• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.23 no.2
• /
• pp.229-234
• /
• 2012

This paper presents channel measurements for wireless body area network(WBAN) and provides performance evaluation from the measurement. We measured the radio propagation in 2.45 GHz ISM band in an anechoic chamber according to various human movements and the position of transmit antennas. Two transmit antennas are mounted on different positions of human body for the purpose of comparing the diversity gain and correlation between the channels in $2{\times}1$ multiple-input single-output(MISO) systems. The experimental results show that the outage capacity is closely related with the correlation coefficient between channels in transmit diversity system.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.13 no.5
• /
• pp.426-435
• /
• 2002

In this paper we present an indoor propagation model for indoor wireless LAN service in the ISM band. We primarily use a 3D ray tracing as well as a patch scattering model in order to take into account the indoor fixtures. Therefore input parameters such as indoor environment parameters and antenna's types, polarizations are considered. As the results, we present fading characteristics and rms delay spread from time delay spread. In order to investigate the accuracy of the presented model, comparisons of predictions with measurement and simulations are performed in indoor wireless LAN service environments. The results show that measurements and simulations are very similar. Therefore in this paper, the effect of presented indoor propagation model is confirmed.

• Journal of the Korean Society for Aviation and Aeronautics
• /
• v.24 no.1
• /
• pp.10-15
• /
• 2016

In this study, The code-carrier divergence test was applied to GPS measurements, and the results were compared and analyzed. The GPS data used for the threshold determination were obtained from Global Navigation Satellite System permanent stations built by the Korea Aerospace Research Institute. At each permanent station, identical dual-frequency receiver and choke ring antenna with radome are installed. The analysis method, root mean square values were compared and analyzed for each permanent station and satellite. As a result, the root mean square value generally decreased as the satellite elevation angle increased although the trend was gentle. Threshold were finally selected based on the average and standard deviation of root mean square for each permanent station. For improving of availability and continuity in real-time operation when the threshold is over the limits, Code-Carrier divergence test values are initialized.

• Proceedings of the KSRS Conference
• /
• 2004.10a
• /
• pp.590-593
• /
• 2004

Extraction of ocean surface current velocity offers important physical oceanographic parameters especially on understanding ocean environment. Although Remote Sensing techniques were highly developed, the investigation of ocean surface current using Synthetic Aperture Radar (SAR) is not an easy task. This paper presents the results of ocean surface current observation using Doppler Centroid of ERS-1 SAR data obtained off the coast of Korea peninsula. We employed the concept, in which Doppler frequency shift and the ocean surface current are closely related, to evaluate ocean surface current. Moving targets cause Doppler frequency shift of the back scattered radar waves of SAR, thus the line-of-sight velocity component of the scatters can be evaluated. The Doppler frequency shift can be measured by estimating the difference between Doppler Centroid of raw SAR data and reference Doppler Centroid. Theoretically, the Doppler Centroid is zero; however, squinted antenna which is affected by several physical factors causes Doppler Centroid to be nonzero. The reference Doppler Centroid can be obtained from measurements of sensor trajectory, attitude and Earth model. The estimated Doppler Centroid was compensated by considering the accurate attitude estimation of ERS-1 SAR. We could verify the correspondence between the estimated ocean surface current and observed in-situ data in the error bound.

• ETRI Journal
• /
• v.39 no.2
• /
• pp.234-244
• /
• 2017

Research interest in three-dimensional multiple-input multiple-output (3D-MIMO) beamforming has rapidly increased on account of its potential to support high data rates through an array of strategies, including sector or user-specific elevation beamforming and cell-splitting. To evaluate the full performance benefits of 3D and full-dimensional (FD) MIMO beamforming, the 3D character of the real MIMO channel must be modeled with consideration of both the azimuth and elevation domain. Most existing works on the 2D spatial channel model (2D-SCM) assume a wide range for the distribution of elevation angles of departure (eAoDs), which is not practical according to field measurements. In this paper, an optimal FD-MIMO planar array configuration is presented for different practical channel conditions by restricting the eAoDs to a finite range. Using a dynamic network level simulator that employs a complete 3D SCM, we analyze the relationship between the angular spread and sum throughput. In addition, we present an analysis on the optimal antenna configurations for the channels under consideration.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2006.04a
• /
• pp.35-39
• /
• 2006

