• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.9A
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• pp.749-754
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• 2005

It is well-known that mobile communication systems are usually limited in their performance and capacity by three major impairments, which are multipath fading, delay spread and co-channel interference (CCI). OFDMA (OFDM-FDMA) system can cope with the multipath fading and delay spread easily due to the beneficial properties of OmM technology. Though OFDMA scheme avoids intra-cell interference using the orthogonality among subcarriers, the scheme contains difficulty of reducing co-channel interference. Therefore, in this paper, adaptive antenna techniques are deployed into OFDMA/TDD system to minimize the co-channel interference induced by adjacent cells and to enhance the uplink performance. For the improvement of downlink performance, we apply TxAA (Transmit Adaptive Array), a kind of transmit diversity technique, utilizing preamble symbols for training antenna may into OFDMA/TDD transmitter side. Simulation results show that the uplink and downlink performance under multipath Rayleigh fading channel improved 9dB and 7dB each compared with the case of single antenna system at target BER $10^{-3}$ .

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.6
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• pp.1130-1141
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• 2015

Conventionally, a pulse radar is used for middle-sized or large-sized ships to detect other ships or obstacles located at a long distance. However, it is hardly equipped for most of the small-sized ships due to mounting and maintenance costs. Therefore, FMCW(frequency modulated continuous wave) radar is suggested as an alternative for the small-sized ships. Since it operates with low power and has good range resolution for relatively close objects, it is eligible for the small-sized ships. In previously proposed FMCW radar system, it only estimates distance and velocity of a target ship placed in the direction of main beam and is hard to detect several ships simultaneously. Thus, we suggest the method for detecting several ships at the same time by applying MUSIC(multiple signal classification) algorithm to FMCW radar signal received by a phased array antenna. In addition, by combining digital beam forming with the MUSIC algorithm, better angle resolution is achievable.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.2
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• pp.214-222
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• 2008

The equivalent circuit for the RLH-TL is proposed considering radiation effects due to the inclusion of a series capacitor and shunt inductor in a unit cell for the right/left-handed transmission line(RLH-TL). The design equations to realize a specific phase shift at a given frequency is also provided. The S-parameters for unit cells with N=1, 3, 5, and 10 are analyzed in various aspects based on the EM and circuit simulations especially for the purpose of controlling radiation along RLH-TL's. A modification formula for the radiation rate per unit cell is also proposed for good agreement between the EM and circuit simulation results.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.2
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• pp.207-213
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• 2013

This study describes an omega-K algorithm for focusing bistatic synthetic aperture radar(SAR) data using bistatic-to-monostatic conversion. Bistatic SAR system considered in this study consists of a transmitting antenna and a physical array of several receiving antennas. The length of the physical array is identical to the SAR synthetic aperture. Unlike the monostatic case, an omega-K algorithm for the bistatic case is difficult to obtain the exact equation in the 2D wavenumber domain. The key of the proposed algorithm is converting the bistatic data into a monostatic one. The effectiveness of the proposed algorithm is proved by simulation and real measurement data.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.8
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• pp.1797-1804
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• 2011

In this paper, I analyzed array organization of MIMO channel antenna and effect of operation environment by evaluating average BER from linear Space-Time Block Code orthogonal design and suggests designing condition of MT antenna for improved BER and the fading index m. To analyze system performance, I used M-PSK and M-QAM modulation, and to use analysis equations I used integrated by Nakagami fading variable, non-integrated Nakagami fading variable. We can get the organization of channel array by using mathematical calculation on matrix. STBE BER performance will decrease as AOA spreading decrease and such loss can be compensated from extending antenna spacing, and changing array organization.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.8
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• pp.830-838
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• 2003

In this paper, TX/RX dual operation microstrip single antenna for satellite communication is designed, analyzed, fabricated and measured. TX/RX frequency ranges are 14.0∼l4.5 GHz, 11.7∼12.75 GHz in respectively and vertical and horizontal polarizations are used for TX and RX. This antenna uses microstrip direct feeding for RX and aperture coupled strip-line feeding for TX and accommodates stacked elements for a high directivity and wide impedance bandwidth. In an analysis of single element, FDTD and MOM was compared and FDTD analysis was more accurate because of the consideration of finite structure and imperfect two ground planes. The proposed structure facilitates generally to an extension of two dimensional array and lower an unwanted radiation by strip-line feed in TX. TX/RX 8${\times}$4 array has a return loss below -10 dB, -14 dB in TX, RX respectively and a gain ranging from 19.1∼20.7 dB in TX, 21.2∼21.8 dB in RX which has a radiation efficiency of 43∼5l %, 52∼57 %.

• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.4
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• pp.617-624
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• 2021

The accurate estimation of the number of signals included in the received signal is required for the AOA(: Angle-of-Arrival) estimation, the interference suppression, the signal reception, etc. AIC(: Akaike Information Criterion) and MDL(: Minimum Description Length) algorithms, which are known as the typical algorithms to estimate the signal number, estimate the number of signals according to the minimum of each criterion. As the number of antenna elements increased, the estimation performance is enhanced, but the computational complexity is increased because values of criteria for entire antenna elements should be calculated for finding their minimum. In order to improve this problem, in this paper, we propose AIC and MDL algorithms based on the beamspace, which efficiently estimate the number of signals while reducing the computational complexity by reducing the dimension of an array antenna through the beamspace processing. In addition, we provide computer simulation results based on various scenarios for evaluating and analysing the estimation performance of the proposed algorithms.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.22 no.5
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• pp.87-92
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• 2022

