Investigation of a heterodyne receiver with open structure mixer at 324 GHz and 693 GHz

The performance of a submillimeter heterodyne receiver using an HCOOH laser local oscillator and an open structure mixer with a Schottky barrier diode has been optimized for 693 GHz. Working at room temperature a single sideband (SSB) system noise temperature of 7,300 K, a mixer noise temperature of 6,100 K and a conversion loss of 12 dB has been achieved. The same receiver system has been investigated at 324 GHz using an HCOOD laser local oscillator yielding a noise temperature of 3,100 K (SSB), a mixer noise temperature of 2,400 K (SSB) and a conversion loss of 10 dB (SSB). An acousto-optical spectrometer has also been constructed, with 1024 channels and a channel-bandwidth of 250 kHz. The system NEP per channel was 2.5×10^–17 W/Hz^1/2 at 324 GHz and 5.0×10^–17 W/Hz^1/2 at 693 GHz.     

Antenna patterns of an open structure mixer at a submillimeter wavelength and of its scaled model

To verify the enhancement in sensitivity of a Schottky barrier diode using a 90° corner reflector at submillimeter wavelength a 651 scaled model of the open structure mixer was constructed and investigated at 2.8 cm wavelength.The results show clearly the advantage of a 90° corner reflector, the reality of the deviations for 45° and 60° corner reflectors found for submillimeter wavelengths, and the equality of the antenna patterns for a 90° corner reflector and a cat-eye (corner cube) reflector.     

The effect of mixer mount loss on the performance of SIS receivers

Tucker's quantum theory of mixing (in the 3-port approximation) is employed with Eisenhart and Khan's equivalent circuit for a junction mounted in waveguide to predict the gain of an SIS mixer as a function of guide impedance, series inductance, junction capacitance, IF load impedance and backshort loos. The improvements which will result from optimisation of these parameters are quantified. It is shown that for optimum performance a backshort VSWR>100 is required, which is hard to realise at high frequencies     

合肥光源逐束团横向反馈系统

 介绍了在合肥光源研制的一套横向(x, y方向)高频、宽带逐束团测量和反馈系统,以及抑制耦合束团不稳定性的初步实验。其中重点介绍了在该系统研制过程中所涉及的部分关键技术：矢量运算模块的开发使得反馈系统的调试简易方便;Notch滤波器用于滤除反馈信号中的直流分量以及回旋频率分量,节省反馈功率;激励条带的研制。初步的反馈实验结果表明：反馈系统开启后不稳定性振荡得到抑制。     

Ka波段TM02模式低磁场相对论返波管初步实验研究

对Ka波段TM₀₂模式低磁场相对论返波管的结构特点、工作原理进行了介绍,详细分析了该器件以TM₀₂模工作的模式选择机制。通过粒子模拟,该器件在1 T引导磁场下获得了功率为493 MW、频率29.3 GHz的微波输出,工作模式及频率与理论设计相一致。随后,基于模拟中的结构参数开展了初步的实验研究,当二极管电压为580 kV、电流为3.56 kA、引导磁场1 T时,获得了功率286 MW、频率29.3 GHz、脉宽约10 ns的微波输出。实验获得的微波频率与数值模拟一致,但是微波功率与数值模拟结果有明显差异,并且微波脉冲后沿有明显的缩短,分析认为在低磁场下后端谐振腔链受到电子轰击是导致该问题的主要原因。     

The development of nonradiative dielectric waveguide transmitting front-end in Ka-band

The operating theory,design method and experimental results of the nonradiative dielectric waveguide (NRD-guide) transmitting front-end in millimeter wave band are related in details in this paper. As a kind of dielectric waveguide,the NRD-guide possesses fine transmission performances, and it can be used to fabricate the millimeter wave hyterodyne integrated circuits. The two kinds NRD-guide transmitting front-ends substantiated in the paper, the voltage controlling oscillator(VCO) and twin-Gunn-diode power-combiner,have very similar structures to each other and possess compact sizes, fine machinery and electric performances.For the VCO front-end in Ka-band, the frequency modulation band is greater than 150MHz, the output power is larger than 20mW.For the power-combiner, the output power is larger than 40mW,the combination efficiency is better than 90%,the frequency stabilization reaches 1.68×10^–5. Combined with the receiving front-end reported before,the transmitter and receiver can be composed to a dielectric waveguide R/T module to be applied in some millimeter wave sub-systems.     

Noise and thermal properties of a submillimeter mixer with the SINS tunnel junction

In this work we present for the first time a low-noise submillimeter receiver with a mixer using Superconductor-Insulator-Normal metal-Superconductor (SINS) junctions. Junctions containing a normal metal layer may be free of the Josephson current and of the related perturbations of mixer operation specific for the standard SIS mixers. This SINS mixer quality is important for the application in the multibeam submillimeter receiver. The SINS mixer stability of operation and independence on the magnetic field have been confirmed in our experiment. Minimum SINS receiver noise in the 290 – 330 GHz band is about 135 K when the junction R_NC is about 30. Noise, conversion gain and thermal properties of the SINS mixer have been studied and compared with the SIS mixers. The limit of SINS mixer operation improvement is discussed at the end of the work.     

The design and development of a 140GHz beam-lead diode subharmonically pumped mixer

The possibility of using beam-lead diodes in the design of a 140GHz subharmonically pumped mixer was investigated. An easily assembled, rugged mixer structure was developed which avoids the problems associated with present production techniques and reduces costs. The construction of the circuit developed makes it ideally suited to space and other environmentally demanding application. Computer analysis techniques were used to predict millimetre-wave performance and a large-scale low-frequency model was used to optimize the circuit. The millimetre-wave mixer was constructed using a circuit implemented on suspended substrate stripline. Results of millimetre-wave performance are presented.     

