• ETRI Journal
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• v.34 no.1
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• pp.24-34
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• 2012

In this paper, the directional carrier sense multiple access/collision avoidance (CSMA/CA) protocol in the immediate acknowledgement mode for IEEE 802.15.3c is analyzed under saturation environments. For the analysis, a sensing region and an exclusive region with a directional antenna are computed probabilistically and a Markov chain model in which the features of IEEE 802.15.3c and the effects of using directional antennas are incorporated is analyzed. An algorithm to find the maximal number of concurrently transmittable frames is proposed. The system throughput and the average transmission delay are obtained in closed forms. The numerical results show the impact of directional antennas on the CSMA/CA media access control (MAC) protocol. For instance, the throughput with a small beamwidth of antenna is more than ten times larger than that for an omnidirectional antenna. The overall analysis is verified by a simulation. The obtained results will be helpful in developing an MAC protocol for enhancing the performance of mmWave wireless personal area networks.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.8
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• pp.970-974
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• 2007

A mixer is a key component in the wireless communication systems. In this paper, we design a mixer which is used in a frequency modulated continuous wave(FMCW) radar system. The frequency sweep range of the radar is from 10 GHz to 11 GHz. The transmitted and received signals of the FMCW radar are applied to LO and RF ports of the mixer, respectively, but the frequency difference between the two signals, which is called "a beat frequency" is under a few KHz and depending on the distance to target. Thus the isolation between the LO and RF ports is very important factor to design this mixer. In this paper we propose a single balanced resistive mixer using GaAs MESFET for this application. We first design a single-ended type resistive mixer using a simulation tool, then design a balanced type to increase the LO-to-RF isolation of the mixer. We fabricated the mixer on the substrate of dielectric constant 10 and thickness 0.635 mm. The measured results show that the isolation and conversion loss of the mixer over the frequency band is 20dB and 10.5dB, respectively. The LO input power for operating the proposed mixer is +3dBm, which is lower than a general conventional mixer's LO power. The 1 dB compression point is 6dBm.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.11
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• pp.1198-1206
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• 2003

In this paper, a MMIC waveguide mixer module based upon the novel suggested mode converter for wave-guide-to-microstrip transition was fabricated and measured. The insertion and return losses of the mode converter was optimized by compensating the discontinuity effect between ridge and microstrip with the modification of 50 $\Omega$ microstrip line pattern. Due to the low loss nature of the mode converter, a millimeter wave MMIC mixer chip can be successfully applied as a waveguide module for mmW waveguide communication system. The measured results of the module showed the successful MMIC chip application in waveguide and the negligible degradation of the supplied chip specification.

• Journal of Advanced Navigation Technology
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• v.22 no.1
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• pp.27-30
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• 2018

In this study, a 40 GHz band pass filter(BPF) employing a hair-pin structure has been designed, fabricated, and characterized for millimeter-wave wireless communication applications. Using the 3 dimensional(3-D) electromagnetic(EM) tool and design equations of the hairpin BPF, the BPF was desgned on the 5 mil-thick Duroid substrate(RT5880) with a relative dielectric constant (${\varepsilon}_r$) of 2.2. The tapping point (t) of the U-shape resonator in the input and output port has been determined using extracted an external Q-factor ($Q_e$). The coupling coefficients between the other resonators are calculated by adjusting the physical dimensions for the desired response of the BPF. The fabricated BPF was characterized using probing method on a probe station. Its measured center frequency(fc) and fractional BW are 41.6 GHz and 7.43 %, respectively. The measured return loss is below -10 dB at the pass band and the insertion loss is 3.87 dB. The fabricated BPF is as small as $9.1{\times}2.8mm^2$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.2
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• pp.218-223
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• 2010

In this paper, a novel CPW(Coplanar Waveguide)-fed UWB(Ultra Wide Band) antenna is designed, implemented, and measured for UWB communications. CPW-fed planar antenna has advantages of wide-bandwidth, low-cost and easy interaction with radio frequency front end circuitry. We have used HFSS(High Frequency Structure Simulator) of Ansoft which is based on the FEM(Finite Element Method) to simulate the proposed antenna. FR-4 substrate of thickness 1.6 mm and relative permitivity 4.4 is used for implementation. The proposed antenna showed VSWR(Voltage Standarding Wave Ratio)${\leq}2$ for the frequency band from 3.1 GHz to 10.6 GHz which is used for ultra wide band communication. Measured peak gains are 2.61, 4.95, 2.89, 7.35 dBi at 3, 6, 8, 11 GHz, respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.9
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• pp.1014-1020
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• 2009

