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We report experimental results on the microfabrication of three types of folded waveguide circuits with a high aspect ratio by using a high-energy X-ray LIGA technique. A W-band folded waveguide with a total of 80 periods was designed for a traveling-wave-tube (TWT) amplifier operating at 90 GHz–100 GHz. The measured return loss and insertion loss of the W-band fabricated circuit were–10 dB and 0.42 dB/cm, respectively. A G-band circuit showed a higher insertion loss of 1.57 dB/cm. An additional circuit fabrication for a 850-GHz folded waveguide TWT was also successfully carried out. The broad-wall angle measured with respect to the narrow wall of the rectangular waveguide was very close to 90◦, indicating an excellent resolution compared to that of other microfabrication techniques, such as deep reactive ion etching (DRIE) and ultraviolet (UV) lithography, electroplating, and polymer replication (LIGA).

Although immune checkpoint inhibitors have emerged as a breakthrough in cancer therapy, a monotherapy approach is not sufficient. Here, we report an immune checkpoint inhibitor-modified nanoparticle for an in situ-assembled tumor vaccine that can activate immune systems in the tumor microenvironment and prevent the long-term recurrence of tumors. Adjuvant-loaded nanoparticles were prepared by entrapping imiquimod (IQ) in photoresponsive polydopamine nanoparticles (IQ/PNs). The surfaces of IQ/PNs were then modified with anti-PDL1 antibody (PDL1Ab-IQ/PNs) for in situ assembly with inactivated tumor cells and immune checkpoint blocking of PDL1 (programmed cell death 1 ligand 1). The presence of anti-PDL1 antibodies on IQ/PNs increased the binding of nanoparticles to CT26 cancer cells overexpressing PDL1. Subsequent near-infrared (NIR) irradiation induced a greater photothermal anticancer effect against cells treated with PDL1Ab-IQ/PNs than cells treated with plain PNs or unmodified IQ/PNs. To mimic the tumor microenvironment, we cocultured bone marrow-derived dendritic cells with CT26 cells treated with various nanoparticle formulations and NIR irradiated. This coculture study revealed that NIR-inactivated, PDL1Ab-IQ/PN-bound CT26 cells induced maturation of dendritic cells to the greatest extent. Following a single intravenous administration of different nanoparticle formulations in CT26 tumor-bearing mice, PDL1Ab-IQ/PNs showed greater tumor tissue accumulation than unmodified nanoparticles. Subsequent NIR irradiation of mice treated with PDL1Ab-IQ/PNs resulted in tumor ablation. In addition to primary tumor ablation, PDL1Ab-IQ/PNs completely prevented the growth of a secondarily challenged CT26 tumor at a distant site, producing 100% survival for up to 150 days. A long-term protection study revealed that treatment with PDL1Ab-IQ/PNs followed by NIR irradiation inhibited the growth of distant, secondarily challenged CT26 tumors 150 days after the first tumor inoculation. Moreover, increased infiltration of T cells was observed in tumor tissues treated with PDL1Ab-IQ/PNs and NIR-irradiated, and T cells isolated from splenocytes of mice in which tumor recurrence was prevented showed active killing of CT26 cells. These results suggest that PDL1Ab-IQ/PNs in conjunction with NIR irradiation induce a potent, in situ-assembled, all-in-one tumor vaccine with adjuvant-containing nanoparticle-bound, inactivated tumor cells. Such in situ nanoadjuvant-assembled tumor vaccines can be further developed for long-term prevention of tumor recurrence without the need for chemotherapy.

