Submillimeter backward wave oscillators

NASA Lewis Research Center is engaged in a program to develop a series of backward wave oscillators (BWO's) for the frequency range 500 to 2000 GHz. Generically BWO's are electron beam traveling wave tubes operating in a dispersive regime in which the group velocity and the phase velocity of the induced electromagnetic wave are in opposite directions. The oscillation frequency of a BWO is controlled by the electron beam velocity (anode voltage).Such tubes because of their frequency tunability, phase locking capability, and large bandwidth are ideal local oscillators for heterdyne receiver/spectrometers.The design of the BWO's will be discussed with emphasis on the etched slow wave structure, zero compression electron beam, long life cathode, and moderate operating voltages.     

An efficient Schottky-varactor frequency multiplier at millimeter waves. Part III. Quadrupler

In this research the efficiency of a millimeter-wave Schottky-varactor quadrupler was studied. Theoretical simulations were carried out by using a nonlinear analysis program to find the optimum embedding impedances for a given diode. Emphasis was placed on the study of optimum idlers at the 2nd and 3rd harmonics, which are essential for a high quadrupling efficiency. For experimental verification a quadrupler for 140–155 GHz output frequency range with fixed idler terminations was constructed. This quadrupler was tested with different output configurations. A 10% tunable bandwidth was obtained with output power in the range of 1.5–2.7 mW whenP _in =40 mW. The highest efficiency measured was 11.3% at 148 GHz with 10 mW input power.     

Low noise completely quasioptical SIS receiver for radioastronomy at 115 GHZ

Completely quasioptical heterodyne SIS receiver for radioastronomical applications at 115 GHz was designed and tested. Gaussian beam two lens input guide system and open structure SIS mixer with immersion lens were used. Integrated quasioptical structure consists of planar equiangular spiral antenna and superconductor—insulator—superconductor (SIS) tunnel junction as a mixing element connected to the antenna via microstrip impedance transformer. The best SIS mixer noise temperature at hot input and for heterodyne frequency 109.8 GHz with IF central frequency 1.4 GHz (DSB) was 28±7 K at the first quasiparticle step and 8±6 K at the second step.     

Effect of an applied magnetic field on the performance of a sis receiver near 300 GHz

We have successfully constructed and tested a superconductor-insulator-superconductor (SIS) receiver for operation at 265–280 GHz using 1 m² area Nb–AlO _x –Nb tunnel junctions fabricated at Stony Brook. The best performance to date is a double sideband (DSB) receiver noise temperature of 129 K at 278 GHz. We find that suppression of the Josephson pair currents with a magnetic field is essential for good performance and a stable DC bias point. Fields as high as 280 gauss have been used with no degradation of mixing performance. We illustrate the improvement in the intermediate frequency (IF) output stability with progressively increasing magnetic fields.     

Novel 53/106 GHz Dual-Band MMW LC Oscillator Implemented in SiGe BiCMOS Technology

In this Paper, we present a fully integrated millimeter wave LC voltage-controlled oscillator (VCO), which employs a novel topology, operating at dual-band frequency of 53.22 GHz-band and 106.44 GHz-band. The low-phase noise performance of –107.3 dBc/Hz and –106.1 dBc/Hz at the offset frequency of 600 kHz, –111.8 dBc/Hz and –110.6 dBc/Hz at the offset frequency of 1 MHz around 53.22 GHz and 106.44 GHz are achieved using IBM BiCMOS-6HP technology, respectively. Two tuning ranges, of 52.7 - 53.8 GHz and 105.4 - 107.6 GHz for the proposed LC VCO are obtained. The output voltage swing of this VCO is around 1.8 V_p-p at the operation frequency of 53.22 GHz and 0.45 V_p-p at 106.44 GHz; the total power consumption is about 16.5 mW. To our knowledge, this is the first oscillator which operates at dual-band frequency above 50 GHz with the best preformance.     

Design and performance of coplanar waveguide slotline bandpass filter

This paper describes the work involved in designing a coplanar waveguide -slotline bandpass filter. The filter designed to achieve at least -30dB insertion loss (S₂₁)in the stopband (8 to 8.5; 9.3 to 10 GHz) and less than -0.2 dB in the passband (8.75 to 9.05 GHz), with a centre frequency of 8.9 GHz. The filter and transition were fabricated on 1.27 mm thick RT-Duriod 6010.2 substrate and S-parameters were tested using standard SMA connectors with an HP-8510A network analyser.     