In this paper, a novel UWB(Ultra Wide-band) antenna with suppressed band of IEEE 802.11a($5.15{\sim}5.825\;GHz$) WLAN was designed and fabricated by using SRR(Split Ring Resonator) with band rejection property. MWS(Micro-wave Studio) of CST company was utilized in the design stage. The antenna was fabricated on a substrate, Rogers 4003, with the thickness of 0.8 mm and relative permittivity of 3.38. The measured result shows that the proposed antenna has a good return loss below -10 dB and group delay below 1nsec over UWB communication band($3.1{\sim}10.6\;GHz$) except WLAN band. It also shows the omni-directional radiation pattern.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.5
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• pp.445-453
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• 2016

This paper presents the implementation and design of the 1T-1R wireless HD video streaming systems over 28 GHz mmWave frequency using 3GPP LTE-TDD standard on NI USRP RIO SDR platform. The baseband of the system uses USRP RIO that are stored in Xilinx Kintex-7 chip to implement LTE-TDD transceiver modem, the signal that are transceived from USRP RIO up or down converts to 28 GHz by using self-designed 28 GHz RF transceiver modules and it is finally communicated HD video data through self-designed $4{\times}8$ sub array antennas. It is that communication method between USRP RIO and Host PC use PCI express ${\times}4$ to minimize delay of data to transmit and receive. The implemented system show high error vector magnitude performance above 25.85 dBc and to transceive HD video in experiment environment anywhere.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.922-925
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• 2002

Klystron which is micro wave amplifier tube are mainly used in fields of science such as accelerator, nuclear fusion, broadcasting, communication fields, and defense industry fields, tract. The quality of Klystron anode and cavity are determined by form accuracy and roughness of the worked surface. Therefore anode and cavity are restricted the from accuracy strictly and the surface roughness be under Rmax 0.03S. As a work material of anode and cavity, the oxygen-free copper, that is used for optical pares of aerospace and laser mirror is selected. An outside diameter of material is $\Phi$100 mm and an inside diameter is $\Phi$30~33 mm. In this study, to find the optimum ultra precision cuffing condition of oxygen-free copper with diamond turning machine, the surface roughness is examined for various diamond toot nose radius, main spindle speed, fred rate and depth of cut. As a result of experiment, we could machined the anode and cavity with a surface roughness within Ra 3.2 nm, a form accuracy within 0.01 $\mu\textrm{m}$.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.10
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• pp.1413-1420
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• 2013

This paper proposes a novel compact MIMO antenna which has miniaturized radiators and their row correlation coefficient, working for the LTE mobile communication, and its SAR is observed. Each of the proposed radiators has a shape of staircase and the bandwidth is twice larger than the conventional PIFA as 600MHz(21%) in 2.5 GHz - 3.15 GHz. And the area of the radiators is $16.5mm{\times}9.7mm$ proper for a handheld device. Also, by adding a planar mushroom decoupling structure between the radiators, the isolation is improved. The design has been carried out using the commercial full-wave time-domain EM solver and the finalized MIMO antenna has the return loss less than -10 dB in the LTE band, the isolation better than 20 dB and the efficiency more than 90% with the gain of 4.3 dB. Regarding the SAR of the antenna, it is observed that the average SAR value of 1g is estimated as 1.37W/Kg, which is lower than the SAR standard.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.7
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• pp.21-29
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• 1989

Using Fresnel diffraction theory a formula is drived for signal intensity variation caused by finite strip obstacles. Signal intensity according to parameter variation of the obstacle is theoretically calculated by a computer and compared with experimental results. For the experiment, an acryl board 3 mm thick was used on which a special material was painted to prevent some reflections and transmissions of the incident wave. 10-element Yagi antennas were used for transmitting and receiving antenna and the frequency was 820 MHz. Finally a tree model was made as a combination of many different finite strip obstacles. Signal attenuation calculated from numerical analysis agree reasonably with experimental data.