Microwave (MW) radiation is increasingly being used for several biological applications. Many investigations have focused on understanding the potential influences of pulsed MW irradiation on biological solutions. The current study aimed to investigate the effects of 3.5 GHz pulsed MW radiation-irradiated liquid solutions on the survival of human cancer and normal cells. Different physiological solutions such as phosphate buffer saline, deionized water, and Dulbecco’s modified Eagle medium (DMEM) for cell culture growth were irradiated with pulsed MW radiation (45 shots with the energy of 1 mJ/shot). We then evaluated physiological effects such as cell viability, metabolic activity, mitochondrial membrane potential, cell cycle, and cell death in cells treated with MW-irradiated biological solutions. As MW irradiation with power density ~ 12 kW/cm2 mainly induces reactive nitrogen oxygen species in deionized water, it altered the cell cycle, membrane potential, and cell death rates in U373MG cells due to its high electric field ~ 11 kV/cm in water. Interestingly, MW-irradiated cell culture medium and phosphate-buffered saline did not alter the cellular viability and metabolic energy of cancer and normal cells without affecting the expression of genes responsible for cell death. Taken together, MW-irradiated water can alter cellular physiology noticeably, whereas irradiated media and buffered saline solutions induce negligible or irrelevant changes that do not affect cellular health.

Cancer immunotherapy takes advantage of immune system to fight against cancer. Current clinical immunotherapies are based on the administration of immune checkpoint inhibitors or immune modulators to reverse the immune suppression. Although robust and long-term tumor suppression is induced in “certain treated population”, single immunotherapy still suffers from limited efficacy in clinic. Combination with nanomedicine would be one of major strategies that can widen the effective patient populations and reduce side effects. The basis in combining nanomedicine and immunotherapy stems from the close relationship of tumor and immune system. Depending on the therapeutic cargo, nanocarriers can not only facilitate stronger innate or adaptive immunity but also reverse of immunosuppression. In the other hand, nanotechnology can potentiate the efficacy of immunotherapy by enhancing the delivery, retention and narrow the toxicity of immunomodulators. The strategies and rationales of nanocarrier design in the context of cancer immunotherapy are discussed in this review.

Although various oral pathogens are inactivated by non-thermal atmospheric pressure plasma (NTAPP), the in vivo effects of NTAPP are poorly understood. The first aim of this study was to examine the antibacterial activity of microwave-pulsed NTAPP against Staphylococcus aureus in artificial saliva to mimic oral environmental conditions. The second aim was to determine the influence of microwave-pulsed NTAPP on human gingival fibroblasts (HGFs). The microwave-pulsed NTAPP reduced bacterial viability (as measured by colony forming units [CFU]) to a greater extent in artificial saliva than in saline. Extending the post-treatment incubation time increased bacterial inactivation in artificial saliva compared to saline. HGFs viability was unaffected by microwave-pulsed NTAPP for bacterial inactivation. Rather, HGFs proliferation increased after a 5-min microwave-pulsed NTAPP. Less tumor necrosis factor alpha was released by microwave-pulsed NTAPP-treated HGFs stimulated with lipopolysaccharide (LPS) than by untreated, LPS-stimulated HGFs; thus, plasma appeared to suppress the inflammatory response. Our study suggests that microwave-pulsed NTAPP may have stronger in vivo antibacterial activity than in vitro activity, and that microwave-pulsed NTAPP may have the additional advantage of suppressing gingival inflammatory responses.

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.

A virtual cathode oscillator (vircator) is a special type of oscillator capable of generating high-power microwaves. We studied an axially extracted vircator by installing a cone-shaped reflector in our pulsed power device, “Chundoong” and numerically studied by using a three-dimensional particle-in-cell simulation, MAGIC. In the simulation, we varied the inner diameter of the reflector between 9 cm and 17 cm; a diameter of 13 cm showed the maximum power enhancement measured at the end of the drift tube position. The dominant oscillating frequencies without and with reflector were determined to be 3.42 GHz and 3.37 GHz, respectively, in the simulation and 3.40 GHz and 3.31 GHz, respectively, in the experiment. The numerically predicted frequencies showed good agreement with those observed during the experiment. The microwave power generated from the conventional axial vircator was 571 MW with the efficiency approximately 20%; which is increased by the interference up to 835 MW with the efficiency of 29.4% with reflector. The microwave power increased to 46% with the reflector. The microwave emission mode from the axial vircator was TM01 with and without reflector, based on the vector electric and magnetic fields observed during the simulation. The presented reflector increases the microwave power significantly. This reflector may possibly be used to increase the microwave power by the interference to increase efficiency of vircator sources. Keywords: Vircator, Cone-shaped reflector, Pulsed power, Chundoong, Particle-in-cell simulation, MAGIC, Power enhancement, Power efficiency

