Minwoo Yi

Theory of Multimode Resonant Backward-Wave Oscillator With an Inclined Electron Beam

A multimode theory of the resonant backward-wave oscillator (BWO) with an electron beam inclined with respect to the surface of a periodic structure-a clinotron-is presented. It is shown that mode interaction provides phase velocity variation in the interaction space. The beam-wave interaction power increases at a favorable phase velocity profile along the interaction space, which manifests as power peaks in the clinotron zone. In contrast, when it is nonfavorable, there is power drop in the bandwidth. Developed multimode theory results are in satisfactory agreement with the theory of a BWO with reflections and with particle-in-cell simulations.

Automodulation Processes in Clinotrons With Low-Focusing Magnetic Field

The automodulation processes in backward-wave oscillator with an inclined electron beam (the clinotron) operating at low-focusing magnetic fields have been studied. The automodulation behavior has been analyzed in the clinotron for different angles of the beam inclination. It has been shown that at low magnetic fields, the RF transverse electric field may cause significant changes in electron trajectories, and hence in the beam-wave interaction power that leads to the automodulation.

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.

Digitized millimeter-wave beam-forming metal reflectarray antenna

Digitized beam-forming metal reflectarray antennas are designed for millimeter-wave region. The phase control of antennas has been implemented by the reconfiguration of rectangular grooves on a metal plate. The antenna has 1,147 elements arranged in an aluminum metal plate. All depths of metal grooves are elaborately manipulated and digitized for designed phase control of high-gain beam-aimed reflectors. We have demonstrated digitized reconfigurable metal reflectarray to steer re-radiated millimeter-wave field from the reflector in a two dimensional plane. The proposed antennas can be a helpful choice for millimeter-wave applications requiring high-gain beam-forming antennas.

Design of an inverse metal only reflectarray antenna for millimeter wave application

An inverse metal only reflectarray antenna consisting of multiple variable height conducting cells is designed at millimeter wave frequency. All reflecting elements are only made up of metal so that there is no dielectric loss in the antenna. Simulation result shows that the radiation efficiency of designed antenna is comparable with conventional parabolic reflector.

A breakdown study on the split horn antenna radiating high power pulses

Breakdown phenomena were studied when high power microwave pulses radiated to the atmosphere through the split horn antenna. The electrical characteristics of radiated signal such as power and pulse width strongly influence on the breakdown phenomena. This paper provides the information about threshold limitations of the antenna to radiate without breakdown phenomena.

Simple phase-matching equation of a 2D metal-only reflectarray for efficient fan-beam generation

A new phase-matching equation of a two-dimensional (2D) metal-only reflectarry is proposed for efficient fan-beam generation. To deduce the new equation, reception characteristics of a flanged parallel-plate waveguide array are used. The 2D metal-only reflectarray for 60 [GHz] was theoretically designed with a reception-based design equation. It showed 19.7 [dBi] antenna gain which is better than 18.7 [dBi] obtained by the previous design equation.