• Journal of the Korea Institute of Military Science and Technology
• /
• v.24 no.1
• /
• pp.50-60
• /
• 2021

For conventional AESA radars, DC-DC power modules using 300 Vdc have low efficiency, high volume, heavy weight, and high price, which have problems in modularity with T/R module groups. In this paper, to improve these problems, we propose a distributed DC-DC power module with high-voltage 800 Vdc and high-efficiency Step-down Converter. In particular, power requirements for modern and future marine weapons systems and sensors are rapidly evolving into high-energy and high-voltage power systems. The power distribution of the next generation Navy AESA radar antenna is under development with 1000 Vdc. In this paper, the proposed highvoltage, high-efficiency DC-DC power modules increase space(size), weight, power and cooling(SWaP-C) margins, reduce integration costs/risk, and reduce maintenance costs. Reduced system weight and higher reliability are achieved in navy and ground AESA systems. In addition, the proposed architecture will be easier to scale with larger shipboard radars and applicable to other platforms.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.21 no.2
• /
• pp.194-201
• /
• 2010

We propose a frequency selective surface(FSS) using double split ring resonators(DSRRs) for isolation enhancement between CDMA and RFID. The structure consists of an outer SRR and an inner SRR, and the gaps are formed in the same direction. By properly adjusting the gap and line width, the resonant frequency and skirt characteristics can be adjusted without varying the unit cell size. The proposed structure has a different field distribution from that of an ordinary SRR for magneto-dielectric materials. One layer consists of $9{\times}9$ unit cells and the other layer was separated by 50 mm. To validate the simulation results, we fabricated the patch antenna and the FSSs, and the measured results show a good agreement with the simulated ones. The electrical size of the unit cell is $0.110\;{\lambda}{\times}0.110\;{\lambda}{\times}0.002\;{\lambda}$, and the size of the two layer FSS is $1.058\;{\lambda}{\times}1.058\;{\lambda}{\times}0.153\;{\lambda}$. The two layer FSS maintain gain in CDMA frequency and has 6.9 dB reduced gain in RFID frequency.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.39 no.2
• /
• pp.92-100
• /
• 2002

The 16-port feed waveguide array with inductive walls analyzed by Galerkin's method of moments are proposed for the DBS reception system mounted on vehicle. First of all, in order to verify the validity of electromagnetic analysis and design for a $\pi$-junction feed waveguide, it is designed and fabricated at DBS band. The measurement results of a $\pi$-junction feed waveguide agree well with the theoretical ones. Based on this design method, an array design for WR-90 standard waveguide is conducted. Since the width of a $\pi$-junction feed WR-90 standard waveguide is larger than a guided wave length in an array design, the difference of amplitude and phase of 8-port array are calculated 2.3 dB and 62 degrees, respectively. The bandwidth with return loss of -20 dB below is about 220 MHz and it doesn't satisfy DBS band. To solve this problem, we propose a novel design that the width of a $\pi$-junction feed waveguide equals to a guided wave length. By the proposed novel design for 8-port feed waveguide array, the difference of amplitude and phase are decreased 1 dB and 13 degrees, respectively. The broad bandwidth of 700 MHz is also realized. The size of 16-port waveguide away compared with WR-90 array is reduced about 10 cm. The measured antenna gain for the fabricated 16-port feed waveguide array is observed 24 dBi above at DBS band.

• Korean Journal of Remote Sensing
• /
• v.34 no.6_3
• /
• pp.1415-1425
• /
• 2018

Kompsat-5 is the first Earth Observation Satellite which is equipped with an SAR in Korea. SAR images are generated by receiving signals reflected from an object by microwaves emitted from a SAR antenna. Because the wavelengths of microwaves are longer than the size of particles in the atmosphere, it can penetrate clouds and fog, and high-resolution images can be obtained without distinction between day and night. However, there is no color information in SAR images. To overcome these limitations of SAR images, colorization of SAR images using Cycle GAN, a deep learning model developed for domain translation, was conducted. Training of Cycle GAN is unstable due to the unsupervised learning based on unpaired dataset. Therefore, we proposed MS Cycle GAN applying multi-scale discriminator to solve the training instability of Cycle GAN and to improve the performance of colorization in this paper. To compare colorization performance of MS Cycle GAN and Cycle GAN, generated images by both models were compared qualitatively and quantitatively. Training Cycle GAN with multi-scale discriminator shows the losses of generators and discriminators are significantly reduced compared to the conventional Cycle GAN, and we identified that generated images by MS Cycle GAN are well-matched with the characteristics of regions such as leaves, rivers, and land.

• Investigative Magnetic Resonance Imaging
• /
• v.13 no.1
• /
• pp.31-39
• /
• 2009

Purpose : This study proposes the keyhole method in order to improve the time resolution of the proton resonance frequency(PRF) MR temperature monitoring technique. The values of Root Mean Square (RMS) error of measured temperature value and Signal-to-Noise Ratio(SNR) obtained from the keyhole and full phase encoded temperature images were compared. Materials and Methods : The PRF method combined with GRE sequence was used to get MR temperature images using a clinical 1.5T MR scanner. It was conducted on the tissue-mimic 2% agarose gel phantom and swine's hock tissue. A MR compatible coaxial slot antenna driven by microwave power generator at 2.45GHz was used to heat the object in the magnetic bore for 5 minutes followed by a sequential acquisition of MR raw data during 10 minutes of cooling period. The acquired raw data were transferred to PC after then the keyhole images were reconstructed by taking the central part of K-space data with 128, 64, 32 and 16 phase encoding lines while the remaining peripheral parts were taken from the 1st reference raw data. The RMS errors were compared with the 256 full encoded self-reference temperature image while the SNR values were compared with the zero filling images. Results : As phase encoding number at the center part on the keyhole temperature images decreased to 128, 64, 32 and 16, the RMS errors of the measured temperature increased to 0.538, 0.712, 0.768 and 0.845$^{\circ}C$, meanwhile SNR values were maintained as the phase encoding number of keyhole part is reduced. Conclusion : This study shows that the keyhole technique is successfully applied to temperature monitoring procedure to increases the temporal resolution by standardizing the matrix size, thus maintained the SNR values. In future, it is expected to implement the MR real time thermal imaging using keyhole method which is able to reduce the scan time with minimal thermal variations.