In this paper, a study was conducted on the design of an array element that can be applied to the AESA radar for seeker. An antenna for application to AESA radar should choose an optimal radiation element to be applied to an array antenna in order to secure electronical beam steering characteristics, and consider beam steering characteristics when designing. In particular, in order to satisfy the wide-angle beam steering characteristics, the wide-angle impedance matching technique should be used to minimize the scan blindness region that may occur during wide-angle steering. As such, securing the stability of system operation is becoming an important design consideration for AESA radar. In this paper, WAIM is applied to the end of the radiation element to improve the characteristics of the radiation element applied to the AESA radar antenna device, and the change in the performance of the active reflection coefficient, which is a stable operation index of the system, is reviewed. The final performance result verified the validity of the proposed method by mathematically synthesizing the simulation data.

• The Journal of the Korea institute of electronic communication sciences
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• v.18 no.6
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• pp.1245-1258
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• 2023

To efficiently manage forest resources, it is essential to deploy multiple unmanned aerial vehicles equipped with various sensors simultaneously. Consequently, the ground control station antenna should not only maintain continuous tracking of the target station but also minimize the impact of radio interference on other unmanned aerial vehicle stations. In this paper, we presented beam forming techniques based on the VPR algorithm within a ground control station constructed using a phased array antenna system. Through simulation experiments in diverse unmanned aerial vehicle operating environments, it was demonstrated that the presented method enables not only the continuous tracking of operational unmanned aerial vehicles but also the suppression of radio interference by establishing a continuous pattern null for multiple operational radio interference sources.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.1789-1793
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• 2008

전자파표면유속계는 홍수유속측정을 위하여 개발된 기기로 평 갈수기에는 유속측정이 불가하여 프로펠러 유속계를 이용하고 있다. 현재 보급된 전자파표면유속계는 하천의 흐름방향에 나란하게 설치하였을 때에만 유속을 측정할 수 있는 기기의 구조상의 한계성 때문에 교량이 없는 지점에서는 유속측정이 불가하여 유량산정을 할 수가 없다. 또한 편각측정이 불가능하여 기기를 각 측선마다 이동 설치하여야 하기 때문에 유속측정시 효율성 떨어진다. 이에 홍수시 유량측정의 효율성을 증대시키고 전자파표면유속계의 활용도를 높이고자 편각측정이 가능하도록 전자파표면유속계의 성능을 개선하는 것이 본 연구의 주된 목적이다. 전자파표면 유속계에서의 편각 측정은 하천의 유속방향을 기준으로 정면에서 측정하면 수평 편각이 0도가 되며 좌우로 안테나를 회전하여 움직인 각도가 측정 편각으로 결정된다. 현장에서 전자파표면유속계의 사용시 편의성을 높이고 유량측정을 효율적으로 하기 위해서는 가급적 편각을 크게 해서 측정을 해야 하지만, 편각이 증가하면 전자파의 물리적 특성 때문에 반사된 신호의 수신 크기가 감소하여 측정이 불가능하게 된다. 이러한 문제를 해결하기 위해서는 유속 측정시 전자파 출력을 기존의 시스템보다 높게 물표면에 발사하여야 하며 안테나를 포함한 RF 모듈의 수신감도 및 지향성이 개선되어야 한다. 이에 편각측정이 가능하도록 이러한 사항에 주안점을 두어 새로운 시스템을 구성하였다. 수신감도 향상을 위해서는 물표면에 반사되어 돌아오는 신호를 가장 먼저 수신하는 안테나의 특성이 중요하며 그 다음 수신용 증폭기, IF 증폭기 순으로 개선이 필요하다. 본 연구에서는 안테나의 형태를 기존 파라볼릭 안테나에서 위상 배열 평면안테나로 변경하였으며, 이에 따른 이점으로는 송수신부를 분리하여 하나의 평면에 두 개의 안테나를 구성할 수 있다는 사항이다. 즉 외형적으로는 하나의 안테나로 보이지만 두 개의 안테나가 하나로 구성된 것이다. 송수신부를 분리하는 형태는 기존 파라볼릭 안테나에선 불가능한 구조로 변경에 따른 수신감도 향상은 수치적으로 10dB 이상 개선하였다. 송수신부 분리가 수신감도에 영향을 미치는 이유는 물표면으로 발사된 송신 신호의 일부가 수신단으로 유입되는 현상으로 누설되는 송신 신호를 최대한 차단하는 분리도가 수신 신호 검출에 직접적인 양향을 주기 때문에다. 평면 안테나를 적용하면 기존 파라볼릭 안테나에서 사용하던 써큘레이터라는 부품을 삭제할 수 있으며, 안테나의 구조적인 분리를 통해서 수신감도를 개선할 수 있었다. 안테나의 지향성은 발사하는 전자파의 빔폭 성능과 일치하며 각도 단위로 표시한다. 각도 값이 작을수록 전자파의 에너지가 한 곳에 집중된다고 말할 수 있다. 즉 빔폭이 크면 측정시 반사면적이 커져 정확한 지점의 유속을 측정하기 어려운 문제가 발생한다. 본 연구를 통해 빔폭은 기존 안테나 대비2도를 개선하였으며 25%의 개선 효과를 얻었다. 또한 수신감도 및 지향성 개선과 더불어 전자파의 출력을 기존 장비 대비하여 1.6배를 증가하여 편각측정을 위한 전자파표면 유속계의 성능을 개선하였다.