• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.23 no.1
• /
• pp.101-107
• /
• 2012

When wireless devises for MICS(Medical Implant Communication Service) or ISM(Industrial Scientific and Medical) bands are designed, it is necessary to verify the performance by using a human body flat phantom. However, most of studies on the phantom are limited to the biological effects of mobile-phone EMF. In this paper, semi-solid phantoms having the electric properties suggested by FCC at MICS and ISM bands are fabricated. The manufactured phantoms satisfy the electric properties($\varepsilon_r=56.7$ and $\sigma=0.94$ at MICS band, $\varepsilon_r=52.7$ and $\sigma=1.95$ at ISM band) at each band. All the composing materials for phantoms are commercially available in domestic market. Two methods using both polyethylene powder and TX-151 and glycerin at each band are proposed for diverse purpose. The electrical properties of the fabricated phantoms are measured by a dielectric probe kit and network analyzer after the lapse of one day (24 hours).

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.21 no.9
• /
• pp.979-986
• /
• 2010

This paper presents an algorithm for retrieving precise radar cross sections(RCS) of various trihedral corner reflectors (TCR) which are external calibrators of synthetic aperture radar(SAR) systems. The theoretical RCSs of the TCRs are computed based on the physical optics(PO), geometrical optics(GO), and physical theory of diffraction(PTD) techniques; that is, the RCS computation includes the single reflections(PO), double reflections(GO-PO), triple reflections(GO-GO-PO), and edge diffractions(PTD) from the TCR. At first, we acquire an SAR image of the area that five TCRs installed in, and then extract the RCS of the TCRs. The RCSs of the TCRs are extracted accurately from the SAR image by adding up the power spill, which is generated due to the radar IRF(Impulse Response Function), using a square window. We compare the extracted RCSs with the theoretical RCSs and analyze the difference between the theoretical and experimental RCSs of the TCR for various window sizes and various backscattering coefficient levels of the adjacent area. Finally, we propose the minimum size of the integration area and the maximum level of the backscattering coefficients for the adjacent area.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.20 no.6
• /
• pp.551-561
• /
• 2009

FH system is very robust to the jamming interference. OFDM system is very good for the high speed communication system. But, it has high PAPR. SC-FDMA system based on OFT-spread OFDM was proposed to reduce high PAPR. Therefore, in this paper, we like to introduce the FH system into SC-FDMA system, which can be best solution to the jamming hostile environment and for the high power efficiency. Also, OFDM is very sensitive to ICI. Especially, ICI generated by frequency offset and phase noise breaks the orthogonality among sub-carriers, which seriously degrades the system performance. We analyze the performance of the FH SC-FDMA system in the PBJ and MTJ channel. In this paper, the ICI effects caused by phase noise, frequency offset and Doppler effects are analyzed and we like to propose the PNFS algorithm in the equalizer to compensate the ICI influences. Through the computer simulations, we can confirm the performance improvement.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.24 no.2
• /
• pp.152-160
• /
• 2013

In this paper, to the aim of wideband SSN(Simultaneous Switching Noise) suppression characteristic, investigation of spiral resonator are used in conjunction with bead which is commonly used for noise suppression method. Bead works effectively to suppress the power noise up to the first harmonic of fundamental frequency, 0.8 GHz, and spiral resonator suppress noise well in the frequency range of SRF(Self Resonance Frequency) which is inversely proportional to the length of spiral. Thus, when bead used in conjunction with a spiral the noise suppression characteristic is determined by the one of higher impedance element of the two in the frequency range and achieves more broadband filtering characteristic. The case for using 22 nH bead turns out 4.8, 2.0, 0, and, 0.6 dB, and the case for using 22 nH bead in conjunction with 3-turns spiral achieves more wideband characteristic of 9.5, 8.3, 6.1, and 9.9 dB power noise suppression performances at the first, second, third, and fourth harmonics, respectively. The peak-to-peak voltage levels decrease from 76 mV to 56 mV using 22 nH bead, and the level decrease rapidly to 34 mV when using in conjunction with bead and 3-turn spiral. Thus more wideband SSN suppression characteristic can be achieved using bead with spiral.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2011.05a
• /
• pp.308-308
• /
• 2011

