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Having the device simplicity and high output-power capacity, the capability of the virtual cathode oscillator (vircator) for emitting high power microwaves is demonstrated. We have investigated the axial-typed vircator in our pulsed power generator, "Chundoong" (Max 600 kV, 88 kA, and 60 ns), and simulated the vircator using the 3-D particle-in-cell simulation code called "MAGIC." We try to find out the position of the virtual cathode inside the drift tube and enhance the power of microwaves by focusing them at the focus point using the ring-typed zone plate with a focal length of 18.8 cm. The dominant frequency is obtained as 3.5 GHz measured by fast Fourier transform, which is in good agreement with simulation frequency. It is found that the mean position of the virtual cathode is almost the same as the A-K gap distance of 10 mm, in which the virtual cathode oscillates from 7.9 mm to 12.1 mm behind the meshed anode, as verified by the simulation results. The maximum output power without the zone plate is obtained as 0.66 GW with the efficiency of 27%, which is maximized up to 1.22 GW with the efficiency of 51% at the focus point by using the zone plate. The microwave emission mode from the vircator is the TM01 mode based on the simulation results. The zone plate contributes significantly in enhancing the power efficiency and determination of the position of the virtual cathode. These observations might be used in developing a high efficient microwave source by using a zone plate under the decision of the position of the virtual cathode. [ABSTRACT FROM AUTHOR]

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Plasma-jet systems and plasma devices of dielectric barrier discharge (DBD) are introduced for biomedical applications. To achieve the purpose of being safe and user friendly, these devices have been developed to avoid electric shock and thermal damage. These types of plasma equipment operate with a sinusoidal voltage of kilovolts at a low frequency of several tens of kilohertz. The plasma jets have been developed with the specific ground-electrode structures according to the various gases in use, such as inert gases, molecular gases, or mixture gases, and air. The Ar-plasma jet with the external ground electrode is operated in a low current of 1–2 mA with the voltage of 1–2 kV. The stable air-jet plasma/plume exiting from a small hole at the cold metal-cap nozzle of the ground electrode can be obtained in a low current of 0.5–1 mA for safety with the voltage of 5–10 kV. Both types of ground electrode, the external electrode and the metal-cap electrode, are applicable to the plasma jets of molecular or mixture gases. The devices for DBD plasmas are shown to be the new advents of plasma stamp, plasma stick, plasma comb, and plasma roller, which operate with the voltage of 2–3 kV. [ABSTRACT FROM PUBLISHER]

In this paper, a novel tunable bandpass filter with an improved J-inverter is suggested. In this resonator, as the loading capacitance is increased, the resonant frequency is decreased. Also, the phase of the admittance inverter has characteristics that are variable by series capacitors and parallel varactor diodes. The electrical length of the inverter always maintains 90° at a given physical length of the inverter, which should be changed for different operating frequencies. This new bandpass filter has a tuning range of 1.8 GHz ∼ 2.45 GHz and an insertion loss of less than 2.5 dB. Also, the bandwidth is almost constant within the tuning range. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:852-855, 2013; View this article online at wileyonlinelibrary.com. DOI: 10.1002/mop.27467 [ABSTRACT FROM AUTHOR]

The design of a differential-mode wideband bandpass filter (BPF) with good common-mode suppression is presented in this article. The structure of the proposed filter is divided to behave like a bandpass or bandstop filter (BSF) under differential- or common-mode operation. The open stubs in the BSF are used to control the 3-dB bandwidth (BW) of the BPF by slightly reducing the 3-dB cut-off BW of the BSF. To validate the design idea, a differential-mode BPF centered at 4 GHz with a 3-dB BW of 55%, near 30 dB common-mode suppression, is designed and fabricated. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:197-200, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27230 [ABSTRACT FROM AUTHOR]

In this article, a frequency-tunable 150W harmonic-tuned power oscillator is presented. The harmonic-tuned power amplifier of the oscillator was designed for improving drain efficiency with a single laterally diffused metal oxide semiconductor transistor using a nonlinear harmonic balance simulation code. The oscillation frequency was tuned by a mechanical phase shifter in the delay-line feedback loop circuit. Experimental results show that the output power and the drain efficiency of the oscillator were almost same as in the power amplifier with the same transistor and operating in the same frequency range. The measured output power and drain efficiency of the fabricated oscillator were 51.8 ± 0.6 dBm and better than 55.9%, respectively, across the 902-928 MHz band. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:1459-1462, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25970 [ABSTRACT FROM AUTHOR]