This paper describes a study and experimental demonstration on a magnetron operating at 2.45 GHz. We checked the characteristics of the 1 kW magnetron. There were two noise sources of magnetron at frequencies of 0.5 Hz and 75 kHz. In order to suppress these noises, we used an external injection locking method. Measurement results showed that the frequency noise suppression was down up to 30 dBc and the phase fluctuation is reduced to 4 degrees when injection input power was 7 W. Power combining experiments were performed using two identical magnetrons. An initial result showed an output power of 2 kW, corresponding to combining efficiency $\pmb{ > 93\%}$ .

Experiments on a 14-vane, double-strapped magnetron oscillator were performed to demonstrate high-power, high-efficiency coherent radiation at 5.8 GHz. The double-strapped magnetron was designed by using the Buneman-Hatree resonance condition, electromagnetic simulations and non-linear three-dimensional particle-in-cell (PIC) simulations. Experiments showed an oscillation output power of 5.3 kW at 5.79 GHz, corresponding to a DC-RF conversion efficiency of 57%. The cathode voltage was 9.2 kV, the collected anode current was 1 A, and the external magnetic field is 7.5 kG. Experimental results for the RF power, oscillation frequency, and efficiency were in good agreement with the corresponding values from non-linear three-dimensional PIC simulations.

This paper describes a design study and experimental demonstration on a cavity-type power combiner producing 80 kW at 464 MHz. The power combiner consists of (1) a 40-way equal phase/amplitude power divider, (2) a cavity-type power combiner, and (3) 40 LDMOS power amplifier modules. The power divider produces equal power and phase through a Ill-way radial power divider and 3-dB Wilkinson dividers. The power combiner is a cylindrical cavity resonating at TM010 mode with 40 input ports. The combined power is extracted through 6-1/8' coaxial transmission line. Measured results of the 40-way power combiner show an output power of 80 kW and combining efficiency of $> 95{\%}$ , which is in a good agreement with HFSS simulation results.

RF design and network analyzer tests of broadband, amplitude-balanced coaxial hybrid junctions are presented. We have designed two 3 dB hybrid splitters with 9 and 12 in. coaxial transmission lines applicable to ITER ICRF for load-resilient operations using ANSYS HFSS. Amplitude-balanced broadband responses were obtained with the combination of impedance reductions of longitudinal and transverse branches in unequal proportion, length change of 50 Ω lines and diameter change of high impedance lines connected transversely to the T-section of the hybrid splitter, respectively. We have fabricated and RF tested the 9 in. coaxial hybrid coupler. We obtained an excellent coupling flatness of −3.2 ± 0.2 dB, phase difference of 4 degrees and return loss of 16 dB in 40–55 MHz. The measured data of 9 in. hybrid splitter is highly consistent with HFSS simulations. We found that the proposed 3 dB hybrid splitter can be tunable with amplitude-balanced, broadband response by changing dielectric insulators to keep the inner and outer conductors of coaxial line apart. The proposed 3 dB hybrid splitter can be utilized for load-resilient operations in a wide range of antenna load variations due to mode transitions or edge localized modes (ELMs) in fusion plasmas.

A Ku-band gyrotron traveling-wave-tube (gyro-TWT) amplifier was investigated. To obtain a wide operating bandwidth, we used a two-stage tapered rectangular waveguide interaction circuit. An electron beam of 27 keV and 3.56 A was produced from a double-anode magnetron-injection-gun (MIG). The measured frequency bandwidth over 10 dB gain in the linear operation region was found to be 18%. The gyro-TWT’s saturated output power was 14.9 kW at 14.4 GHz, corresponding to a saturated output power gain of 27.4 dB and an efficiency of 15.5%. The measured experimental results were in agreement with those of non-linear numerical simulations.

