X-band AlGaN/GaN HEMTs with high microwave power performance

An X-band AlGaN/GaN high-electron-mobility transistor (HEMT) on SiC substrate with high microwave power performances has been achieved. Its small-signal characteristics with a gate-length of 0.4 μm showed a unity current gain cut-off frequency (fT) of 22 GHz and a maximum oscillation frequency (fmax) of 65 GHz. The GaN HEMT device with a gate width of 1 mm exhibited a continuous-wave saturated output power of 10.2 W and a linear gain of 14.8 dB at 8 GHz, and successfully achieved the power-added efficiency ...     

Physical simulations and experimental results of 4H—SiC MESFETs on high purity semi-insulating substrates

In this paper we report on DC and RF simulations and experimental results of 4H-SiC metal semiconductor field effect transistors (MESFETs) on high purity semi-insulating substrates. DC and small-signal measurements are compared with simulations. We design our device process to fabricate n-channel 4H-SiC MESFETs with 100 μm gate periphery. At 30 V drain voltage, the maximum current density is 440 mA/mm and the maximum transconductance is 33 mS/mm. For the continuous wave (CW) at a frequency of 2 GHz, the maximum output power density is measured to be 6.6 W/mm, with a gain of 12 dB and power-added efficiency of 33.7%. The cut-off frequency (fT) and the maximum frequency (fmax) are 9 GHz and 24.9 GHz respectively. The simulation results of fT and fmax are 11.4 GHz and 38.6 GHz respectively.     

Fabrication and characterization of graphene derived from SiC

Using novel ideas for the fabrication of epitaxial graphene(EG)on SiC,two forms of graphene termed as vertical aligned graphene sheets(VAGS)and graphene covered SiC powder(GCSP)were derived,respectively,from SiC slices and SiC powder,aimed for applications in energy storage and photocatalysis.Herein,the fabrication procedures,morphology characteristics,some intrinsic physical properties and performances for applications in field effect transistor(FET)and cold cathode field emission source are revealed and analyzed based on the graphene materials.The EG on a 2-inch SiC(0001)showed an average sheet resistance about 720/with a non-uniformity 7.2%.The FETs fabricated on the EG possessed a cutoff frequency 80GHz.Based on the VAGS derived from a completely carbonized SiC slice,a magnetic phase diagram of graphene with irregular zigzag edges is also reported.     

A staggered double vane circuit for a W-band traveling-wave tube amplifier

Based on the combination of a staggered double vane slow wave structure(SWS) and round electron beam,a 200-W W-band traveling-wave tube(TWT) amplifier is studied in this paper.The main advantages of round beam operation over the sheet beam is that the round beam can be formed more easily and the focus requirement can be dramatically reduced.It operates in the fundamental mode at the first spatial harmonic.The geometric parameters are optimized and a transition structure for the slow wave circuit is designed which can well match the signal that enters into and goes out from the tube.Then a TWT model is established and the particle-in-cell(PIC) simulation results show that the tube can provide over 200-W output power in a frequency range of 88 GHz-103 GHz with a maximum power of 289 W at 95 GHz,on the assumption that the input power is 0.1 W and the beam power is 5.155 kW.The corresponding conversion efficiency and gain at 95 GHz are expected to be 5.6% and 34.6 dB,respectively.Such amplifiers can potentially be used in high power microwave-power-modules(MPM) and for other portable applications.     

A G-band terahertz monolithic integrated amplifier in 0.5-μm InP double heterojunction bipolar transistor technology

Design and characterization of a G-band(140–220 GHz) terahertz monolithic integrated circuit(TMIC) amplifier in eight-stage common-emitter topology are performed based on the 0.5-μm In Ga As/In P double heterojunction bipolar transistor(DHBT). An inverted microstrip line is implemented to avoid a parasitic mode between the ground plane and the In P substrate. The on-wafer measurement results show that peak gains are 20 dB at 140 GHz and more than 15-dB gain at 140–190 GHz respectively. The saturation output powers are-2.688 dBm at 210 GHz and-2.88 dBm at 220 GHz,respectively. It is the first report on an amplifier operating at the G-band based on 0.5-μm InP DHBT technology. Compared with the hybrid integrated circuit of vacuum electronic devices, the monolithic integrated circuit has the advantage of reliability and consistency. This TMIC demonstrates the feasibility of the 0.5-μm InGaAs/InP DHBT amplifier in G-band frequencies applications.     

