, delivers good characteristics in terms of 3 dB power splitting and consistent $90^{\circ}$ (${\pm}5^{\circ}$) phase shifting over a wide bandwidth. In turn, the proposed CP DRA, for the employment of the WHC, in place of conventional designs, provides a significant enhancement on AR bandwidth and impedance matching. The antenna prototype with the WHC exhibits a 3 dB AR bandwidth of 48.66%, an impedance bandwidth of 52.5% for voltage standing wave ratio (VSWR) ${\leq}2$, and a bandwidth of 44.66% for a gain of no less than 3 dBi. Experiments demonstrate that the proposed WHC is suitable for broadband CP DRA design.

• ETRI Journal
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• v.27 no.5
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• pp.484-490
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• 2005

We fabricated 40 Gb/s front-end optical receivers using spot-size converter integrated waveguide photodiodes (SSC-WGPDs). The fabricated SSC-WGPD chips showed a high responsivity of approximately 0.8 A/W and a 3 dB bandwidth of approximately 40 GHz. A selective wet-etching method was first adopted to realize the required width and depth of a tapered waveguide. Two types of electrical pre-amplifier chips were used in our study. One has higher gain and the other has a broader bandwidth. The 3 dB bandwidths of the higher gain and broader bandwidth modules were about 32 and 42 GHz, respectively. Clear 40 Gb/s non-return-to-zero (NRZ) eye diagrams showed good system applicability of these modules.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.12 no.3
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• pp.17-24
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• 2003

One of the most important performance criteria related to the gain tuning of controller for CNC machining center is the contour error. This study analyzed circular error by the axis-matched and mismatched cases. To reduce ellipse and radius error, it is necessary to set the gain for each axis to be same bandwidth and high response. Based on the analysis in the frequency domain, we simulate feed system by mathematical model and then predict bandwidth of each axis. For analysis of structure vibration while the each axis is moving, we try the various of measuring method and position loop is improved by jerk limit.