Tae-Weon Kang

Dependence of microwave absorbing property on ferrite volume fraction in MnZn ferrite-rubber composites

The effective complex permeability and permittivity spectra in composites with various ferrite volume fractions were calculated using the Bruggeman effective medium theory. The matching conditions for the maximum microwave absorption were determined by substituting the complex permeability and permittivity in the equation for the impedance matching condition. The minimum reflection loss increases from -5 to -40 dB as the ferrite volume fraction increases for /spl nu//sub f/<0.26, where single dip of minimum reflection loss was observed. However, two matching conditions were observed for v/sub f//spl ges/0.26, and two minimum reflection losses shown to be about -40 dB. The results indicate that a microwave absorber with reflection loss of about -40 dB can be designed by controlling the ferrite volume fraction in MnZn ferrite-rubber composites in the frequency range 0.8-12 GHz.

Development of a 3.5-mm Coaxial Microcalorimeter for RF and Microwave Power Standards at KRISS

We have developed a 3.5-mm coaxial microcalorimeter that will become a national power standard up to 26.5 GHz. Several core parts such as a thermostat, an adiabatic line, a thermopile, and reference standards are described in detail. Some measurement data are shown for a system performance check. A finite-element method simulation of the adiabatic line is shown. A model of the effect of the adiabatic line on thermopile measurement is introduced. Effective efficiency at selected frequencies is presented for the reference standards.

On the uncertainty in the current waveform measurement of an ESD generator

The uncertainty in the current waveform measurement of an electrostatic discharge (ESD) generator is evaluated. The measurands are the current amplitude and the rise time of the output current waveform of the ESD generator. An intuitively simple model is proposed to evaluate the uncertainty in the current amplitude measurement. Type A and Type B evaluations for all contributions to the measurement uncertainty are performed to obtain the combined standard uncertainty. The evaluated expanded uncertainty (95.5% confidence level) of the current amplitude and the rise time at ESD voltages of 2, 4, 6, and 8 kV are within the specification of IEC 61000-4-2. The results show that the uncertainty in the current amplitude measurement stems from the voltage reading of the measuring equipment, the difference between the displayed and the actual voltages of the discharge tip of the ESD generator, and the inaccuracy of the delta time measurement of an oscilloscope, whereas the uncertainty in the rise time measurement mainly originates from the measuring equipment.

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.

Design, Construction, and Performance Evaluation of a Cryogenic 7-mm Coaxial Noise Standard

A cryogenic 7-mm coaxial noise standard at 77.35 K has been designed and constructed. A ferrite composite-matched termination was used as a thermal noise source in the frequency range of 4.5-18 GHz. The noise temperature of the noise standard has been determined by measuring the temperature distribution and attenuation constant of a thermally isolated coaxial line and the attenuation of the output connector. The effective noise temperature has been evaluated to be 84.07-92.21 K with an uncertainty of 1.26-1.67 K (k = 2)

Novel attenuation standards at microwave frequencies and evaluation of their uncertainty

We have developed two coaxial-type microwave attenuation standards using the power ratio transfer method. One standard operates in the frequency range of 18 GHz to 26.5 GHz, and has a dynamic range of 80 dB. Its expanded uncertainty (k = 2) is estimated to be 0.01 dB/80 dB. The other operates in the frequency range of 26.5 GHz to 40 GHz, and has a dynamic range of 60 dB and an expanded uncertainty of 0.009 dB/60 dB. We present an example for calibration of a 40 dB step attenuator using the attenuation standard in a series radio-frequency substitution scheme. The expanded uncertainty (k = 2) is 0.01 dB including the mismatch uncertainty.

Field-calibrated electro-optic probe using interferometric modulations

A very concise field-calibrated electro-optic probe using interference of modulated beams is presented. A model for interferometric electro-optic sensing with a sensor probe is proposed, utilizing the interference fringing slopes and field-induced electro-optic phase retardations. The sensing dynamic range is experimentally explored by investigating the modulation slopes and retardations with respect to the probe beams polarizations. The probe shows a dynamic range ≥45 dB over the microstrip lines. This sensitivity is acceptable for realizing electric field imaging of radiative electronic devices. The absolute sensitivity of the probe is also determined with a micro-TEM cell that generates accurate electric fields with calculable strength for probe calibrations.

Reproducibility and uncertainty in radiated emission measurements at open area test sites and in semianechoic chambers using a spherical dipole radiator

Radiated emission (RE) measurements have been made in a 3 m semianechoic chambers (SACs) and at a 10 m open area test sites (OATSs) using a spherical dipole radiator (SDR) as a reference emitter. To compare the electric field strengths of the SACs with those of the OATSs, the analytical extrapolation factor for the SDR is employed. For the experiments, 23 discrete frequencies are chosen in the frequency range of 30 to 1000 MHz. The resultant reproducibility (2/spl sigma/) was 7.3 and 6.0 dB for the SAC and the OATS measurements respectively. To account for the possible contributions to the overall uncertainty, the expanded uncertainty (k=2) is evaluated and found to be 5.1 and 5.3 dB for the SAC and OATS measurements, respectively.

A W-Band Millimeter-Wave Power Standard Transfer System Using the Direct Comparison Method

This paper introduces a W-band millimeter-wave power standard transfer system using the direct comparison method. The transfer system was developed to evaluate the effective efficiency and calibration factor of a W-band waveguide power sensor. The evaluation method and the measured results of the directional coupler that characterizes the calibration system are studied. The uncertainties of the standard transfer system are investigated, and the major uncertainty contributors are discussed as well. The performance of the realized W-band power standard transfer system was verified by comparing results with reference values.

Determining Noise Temperature of a Noise Source Using Calibrated Noise Sources and an RF Attenuator

A system to measure the noise temperature (NT) of noise sources is implemented in the frequency range of 18-26.5 GHz for the case where noise sources commercially available have only one nominal NT, e.g., 9500 K being equivalent to 15-dB excess noise ratio. For the Y-factor method, two noise sources, i.e., a noise source and another with a radio-frequency attenuator, serve as the standard noise sources. The noise power output of the noise sources are measured using a commercial noise figure measurement instrument. Measurement results are presented, and its uncertainty has been evaluated to be 0.23-0.25 dB (k = 2) .