Heterogeneous integration of InP HEMTs on quartz wafer using BCB bonding technology

Heterogeneous integrated InP high electron mobility transistors(HEMTs)on quartz wafers are fabricated successfully by using a reverse-grown InP epitaxial structure and benzocyclobutene(BCB)bonding technology.The channel of the new device is In_0.7Ga_0.3As,and the gate length is 100 nm.A maximum extrinsic transconductance gm,max of 855.5 mS/mm and a maximum drain current of 536.5 mA/mm are obtained.The current gain cutoff frequency is as high as 262 GHz and the maximum oscillation frequency reaches 288 GHz.In addition,a small signal equivalent circuit model of heterogeneous integration of InP HEMTs on quartz wafer is built to characterize device performance.     

Long-term optical and radio variability analysis of BL Lacertae 2200+420

Based on the radio light curves in 22 GHz and 37 GHz from the Metsahovi monitoring program and the optical light curves in BVRI bands from previously published results and the"Whole Earth Blazar Telescope"(WEBT)archives,we analyze the time delay among 22 GHz,37 GHz and optical bands(B,V,R,I)of BL Lacertae by means of discrete correlation method.The results suggest there exist strong correlation among 22 GHz,37 GHz and optical bands(B,V,R,I)with zero-lag.The 37 GHz lags behind R band by 11 months.The correlation of brightness and color index among BVRI bands,brightness and spectral index between 37GHz and 22 GHz are also investigated.The results show a clear trend of bluer-when-brighter.     

High-performance evanescently-coupled uni-traveling-carrier photodiodes

A new evanescently-coupled uni-traveling-carrier photodiode (EC-UTC PD) based on a multimode diluted waveguide (MDW) structure is fabricated, analysed and characterized. Optical and electrical characteristics of the device are investigated. The excellent characteristics are demonstrated such as a responsivity of 0.36 A/W, a bandwidth of 11.5 GHz and a small-signal 1-dB compression current greater than 18 mA at 10 GHz. The saturation current is significantly improved compared with those of similar evanescently-coupled pin photodiodes. The radio frequency (RF) bandwidth can be further improved by eliminating RF losses induced by the cables, the probe and the bias tee between the photodiode and the spectrum analyzer.     

磁场构型的影响及用于RIKEN的RIBF项目的新型ECR离子源

We measured the main plasma parameters(density of electron,temperature of electron and ion confinement time)and beam intensity of various heavy ions as a function of B_(min).The B_(min) strongly affects the field gradient at the resonance zone,consequently the plasma parameters and beam intensity are changed. Based on these experimental results,we started to construct new 18GHz ECRIS and make a detailed design of the 28GHz SC-ECRIS for RIKEN RI beam factory project.     

Multi-band microwave metamaterial absorber based on coplanar Jerusalem crosses

The influence of the gap on the absorption performance of the conventional split ring resonator(SRR) absorber is investigated at microwave frequencies. Our simulated results reveal that the geometry of the square SRR can be equivalent to a Jerusalem cross(JC) resonator and its corresponding metamaterial absorber(MA) is changed to a JC absorber. The JC MA exhibits an experimental absorption peak of 99.1% at 8.72 GHz, which shows an excellent agreement with our simulated results. By simply assembling several JCs with slightly different geometric parameters next to each other into a unit cell, a perfect multi-band absorption can be effectively obtained. The experimental results show that the MA has four distinct and strong absorption peaks at 8.32 GHz, 9.8 GHz, 11.52 GHz and 13.24 GHz. Finally, the multi-reflection interference theory is introduced to interpret the absorption mechanism.     

Double-layer microwave absorber of nanocrystalline strontium ferrite and iron microfibers

Microwave absorption properties of the nanocrystalline strontium ferrite (SrFe₁₂O₁₉) and iron (α-Fe) microfibers for single-layer and double-layer structures are investigated in a frequency range of 2 GHz-18 GHz. For the single-layer absorbers, the nanocrystalline SrFe₁₂O₁₉ microfibers show some microwave absorptions at 6 GHz-18 GHz, with a minimum reflection loss (RL) value of -11.9 dB at 14.1 GHz for a specimen thickness of 3.0 mm, while for the nanocrystalline α-Fe microfibers, their absorptions largely take place at 15 GHz-18 GHz with the RL value exceeding -10 dB, with a minimum RL value of about -24 dB at 17.5 GHz for a specimen thickness of 0.7 mm. For the double-layer absorber with an absorbing layer of α-Fe microfibers with a thickness of 0.7 mm and matching layer of SrFe₁₂O₁₉ microfibers with a thickness of 1.3 mm, the minimum RL value is about -63 dB at 16.4 GHz and the absorption band width is about 6.7 GHz ranging from 11.3 GHz to 18 GHz with the RL value exceeding -10 dB which covers the whole K_u-band (12.4 GHz-18 GHz) and 27% of X-band (8.2 GHz-12.4 GHz).     

