• ETRI Journal
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• v.25 no.1
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• pp.19-24
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• 2003

This paper describes the performance of a Ku-band 5-bit monolithic phase shifter with metal semiconductor field effect transistor (MESFET) switches and the implementation of a ceramic packaged phase shifter for phase array antennas. Using compensation resistors reduced the insertion loss variation of the phase shifter. Measurement of the 5-bit phase shifter with a monolithic microwave integrated circuit demonstrated a phase error of less than $7.5{\circ}$ root-mean-square (RMS) and an insertion loss variation of less than 0.9 dB RMS for 13 to 15 GHz. For all 32 states of the developed 5-bit phase shifter, the insertion losses were $8.2{\pm}1.4$dB, the input return losses were higher than 7.7 dB, and the output return losses were higher than 6.8 dB for 13 to 15 GHz. The chip size of the 5- bit monolithic phase shifter with a digital circuit for controlling all five bits was 2.35 mm ${\times}$1.65 mm. The packaged phase shifter demonstrated a phase error of less than $11.3{\circ}$ RMS, measured insertion losses of 12.2 ${\pm}$2.2 dB, and an insertion loss variation of 1.0 dB RMS for 13 to 15 GHz. For all 32 states, the input return losses were higher than 5.0 dB and the output return losses were higher than 6.2 dB for 13 to 15 GHz. The size of the packaged phase shifter was 7.20 mm${\times}$ 6.20 mm.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.7
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• pp.1240-1246
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• 2000

The finite-difference time-domain (FDTD) method is applied to analyze a single step microstrip discontinuity in the substrate, and an equivalent circuit model comprised of two inductors and a capacitor has been developed using the numerical results. The microstrip discontinuity newly introduced in this paper has a thickness change of the substrate in the longitudinal direction with a uniform strip width. The discontinuity can be applied to the feeding circuit design for the patch antennas and interconnections between microwave circuit modules. The simulation results are compared with those computed by HFSS, and two results showed a good agreement. An equivalent circuit developed from the FDTD results, which is accurate within 2.4% in magnitudes of $S_{11}$ and $S_{21}$,can be applied for the computer-aided design of microwave circuits.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.124-128
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• 1999

We report microwave properties of high-T$_c$ superconducting (HTS) microstrip antennas without impedance matching circuits, where the impedance mismatching is obvious under the critical temperature (T$_c$). The superconducting thin films used in this report were YBa$_2Cu_3O_{7-x}$ (YBCO) films deposited on MgO substrates produced by pulse laser deposition (PLD) technique. At around T$_c$, 86 K the reflection coefficient rapidly drops, and the standing wave ratio (SWR) becomes almost unity, and the characteristic impedance based on the Smith chart is nearly 50 ${\Omega}$. The reflection coefficient and the SWR of the HTS microstrip antenna were - 62.52 dB and 1.0015, respectively, at the resonant frequency of 11.812 CHz at 86 K.

• Proceedings of the KSRS Conference
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• 2008.10a
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• pp.324-327
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• 2008

Microwave remote sensing has great potential, especially in monsoon Asia, since optical observations are often hampered by cloudy conditions. The radar backscattering characteristics of rice crop were investigated with a ground-based automatic scatterometer system. The system was installed inside a shelter in an experimental paddy field at the National Institute of Agricultural Science and Technology (NIAST) before transplanting. The rice cultivar was a kind of Japonica type, called Chuchung. The scatterometer system consists of X-band antennas, HP8720D vector network analyzer, RF cables, and a personal computer that controls frequency, polarization and data storage. This system automatically measures fully-polarimatric backscattering coefficients of rice crop every 10 minutes, accompanied by a digital camera that takes pictures in a fixed position with the same interval. The backscattering coefficients were calculated by applying a radar equation. Plant variables, such as leaf area index (LAI), biomass, plant height and weather conditions were measured periodically throughout the rice growth season. We have performed polarimetric decomposition of paddy data such as single, double and volume scattering to extract the scattering information effectively. We investigated the relationships between backscattering coefficients and the plant variables.