A double-anode magnetron-injection gun (MIG) was designed. The MIG is for a W-band 10-kW gyrotron. Analytic equations based on adiabatic theory and angular momentum conservation were used to examine the initial design parameters such as the cathode angle, and the radius of the beam emitting surface. The MIG’s performances were predicted by using an electron trajectory code, the EGUN code. The beam spread of the axial velocity, Δvz/vz, obtained from the EGUN code was observed to be 1.34% at α = 1.3. The cathode edge emission and the thermal effect were modeled. The cathode edge emission was found to have a major effect on the velocity spread. The electron beam’s quality was significantly improved by affixing non-emissive cylinders to the cathode.

The biochemistry and microbial ecology of 2 similar types of watery (mul) kimchi, containing sliced and unsliced radish and vegetables (nabak and dongchimi, respectively), were investigated. Samples from kimchi were fermented at 4, 10, and 20 °C were analyzed by plating on differential and selective media, high-performance liquid chromatography, and high-throughput DNA sequencing of 16S rDNA. Nabak kimchi showed similar trends as dongchimi, with increasing lactic and acetic acids and decreasing pH for each temperature, but differences in microbiota were apparent. Interestingly, bacteria from the Proteobacterium phylum, including Enterobacteriaceae, decreased more rapidly during fermentation at 4 °C in nabak cabbage fermentations compared with dongchimi. Although changes for Proteobacterium and Enterobacteriaceae populations were similar during fermentation at 10 and 20 °C, the homolactic stage of fermentation did not develop for the 4 and 10 °C samples of both nabak and dongchimi during the experiment. These data show the differences in biochemistry and microbial ecology that can result from preparation method and fermentation conditions of the kimchi, which may impact safety (Enterobacteriaceae populations may include pathogenic bacteria) and quality (homolactic fermentation can be undesirable, if too much acid is produced) of the product. In addition, the data also illustrate the need for improved methods for identifying and differentiating closely related lactic acid bacteria species using high-throughput sequencing methods.

Sensory characteristics and chemical properties of 9 commercial dongchimi (Korean watery radish kimchi) liquid varieties were investigated using sensory descriptive analysis and instrumental analyses. Dongchimi was analyzed for pH, titratable acidity, soluble solids, salinity, organic acids, sugars, ethanol, and amino acids. Arginine, glutamic acid, and proline were the key amino acids. Lactic acid was the main organic acid in mature dongchimi. Based on sensory descriptive analysis, 4 appearances, 10 odors, 5 flavor/taste, and 3 mouthfeel sensory attributes were developed. Descriptive sensory and instrumental results showed that a white hue was associated with garlic, leek, and chili odors, glutamic acid, acetic acid, lactic acid, ethanol, and mannitol. Samples with a yellow hue were associated with turbidity, moldy and yeast odors, salty taste, fructose, glucose, and malic acid.

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.

In this paper, we present design and measurement of LNA(Low Noise Amplifier) based on GaN HEMT(Gallium Nitride High Electron Mobility Transistor) to reduce the total noise figure of radar receiver and for robustness of LNA. In radar receiver using LNA based on GaAs(Gallium Arsenide) technology, limiter is necessary at the very front of the radar receiver to protect LNA. As a result, total noise figure of radar receiver is deteriorated. In this research, measured noise figure of LNA based on GaN HEMT is below 2 dB. In the case of commercialized GaAs LNA, recommended maximum input power is about 30 dBm. On the other hand, GaN HEMT LNA which is designed and measured is burned-out when input power is 43 dBm and robustness is guaranteed at input power 45.4 dBm. Key words: LNA, GaN HEMT, Robustness, Current Limit ‡wx ˆ3‰Š 5wx‹9Œ wx . Ž ‘+C’“(Department of Wireless Communications Engineering,, Kwangwoon University) *ˆ3‰Š(Samsung Thales, Co, Ltd) `Manuscript received December 24, 2014 ; Revised February 5, 2015 ; Accepted February 6, 2015. (ID No. 20141224-105)`Corresponding Author: Jin-Joo Choi (e-mail: jinchoi@kw.ac.kr)