Frequency Lock of an Optically Pumped FIR Ring Laser at 803 and 1626 GHz

We report an automatic frequency control (AFC) for an optically pumped far infrared (FIR) ring laser applicable for high resolution THz sideband spectroscopy by mixing a fraction of the laser power and a harmonic of a phase-locked synthesizer on a planar Schottky diode. We achieve a relative frequency accuracy of about 0.5 kHz rms at 803 GHz ( ¹⁵ NH ₃ ) and about 1 kHz rms at 1626.6 GHz (CH ₂ F ₂ ) over hours of lock time. The absolute frequency accuracy is estimated to be about 5 kHz at 1626.6 GHz.     

Computer studies on the space charge dependence of avalanche zone width and conversion efficiency,of single driftp +nn+ andn +pp+ indium phosphide impatts

The effect of mobile space charge on avalanche zone width and conversion efficiency of single drift region (SDR) indium phosphide impatts at 12 and 60 GHz has been investigated. The results show thatp ⁺nn⁺ InP diodes have a narrower avalanche zone and a higher conversion efficiency compared ton ⁺pp⁺ diodes for both the frequencies at normal operating current densities. The expansion of avalanche zone and efficiency degradation at high current levels are more pronounced inp ⁺nn⁺ at 12 GHz and inn ⁺pp⁺ at 60 GHz.     

Magnetic and electromagnetic absorption properties of FeNi alloy nanoparticles supported by reduced graphene oxide

FeNi alloy nanoparticles (NPs) supported by reduced graphene oxide (RGO) (FeNi/RGO nanocomposites) were successfully synthesized through in‐situ reduction. Large amounts of sphere‐like FeNi NPs are uniformly deposited on the RGO nanosheets. The magnetic hysteresis measurement reveals the ferromagnetic behavior of the nanocomposites at room temperature. According to the electromagnetic (EM) characteristics, the FeNi/RGO nanocomposites show outstanding EM absorption properties in the 2–18 GHz range, as evidenced by the wide effective absorption bandwidth (up to 3.3 GHz, with reflection loss R_L < –10 dB) and a minimal R_L (–32 dB) at 12.4 GHz with a thickness of 1.5 mm. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Operation of a 32 GHz gyrotron

The design and operation of a 32 GHz pulsed gyrotron are reported. The device is step-tuned between the TE_1,2 (24.16 GHz) and TE_0,2 (31.78 GHz) modes with cathode voltages ranging from 30 to 40kV and beam current up to 5.0A. Experimental frequencies are in close agreement with the self-consistent calculated values and in the TE_2,2 resonator mode an output peak power of 6kW corresponding to an 18% efficiency was measured by using a fast response calorimeter with a thermal sensitivity of 0.1°C/Wmin.     

High-frequency study of the orbital ordering resonance in the strongly correlated heavy fermion metal CeB<Subscript>6</Subscript>

A recently discovered magnetic resonance in the orbitally ordered phase of CeB₆ (orbital ordering resonance) is studied in a wide frequency range v = 44–360 GHz. The g-factor for this resonance was found to increase with frequency from g(v = 44 GHz) ∼ 1.55 to g(v > 250 GHz) ∼ 1.7. In addition to the orbital ordering resonance, a new magnetic resonance with a g-factor of 1.2–1.3 was detected for frequencies exceeding 200 GHz. Presented at the 5th Asia-Pasific EPR/ESR Symposium, August 24–27, 2006, Novosibirsk, Russian Federation.     

