• Proceedings of the KAIS Fall Conference
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• 2010.05a
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• pp.18-23
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• 2010

4$\times$4 Butler Matrix structure has been presented in this paper. It can passes the signal with equal power level and phase difference in the 824MHz to 894MHz frequency of the cellular band. Conventional Butler Matrix was implemented as a single layer substrate structure, but in this paper, we use multi-layer substrate structure and eventually we could get it reduced in size than others. We also used the LTCC coupler to reduce the size effectively, instead of using $90^{\circ}$ hybrid coupler composed of microstrip structure. we used Designer V3.5 Ansoft HFSS V11 for design of 4$\times$4 Butler matrix. Finally, we get good agreements between simulation and experimental results.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.22 no.3
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• pp.49-55
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• 2022

In the next generation mobile communication systems, hybrid massive multiple-input multiple output (MIMO) can be used to highly improve an achievable rate without increasing the number of RF chains. Recently, successive-interference-cancellation (SIC) based hybrid precoder design scheme was proposed to reduce the complexity. However, since this scheme uses simple diagonal matrix for baseband precoding, it cannot solve an interference problem between the transmitted streams. Also, there is a limitation for improving the data rate because of the use of one phase shifter for analog precoding. To solve these problems, in this paper we propose a digital precoding based on the SVD of the effective channel and an analog precoding using two phase shifters. Through simulation, we show that the proposed scheme has better achievable rate and SINR performances than the conventional one.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.7
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• pp.661-668
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• 2004

A novel method to reject the spurious signals which are occurred at Weaver-type low-IF transmitter was proposed in this paper. The spurious signals are generated by the gain and phase imbalances of I/Q channel or imperfect characteristics of 90$^{\circ}$ phase shifter in local oscillator for I/Q channel source. By deriving the gain and phase-based functions from RF spurious signal with the channel imbalance information, the lie channel imbalances were deduced as functions with magnitude and sign dependent on I/Q channel imbalance degree. The proposed method compensates the estimated I/Q channel imbalances by correlation values between the down-converted signal obtained by squaring the output signal itself using a simple mixer and the modified baseband signal. By comparing two signals after A/D conversion, the magnitude and sign of each type of imbalances can be determined separately and simultaneously. Based on the I/Q channel imbalance compensation, the spurious signals can be reduced by adjusting the gain and phase values of I or Q channel signal. The way to estimate the channel imbalances of the up-conversion mixer was presented and verified by using theoretical derivations and computer simulations.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.10
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• pp.1050-1060
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• 2009

In this paper, a X-Band T/R-module for SAR(Synthetic Aperture Radar) systems based on active phased array antennas is designed and fabricated. The T/R modules have a and width of more than 800 MHz centered at X-Band and support dual, switched polarizations. The output power of the module is 7 watts over a wide bandwidth. The noise figure is as low as 3.9 dB. Phase and amplitude are controlled by a 6-bit phase shifter and a 6-bit digital attenuator, respectively. Further the fabricated T/R module has est and calibration port with directional coupler and power divider. Highly integrated T/R module is achieved by using LTCC(Low Temperature Co-fired Ceramic) multiple layer substrate. RMS gain error is less than 0.8 dB max. in Rx mode, and RMS phase error is less than $4^{\circ}$ max. in Rx/Tx phase under all operating frequency band, or the T/R module meet the required electrical performance m test. This structure an be applied to active phase array SAR Antennas.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.6
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• pp.570-579
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• 2009

In this paper, we presented a Vt-DRO with a wide electrical frequency tuning range, using open-loop gain method. The Vt-DRO was composed of 3-stages, resonator, amplifier and phase shifter. In order to satisfy an oscillation condition, we determined magnitude and phase of each stage. The measured S-parameter of cascaded 3-stages shows open-loop oscillation condition. Also, using measured open loop group delay, we derived the relation for electrical frequency tuning range. The Vt-DRO was implemented by connecting the input and the output of the designed open-loop and resulted in closed-loop. As a results, tuning-range of Vt-DRO is 82 MHz, which is close to the predicted results for tuning voltage 0${\sim}$10 V and shows linear frequency tuning at the center frequency of 5.3 GHz. The phase noise is -104 ${\pm}$1 dBc/Hz at 100 kHz offset frequency and power is 5.86${\pm}$1 dBm respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.5
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• pp.413-420
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• 2009

We propose a novel feed network for a $2{\times}2$ array antenna to form a sectoral conical beam. The proposed feed network, which is a symmetrical structure, consists of four $90^{\circ}$ hybrids, a crossover, and four $90^{\circ}$ delay lines. To verify the performance of the feed network a $2{\times}2$ array antenna and the feed network are fabricated on a microstrip structure, and the radiation patterns are measured at the center frequency of 2.57 GHz. The maximum radiation is measured at the $45^{\circ}$ elevation angle and at the $45^{\circ}$, $135^{\circ}$, $225^{\circ}$, and $315^{\circ}$ azimuth angles depending on the choice of the input port of the feed network.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.210-211
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• 2009

