Jong-Won Yang

Full-wave simulation of frequency diverse array antenna using the FDTD method

This paper describes 2-D analysis of a frequency diverse transmit array antenna with a periodic modulated pattern in range using the finite difference time domain methods. The elements of applied linear array are equally spaced and have same phase but operated at different frequencies. The result pattern of frequency diverse array forms range-dependent beam patterns whereas conventional array pattern forms same beam patterns in far field range. This range-dependent beam pattern provides more flexible beam scan options and lessens undesirable interferences such as multipath. The simulation results for radiation patterns of open-ended waveguide (OEG) antenna array are presented. The characteristics of radiation pattern were investigated by the each different simulation for frequency offset change, radiation element space change and array number change.

Direct Real-Time Power Measurement of a High-Power Electron Cyclotron Maser by a Simple One-Point Schottky Detector Signal

Measurements of the absolute power of high-power millimeter/THz wave generators have been considered to be highly variable and to occasionally produce faulty results owing to experimental difficulty. In this study, we propose a calibration-free method for real-time power measurement of an electron cyclotron maser system, a so-called gyrotron. We demonstrate the feasibility of the method by using a recently developed W-band gyrotron with a peak power of tens of kilowatts. The technique is based on transmitter antenna power measurement by using the Friis transmission equation with a defined gyrotron antenna gain. The new technique will allow extremely simple and accurate real-time measurement of output power over a wide dynamic range ( dB) for continuous wave sources to high-power millimeter/THz wave sources with nanosecond pulse lengths.

Design of high power split waveguide array in W-band

Split waveguide array for high power applications in W-band is designed. The split waveguide array is composed of 4-way H-plane power divider, 4-way E-plane split waveguides, waveguide transition and 4×4 waveguide array. In order to design high power antenna with high gain and compact size in W-band, E-plane split waveguides and H-plane power divider are chosen. The designed high power split waveguide array has a good performance of above 20 dBi gain.

Two-tier calibrated electro-optic sensing system for intense field characterization of high-power W-band gyrotron.

We present a field-calibrated electro-optic sensing system for measurement of the electric field radiating from a high-power vacuum oscillator at ~95 GHz. The intense electric field is measured in absolute scale via two probe-calibration steps, associated with a photonic heterodyne scheme. First, a micro-electro-optic probe, fabricated to less than one-tenth the oscillation wavelength scale to minimize field-perturbation due to the probe, is placed on the aperture of a field-calculable WR-10 waveguide to calibrate the probe in V/m scale. Then, using this arrangement as a calibrated reference probe at the first-tier position, another probe-bulkier, and thus more robust and sensitive but not accessible to the aperture-is calibrated at the second-tier position away from the waveguide aperture. This two-tier calibrated probe was utilized to diagnose the sub-MV/m scale of intense electric fields and emissions from a high-power W-band gyrotron. The experimental results obtained proved consistent with calculated analytical results-verifying the efficacy of the developed system.

Optimal Design of −40-kV Long-Pulse Power Supply

This paper proposes a compact high-voltage pulse electron gun power supply (EGPS) consisted of interleaved capacitor-charging power supply (CCPS) with a series-resonant converter (SRC) to drive the electron tube. Requirement specifications are -40 kV, -7 A (280 kW), and continuous output lower than ±1% ripple stability lasted few seconds with <;1 ms charging and discharging times. To meet the design specifications, eight stacks operate in parallel, and each stack has a 45° phase shift switching pulse width modulation (PWM) method. Each designed CCPS can supply -40-kV voltage and -0.9-A current. In addition, the proposed CCPS has the SRC to reduce the switching loss. The SRC is a famous topology, which presents main characteristics such as high-power density and efficiency. To prove the validity, this paper is confirmed by the simulation and experimental results of the fabricated -40-kV output CCPS with water load. Then, we implemented the fabricated EGPS to the electron tube.

Micro-fabricated millimeter wave vacuum electronic devices

0.1 THz Coupled Cavity Backward-wave Oscillator (CCBWO) is being developed utilizing two-step X-ray lithography. The characteristics of this 0.1 THz CCBWO are investigated through cold and hot tests.

Indoor sensor array test-bed(SATB) for direction finding applications at communication-band

An efficient sensor array test-bed compatible with direction finding indoor test applications at communication-band is developed. It provides the test flexibility of DF accuracy including the different antenna configuration, DF algorithms and modulation schemes considering with instrumental errors induced by multi-channel receivers. The ability of test-bed is useful for system designers who are involved in the development of DF system at communication-band. Further research will be investigated the DF accuracy of FHSS and the effects of interference signal, frequency offset and integration time.

Electric field measurement with Electro-Optic sensor of high power W-band gyrotron

We present electric field measurement with Electro-Optic (EO) sensor of high power W-band gyrotron. EO sensors serve as minimally invasive field receivers as compared to metal-based electronic field probes. A rectangular waveguide WR-10 for W-band is used in order to calibrate the probe since the field strength inside the waveguide can be accurately calculated based on the output power measured by RF power meter. Then, the performance of the sensor is evaluated by high power W-band gyrotron and its measurement result of power is compared with that of calorimeter.

Ultra High-Gain Displaced-Axis Metal Reflectarray Antenna for Millimeter-Wave Region

We design a displaced-axis Gregorian dual antenna in the form of a metal reflectarray antenna for millimeter wave region, W-band. Unlike a reflectarray composed of printed patch antennas on a dielectric substrate, metallic rectangular waveguide unit-cells are proposed to avoid the loss of substrate and take an advantage of ease of typical metal machining fabrication. In this paper, the radiation characteristics of constructed metal reflectarray antennas show ultra high-gain antenna over 50 dBi at a target frequency in W-band. The experimental measurements are conducted in millimeter-wave compact range antenna measurement system.

Induction Voltage Adder for High Power Pulse Generator

In this paper, we have proposed high power generator with Induction Voltage Adder of three cells. IVA which has n cells can generate n-th times high power pulse, is a more stable system than Marx generator in the view of breakdown. We applied amorphous metal magnetic cores as an energy storing material for IVA rather than ferrite cores because of their higher magnetic flux swing to make it more compact system and the loss of it was also considered in the design. For driving the IVA, we design Blumlein pulse generators which are filled with pure water for high dielectric constant and high breakdown field strength, and triggered by single Marx generator. We have presented the PSPICE simulation and its test result.Keywords : Induction Voltage Adder(유도전압합성기), High Power Pulse Generator(고출력 펄스발생기), Marx Generator (막스 펄스발생기), Blumlein PFL(블룸라인 펄스형성기)