Design and experimental operation of a 165-GHz, 1.5-MW,coaxial-cavity gyrotron with axial RF output

The development of a coaxial-cavity gyrotron operating in TE_31,17 mode at 165 GHz is presented. The selection of the operating frequency and mode are based on the limitations imposed by the maximum held of the superconducting (sc) magnet at Forschungzentrum Karlsruhe, Institut fur Technische Physik (FZK), the use of the inverse-magnetron injection gun (IMIG) of the 140-GHz, TE_28,16 coaxial gyrotron and the possibility of transforming the cavity mode to a whispering gallery mode (WGM) appropriate for the dual-beam quasioptical (q.o.) output coupler and the two output windows, which are foreseen for the next lateral output version of the tube. The tube with axial output has been tested at FZK to deliver maximum output power of 1.17 MW in the designed TE_31,17 mode with 26.7% efficiency at 164.98 GHz. Maximum efficiency of 28.2% was achieved at 0.9-MW output power. The design operating point with output power 1.36 MW and 36.7% efficiency was net accessible because of beam instabilities at high electron-velocity ratio α, presumably caused due to high electron-velocity spread. Power at higher frequencies was also detected: 1.02 MW at 167.16 GHz in TE_32,17 mode with 26.88 efficiency, 0.63 MW at 169.46 GHz in TE_33,17 mode with 18% efficiency, and 0.35 MW at 171.80 GHz in TE_31,17 mode with 13.3% efficiency     

A Mode Converter with Multi-waveguide Output from the TE01 Circular Waveguide Mode to the TE10 Rectangular Mode for Millimeter Wave Gyro-device Applications

A mode converter with multi-waveguide output for millimeter wave gyro-device applications is proposed in this article, which is used to convert the TE₀₁ circular waveguide mode into the TE₁₀ rectangular waveguide mode. Computer simulations with Ansoft HFSS code show that the energy transmission coefficient of larger than 95.96% may be reached in the frequency range from 34.094 GHz to 35.8 GHz (a bandwidth of 1.706 GHz) at a VSWR of lower than 1.5 for the input operating mode.     

Investigation of Nd:YVO4/YVO4 composite crystal and its laser performance pumped by a fiber coupled diode laser

Thermal effect control is critical to scale the output power of diode end-pumping solid lasers to several watts up and beyond. Diffusion bonding crystal has been demonstrated to be an effective method to relieve the thermal lens for the end-pumping laser crystal. The temperature distribution and thermal lens in Nd:YVO₄/YVO₄ composite crystal was numerically analyzed and compared with that of Nd:YVO4 crystal in this paper. The end-pumping Nd:YVO₄/YVO₄ composite crystal laser was set up and tested with z cavity. The maximum output power of 9.87 W at 1064 nm and 6.14 W at 532 nm were obtained at the pumping power of 16.5 W. The highest optical-optical conversion efficiencies were up to 60% at 1064 nm and 40% at 532 nm, respectively.     

Flashlamp pumped color center lasers

Flashlamp pumped tunable operation of F_A(II) and F_B(II) center lasers is reported. Threshold pump energies as low as 400 mJ, output energies of nearly 70 mJ and an efficiency of 0.1% have been achieved. The width of the emission spectrum of initially 70 GHz with a Littrow grating tuner was reduced to 1.5 GHz using a grazing incidence grating configuration. The scalability of the system is discussed.     

面向5G多波束应用的紧凑宽带Rotman透镜设计

提出了一种基于等光程差原理设计的紧凑宽带Rotman透镜波束赋形网络,用于5G毫米波通信的天线阵列多波束实现。首先,详细介绍了Rotman透镜的基本原理;然后,利用二等分功分器替代传统的单端口馈电模式,产生高定向波束,降低相邻端口处的能量损失以及透镜内部能量的散射;最后利用切比雪夫多枝节匹配变换器,优化原有的锥形阵列输出端口,在保证宽频带的条件下,缩短原有匹配端口尺寸,使得透镜整体尺寸减少20%,实现了Rotman透镜的紧凑性。改进模型的实测结果表明,该透镜工作频带为16.5～33.8 GHz,其中在17.2～32 GHz,S₁₁优于15 dB,扫描角度为±30°。该透镜结构简单紧凑,能够有效地为相邻阵元提供稳定的相位差信号,很好地实现5G毫米波阵列多波束的目标。     

A 100 kW, 140 GHz pulsed gyrotron

The design and operation of a 100 kW, 140 GHz pulsed gyrotron are reported. To our knowledge, this is the highest frequency at which high gyrotron output power (>-100 kW) has been achieved. Results are presented for gyrotron operation in the range of magnetic field from 4 to 7 T, voltage from 23 to 80 kV and current up to 7.5 A. Near a value of magnetic field of 5.4 T, and output power of 100 kW was obtained at 140.4 GHz in single mode operation in the TE₀₃₁ resonator mode.     