宽带非均匀半径渐变TE0n-TE0(n+1)模式转换器的设计研究

基于耦合波理论，对两类半径渐变圆波导TE_0n-TE_0(n+1)模式转换器进行理论分析、数值计算和仿真模拟.均匀半径渐变波导高功率模式转换器，采用中心频率为17.14GHz、六周期TE₀₂-TE₀₃模式和中心频率为34.30GHz、六周期TE₀₁-TE₀₂模式两种设计参数.非均匀半径渐变波导高功率模式转换器，采用中心频率为34.30GHz、六周期TE 关键词： 模式转换器 耦合波理论 非均匀半径渐变 转换带宽     

法拉第旋转对空间被动微波遥感的影响及消除

法拉第旋转是空间被动微波遥感重要的误差来源之一.本文研究了法拉第旋转变化的机理;分析了法拉第旋转对微波辐射计观测精度的影响;着重就1.4 GHz 正交极化通道亮温T_v以及10.7 GHz 相关极化通道亮温U的法拉第旋转校正展开讨论.通过仿真2006年海南某观测站点全年的星载微波辐射计观测数据并利用蒙特卡罗法模拟噪声的影响,分析比较了使用辅助数据(IRI 模型法)和极化模式(Yueh方法和Ribó方法)两种途径对法拉第旋转的校正效果,进而提出了一种应用IGS 关键词： 法拉第旋转 微波遥感 微波辐射计 国际GNSS服务网(IGS)     

Saturation recovery EPR and ELDOR at W-band for spin labels

A reference arm W-band (94 GHz) microwave bridge with two sample-irradiation arms for saturation recovery (SR) EPR and ELDOR experiments is described. Frequencies in each arm are derived from 2 GHz synthesizers that have a common time-base and are translated to 94 GHz in steps of 33 and 59 GHz. Intended applications are to nitroxide radical spin labels and spin probes in the liquid phase. An enabling technology is the use of a W-band loop-gap resonator (LGR) [J.W. Sidabras, R.R. Mett, W. Froncisz, T.G. Camenisch, J.R. Anderson, J.S. Hyde, Multipurpose EPR loop-gap resonator and cylindrical TE₀₁₁ cavity for aqueous samples at 94 GHz, Rev. Sci. Instrum. 78 (2007) 034701]. The high efficiency parameter (8.2 GW^−1/2 with sample) permits the saturating pump pulse level to be just 5 mW or less. Applications of SR EPR and ELDOR to the hydrophilic spin labels 3-carbamoyl-2,2,5,5-tetra-methyl-3-pyrroline-1-yloxyl (CTPO) and 2,2,6,6,-tetramethyl-4-piperidone-1-oxyl (TEMPONE) are described in detail. In the SR ELDOR experiment, nitrogen nuclear relaxation as well as Heisenberg exchange transfer saturation from pumped to observed hyperfine transitions. SR ELDOR was found to be an essential method for measurements of saturation transfer rates for small molecules such as TEMPONE. Free induction decay (FID) signals for small nitroxides at W-band are also reported. Results are compared with multifrequency measurements of T_1e previously reported for these molecules in the range of 2–35 GHz [J.S. Hyde, J.-J. Yin, W.K. Subczynski, T.G. Camenisch, J.J. Ratke, W. Froncisz, Spin label EPR T₁ values using saturation recovery from 2 to 35 GHz. J. Phys. Chem. B 108 (2004) 9524–9529]. The values of T_1e decrease at 94 GHz relative to values at 35 GHz.     

Measured mixer noise temperature and conversion loss of a cryogenic Schottky diode mixer near 800 GHz

We accurately measured the noise temperature and conversion loss of a cryogenically cooled Schottky diode operating near 800 GHz, using the UCB/MPE Submillimeter Receiver at the James Clerk Maxwell Telescope. The receiver temperature was in the range of the best we now routinely measure, 3150 K (DSB). Without correcting for optical loss or IF mismatch, the raw measurements set upper limits ofT _M=2850 K andL _M=9.1 dB (DSB), constant over at least a 1 GHz IF band centered at 6.4 GHz with an LO frequency of 803 GHz. Correction for estimated optical coupling and mismatch effects yieldsT _M=1600 K andL _M=5.5 dB (DSB) for the mixer diode itself. These values indicate that our receiver noise temperature is dominated by the corner cube antenna's optical efficiency and by mixer noise, but not by conversion loss or IF mismatch. The small fractional IF bandwidth, measured mixer IF band flatness from 2 to 8 GHz, and similarly good receiver temperatures at other IF frequencies imply that these values are representative over a range of frequencies near 800 GHz.