• KSII Transactions on Internet and Information Systems (TIIS)
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• v.4 no.6
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• pp.989-1005
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• 2010

Cooperative diversity is a technique with which a virtual multiple antenna array is established among the single antenna users of the wireless network to realize space diversity. Signal space diversity (SSD) is a bandwidth-efficient diversity technique, which uses constellation rotation and interleaving techniques to achieve diversity gain. A new cooperative diversity scheme with rotated constellations (RCCD) is proposed in this paper. In this scheme, data are modulated by using a rotated constellation, and the source and the relays transmit different components of the modulated symbols. Since any one of the components contains full information of the symbols, the destination can obtain multiple signals conveying the same information from different users. In this way, space diversity is achieved. The RCCD scheme inherits the advantage of SSD - being bandwidth-efficient but without the delay problem of SSD brought by interleaving. The symbol error rate of the RCCD scheme is analyzed and simulated. The analysis and simulation results show that the RCCD scheme can achieve full diversity order of two when the inter-user channel is good enough, and, with the same bandwidth efficiency, has a better performance than amplify-and-forward and detect-and-forward methods.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.3
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• pp.227-247
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• 2015

An X-band $8{\times}16$ dual-polarized active phased array antenna system has been implemented based on the substrate integrated waveguide(SIW) technology having low propagation loss, complete EM shielding, and high power handling characteristics. Compared with the microstrip case, 1 dB less is the measured insertion loss(0.65 dB) of the 16-way SIW power distribution network and doubled(3 dB improved) is the measured radiation efficiency(73 %) of the SIW sub-array($1{\times}16$) antenna element. These significant improvements of the power division loss and the radiation efficiency using the SIW, save more than 30 % of the total power consumption, in the active phased array antenna systems, through substantial reduction of the maximum output power(P1 dB) of the high power amplifiers. Using the X-band $8{\times}16$ dual-polarized active phased array antenna system fabricated by the SIW technology, the main radiation beam has been steered by 0, 5, 9, and 18 degrees in the accuracy of 2 degree maximum deviation by simply generating the theoretical control vectors. Performing thermal cycle and vacuum tests, we have found that the SIW array antenna system be eligible for the space environment qualification. We expect that the high efficiency SIW array antenna system be very effective for high performance radar systems, massive MIMO for 5G mobile systems, and various millimeter-wave systems(60 GHz WPAN, 77 GHz automotive radars, high speed digital transmission systems).

• Journal of Space Technology and Applications
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• v.1 no.1
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• pp.33-40
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• 2021

Based on the requirements of a total weight of 42 kg or less, the NEXTSat-2 SAR (synthetic aperture radar) system was developed. As the NEXTSat-2 is a small-sized satellite, the SAR system was designed to account for about 40% of the dry mass of the payload relative to the total mass. Among the major components of the SAR system - which are an antenna, an RF transceiver, a baseband signal processor, and a power unit - a part with a particularly large dry mass is the antenna, the core of the SAR system. Whereas various selections are possible in consideration of gain and efficiency when designing the antenna, the micro-strip patch array antenna was adopted by reflecting the dry mass, power, and resolution required by the NEXTSat-2 project. In order to meet the mission requirement of the NEXTSat-2, the antenna was developed with a frequency of 9.65 GHz, a gain of 42.7 dBi, and a return loss of -15 dB. The performance of the antenna was verified by conducting a field test onboard the vehicle.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.89.2-89.2
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• 2012

Radiation Belt, discovered by Van Allen in 1958, is a region energetic particles are trapped by the Earth's magnetic field. To measure charged particles and fields in the radiation belt, RBSP(Radiation Belt Storm Probes) mission will be launched in September 2012 by NASA. RBSP mission consists of two spacecraft having orbit from 600 km to 30,000 km and rotates the Earth twice a day. This mission is not designed just for scientific purpose but have operational function broadcasting real time data for space weather monitoring. As a program of KASI-NASA cooperation, KASI is constructing RBSP data receiving antenna that will be installed by April in Daejeon. With this antenna system, NASA can receive RBSP data for 24 hours and KASI also get space weather information to protect Korean GEO satellites. In this presentation, we will discuss how we use RBSP data for space weather forecasting. In addition, we will talk about science topics that can be achieved by RBSP mission. Especially we focus on the dusk-side electron precipitation that has been considered as a main mechanism of electron dropout events. We show the dusk-side precipitation is closely associated with radiation belt electron loss with NOAA-POES data, and why RBSP mission is important to understand radiation belt physics.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.2
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• pp.18-28
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• 1989

