• Korean Journal of Optics and Photonics
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• v.17 no.1
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• pp.7-17
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• 2006

In this paper, we proposed an optical true time-delay (TTD) for planar phased array antennas (PAAs), which is composed of a wavelength-dependent optical true time delay (WDOTTD) followed by a wavelength-independent optical true time delay (WIOTTD). The WDOTTD is a fiber Bragg gratings (FBGs) Prism and the WDOTTD is a fiber delay-lines matrix of which each component consists of a certain length of fiber connected to cross-ports of a 2${\times}$2 MEMS switch. A 10-GHz 2-bit${\times}$4-bit two-dimensional optical TTD has been fabricated by cascading a WDOTTD with a maximum time delay of 810 ps to a WIOTTD of $\pm$50 ps. Time delay and insertion loss for each radiation angle have been measured. Time delay error for the WIOTTD has been measured to be less than $\pm$1 ps. We have also designed a two-dimensional 10-GHz PAA composed of 8${\times}$8 microstrip patch antenna elements driven by the proposed TTD. The radiation patterns of this PAA have been obtained by simulation and analyzed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.11
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• pp.5214-5218
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• 2011

In this paper, bandwidth improvement of a series-fed two dipole array(STDA) antenna applicable for mobile communication base station antennas is studied. The proposed STDA antenna consists of two strip dipole antennas with different lengths which are connected directly trough a coplanar stripline(CPS). By adjusting the spacing between the two dipoles and the length of the second dipole, the bandwidth of the STDA can be enhanced. In addition, an integrated balun composed of a short-circuited microstrip line and a slot line is utilized to minimize the area required for a feeding part, and a broadband impedance matching is obtained by adjusting the feeding point. Based on the proposed antenna structure, an STDA antenna covering the frequency band ranging from 1.75 GHz to 2.7 GHz, which includes almost all the existing mobile communication frequency bands, with more than 5 dBi gain is designed and fabricated on an FR4 substrate with dielectric constant of 4.4 and thickness of 1.6mm, and experimentally tested. The fabricated antenna shows impedance bandwidth of 49%(1.7-2.8 GHz) for VSWR<2, a gain higher than 5.5 dBi, and a front-back ratio better than 12 dB.

• Korean Journal of Optics and Photonics
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• v.33 no.1
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• pp.11-21
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• 2022

We have investigated the optimal design of an aperiodic optical phased array (OPA) for use in light detection and ranging applications. Three optimization algorithms - particle-swarm optimization (PSO), a genetic algorithm (GA), and a pattern-search algorithm (PSA) - were employed to obtain the optimal arrangement of optical antennas comprising an OPA. The optimization was performed to obtain the minimal side-lobe level (SLL) of an aperiodic OPA at each steering angle, using the three optimization algorithms. It was found that PSO and GA exhibited similar results for the SLL of the optimized OPA, while the SLL obtained by PSA showed somewhat different features from those obtained by PSO and GA. For an OPA optimized at a steering angle <45°, the SLL value averaged over all steering angles increased as the angle of optimization decreased. However, when the angle of optimization was larger than 45°, low average SLL values of <13 dB were obtained for all three optimization algorithms. This implies that an OPA with high signal quality can be obtained when the arrangement of the optical antennas is optimized at a large steering angle.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.5
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• pp.18-24
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• 2010

This paper propose a dual-layer beam-forming technique for MIMO-OFDM systems. Dual-layer beam-forming is a capacity enhancing technique to transmit two streams of source data with more than two transmit and receive antennas. Beamforming is a technique to enhance the link-level performances gain using antenna array with the small inter element distance. The proposed scheme can obtain both high capacity of spatial multiplexing and antenna array gain of beamforming for MIMO-OFDM systems. Therefore, it provides better BER performance than the traditional spatial multiplexing and beamforming techniques under the same simulation environment.