In this letter, a novel design method of tapped-line gap-coupled half-wavelength band-pass filter (BPF) using J- or K-inverter is proposed. A model of tapped-line is composed of shunt stub and the additional transmission line that has the electrical length of the negative value. The electrical lengths of the stub and line are functions of the line's impedance and the inverter that has a variable of filter's bandwidth. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1253–1256, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22417 [ABSTRACT FROM AUTHOR]

An X-band, low-noise, linearized microwave power amplifier module consisting of a low-noise solid-state amplifier (SSA), predistortion linearizing circuit, and low-gain helix traveling wave tube (TWT) is designed and tested in order to demonstrate both reduced noise figure and suppressed intermodulation distortion ratio. Two-tone intermodulation distortion (IMD) ratios are predicted from simulations obtained from modeling of the TWT, linearizing circuit, and SSA by the use of Agilents Advanced Design System simulation code. Simulated IMD ratios are in good agreement with measured results. Measurements show a noise figure of 2.2 dB at 9.5 GHz and the third-order IMD ratio of -53 dBc at 10 dB input back off from the input P1dB point It is found that both noise figure and IMD ratio are significantly improved compared with conventional helix-TWTs and microwave power modules. [ABSTRACT FROM AUTHOR]

Describes the studies and experimental results of 35 GHz, two-cavity gyroklystron amplifier. Major components of the two-cavity gyroklystron amplifier; Comparison of the results with nonlinear simulations; Conclusion.

In this article, a drain-source voltage and current waveforms measurement method for a fabricated power amplifier is presented. Harmonic components of the drain-source voltage and the current were obtained using measured output voltage and harmonic ABCD matrices of a load matching network. The drain-source voltage and current waveforms of a fabricated power amplifier that is operated nonlinearly were successively measured using the proposed measurement method without any influence in the power amplifier operation. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:2335-2337, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27100 [ABSTRACT FROM AUTHOR]

This article introduces a low-cost phase detection radar aimed at measuring the human heartbeat and respiration signals without any physical connections to the human body. A continuous-wave radar targeting the chest will detect the phase difference, resulted by the time-varying target position of the heartbeat, between the transmitted signal and the reflected signal. We have tested the developed radar to measure the heartbeat and respiration signals at a distance of about 40 cm from the chest. [ABSTRACT FROM AUTHOR]

Asymmetric magnetic field geometry is explored by inserting three metal tuners asymmetrically into the resonators of the A6 magnetron. The authors investigate the operating characteristics of a relativistic magnetron with asymmetrically perturbed radio-frequency (rf) magnetic fields caused by metal tuners using a three dimensional, electromagnetic particle-in-cell code MAGIC3D. By configuring perturbed rf magnetic fields, the operating characteristics of a relativistic magnetron are superior compared to those using uniform rf magnetic fields. Most significantly, by creating asymmetrically perturbed rf magnetic fields, the output power of the A6 magnetron increased by about 40% compared to the case of uniform rf magnetic fields. [ABSTRACT FROM AUTHOR]

Nucleic acid-based adjuvants have recently emerged as promising candidates for use in cancer vaccines to induce tumor-suppressing immune cells. In this study, we tested whether complexation of a nucleic acid-based adjuvant with chitosan (CTS) modulates immune adjuvant functions. As a nucleic acid-based adjuvant, we used toll-like receptor 3-recognizing RNA adjuvant (RA). Negatively charged RA formed nanoscale polyplexes with cationic CTS that possessed positive zeta potentials. RA/CTS polyplexes exerted dendritic cell (DC)-maturation effects without causing significant DC toxicity. This DC-maturation effect was CTS molecular weight dependent, with RA/CTS polyplexes with a CTS molecular weight of 340 kDa (RA/CTS 340K) producing the greatest effect. Subcutaneous injection of RA/CTS 340K polyplexes with the model tumor antigen ovalbumin exerted a preventive effect against challenge by ovalbumin-expressing tumor cells. It also provided greater inhibitory effects against a second challenge with the same tumor cells compared with other treatments. These protective effects of subcutaneous RA/CTS polyplex treatment were associated with the highest tumor antigen-specific humoral and cellular immune responses after tumor challenge, and with the greatest infiltration of CD4 helper T cell and CD8 T cell into the tumor tissues. Mice vaccinated with ovalbumin and RA/CTS polyplexes showed complete survival, even after repeated challenge with tumor cells. Our results suggest the potential of RA/CTS polyplexes as effective nanoadjuvants in the design of tumor vaccines and cancer immunotherapy. [ABSTRACT FROM AUTHOR]