Jin-Joo Choi

Initial hot-tests on a 28 GHz five-cavity gyroklystron amplifier

Experiments on a 28 GHz, five cavity gyroklystron amplifier are underway. Initial hot tests show that the stable amplified radiation produces a peak power of 50 kW at 27.85 GHz. A strong oscillation in the output cavity with power exceeding 200 kW is measured near the amplifier operating point. A careful magnetic field tuning near 10 kG is currently underway to optimize the amplifier performance. Experimental results and comparison with numerical simulation results are presented.

2.46 GHz solid-state high-power oscillator with planar cavity resonator

In this paper, we have studied a high power oscillator of a high RF output power and a good phase noise. We designed the high power oscillator using LDMOS(laterally diffused metal oxide semiconductor) device by the use of an Agilent advanced design system (ADS). We also designed the rectangular cavity resonator in order to obtain a good phase noise by using a 3-D high frequency structure simulator (HFSS) code. In Section II, the simulation and measurement results of the planar cavity resonator (PCR) were described. In section III, the output characteristics of a high power oscillator using PCR was described.

1.5 kW solid-state pulsed microwave power amplifier for S-band radar application

This paper describes the design and performance of a 1.5 kW solid-state pulsed power amplifier, operating over 2.7-2.9 GHz at a duty of 10 percent and with a pulse width of 100 us for radar application. The solid-state pulsed power amplifier configures a series of 8-stage cascaded power amplifiers with different RF output power levels. Low loss Wilkinson combiners are used to combine output powers of six 300 W high power solid state modules. Tests show peak output power of 1.61 kW, corresponding to PAE of 26.2 % over 2.7-2.9 GHz with a pulse width of 100 us and a PRF of 1 kHz.

Pulse Operation of an Inverse Class-F GaN Power Amplifier

This paper presents an inverse class-F power amplifier (PA) based on gallium nitride (GaN) high electron mobility transistor (HEMT) at 1 GHz. The implemented PA has a peak power-added-efficiency (PAE) of 74.1%, drain efficiency (DE) of 77.36%, and a gain of 13.76 dB at an output power of 39.58 dBm with a continuous wave operation at 28 volts. We have carried out the experiments with various pulsed operating conditions. A RF performance peak PAE of 74.28% with drain efficiency of 77.57% and a gain of 13.73 dB, at an output power of 39.66 dBm, was obtained at a pulse width of 100 mus with a duty of 10%. To evaluate the linearity of the inverse class-F amplifier, two-tone measurements have been tested. At a tone spacing of 100 kHz, the measured third-order intermodulation distortion (IMD3) was 13.2 dBc at peak PAE.

Simulations of a 1 MW, 700 MHz klystron using MAGIC PIC-code

A KOMAC (Korea Multipurpose Accelerator Complex) klystron tube operating with a maximum output power of 1 MW at 700 MHz is analyzed by the use of 2-D particle-in-cell code, MAGIC in order to validate the design parameters.

Particle-in-cell code simulations and experiments of a rising-sun magnetron oscillator

A high power rising-sun magnetron oscillator is designed to operate at 9.5 GHz. A time evolved electron flow exhibits nine space charge spokes in the MAGIC3D PIC simulations, which confirms the /spl pi/-mode oscillation in the eighteen vanes rising-sun magnetron. We investigated five operating points for /spl pi/-mode by the use of the PIC code. Simulations show that the highest efficiency is 74% at 36 W, 6.5 kG corresponding to a magnetron power of 530 kW where the oscillation frequency and anode current are 9.502 GHz and 20 A, respectively. Comparison of MAGIC3D simulation results and experiments is presented.

Measurements of Dielectric Properties at Ka-Band Using a Fabry-Perot Hemispherical Open Resonator

A Fabry-Perot hemispherical open resonator is designed and constructed in order to measure dielectric properties of BeO in the Ka-band (26 – 40 GHz) frequency range. Based on both analytic calculations and simulations by a 3-D finite element electromagnetic code, HFSS, the hemispherical open resonator is designed to excite a TEM0,0,17 mode at 28 GHz. The TEM0,0,17 mode is experimentally identified by a field perturbation technique. Dielectric measurements are made by both frequency variation and length variation methods. Measurements show that permittivity and loss tangent of BeO are 6.69 and 6.5 × 10−4 - 7.2× 10−4, respectively, in the frequency range of 26 – 34 GHz.

An Iron-Free Magnetron-Injection-Gun for a 28GHz, 200kW Gyroklystron Amplifier

A design study of a double-anode magnetron-injection-gun is performed to incorporate the electron gun into a high power 28GHz gyroklystron amplifier operating at 70kV and 8.2A. The electron gun is designed to be used in a tapered magnetic field in the cathode region produced from an iron-free superconducting magnet. An electron trajectory code predicts a beam axial velocity spread of 5.9% at α = 1.5, 70kV, 8.2A and 10.4kG, which is a high quality electron beam suitable for the high gain, high efficiency, five-cavity gyroklystron amplifier. The successful design of the high quality electron gun is attributed to a longer gap between the modulating anode and the grounded anode compared with the case of the first 28GHz electron gun built with an iron enclosed electromagnet.

Introduction to the proto-type plasma jets of AC, RF, and MW-discharges in Korea Plasma-Bio Research Center

The various types of atmospheric pressure plasma jets (APPJs) have been developed as the proto-type of user friend in Plasma-Bio Research Center (PBRC), Korea. According to the power sources the discharge-types are DC & a low frequency AC, RF, and micro-wave. (i) The plasma jet devices of DC-type and DBD-types have been made as the portable hand-carriers using DC-battery installed. (ii) AC-type jets with the frequency of a few tens of kHz have been developed with respect to the miniature and user-friend with the electric-safety using for the applications of human body and biology. In the proto-type device for the biomedicine applications the current is adjustable in the range from the low current of 0.1 mA to the high current of a few mAs. The inert gases or mixed gases are used. Especially, for the applications of semiconductor doping process, the single channel and the multi-channel of jet-doping systems are developed in the current range of a few or several tens of mA. (iii) RF-plasma jet is introduced with the power of 13.56 MHz. The RF power is adjustable in the range less than 100 W. The single channel of the proto-type device is shown with the discharge of inert gas for the biomedicine applications. (iv) Two-types of MW-plasma jets are developed. One is the proto-type MW-jet equipped with the miniature power source of semiconductor circuit which has been developed in this study. The frequency range is several hundreds of MHz and the power is adjustable in the range of several tens of Watt. The harmonic-tuned power amplifier of the oscillator was designed for improving drain efficiency with a single Laterally Diffused Metal Oxide Semiconductor (LDMOS) transistor using a non-linear harmonic balance simulation code. The other is the high power MW-jet system with the commercial MW-power sources. This Microwave plasma was excited at 2.45 GHz frequency and 0.8 W average power with a pulse generating width of 20μs and pulse generating period 2500μs. For the various applications this system is adjustable with respect to the peak power, the duration of pulse generation, and the pulse width of microwave.

A Study on Design and Fabrication of SRD Impulse Generator and Antenna for Ground Penetrating Radar System

In this paper, a ground penetrating radar(GPR) system is implemented for landmine detection. The performance of the GPR system is associated with the characteristics of local soil and buried target. The choice of the center frequency and the bandwidth of the GPR system are the key factors in the GPR system design. To detect a small and shallow target, the higher frequencies are needed for high depth resolution. We have been designed, fabricated and tested a new impulse generator using step recovery diodes. The measured impulse response has an amplitude of 6.2V and a pulse width of 250ps. The implemented GPR system has been tested real environmental conditions and has proved its ability to detect a small buried target.