With a growing concern about the state of infrastructure worldwide, the demand for the development of reliable nondestructive testing techniques (NDT) is ever increasing. Among possible NDT techniques. microwave method is proven to be effective in fast and non-contact inspection of concrete structures and inclusions inside concrete. It is also found that the microwave method has a potential in detecting the delamination between fiber reinforced polymer (FRP) plate and concrete. On the other hand, ultrasonic method can be another way to find the delamination. In this paper, the research work needed for the development of a reliable microwave method and ultrasonic method is studied in actual measurements of concrete specimens reinforced with FRP. Concrete specimens are made with FRP and artificial delamination inside. A microwave measurement system with horn antennas with high center frequency and broad frequency bandwidth are used to image inside concrete specimens for the detection of debonding. between concrete and FRP. Also, the equipment of ultrasonic method which is commercialized are used at the same condition. Both of the results are analyzed in comparison of each other. Microwave and ultrasonic methods have been used for the detection of debonding between concrete and fiber-reinforced plastic (FRP).

• Journal of the Korean institute of surface engineering
• /
• v.41 no.4
• /
• pp.134-141
• /
• 2008

We have developed a numerical model for a remote ICP(inductively coupled plasma) system in 2D and 3D with gas distribution configurations and confirmed it by plasma diagnostics. The ICP source has a Cu tube antenna wound along a quartz tube driven by a variable frequency rf power source($1.9{\sim}3.2$ MHz) for fast tuning without resort to motor driven variable capacitors. We investigated what conditions should be met to make the plasma remotely localized within the quartz tube region without charged particles' diffusing down to a substrate which is 300 mm below the source, using the numerical model. OES(optical emission spectroscopy), Langmuir probe measurements, and thermocouple measurement were used to verify it. To maintain ion current density at the substrate less than 0.1 $mA/cm^2$, two requirements were found to be necessary; higher gas pressure than 100 mTorr and smaller rf power than 1 kW for Ar.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.26 no.12B
• /
• pp.1724-1732
• /
• 2001

In this paper, a technique for increasing the bandwidth of microstrip array antennas using the parallel coupled lines on a single layer is presented. Four types of wideband microstrip array antenna are designed and the characteristics of each type are analyzed. In addition, an iterative method using a distributed network is proposed to design the parallel coupled lines as a wideband impedance matching network. Measurements show that the proposed antennas provide wider bandwidths ∼1.7 times those of conventional microstirp array antennas, while the sizes of proposed antennal are the same as that of a conventional array. And low cross-polarization level can be obtained through symmetrical locations of the parallel coupled lines section

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.08a
• /
• pp.306-306
• /
• 2010

A high density (> $10^{11}\;cm^{-3}$) and low electron temperature (< 2 eV) plasma is produced by using a conventional HF (13.56 MHz) plasma enhanced chemical vapor deposition (PECVD) with an additional ultra high frequency (UHF, 314 MHz) plasma source utilizing two parallel antenna assembly. It is applied for the high rate synthesis of high quality nanocrystalline silicon (nc-Si) films. A high deposition rate of 1.8 nm/s is achieved with a high crystallinity (< 70%), a low spin density (< $3{\times}10^{16}\;cm^{-3}$) and a high light soaking stability (< 1.5). Optical emission spectroscopy measurements reveal emission intensity of $Si^*$ and $SiH^*$, intensity ratio of $H{\alpha}/Si^*$ and $H{\alpha}/SiH^*$ which are closely related to film deposition rate and film crystallinity, respectively. A high flux of precursor and atomic hydrogen which are produced by an additional high excitation frequency is effective for the fast deposition of highly crystallized nc-Si films without additional defects.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.41 no.3
• /
• pp.213-221
• /
• 2005

In order to get more accurate GPS position with the changes of the inner configuration setting of GPS receiver, the authors carried out measurements of the position at known it with one antenna and two GPS receivers manufactured by same company. We have investigated the accuracies of positions according to the change of the maskangle and receiving mode of output data in inner configuration of GPS receivers, and analyzed the relationships between numbers of satellites visibility and maskangles, and values of HDOP and maskangles. When the maskangles in inner configuration were set below 20 degree, the accuracies of positions were high. But if they were became bigger than 25 degree, standard deviations ot position errors and HDOPS of positions were became bigger. Numbers of satellites visibility(y) and maskangles(x) have relations with a formula, y = -0.1662x+9.9225, and values of HDOP(y) and maskangles(x) have relations with a formula, y = 0.6035 $e^{0.0517x}$. The results of position accuracies observed by two GPS receivers to the known position at same time were that average errors of position fixs by GPS receiver configured with NMEA0183 mode were 6.7m and standard deviations were 1.5m, and them by GPS receiver configured with binary mode were 5.0m and standard deviations were 1.1m respectively.