Taking advantage of X-ray LIGA system, we fabricated sub-teraherz folded waveguide circuits. Small signal gain in a W-band folded waveguide TWT was measured to be 15 dB. Folded waveguide circuits operating at both 220 GHz and 850 GHz were fabricated. Cold tests shows 10 dB return loss and 6 dB transmission characteristics of circuits in G-band.

This paper presents a design and fabrication of Ku-band power amplifier using Gallium Nitride High Electron Mobility Transistor (GaN HEMT) die. In order to fabricate the low-cost Ku-band power amplifier, a Printed Circuit Board(PCB) was used for input/output matching circuits instead of manufacturing process to use an expensive substrate. The measured output power is 42.6 dBm, the drain efficiency is 37.7 % and the linear gain is 7.9 dB under pulse operation at the frequency of 14.8 GHz. Under the continuous wave(CW) test, the output power is 39.8 dBm, the drain efficiency is 24.1 % and the linear gain is 7.2 dB.Key words: Ku-Band, GaN HEMT Die, Low-Cost, Power Amplifier LMN62013OPQRSA8MN#(TU$%MNVIW.X YZ [\]^[ (Department of Wireless Communications Engineering, Kwangwoon University) *QRSA8(Samsung Thales) Manuscript received February 4, 2014 ; Revised March 11, 2014 ; Accepted April 16, 2014. (ID No. 20140204-016)Corresponding Author: Jin-Joo Choi (e-mail: jinchoi@kw.ac.kr)

출발물질인 TTIP로부터 이산화티탄 졸을 합성하여 무기물로 사용하고 유기물로서 실란커플링제인 methacryloxypropyltrimethoxysilane (MPTMS), aminopropyl triethoxysilane (APS), glycidoxypropyl trimethoxysilane (GPTMS), vinyltriethoxysilane(VTES)을 2종 혹은 3종씩 복합 사용하여 유-무기 하이브리드 코팅 용액을 제조하였다. 그 후 코팅 용액을 기재인 PC시트 위에 스핀 코팅시키고, 열경화 시켜 하드코팅 막을 제조하였다. 2종 실란커플링제를 혼합하여 제조된 코팅 막들은기재와의 부착력과 연필경도가 우수하지 못했으나, 3종 실란커플링제를 혼합하여 제조한 코팅 막은 2H~4H의 향상된연필경도와 5B의 우수한 부착력을 나타내었다. 이산화티탄 졸의 첨가량이 20 g인 코팅 막의 굴절률은 550 nm에서 1.56을 나타내었으나 이산화티탄 졸의 첨가량을 20 g에서 30 g으로 증가시킨 경우, 코팅 막의 굴절률이 1.63으로 향상되었다.

Non-thermal atmospheric pressure plasma jet could generate various kinds of radicals on biosolution surfaces as well as inside the biosolutions. The electron temperature and ion density for this non-thermal plasma jet have been measured to be about 0.8~1.0 eV and 1 × 1013 cm−3 in this experiment, respectively, by atmospheric pressure collisional radiative model and ion collector current. In this context, the hydroxyl OH radical density inside the biosolutions has been also investigated experimentally by ultraviolet absorption spectroscopy when the Ar non-thermal plasma jet has been bombarded onto them. It is found that the emission and absorption profiles for the other reactive oxygen species such as NO (226 nm) and O2*− (245 nm) are shown to be very small inside the biosolution in comparison with those for the OH radical species. It is found that the densities of OH radical species inside the biosolutions are higher than those on the surface in this experiment. The densities of the OH radical species inside the deionized water, Dulbecco’s modified eagle medium, and phosphate buffered saline are measured to be about 2.1 × 1016, 1.1 × 1016, and 1.0 × 1016 cm−3, respectively, at 2 mm downstream from the surface under optimized Ar gas flow of 200 sccm. It is also found that the critical hydroxyl OH radical density for the lung cancer H460 cells to experience an apoptosis is observed to be around 0.3 × 1016 cm−3 under 1 min plasma exposure in this experiment.