In this paper, we describe a pointing accuracy establishment and efficiency measurement of 13.7 m antenna for observing cosmic radio wave which is in the first stage just after finishing its installation. The initial stage of pointing model, 1 and 2 were set up with the observational data of Sun and Moon which are large in visual diameter and also strong in radio intensity. Based on this model, model 3 and 4 were established within the available operational range, i.e., 3.8" in azimuth deviation, 10.5" in elevation deviation, with the observational data of SiO maser source which is a point source and distributed in overall sky. Both apeture efficiency anhd beam efficiency were measured by observing Venus whose brightness temperature is well-known. The resulting corrected efficiencies were 35% and 50% respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.9
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• pp.829-834
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• 2009

In this paper, a HediaFLO/GPS/Bluetooth antenna is designed for mobile handset with metallic chassis. It is consisted of two metal plates with 7.6 mm gap, a connection plate and source between two plates. It can be analyzed as U-slot antenna of $0.5\;{\lambda}$, array of shorted patches each application bands. Simulated and measured performance of the proposed antenna show that it has enough possibility to reuse metallic chassis itself as radiator without any additional space for antenna.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.4 no.1 s.6
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• pp.89-95
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• 2005

In this paper, a quad-band antenna for GSM/GPS/DCS/US-PCS handsets is proposed. The proposed antenna is low-profile for mounting in limited inner space of a handset. It consists of three open points with quarter wave length for multi-band operation. The ground plane below the patch is removed for wide-bandwidth without the variation of antenna size and the slot is added at the center of the patch for convenient matching in high frequency band. It provides a enough bandwidth within VSWR 3:1 at all bands. In addition, the measured peak gains are between -2.19 and 2.09 in anechoic chamber (10m$\times$6m$\times$4m).

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.4
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• pp.353-359
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• 2004

In this paper, the single-layer slotted waveguide array antenna is designed, which consists of two par the slot plate and the structure of waveguide. The key difficulty in mass production is the realization of perfect electrical contact between the two parts. Therefore the single-layer slotted waveguide array antenna is presented with a dumbbell patch and a choke. The choke can prevent from the leakage between the slot plate and waveguide, while the choke in the adjacent waveguide incurs space dissipation. To reduce the spacing of antennas about a dumbbell patch is utilized. the 16${\times}$16 array antenna gain of 27.2 ㏈ with 45 % aperture efficiency is obtained.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.7
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• pp.55-61
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• 2004

This paper proposes an antenna selection and switching system between spatial multiplexing and diversity techniques. The proposed system overcomes spatial correlation by using antenna selection method and improve bit error performance with switching encoding nudes between a spatial multipexing encoder and a diversity encoder. Therefore, in a 4 transmit and 2 receive antenna system first, the proposed system selects 2 transmit antennas, and next, switches encoding modes between Space-Time Transmit Diversity and BLAST according to instantaneous channel information. Computer simulations showed that the proposed system improves about 2 or 3 ㏈ SNR in low correlated channel and about 3 ㏈ SNR in highly correlated channel rather than a 2 by 2 antenna switching system.

• Journal of Communications and Networks
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• v.13 no.5
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• pp.456-462
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• 2011

This paper investigates the outage behavior of peak interference power limited cognitive radio (CR) networks with multiple transmit antennas. In CR-multi-input single-output (MISO) channel, the total transmit power is distributed over the transmitantennas. First, we use the orthogonal space-time codes (STC) to achieve the transmit diversity at CR-receiver (rx) and investigate the effect of the power distribution on the interference power received at the primary-receiver (P-rx). Then, we investigate the transmit antenna selection (TAS) scheme in which the CR system selects the best transmit antenna and allocates all the power to the selected best antenna. Two transmit antenna selection strategies are proposed depending on if feedback channel is available or not. We derive the closed form expressions of outage probability and outage capacity of all schemes with arbitrary number of transmit-antennas. We show that the proposed schemes significantly improve the outage capacity over the single antenna systems in Rayleigh fading environment. We also show that TAS based scheme outperforms the STC based scheme when peak interference power constraint is imposed on the P-rx only if a feedback channel from CR-rx to CR-transmitter is available.