Ki-Chai Kim

The Design of Calculable Standard Dipole Antennas in the Frequency Range of 1~3 GHz

This paper presents the design of a calculable standard dipole antenna with a hybrid balun in the frequency range of 1 GHz to 3 GHz. A new formula of the antenna factor for a dipole antenna with a hybrid balun is derived using the power mismatch-loss concept. The antenna factors derived in this paper are in good agreement with the results calculated from S-parameters. The design results show that the calculable dipole antenna with a hybrid balun can be characterized by power mismatch-loss component factors.

Breakdown Characteristics of SF6 and Liquefied SF₆ at Decreased Temperature

SF 6 gas has been used as arc quenching and insulating medium for high and extra high voltage switching devices due to its high dielectric strength, its excellent arc-quenching capabilities, its high chemical stability and non toxicity. Despite of its significant contributions, the gas was classified as one of the greenhouse gas in the Kyoto Protocol. Thus, many researches are conducted to find out the replacement materials and to develop the SF 6 gas useless electrical equipment. This paper describes experiments on the temperature change-related breakdown characteristics of SF 6 gas (SF 6 ) and SF 6 liquid (LSF 6 ) in a model GIS(Gas-Insulated Switchgear) chamber in order to show the possibility of more stable and safe usages of SF 6 gas. The breakdown characteristics are classified into three stages, namely the gas stage of SF 6 according to Paschens law, the coexisting stage of SF 6 gas with liquid in considerable deviation at lower temperature, and the stage of LSF 6 and remaining air. The result shows that the ability of the LSF 6 insulation is higher than the high-pressurized SF 6 . Moreover, it reveals that the breakdown characteristics of LSF 6 are produced by bubble-formed LSF 6 evaporation and bubbles caused by high electric emission and the corona. In addition, the property of dielectric breakdown of LSF 6 is determined by electrode form, electrode arrangement, bubble formation and movement, arc extinguishing capacity of the media, difficulty in corona formation, and the distance between electrodes. The bubble formation and flow separation phenomena were identified for LSF 6 . It provides fundamental data not only for SF 6 gas useless equipment but also for electric insulation design of hightemperature superconductor and cryogenic equipment machinery, which will be developed in future studies.

A study for grounding effect to improve performance of WWAN

Electromagnetic interference (EMI) from a LCD panel deteriorates the performance of wireless network system (with wireless network cards: Wireless Wide Area Network (WWAN) card) in a notebook. One of the main EMI noise factor, for the wireless network system, is the grounding effect of the antenna in the system. In this paper, the approach to solve the EMI noise of the system is introduced; by using the grounding methods of the system. In order to measure the EMI noise of the WWAN itself, the standard JIG system is developed. Most grounding effects are confirmed experimentally. Because the EMI noise of the WWAN system is difficult to reduce, it is important to know the antenna (with the coaxial cable) itself.

Shielding Effectiveness of a Collinear Unequal Paired-Narrow-Slot Array in Conducting Screens

This letter presents a method that offers the simple calculation of the electric shielding effectiveness of a collinear unequal narrow slot array in a planar conducting screen. An integral equation for an aperture electric field on the unequal narrow slot array is used instead of coupled integral equations for a multiple slot and solved by applying Galerkins method of moments. Numerical results illustrate the shielding effectiveness and aperture electric field distributions of the collinear unequal two-narrow slot array by using single integral equation.

Breast cancer detector using microwave tomography image technology

In this paper, image reconstruction of breast cancer detector using microwave tomography is investigated. The breast cancer detection system under development uses 16 transmit/receive antennas. This is the microwave tomography system operating in the frequency range of 500-3000MHz. To solve a 2D inverse scattering problem, we tried two methods. One is the method of moment for forward problem and the Simplex method as optimization algorithm. The other is the FDTD(Finite Difference Time Domain) method and Gauss- Newton algorithm. The results of the reconstructed image showed that we can detect the position of the tumor exactly.

The Characteristic of Electric Field Penetration into Infinite Conducting Plane with an Aperture Due to HEMP Incidence

This paper presents the comparison of electric field penetration in Bell laboratories and IEC 61000-2-9 standard when HEMP source penetrates through an aperture in a planar conducting plane of infinite extent. HEMP electric field distributions assume in order to interpret this problem. Integral equation is derived and solved by Galerkin`s method of moments for calculating the penetrating electric field. It is shown that penetrated electric field of IEC 61000-2-9 standard is greater than the Bell Laboratories waveform in resonance of lower frequency band, but those waveforms are similar in shape to frequency domain.

Complex Antenna Factors of Resistor Loaded Dipole Antennas with Coaxial Cable Balun

This letter presents the characteristics of complex antenna factors of a resistor loaded dipole antenna with a balun consisting of two coaxial feeders (coaxial cable balun). The resistor loading is used to realize dipole antennas with higher fidelity than unloaded dipole equivalents. The complex antenna factor for a resistor loaded dipole antenna with coaxial cable balun is derived by extending the power loss concepts. The numerical results show that the series resistor loaded dipole antenna offers higher fidelity than the unloaded dipole. The result of the calculated complex antenna factors are in good agreement with that of the measured results.

Near Fields around Metallic Walls due to a Nearby Dipole Source with Applications to EMC

This paper discusses the near field characteristics of a dipole source located near conducting metallic walls from an electromagnetic compatibility (EMC) point of view. An integral equation for a dipole source near a metallic wall is derived and solved by applying Galerkin’s method of moments (MoM). The results show that in the regions outside the dipole source, total electric near fields decrease gradually in magnitude with an increasing field point from the dipole source. But in the regions inside the dipole source, total electric near fields decrease rapidly with a dipole position of h≤ 0.3λ. For a dipole position of h≥0.7λ, the peaks and nulls of the total near electric field occur periodically in the regions inside the dipole source, and the fluctuation period is almost 0.5λ. The worst position for a receptor location is along the z-axis, and a range of a half-magnitude of the maximum near electric field in the principal H-plane is about two times broader than that of the principal E-plane. Experimental measurements are also presented to validate the theory.

A Study on Characteristics of Insulation Breakdown and Surface Discharge by the Mixing Ratio of Dry Air/O 2 gas mixtures

This paper presents the discharge characteristics and economic feasibility of a Dry and a mixture gas in order to review alternative. From AC discharge experiment in an quasi-uniform field, it was found that the optimal mixing ratio which breakdown voltage and surface flashover voltage were the highest was 70/30 and that the pressure dependence on the breakdown voltage was higher than that of the surface flashover voltage in the Dry and the mixture gas. The mixing ratio (70/30) and the tendency of the pressure dependence were described in detail based on physical factors (impact ionization coefficient, electron attachment coefficient, secondary electron emission coefficient) involved in discharge mechanism and a electron source, respectively. In addition, the performance insulation and the economic feasibility of the Dry and the mixture gas were discussed so that Dry mixture gaswas more suitable than mixture gas to the alternative.

Transmission Characteristics on Dimensional Tolerances of Millimeter-Wave Rectangular Waveguides

This paper presents the influence on the transmission characteristics of dimensional tolerances of rectangular waveguides usually used as a low-loss transmission line in the millimeter-wave band. We derived the Green`s functions of the waveguide with eigenfunction expansion method. The reflection coefficient of the waveguide with a post is calculated by using internal impedance in order to investigate the influence of dimensional tolerances of the waveguide. In order to check the validity of the theoretical analysis, the calculated reflection coefficients are compared with the measured results.