Wan-Soo Nah

This work presents a new method for enhancing the performance of a dual band Planer Inverted-F Antenna (PIFA) and its lumped equivalent circuit formulation. The performance of a PIFA in terms of return loss, bandwidth, gain, and efficiency is improved with the addition of the proposed open stub in the radiating element of the PIFA without disturbing the operating resonance frequencies of the antenna. In specific cases, various simulated and fabricated PIFA models illustrate that the return loss,

This paper presents 3-D optimal shape design method of ferromagnetic pole pieces for magnetic resonance imaging (MRI) devices of open permanent magnet type. The design method is based on a continuum sensitivity analysis in conjunction with the boundary integral equation method (BIEM). The magnetic poles of an open magnet assembly are designed by the proposed method and the conventional shimming method. Magnetic field strength, ppm order homogeneity and working space volume are compared between t

In this paper, a coplanar symmetrical meander line structure is presented, and an equivalent circuit model is proposed to allow estimation of its electrical characteristics based on numerical modeling. The parasitic couplings in the proposed structure are considerably different from those of a simple meander line with a ground structure below it. Analysis and derivation of inductive and capacitive couplings and of resistance in the effective frequency band are addressed in detail, and the effect

In this article, a high-power, high-efficiency inverted Doherty power amplifier (PA), having a more compact load network than that of the conventional Doherty amplifier, was designed and implemented for wide-band code-division multiple access (WCDMA) base-station applications. Its configuration and working principle are compared with the conventional Doherty amplifier. For experimental verification, we implemented an inverted Doherty amplifier, using a 190 W peak-envelope-power (PEP) laterally d

As the available space in the board of a mobile device becomes smaller and more compact, circuit elements and transmission lines are arranged in very close proximity, especially from the antennas which are usually installed on the same board. Due to the various on-board antennas which are designed in small space, the transmission lines on the board are electromagnetically interfered, resulting in the performance degradation of the circuit. So the engineers and circuit designers should find the l

High T/sub c/ superconductors, such as Bi-2223, have been promising candidates for an electrical busbar because the busbar has a relatively low self magnetic field. It has been found that the critical current of Bi-2223 stacked tapes is much less than the total summation of critical currents of each tape, which is mainly attributed to the self magnetic fields. Furthermore, since the critical current degradation of Bi-2223 tape is greater in the normal magnetic field (to the tape surface) than in

As we stack HTS tapes, the critical current of stacked tapes is much less than the total summation of the critical current of each tape. This is mainly due to self magnetic field effects, and its behavior has been analyzed by load line or numerical methods with some assumptions. In this paper, we propose a simple numerical model to calculate the critical current of stacked tapes more exactly. To do this, we measured J/sub c/-B curves of a HTS tape for various values of external magnetic fields a

This study presents a new efficient alternative procedure for the assessment of the well-stirred (ws) condition of a mode-stirred reverberation chamber (RC) using newly developed coupling transfer gain functions. Coupling transfer voltage and current gain functions of the RC environment are developed from the ABCD parameters of the measured two-port S parameters in an RC. The proposed procedure involves the determination of the frequency corresponding to the well-stirred operation (fwso) of RC t