Soon Ik Jeon

Switchable Quad-Band Antennas for Cognitive Radio Base Station Applications

A novel antenna configuration for quad-band operation is presented. The quad-band antenna has a directional radiation pattern in four frequency bands, i.e., B1 (800-900 MHz), B2 (1.7-2.5 GHz), B3 (3.3-3.6 GHz), and B4 (5.1-5.9 GHz), covering all spectrums for existing wireless applications, such as GSM, PCS, WCDMA, WiFi, and WiMax. The operating frequency of the quad-band antenna can be adjusted by the use of a MEMS switch, making it suitable for cognitive radio applications. First a switchable quad-band antenna element is introduced. Then a two-element antenna array is developed to increase the antenna gain for base station applications featuring a gain value of about 9-11 dBi over all four frequency bands.

Design and Test of a Mobile Antenna System With Tri-Band Operation for Broadband Satellite Communications and DBS Reception

The tri-band mobile antenna system for broadband multimedia services in the Ka/K-band and a simultaneous direct broadcast service in the Ku-band has been developed. The radiating part of the antenna consists of a shaped dual reflector system and a tri-band feed of circular polarization. The low-profile offset main reflector has an aperture size of 60 cm 20 cm; therefore, a fan beam is formed which is sharp in azimuth and wide in elevation. The feed system contains a protruding dielectric rod for Ka/K-band and 2 2 active phased array. The latter provides the beam for Ku-band along with four fast electrical beams for stable satellite tracking. The new tracking algorithm based on a fusion technique involving various sensors and fast electrical beams has also been introduced. The antenna system was mounted on a large ship and a test car, and successfully operated via Koreasat-3.

Importance of phase unwrapping for the reconstruction of microwave tomographic images.

Microwave image reconstruction is typically based on a regularized least-square minimization of either the complex-valued field difference between recorded and modeled data or the logarithmic transformation of these field differences. Prior work has shown anecdotally that the latter outperforms the former in limited surveys of simulated and experimental phantom results. In this paper, we provide a theoretical explanation of these empirical findings by developing closed form solutions for the field and the inverted electromagnetic property parameters in one dimension which reveal the dependency of the estimated permittivity and conductivity on the absolute (unwrapped) phase of the measured signal at the receivers relative to the source transmission. The analysis predicts the poor performance of complex-valued field minimization as target size and/or frequency and electromagnetic contrast increase. Such poor performance is avoided by logarithmic transformation and preservation of absolute measured signal phase. Two-dimensional experiments based on both synthetic and clinical data are used to confirm these findings. Robustness of the logarithmic transformation to variation in the initial guess of the reconstructed target properties is also shown. The results are generalizable to three dimensions and indicate that the minimization form with logarithmic transformation offers image reconstruction performance characteristics that are much more desirable for medial microwave imaging applications relative to minimizing differences in complex-valued field quantities.

Design considerations of satellite-based vehicular broadband networks

Convergence between wireless networks is the main trend in current and future wireless communications. The distinct advantage of satellite and terrestrial network integration is the possibility to provide ubiquitous multimedia services in vehicles at any location. The key design considerations of mobile broadband satellite access technologies are given in this article. After presenting the conceptual models of a system and services, the design issues of satellite network synchronization and burst demodulation are described. The design considerations of medium access control, resource management, capacity, and buffer controls for internetworking are given. Also, the active antenna issues are provided along with a sample design.

A NEW TYPE OF WIDEBAND SLOT-FED U-SLOTTED PATCH ANTENNA

A slot-fed U-slotted patch antenna is de eloped as an aperture-coupling structure, and is compared to the existing feed types. Its wideband mechanism is explained, and its samples for Kuand S-bands are designed, simulated, and tested. A bandwidth of about 42% for VSWR less than 2:1; and 30.1% for y3 dB peak gain are obtained. Q 1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 22:

A review of breast tissue classification in mammograms

For women in the U.S. breast cancer is the most commonly diagnosed cancer besides skin cancer and has become one of the major health issues in recent decades. Early detection through screening is one of key factors to reduce the death rates. The strong correlation between abnormality of breast tissues presented in mammograms and breast cancer shows that radiologists could benefit from Computer-Aided Diagnosis (CAD) systems with abilities of automated breast tissueclassification. This paper reviews recent advances in classification technologies of breast tissues. The major contribution of this paper is that we extensivelydiscuss recent breast tissue classification technologie sand compare three different types of approaches. According to our survey, we found that machine learning approaches could be chosen as anappropriate classification technology for a CAD system, considering efficiency and compatibility.

Theoretical analysis for beam pointing accuracy of stair-planar phased array antenna with tracking beam

In this paper, the stair-planar phased array antenna with tracking beam is introduced and the beam pointing characteristics are theoretically analyzed from numerical simulation. The vehicular antenna was developed as engineering model to provide the satellite internet services in mobile environment. Especially, radiator subarrays of this antenna are arranged like stairs to design for low profile. This structure brings about the pointing error between the main and tracking beams due to the difference of each frequency. To solve this trouble, two treatments using RF cable length compensation and 2/sup nd/ level phase compensation are investigated. In addition, this analytic model of beam steering will help to design and evaluate the antenna beam pattern.

Active phased array antenna for mobile multimedia services via satellite

This paper introduces an active phased array antenna for mobile DBS service. The main idea for the antenna is to use twelve active array elements for cost effectiveness. For this purpose, the attractive hybrid tracking method with two-dimensional array structure is also used. The electronic beam scan coverage of this antenna is over 24 degrees wide in elevation, and 12 degrees in azimuth. The high-speed tracking capability of this antenna for fast moving vehicles gives other applications in satellite mobile multimedia services like mobile internet services by satellite hybrid link. Finally, this paper also introduces recent results for developing active phased array antennas for the high-speed data communications via satellite.

Low sidelobe design by position perturbation in mobile array antenna for satellite communications

This work presents the low sidelobe pattern design of a mobile terminal antenna for satellite communications. This is important to protect interferences from neighboring satellites, which is regularized by international unions such as ITU. To synthesize the array beam pattern with low sidelobes, the position of the array elements is perturbed and optimized by a genetic algorithm. In addition, the characteristics of the optimized array beam patterns are investigated according to the number of array elements. Furthermore, the illustrative antenna, which is a mobile array antenna with a stair-planar configuration for satellite multimedia communication, is introduced to verify this optimizing technique.

A support vector machine based classifier to extract abnormal features from breast magnetic resonance images

Magnetic resonance imaging (MRI) is one of the high quality technologies to detect the breast cancer. This study proposes a new framework to extract abnormal features in Magnetic Resonance (MR) images by concentrating on the key aspect of the features: generating a unique input sequence to apply the Support Vector Machine (SVM) classifier. The main contribution of the proposed approach is the improvement of an accuracy in identifying abnormal features using SVM classifier. This approach is also less sensitive to noise in detecting the breast cancer. In order to evaluate the improved performance of the proposed SVM classifier, the results of traditional Decision Tree (DT) classifier has been compared with that of SVM.