CW Operation of a Submillimeter Wave Gyrotron (Gyrotron Fu IV) for High Stability of the Output Frequency

The first cw operation of our submillimeter wave gyrotron (Gyrotron FU IV) using a 12 T superconducting magnet has been successfully carried out. Output power is more than 20 W at a frequency of 301 GHz in the TE₀₃₁ resonant cavity mode. Time-resolved frequency measurement s shows that the frequency fluctuation of the gyrotron output is smaller than 2 MHz. This frequency fluctuation is mainly due to the fluctuation in the output voltage of the power supply.     

Diode-pumped passively mode-locked Nd:GdVO<Subscript>4</Subscript> laser with a GaAs saturable absorber mirror

We report on a diode end-pumped passively mode-locked Nd:GdVO₄ laser. By using a GaAs wafer simultaneously as the saturable absorber and the output coupler, stable continuous-wave mode locking was achieved. The pulse width was measured to be 18.9 picoseconds at a repetition rate of 370 MHz. The most remarkable property of the laser is that its repetition rate can be changed from 370 MHz to 3.348 GHz by simply changing the cavity length. An average output power of 3.46 W at a 3.348 GHz repetition rate was obtained with a 14 W pump power. To our knowledge, this is the first demonstration of a passively mode-locked Nd:GdVO₄ laser using a GaAs wafer as the saturable absorber. PACS 42.55.Rz; 42.60.Fc; 42.55.Xi.     

主动锁模掺铒光纤环形激光器有理数谐波调制技术

成功地利用有理数谐波锁模技术在主动谐波锁模掺铒光纤环形激光器中获取数倍于调制频率f_m的高重复率脉冲序列,所得最高锁模脉冲重复频率f_p＝4f_m≈6GHz．根据实验结果,本文指出有理数谐波锁模输出高阶光脉冲的物理机制、导致高阶输出脉冲脉宽展宽和幅度不稳定的原因以及消除幅度不稳定的具体办法．     

Kα波段TE01模基波回旋速调放大器的设计与实验

在回旋速调放大器自洽非线性大信号理论分析和数值计算的基础上,给出了一支Kα波段TE₀₁模4腔基波回旋速调放大器的设计方案,并完成了样管的研制.同时对样管进行了热测实验,得到了如下实验结果:注电压为70 kV,电流为10 A,输入功率为60 W,磁场强度1.31 T,中心频率34 GHz,峰值功率245 kW,平均功率大于3 kW,增益36.1 dB,效率 35%,3 dB带宽大于280 MHz. 关键词： 回旋速调放大器 注-波互作用 群聚腔 输入腔     

基于二维Meniscus透镜的准光功率合成器

为了实现大功率容量和高效率的空间功率合成,将基于波导腔体的二维Meniscus透镜用于毫米波功率合成器的设计.对透镜中传输的主模(TE10波)的散射效应进行了分析,并且设计了匹配层减小透镜结构带来的反射.在30 GHz频率上利用Rexolite介质的Meniscus透镜设计出了10路功率合成器,对不同结构的功率合成器和不同参数的透镜进行了研究,得到了最终的优化结果.CST-MMW的仿真结果表明该功率合成器在30 GHz合成效率可以达到92.6%,并且其80%以上效率工作带宽可以覆盖整个Ka波段.     

Passively mode-locked Nd:YVO4 laser with up to 13 GHz repetition rate

We demonstrate passive mode locking of a Nd:vanadate (Nd:YVO₄) laser to repetition rates of up to 13 GHz. With Ti:sapphire pumping, we achieved mode locking at 13 GHz with 310 mW of average output power and pulse widths of 9.5 ps. With diode pumping, we achieved mode locking at a repetition rate of 12.6 GHz with 198 mW of average output power and a pulse duration of 8.3 ps. Received: 6 July 1999 / Published online: 30 July 1999     

Detailed Consideration of Experimental Results of Gyrotron FU CW II Developed as a Radiation Source for DNP-NMR Spectroscopy

A CW gyrotron for the sensitivity enhancement of NMR spectroscopy through dynamic nuclear polarization has been designed. The gyrotron operates at the second harmonic and frequency of 394.6 GHz with the main operating mode TE_0,6. Operating conditions of other neighboring cavity modes such as TE_2,6 at frequency of 392.6 GHz and TE_2,3 at frequency of 200.7 GHz were also considered. The experimental conditions of the gyrotron at low and high voltages are simulated. The output power of 56 watts corresponds to the efficiency of 2 percent at low voltage operation and frequency of 394.6 GHz is expected.     

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.