• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.11
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• pp.857-867
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• 2018

Active array radar is evolving into digital active array radar. Digital active array radar has many advantages for making several simultaneous radar beams from the digital receive data of each element. A digital-type transceiver(TR) module is suitable for this goal in radar. In this work, the design results of an L-band digital TR module are presented to verify the possibility of fabrication for a digital active array antenna. This L-band digital TR module consists of a gallium-nitride-type HPA to achieve a more than 350-W peak output power and one-chip transceivers that include a digital waveform generator and analog digital converter. The receiving gain was 47 dB, the noise figure was less than 2 dB, and the final output type of the four channel receiving paths was one optic signal.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.12A
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• pp.991-997
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• 2009

Transmit beamforming is simple method to achieve the full diversity gain that is available in multiple antenna(MIMO) wireless systems. Unfortunately, the prior condition to achieve this gain requires perfect channel knowledge at both transmitter and receiver, which is impractical on account of limited feedback link. Therefore, for the practical system, codebook based feedback scheme is often employed, where the beamforming vector is selected from the codebook to maximize the output signal-to-noise ratio (SNR) at receiver, and the receiver only sends back the index of the best beamforming vector to the transmitter. In this paper we derive analytical expression of average bit error rate (BER) for the codebook based transmit beamforming MISO system over the feedback error channel. Using this analytical result, we present optimum codebook indexing scheme to improve the performance of this system. From some selected numerical examples we show that our proposed codebook indexing scheme can provide nonnegligible performance improvements in terms of average BER over the severe feedback error channel.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.3
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• pp.261-268
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• 2016

In this paper, dual-polarized monopulse cassegrain antenna for W-band millimeter-wave seeker was proposed and the performances were verified by the measured results of the fabricated antenna. Dual-polarized monopulse Cassegrain antenna consists of main/subreflector, dual-polarized feed horn and monopulse comparator. The proposed feed horn has $2{\times}2$ array square waveguide feeding structure to make monopulse signals and it was designed using 90 degree rotational symmetric structure to receive dual-polarized signals. At the sum and difference channel, the measured vertical and horizontal polarization radiation pattern were similar. Measurement gains are 35.1 dBi for v-pol. and 35.6 dBi for h-pol. at the center frequency with 0.5dBi difference between each polarization and the side lobe level is below -21.6 dB.

• Journal of Advanced Navigation Technology
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• v.6 no.2
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• pp.130-137
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• 2002

We present Space-Time Trellis Coded Code Division Multiple Access systems, which maintain the full diversity and coding gain of Space-Time Trellis Codes(STTC) and have the immunity to performance degradation caused by multipath fading. These STTC CDMA systems are constructed by adding the spreading and despreading processes of PN codes to STTC systems. In multipath fading channels, delay spreaded signals are detected and combined, then decoded. According to the combining and decoding methods, there are four decoding methods. There are optimum ML decoding without combining, adding multipath signals in each receive antenna before decoding, combining multi path signals in each antenna before decoding, and combining all received signals before decoding. Performance of these methods is proportional to complexity. Besides, all methods are shown to compensate the irreducible error rate which appears in multipath fading channels.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.12 s.91
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• pp.1141-1146
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• 2004

The antenna array for receiving satellite broadcasting of Koreasat III is proposed. A cavity-backed slot antenna array is proposed to reduce feed line loss, increase the radiation efficiency, and make the feed network simple. A sub-array consists of $2{\times}4$ slot elements backed by a single cavity. By proper choice of dimensions it is shown that the proposed antenna has characteristics of the high radiation efficiency and the broad frequency bandwidth. Antenna characteristics for the array antenna with 256 elements are measured in Ku-band. A single cavity backed-sub-array has the gain of 18 dEi. The gam of the total antenna array(256 elements) is Over 33 dEi.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.11
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• pp.1225-1232
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• 2009