• Proceedings of the KSRS Conference
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• 2008.10a
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• pp.22-25
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• 2008

Aperture synthesis with platform motion has been presented as a useful tool to achieve the high spatial resolution imaging. Using a motion induced synthetic aperture radiometer (MISAR), a passive microwave image can be achieved with a small number of antennas. Moreover, the MISAR is capable of imaging better than the case without motion, using the same configuration of antenna array. With a platform motion, visibility can be sampled more efficiently, and as a result the imaging performance of the MISAR shows higher quality than the case without platform motion. In this paper, the advantage of MISAR is demonstrated experimentally. Using a laboratory model of inteferometric radiometer, the point source images are obtained under the condition with platform motion and without platform motion. In the experimental results, the point source response of the MISAR shows better quality of sidelobe level and beam efficiency than the case without platform motion.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.11a
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• pp.300-304
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• 2002

We fabricated thick film monopole antennas using Mo-doped $BiNbO_{4}$ ceramics and investigated their electrical properties as a function of the Mo-doping concentration. Compared with undoped $BiNbO_{4}$ ceramics, 10 at.% Mo-doping improved microwave dielectric properties of ceramics by increased sintered density as well as decreased space charge density. Further increase in the Mo-doping concentration caused formation of $Bi_{2}MoO_{6}$ phases, resulting in deterioration of the microwave characteristics. The gain and bandwidth of the ceramic monopole antenna were also greatly affected by the Mo-doping concentration. When Mo-doping concentration was 10 at%, highest gain of ~0.7dBi with lowest bandwidth of 30% at 2.3GHz was obtained.

• Journal of the Semiconductor & Display Technology
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• v.17 no.2
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• pp.20-25
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• 2018

In this paper, we have designed circularly polarized array antenna for 5.8GHz microwave wireless power transmission. To obtain high antenna gain, we studied a single patch antenna, a $2{\times}1$ array antenna, a $2{\times}2$ array antenna, a $2{\times}4$ array antenna, and a $4{\times}4$ array antenna. Commonly, characteristics of each antenna have a frequency of 5.8 GHz and Right Hand Circular Polarization(RHCP) of circular polarization. Also, the results were obtained with the design to each antenna that the return loss was less than -10dB and the axial ratio was less than 3dB. The gain of the antennas was 6.08dBi for a single patch antenna, 9.69dBi for a $2{\times}1$ array antenna, 12.99dBi for a $2{\times}2$ array antenna, 15.72dBi for a $2{\times}4$ array antenna and 18.39dBi for a $4{\times}4$ array antenna. When the elements of the array antenna were increased, it was confirmed that it increased by about 3dBi.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.3
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• pp.247-252
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• 2013

In this paper, a microwave tag system of a frequency-scanning type is proposed with multi-resonators using defected ground structures. While a conventional chip-based RFID stores time-sequential codes, the proposed type achieves pure passive tags by using multi-resonant bits over a frequency range. Moreover, the resonators of the spiral defected ground structures implemented on the back side of transmission lines have advantages of the excellent bandstop characteristics as well as the bit-error avoidance by the re-radiation on normal resonators. The proposed microwave tag is designed with UWB antennas at 3~7 GHz. From the experimental results in an anechoic chamber, it has been verified of the excellent recognitions for various 5-bits identification codes.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.12
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• pp.1124-1131
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• 2011

In this paper, image reconstruction algorithm for breast cancer detection using MT(Microwave Tomography) was investigated. The breast cancer detection system under development uses 16 transmit/receive antennas. The signal waveform was a sinusoidal wave at 900 MHz. To solve the 2D inverse scattering problem, we used the 2D FDTD (Finite Difference Time Domain) method for forward calculation and LMA(Levenberg-Marquardt Algorithm) for optimization. The result of the image reconstruction using the numerical phantom by MRI(Magnetic Resonance Imaging) obtained from real patient of breast cancer showed that we can detect the position of the tumor accurately.

• Journal of the Korean Society of Hazard Mitigation
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• v.5 no.2 s.17
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• pp.1-8
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• 2005

Microwave tomographic imaging technology using a bi-focusing operator has been developed in order to detect the internal voids/objects inside concrete structures. The imaging system consists of several cylindrical or planar array antennas for transmitting and receiving signals, and a numerical focusing operator is applied to the external signals both in transmitting and in receiving fields. In this study, the authors developed 3-dimensional (3D) electromagnetic (EM) imaging technology to detect such damage and to identify exact location of steel rebars or dowel. The authors have developed sub-surface two-dimensional (2D) imaging technique using tomographic antenna array in previous works. In this study, extending the earlier analytical and experimental works on 2D image reconstruction, a 3D microwave imaging system using tomographic antenna way was developed, and multi-frequency technique was applied to improve quality of the reconstructed image and to reduce background noises. Numerical simulation demonstrated that a sub-surface image can be successfully reconstructed by using the proposed tomographic imaging technology. For the experimental verification, a prototype antenna array was fabricated and tested on a concrete specimen.