This paper reports a Ku-band, wide band Gyrotron-Traveling-wave-tube(Gyro-TWT) that is currently being developed at Kwangwoon University. The Gyro-TWT has a two stage linear tapered interaction circuit to obtain a wide operating bandwidth. The linearly-tapered interaction circuit and nonlinearly-tapered magnetic field gives the Gyro-TWT a wide operating bandwidth. The Gyro-TWT bandwidth is 23%. The 2d-Particle-in-cell(PIC) and MAGIC2d code simulation results are 17.3 dB and 24.34 kW, respectively for the maximum saturated output power. A double anode MIG was simulated with E-Gun code. The results were 0.7 for the transvers to the axial beam velocity ratio (=alpha) and a 2.3% axial velocity spread at 50 kV and 4 A. A magnetic field profile simulation was performed by using the Poisson code to obtain the grazing magnetic field of the entire interaction circuit with Poisson code.

Hexagonal Ba-ferrites are widely suggested as materials for small antennas. In this paper, the sintering behavior and magneto-electric properties of Ba 3 Co 2-2x Mn 2x Fe 24 O 41 (0.1≤x≤0.5) ceramics were investigated for small antenna application. All samples of Ba 3 Co 2-2x Mn 2x Fe 24 O 41 ceramics were prepared by the solid-state reaction method and sintered at 1250℃. From the XRD patterns of the sintered Ba 3 Co 2-2x Mn 2x Fe 24 O 41 ceramics, the Z-type phases were found to be the main phases. The real part of permittivity and permeability of the Ba 3 Co 2-2x Mn 2x Fe 24 O 41 ceramics decreased with frequency. On the other hand, loss tangents of permittivity and permeability tended to behave opposite to real part of permittivity and permeability. The real part of permeability was affected by Mn additions. The real part of permittivity, the loss tangent of permittivity and the real part of permeability, the loss tangent of permeability of Ba 3 Co 0.2 Mn 0.8 Fe 24 O 41 ceramics were 19.774, 0.176 and 15.183, 0.073, respectively, at 510 MHz. In order to investigate the effect of magneto-dielectric ceramics on antenna, PIFA (Planar Inverted F Antenna) was simulated with CST (Computer Simulation Technology). The operating frequency of antenna was decreased without considerable change of bandwidth by using the Ba 3 Co 0.2 Mn 0.8 Fe 24 O 41 ceramics as the carrier.

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

A new class of compact and lightweight S-band 1 kW traveling-wave tube (TWT) is being developed for a microwave power module (MPM) that will be used for phased antenna array radar applications. The proposed S-band MPM provides a tenfold peak power increase compared to state-of-the-art S-band MPMs. In this paper, the design of the vacuum power booster TWT part of the MPM is presented. The compact and lightweight S-band TWT is driven by a 6 kV, 0.9 A electron beam. The amplifier is predicted by large-signal simulations to generate over 1 kW at S-band with 25 dB saturated gain and over 40% efficiency. The stability from unwanted oscillations has been investigated. To suppress the oscillations, the helix circuit has been coated with carbon composite material. The coaxial input and output antennas have been fabricated. For efficiency enhancement, a multi-stage depressed collector (MDC) has been designed using a 3D particle-in-cell (PIC) simulator, VORPAL. The collector design makes use of a current loop based on a feedback mechanism for effective design process. The integrated designs of a helix circuit, an electron gun, a periodic permanent magnet (PPM), antennas, and a collector are presented.