In this paper, a parabolic edge planar monopole antenna for indoor DTV reception is presented. The antenna has broadband property with the planar monopole and ground of parabolic edges. It is designed close to self-complementary structure as changing curvature of edges of monopole and ground. Monopole and ground conductors of the antenna are on the same plane, and excited through CPW feeding. It is fabricated on an FR4 dielectric substrate of $\varepsilon_r=4.4$, and the dimension is $40\;mm{\times}200\;mm{\times}1.6\;mm$. Return loss is larger than 10 dB in 470~806 MHz. Maximum gain is 1.86 dBi on E-plane at 810 MHz and 3.86 dBi on H-plane at 600 MHz.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.7
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• pp.45-52
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• 2008

In typical cellular systems using frequency reuse scheme, the terminal suffers a performance degradation due to the intercell interference signals from adjacent cells as the terminal moves toward the cell boundary. In this paper, a signal transmission and reception scheme which achieve spatial multiplexing and beamforming gain from a distributed MIMO (multiple-input multiple-output) channel using multiple-antenna terminal is proposed for the spectral efficiency enhancement in a multi-cell downlink environment, when geographically separated base stations cooperatively transmit signals. In particular, we analyze the effective signal-to-interference ratio and spectral efficiency of the proposed scheme for different frequency reuse patterns and for varying numbers of receive antennas, and compare with the performance of the MRC (maximal ratio combining) reception scheme in typical cellular systems. We evaluate the amount of transmission efficiency of the scheme by comparing the performance near the cell boundary where the strong intercell interference is experienced.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.7
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• pp.747-756
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• 2014

In this paper, we propose a path loss model with the multiple antennas using diversity effect. Currently wireless communication systems use the multiple antennas in order to improve the channel capacity or diversity gain. However, until recently, many researches on path loss model only consider geographical environment between the transmitter and the receiver. There is no study about path loss model considering diversity effect. Nowaday wireless communication use the multiple antennas and we in common find examples using diversity scheme that is method in order to enhance a channel capacity. Moreover we anticipate that it work harder in future researches. But in this communication system, path loss model isn't established that predict strength of received signal. So, in order to predict strength of received signal, we take changing SNR by diversity gain. When exceeding the number of antennas of receiver are 7 in proposed model, diversity effect is saturated. Therefore we consider the number of antenna of receiver until 10. We find RMSE between proposed model and value of calculation is 1. We calculate the diversity gain by conventional BER curve. Proposed model can predict loss of received signal in system using multiple antennas.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.3
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• pp.399-404
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• 2002

본 논문에서는 Hybrid $SC/MRC-{L_c}/L$ 다이버시티 수신 기법과 콘볼루션 부호화 기법을 각각 또는 함께 이용할 때의 Multi-Carrier DS-CDMA시스템의 성능 개선을 구하였다. 우선 다중경로 페이딩 및 다중접속간섭의 영향을 분석하고, 두 기법에 의한 성능 개선 정도를 구하여 비교, 분석하였다. Hybrid SC/MRC-Lc/L 수신에서는 각각의 반송파에 대하여 상관을 취하고 상관기 출력들 중에서 가장 큰 신호성분을 {$L_c}$개 만큼 선택하여 최대비 합성하며, 콘볼루션 부호화는 다중경로 다중경로 페이딩 및 다중접속간섭에 의하여 발생된 오류를 정정 및 검출한다. 분석 결과, 콘볼루션 부호화 기법을 채용함으로서 성능이 현저하게 개선되는데, 보호이득과 전력제한 사이에 trade off를 고려하여 부호화 율 (r)을 선택할 필요가 있다는 것과 하이브리드 $SC/MRC-{L_c}/L$ 수신에서는 입력 다이버시티 가지의 수 (L)가 많을수록 선택의 폭이 넓어지며, 적절한 숫자의 다이버시티 가지의 선택이 시스템의 복잡성과 성능 대 배용 등을 결정한다는 것을 알 수 있었다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.5C
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• pp.444-452
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• 2012

The detection performances, in this paper, are derived according to combination of the multiband GNSS signals in broadband jamming environments. The detection probabilities depending on the false alarm probabilities are derived and presented via Monte-Carlo simulation under the assumption as follows: the GNSS signals are perfectly orthogonal and simultaneously received by the receiver using non-coherent correlation.