In this study, we propose characteristics improvement methods according to via hole plating method for FBAR Duplexer with US PCS($T_x$:1850MHz~1910MHz, $R_x$:1930MHz~1990MHz) bandwidth which is used for wireless systems. Also, we designed and fabricated 3.8*3.8*1.8mm size microminiature FBAR Duplexer based on this proposal. First of all, in this study, we fabricated pentagon shape resonators by different size to make filter combination, and their quality factor(Q) are 687 with 6.6% of $k_{eff}^2$. Using this resonators, designed 3*2Type $T_x$ filter and 3*4Type $R_x$ filter. The transmission line, which works as phase shifter, is designed with $210{\mu}m$ in width and 18mm in length Stripline type. Inductor, which is used for matching component, is designed with width of $75{\mu}m$, a technically achievable minimum width. And adopted plating method of filling via hole with conductive epoxy for improved grounding and thermal conductivity. Using these configuration with all of the matching component values, we found Duplexer characteristics of -1.57dB ~ -1.73dB in insertion loss, -56dB in attenuation at 1850MHz~1910MHz of $T_x$ band. Also, found -2.71 dB ~ -3.23dB in insertion loss, -58dB in attenuation at 1930MHz~1990MHz of $R_x$ band.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.5
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• pp.388-396
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• 2010

In this study, we propose characteristics improvement methods according to via hole plating method for FBAR Duplexer with bandwidth($T_x4: 1850 MHz ~ 1910 MHz, $R_x$:1930 MHz ~ 1990 MHz) which is used for wireless systems. Also, we designed and fabricated $3.8{\times}3.8{\times}1.8mm$ size microminiature FBAR Duplexer based on this proposal. First of all, in this study, we fabricated pentagon shape resonators by different size to make filter combination, and their quality factor(Q) are 687 with 6.6% of ${k_{eff}}^2$. Using this resonators, we designed $3{\times}2$ Type $T_x$ filter and $3{\times}4$ Type $R_x$ filter. The transmission line, which works as phase shifter, is designed with 210 ${\mu}m$ in width and 18 mm in length Stripline type. Inductor, which is used for matching component, is designed with width of 75 ${\mu}m$, a technically achievable minimum width. And adopted plating method of filling via hole with conductive epoxy for improved grounding and thermal conductivity. Using these configuration with all of the matching component values, we found Duplexer characteristics of -1.57 dB ~ -1.73 dB in insertion loss, -56 dB in attenuation at 1850 MHz ~ 1910 MHz of $T_x$ band. Also, found -2.71 dB ~ -3.23 dB in insertion loss, -58 dB in attenuation at 1930 MHz ~ 1990 MHz of $R_x$ band.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.1
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• pp.111-118
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• 2005

The shape of vertical pattern of base station antenna affects greatly quality of the communication of not only a service zone but also adjacent cells and then it is an important point to be considered in designing cell coverage. Currently type of vertical patterns to be applied to base station antenna are divided into five classes. In designing antenna, these five classes are applied solely or compositely according to the environment to be used antenna. In this paper, the dual polarized antenna for base station that is with a continuous electrical down tilting and with a shaped beam pattern, that an upper side lobe is suppressed and a lower null is filled, is designed and fabricated for synthesizing of the shape beant the pattern synthesis methods proposed by R. S. Elliott is used sequentially and for the electrical don tilting, the phased array theory is applied. Measured results show the down tilting range from 0° to 14°, the gain of Min. 13.3dBi and the upper side lobe of Max. -23dB. And we verified that upper side lobe is not to vary greatly and null filling performance is favorable overall.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.3
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• pp.1-6
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• 2008

A dual band I/Q modulator which converts baseband input signals to 2.4GHz or 5GHz RF output has been proposed. The dual band I/Q modulator for 2.4GHz and 5GHz wireless LAN applications consists of $90^{\circ}$ phase shifter and wideband mixer. The I/Q modulator showed 15dB conversion loss at 2.4GHz and 16dB conversion loss at 5GHz. The sideband suppression is about 15dBc at 2.4GHz and 16dBc at 5GHz. Measured data shows 8.5% EVM at 2.4GHz, and 10% EVM at 5GHz for QPSK with symbol rate of 11Mbps. A carrier rejection is about 40dBc at 2.4GHz/5GHz band, and the I/Q modulator satisfied the output wireless LAN spectrum mask with baseband input signal.