하천에서 유량을 산정하기 위해서 전자파표면유속계를 이용하여 표면유속을 측정하고 수심평균유속환산계수 0.85를 일률적으로 적용하여 수심평균유속을 산정하고 있다. 이 수심평균유속환산계수 0.85의 적절성에 대한 논의가 지속되어져 왔으나 그 동안에는 이에 대한 현장검증을 할 수 있는 방법이 없었던 실정이다. 하지만 최근 들어서는 ADCP(Acoustic Doppler Current Profiler)의 하천용 Application인 StreamPro ADCP가 개발되어 이를 이용하면 홍수기에 수심별 유속을 측정할 수 있다. 다만 홍수기에 StreamPro ADCP의 적용시에는 여러 가지 높은 위험성이 상존하는 것은 인지의 사실이지만, 그 외의 별다른 방법이 없는 실정이다. 따라서 홍수기에 StreamPro ADCP를 이용하여 수심별 유속을 측정하고 이와 동시에 측정한 표면유속을 이용하여 수심평균유속환산계수를 산정하여 기존에 환산계수로 적용하고 있는 0.85의 적절성을 파악하고자 하였다. 흐름조건별 수심평균유속환산계수 산정을 위하여 평수기 용담 수자원시험유역의 동향지점에서 수심평균유속환산계수를 산정한 결과 0.632~1.352로 넓게 분포하고 있음을 파악하였다. 이렇게 계수가 실제 적용하는 0.85와는 크게 차이가 나는 이유로는 수심이 얕아서 바닥마찰의 영향이 크기 때문인 것으로 판단되었다. 이에 본 연구에서는 여러 지점에서 홍수기 수심별 유속의 실측을 통하여 수심평균유속환산계수 분포정도를 산정하고자 하였다. 대청댐 상류의 수통수위표가 위치해 있는 적벽대교지점에서 StreamPro ADCP를 이용하여 수심평균유속환산계수를 산정한 결과 0.735~0.986 사이에 분포하고 있다. 측정한 결과의 수심평균유속환산계수의 평균값은 0.853으로 기존에 수심평균유속의 산정을 위하여 적용하고 있는 0.85와 거의 일치함을 보이고 있다. 측정당시 수심이 3.6 m에 이르고 있고 유속 또한 1.55 m/s에 이르고 있어 홍수시 일반하천에서 발생하는 수위와 유속임을 감안할 때, 0.735~0.986의 수심평균유속환산계수는 홍수시 순간적인 변화의 폭이 큼을 알 수 있다. 이렇게 순간적인 변화가 큰 이유로는 난류의 성분이 강해서 나타나는 것으로 이를 평균하면 0.853으로 나타나고 있어 홍수시에 수심평균유속환산계수를 0.85를 사용하여도 무방함을 알 수 있다. 동향지점에서 홍수기에 수심별 유속의 실측을 통하여 수심평균유속환산계수를 산정하고자 하였다. 그러나 이 지점은 강한 와류로 인하여 ADCP가 심하게 흔들림으로 인하여 순간적인 유속의 차이가 최대 4배까지 보임을 알 수 있다. 이로 인하여 수심평균유속환산계수의 범위는 0.233~0.983에 이른다. 측정당시 표면유속이 2.07 m/s 인 것을 감안하여 이 표면유속에 상응하는 수심별 유속 자료만을 이용하여 산정시, 수심평균유속환산계수는 0.876이다. 하천의 하류지점에서 수심별 유속을 측정하여 수심평균유속환산계수를 산정하고자 한강하류로 유입하는 굴포천의 구교 및 박촌1교 지점에서 유속측정을 실시하였다. 이들 두 지점은 홍수기에 조차도 유속이 1 m/s 에 이르지 못하는 지점으로, 수심평균유속환산계수를 산정한 결과 각각 0.826, 0.833을 나타내고 있어, 수심평균유속환산계수 0.85가 홍수기뿐만 아니라 평 갈수기에도 적용할 수 있는 가능성을 확인하였다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.14 no.12
• /
• pp.1239-1247
• /
• 2003