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

This paper reports on a wideband amplification mechanism involving an impulse electron beam. To prove broadband amplification with the impulse beam, we perform 3-dimensional particle-incell (3D PIC) code simulation. An impulse electron beam with a pulse width of 1 ns with electric potential 17.2 kV is injected into an interaction circuit of a coupled-cavity traveling-wave-tube (CCTWT) driven by a continuous-wave (CW) signal of 29.1 GHz. The resulting output bandwidth was 2.96%, and the peak output power of 713 W was the same as that obtained with CW operation at a single frequency. The simulation yielded very similar results with ultra short impulse signal from the simulation.

An impedance measurement system for an atmospheric microwave-induced plasma is proposed using equivalent transmission line theory and a de-embedding process of an input impedance. An argon plasma was generated by using a microwave-induced discharge. The generator consists of a 2.45 GHz solid state power oscillator (SSPO), a circulator, a directional coupler, a three-stub tuner, a gas flow meter, and a plasma jet. The microwave source power was varied from 10 to 25 W, and the argon gas flux was varied from 1 to 5 L/min at atmospheric pressure. The experimental results for the microwave-induced plasma show the impedance behaviors of the resistance and the inductive reactance. The near unity voltage standing wave ratio (VSWR) from the experiment results ensures that the proposed measurement system is valid.

The feasibility of designing and modeling a multistage depressed collector (MDC) by using 3D conformal finite-difference time-domain (CFDTD) particle-in-cell (PIC) simulations as implemented in 3D PIC code, VORPAL has been studied. A simple circuit model employing feedback mechanisms has been implemented to provide stable time-dependent voltages for each stage of the depressed collector, and an arbitrary space-time dependent spent-beam distribution is given in our timedomain simulations. We demonstrate the design of a five-stage depressed collector recovering a triangular-like spent-beam distribution imported from a large signal simulation, achieving an energy recovery efficiency of 75%. The MDC after optimization can be integrated into the limited space of an S-band traveling wave tube for a compact microwave power module (MPM).

Department of Chemical and Biochemical Engineering, Konyang University, 26 Nae-dong, Nonsan-si, Chungnam 320-711, Korea*Technical Research Institute, Hanjin Chemical Co., LTD 333 Gocheon-dong, Uiwang-si, Gyeonggi 437-801, Korea **K.L. Tech Co., LTD, 68 Yu-ri, Bongdam-up, Hwaseong-si, Gyeonggi 445-872, Korea(Received 1 December 2010; accepted 4 January 2011)

NCO terminated polyurethane prepolymers were synthesized from isophorone diisocyanate(IPDI), poly (tetramethylene glycol)(PTMG) and dimethylol propionic acid(DMPA). Subsequently, waterborne polyurethanes were prepared by capping the NCO groups of polyurethane prepolymers with different types of silane coupling agents, such as methyltrimethoxysilane(MTMS), glycidoxypropyl trimethoxysilane(GPTMS), methacryloxypropyl trimethoxysilane (MPTMS) and aminopropyl triethoxysilane(APS). The average particle size of the waterborne polyurethane solutions was increased by adding silane coupling agents. Also, the coating films prepared from GPTMS, MPTMS and APS, exhibited better pencil hardness than those from pure waterborne polyurethane. On the other hand, the coating films from MTMS did not show an improved pencil hardness than those from pure waterborne polyurethane.

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.

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

We present simulation results on wideband millimeter wave amplification on a coupled-cavity traveling-wave-tube driven by an ultra short impulse signal. The impulse signal of pulse width of 1 nsec modulated with a carrier frequency of 29.1 GHz is injected into the amplifier. The resulting output spectra were found to be wideband with a 2.4% fractional bandwidth at a center frequency of 29.1 GHz, where peak output power of 658 W remained same as that obtained at CW operation with a single drive frequency of 29.1 GHz.

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.