The potential of the superconductor-vacuum-superconductor junction as a mixing element at submillimetre wavelengths

By removing the solid insulator in the superconductor-insulator-superconductor junction and making use instead of the vacuum as the tunnelling medium it should be possible to reduce the junction capacitance by a factor of about ten. This would facilitate the development of tunnelling receivers for submillimetre wavelengths by making it possible to fabricate junctions of normal size with electrical properties appropriate for high-frequency operation.     

SHF频段超宽带高温超导滤波器的研制

针对超宽带通信系统的发展趋势,采用1/4波长短截线结构设计了一个工作于超高频(SHF)频段的超宽带高温超导滤波器,滤波器的中心频率为4.2 GHz,相对带宽为50%,讨论了1/4波长短截线结构滤波器的设计原理,给出了所设计超宽带滤波器的理论曲线、模拟仿真结果。实际制作的超宽带高温超导滤波器的测量曲线与模拟仿真曲线基本吻合,得到了满意的结果。     

Filtering characteristics of film-coated long-period fiber gratings operating at the phase-matching turning point

We present novel filtering characteristics of film-coated long-period fiber gratings (LPFGs) operating at phase-matching turning point (PMTP). The 3 dB bandwidth of a single broadband dip depends greatly on the film refractive index and thickness. A π-phase-shift in the grating center produces two band-rejection peaks between which the separation reaches 375 nm. This separation increases with the number M (M > 1) of π-phase-shifts that divide the LPFG uniformly. The central loss is constant at zero for odd M, whereas decreases with M for even M. Increasing film thickness and refractive index result in blue shifts of the dual peaks and enlarge the separations, which exhibits excellent tunabilities.     

涂料颜色配方预测的人工神经网络模型实验研究

人工神经网络技术近年来在颜色空间变换或色域映射的研究中显示了特有的效果。人工神经网络用于粉末涂料配方的预测,其特点是用BP算法神经网络建立粉末涂料反射样品的标准色度参数与配方浓度参数之间的映射关系。通过对典型颜色样本训练和预测,结果表明基于多隐层BP网的模型可以实现粉末涂料样品的配方浓度空间与标准三刺激值颜色空间的相互映射,即用BP网络实现粉末涂料的配方预测。     

The spin-1 anisotropic Heisenberg antiferromagnet on a square lattice at low temperatures

In this paper we study the low temperature behavior of the quantum S=1 Heisenberg antiferromagnet with exchange and single-site anisotropies on the square lattice. The properties of the model change drastically as the single-site anisotropy D varies from very small to very large values. A quantum phase transition takes place at a critical value D=D_C. We study the low D phase using a self-consistent harmonic approximation and a schematic phase diagram is proposed.     

Stability considerations of a high-temperature superconductor tape at different operating temperatures

Stability of a Bi-2223/Ag multifilamentary composite conductor against fast transport current ramps was studied by using a numerical model. The model was based on the two-dimensional magnetic diffusion and heat conduction equations. Calculations were carried out both in an adiabatic mode and pool boiling modes in liquid helium, hydrogen and nitrogen. When estimating the heat load (AC losses), real temperature dependent current density–electric field characteristics were used. The results computed by the finite element method are presented and discussed with special emphasis on differences of the stability considerations between high-temperature and low-temperature superconductors.     

Magnetic transition of ferromagnetic material at high pressure using a novel system

A system for the investigation of the magnetic properties of materials under high pressure is fabricated based on diamond anvil cell （DAC） technology. The system is designed with an improved coil arranged around the diamond of a non-magnetic DAC. Using this system, the magnetic transition of ferromagnetic （Fe） sample under increasing pressure can be observed. We successfully obtain the evolution of magnetic properties as a function of applied pressure reaching 26.9 GPa in the Fe sample. A magnetic transition is observed at approximately 13 GPa, which is consistent with the theoretical prediction.     

光学相关器的研究进展及军事应用

介绍了范德卢格特型和联合变换型光学相关器的基本原理和结构,给出了目前世界各国光学相关器的最新研究进展情况,最后探讨了其在军事上的应用前景及下一步的重点研究方向。     

一种简化维里型状态方程预测高温甲烷PVT关系

为满足描述爆轰环境下高温气体高温、中高压状态的需求,本文提出了一种基于Lennard-Jones(LJ)势能函数的简化维里型状态方程Han-Long(HL).应用HL状态方程计算了甲烷1000 K以上112组理论和实验数据,计算所得体积平均绝对偏差约为1%,最大误差为3.28%,远低于DMW状态方程和BS状态方程的计算偏差.采用HL状态方程计算了甲烷冲击试验的热力学数据,计算所得体积偏差均小于3%.结果表明,HL状态方程能够很好的描述高温甲烷的热力学状态.     

The development of a facility for radio‐frequency experiments at ISIS

Ferromagnetism has been observed in a family of organic molecular crystals based on the nitronyl nitroxide radical. We present the results of μSR experiments on a number of nitronyl nitroxide compounds. The zero‐field spin precession of muons implanted in diamagnetic states can be used to follow the magnetic order parameter as a function of temperature. Five of the materials studied show magnetic transitions, although the transition temperature and the nature of the magnetic ground state in each case are quite different. μSR can be used to study these ground states and thus help to relate the observed magnetic properties to the crystal structure of each material. This revised version was published online in July 2006 with corrections to the Cover Date.