OFDM(orthogonal frequency division multiplexing) communications system is very attractive for the high data rate transmission in the frequency selective lading channel. Since OFDM has high PAPR(peak-to-average power ratio), OFDM signal may be distorted by the nonlinear HPA(high power amplifier). In this paper, we propose the DSI(dummy sequence insertion) method for OFDM communication system. Some sub-carriers are inserted for PAPR reduction. They carry the specified dummy data sequence which are used for only PAPR reduction and do not work as side information like the conventional PTS(partial transmit sequence) or SLM(selected mapping) method. We use the complementary sequence and the combination of the correlation sequence as the dummy sequence. Flipping technique is used for the DSI method to get the effective PAPR reduction. It is important that BER of the proposed method is independent of the damage of the dummy data sequence. And DSI method has better spectral efficiency than the conventional block coding. On the other hand, threshold PAPR method is applied to cut down the processing time. However, this DSI method is not better than the conventional PTS method in the respect of the PAPR reduction performance. The DSI method includes the threshold PAPR lower than the PAPR of the OFDM signal, reduces the processing time and improves the BER performance.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.18 no.2 s.117
• /
• pp.183-190
• /
• 2007

This paper presents the design of 860 MHz band transmitter for improving power amplifier's linearity using Cartesian feedback method. For eliminating the effects of gain, phase mis-match, and DC offset, we estimate the property variations using ADS software. The implemented Cartesian feedback transmitter exhibits IMD3 of -54 dBc at an output power of 43 dBm and this result shows that the linearity is improved for 22.4 dB, compared with the test of the power amplifier without Cartesian feedback system. Thus, we verify that the proposed Cartesian feedback transmitter can be applied to narrow-band transmitter systems.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.18 no.2 s.117
• /
• pp.151-157
• /
• 2007

We have presented a compact two-wire helical antenna adopted an open stub in opposite to a feeding point, which is for a T-DMB antenna of mobile devices. By adjusting the length of the open stub or pasting a dielectric material on the open stub, the input impedance around 200 MHz, bands of the T-DMB, can be easily control, even though the total height of the antenna is less than 8 cm(0.053 $\lambda$ at 200 MHz). The operating mechanism of the antenna is explained by using equivalent circuits of two modes, an unbalanced mode and a balanced mode. Based on the analysis of the equivalent circuits, the effects of using the open stub are validated. Several proposed antennas have been fabricated and measured. One of the fabricated antennas has -10 dB impedance bandwidth of $196{\sim}204$ MHz(8 MHz) whose value covers one channel of the T-DMB(6 MHz). The measured $S_{21}$ of the antenna is -38.6 dB which is about 17 dB higher than that of a monopole antenna whose height is same with the proposed antenna.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.18 no.3 s.118
• /
• pp.273-281
• /
• 2007

This paper presented design for a dipole antenna operated at 900 MHz band RFID tag, and antenna performance varied by the sticked material was experimentally evaluated. When dipole antenna was sticked by the material having a difffrent electric characteristic such as dielectric material, fero-magnetic material and conductor, variations of antenna return loss and radiation pattern according to the sticked material kinds, size, and height between antenna and the sticked plate were experimentally observed and evaluated. When antenna was sticked by dielectric surface, the measured return loss and radiation pattern by affection of different dielectric permittivity ratio showed resonant frequency shift of about 40 MHz and relative attenuation of 1 dB to 3 dB. Even though frequency shift by size variation of the sticked plate was observed, the measured radiation pattern of dipole antenna located on the sticked plate was similar with one without backside plate. In the case of conductor or fero-magnetic material as the sticked ground plate, because of frequency shift and phase difference by distance between dipole antenna and the sticked ground plate, amplitude decrease of radiation pattern at 910 MHz was observed about 5 dB above.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.25 no.1
• /
• pp.83-91
• /
• 2014

The passive UHF RFID tags for item-level tagging are now explosively used in the supply chain and retail applications as they have several advantages, the two most relevant are cost and a longer read range. However, the signal interference problem between RFID tags and smart devices in real world is expected according to the smart-phone and tablet market growth together. The performance of RFID tags can be significantly less. The popular examples are the read-success rates and read range reduction. Especially, KT Corp. recently emphasized the serious signal interference at 900 MHz of LTE and old RFID frequencies through their public demonstration. By popular demands, this paper suggests the interference tolerance measurement method between the passive UHF RFID tag and the transmitted signal from a smart device. In addition, we selected three passive UHF RFID tags(Inlay) available on the market and quantitatively evaluated read range reduction results by interference signals using the PCR(Performance Change Rates) index. As a result, the LTE system is about three times as effective as the WCDMA system in terms of interference effects, and the read range performance of two RFID tags about 60 % drop.