• ETRI Journal
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• v.35 no.3
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• pp.378-385
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• 2013

An S-band multifunction chip with a simple interface for an active phased array base station antenna for next-generation mobile communications is designed and fabricated using commercial 0.5-${\mu}m$ GaAs pHEMT technology. To reduce the cost of the module assembly and to reduce the number of chip interfaces for a compact transmit/receive module, a digital serial-to-parallel converter and an active bias circuit are integrated into the designed chip. The chip can be controlled and driven using only five interfaces. With 6-bit phase shifting and 6-bit attenuation, it provides a wideband performance employing a shunt-feedback technique for amplifiers. With a compact size of 16 $mm^2$ ($4mm{\times}4mm$), the proposed chip exhibits a gain of 26 dB, a P1dB of 12 dBm, and a noise figure of 3.5 dB over a wide frequency range of 1.8 GHz to 3.2 GHz.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.1
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• pp.28-31
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• 2018

This paper investigates the ground reflection effect on the channel capacity of an orbital angular momentum (OAM) multi-mode transmission system that uses uniform circular array (UCA) antennas. The ground-reflected signals cause inter-mode interferences between the OAM modes, and lead to system performance degradation. The OAM multi-mode channel capacity severely degrades owing to the ground reflection as the transmission distance increases. Increasing the UCA height above the ground and using highly directive array elements can mitigate the ground reflection effect and increase the channel capacity.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.05a
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• pp.111-114
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• 2003

It has well known that MUSIC and ESPRIT algorithms estimate angle of arrival(AOA) with high resolution by eigenvalue decomposition of the covariance matrix which were obtained from the array antennas. In the case that 2-D large-sized array antenna is required, however, one of the disadvantages of MUSIC and ESPRIT is that they are computationally ineffective, and then they are difficult to implement in real time. To alleviate the computational complexity, several method using neural model have been study. For multiple signals, those methods require huge training data prior to AOA estimation. This paper proposes the algorithm for AOA estimation by interconnected hopfield neural model. Computer simulations show the validity of the proposed algorithm.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.8 no.4
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• pp.275-280
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• 2015

In this paper, we studied for modified MUSIC algorithm of direction of arrival (DOA)estimation. Modified MUSIC algorithm search optimal covariance matrix using singular value decomposition and Bayes method, and desired signals are estimated by updating weight. In order to estimation of desired signals, we used sub spatial method of MUSIC algorithm. General MUSIC algorithm can estimate a desired signal in case of non-correlation signal. But, general MUSIC algorithm in case of correlation signal can not estimate a desired signals and resolution is decreased. Though simulation in case of correlation signal, we analyze to compare proposed MUSIC algorithm with general MUSIC algorithm.

• Journal of the Korea Institute of Military Science and Technology
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• v.12 no.2
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• pp.182-190
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• 2009

GPS receivers can be disrupted by intentional or unintentional jamming, then it is unable to receive GPS signals and it is impossible to get the correct navigation results. Anti-jamming schemes using array antennas are being studied well due to high performance of those, and the efforts to apply them to GPS receiver are also being done. A GPS receiver structure for a multiple beam-forming scheme among those schemes has been proposed in this paper, and the performance is also compared with that using a general GPS receiver structure. For a general GPS receiver structure, each satellite signal which is formed by a beam-forming scheme is summed to be processed in a part of digital signal processing. For a proposed GPS receiver structure, however, each satellite signal is respectively processed by a designated channel in a part of digital signal processing. Finally, it is confirmed that the proposed GPS receiver structure is superior to a general GPS receiver structure in a point of the carrier to noise power ratio and the navigation accuracy using a software platform.

• Journal of Communications and Networks
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• v.10 no.2
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• pp.118-126
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• 2008

The use of beamforming is effective for users in limited power environments. However, when it is applied to the downlink of a cellular system with universal frequency reuse, users near the sector boundary may experience significant interference from more than one sector. The use of a minimum mean square error (MMSE)-type receiver may not sufficiently cancel out the interference unless a sufficient number of receive antennas are used. In this paper, we consider the use of inter-sector beamforming that cooperates with a neighboring sector in the same cell to mitigate this interference problem in time-division duplex (TDD) environments. The proposed scheme can avoid interference from an adjacent sector in the same cell, while enhancing the transmit array gain by using the TDD reciprocity. The performance of the proposed scheme is analyzed in terms of the output signal-to-interference-plus-noise power ratio (SINR) and the output capacity when applied to an MMSE-type receiver. The beamforming mode can be analytically switched between the inter-sector and the single-sector mode based on the long-term channel information. Finally, the effectiveness of the proposed scheme is verified by computer simulation.