Interconnecting solved subsystems

A tableau approach to the interconnection of solved sub-systems is presented which preserves their separate identity, but which allows full use of available sparse-matrix techniques.     

面向毫米波遥感成像的双极化毫米波探测器

针对多极化毫米波遥感成像重大需求,报道了一种高集成度双极化毫米波探测器。探测器采用固态电子学方案,通过喇叭天线接收毫米波信号,利用正交模耦合器进行极化信号分离,采用两级低噪放芯片放大信号,通过肖特基二极管实现功率检测。每支探测器集成两路接收通道,每个接收通道可同时探测水平与竖直两个极化方向信号。经测量,探测器探测频段为W波段(75～110 GHz),平均等效噪声温差达到0.3 K(@10 ms),尺寸不足155 mm×15 mm×20 mm,质量<0.3 kg。利用该探测器实现城市环境双极化毫米波遥感成像,成像结果表明,相比于单极化遥感成像,双极化遥感成像可以获得更多极化信息,可对城市环境下常见物品进行突出显示,这有助于今后进行自动物品识别、轮廓提取与远程物质成分识别。     

Solution of interconnected subsystems

A method is given for solving a large system consisting of interconnections of smaller sybsystems. The method solves each subsystem separately, derives and solves a set of interconnection equations and then obtains the solution of the whole system. Sparse matrix solution techniques are used.     

Emerging trends in millimeter-wave CAD

This paper discusses three emerging trends in the area of millimeter-wave (mm-wave) electromagnetic (EM) simulation and computer-aided design (CAD). Diakoptics techniques for frequency- and time-domain EM-simulation methods are needed for mm-wave circuit design. Development of artificial neural network (ANN) models is likely to result in an efficient use of EM simulators. Possible applications of knowledge-based tools are suggested for initial stages of the design process     

Tuneable millimeter-wave gyrotrons

In the course of developing a low-power, tuneable millimeter-wave source, two gyrotrons have been constructed. Gyrotron I was a fixed-frequency device operating at 120 GHz while Gyrotron II produced more than 20 lines in the frequency range 130 to 260 GHz. The design of tuneable gyrotrons is discussed with reference to the Gyrotron II results.     

Two-terminal millimeter-wave sources

Basic principles of operation, fundamental power-generation capabilities, and fabrication technologies are reviewed for three groups of two-terminal devices, i.e., resonant-tunneling diodes (RTDs), transferred-electron devices (TEDs), and transit-time diodes. The paper focuses on devices for frequencies above 30 GHz, and an overview of recent research in this area and of various state-of-the-art laboratory results is given. As an outlook, the potential of some new material systems for high-power devices is discussed     

Printed millimeter-wave reflectarrays

Periodic and quasi-periodic structures printed on a dielectric substrate can be employed to control reflection and transmission properties of incident waves as a function of structure geometry. This can be done mostly independently for both polarizations. These structures thus allow the realization of different kinds of filters and polarizers. Local variation of the element geometry on a substrate with backside metallization — resulting in respective variations of the reflection phase angle — can be employed to design printed reflectarray antennas. Including the dual polarization properties of such antennas, dual function or dual frequency antennas can be built, or these properties can be exploited for the realization of compact, low-profile folded reflector antennas. Examples for a number of antennas are presented, including dual radiation characteristics, dual frequency operation, and very compact, low loss folded reflector antennas     

Advanced research in millimeter-wave vacuum electronics

Selected basic research efforts currently sponsored by the U.S. Department of Defense (DOD) and the National Science Foundation (NSF) are reviewed. Major achievements are highlighted and remaining obstacles are discussed. Future advances are suggested. Opinions expressed are solely those of the author.     

Propagation studies in millimeter-wave link systems

The overall performance characteristics of ground-level millimeter-wave links are analyzed. Transmission reliability is examined on the basis of statistical data on pertinent meteorological variables and as a function of various link design parameters. Link systems operating under climatic conditions roughly characteristic of those prevailing along the mid-Atlantic coast of the United States are found to he limited most severely by attenuation due to rainfall. For a required degree of transmission reliability, trade-offs between the basic link design parameters are seen to lead to a certain range of hop distance and a corresponding range of transmitter power level. Detrimental effects due to reflection and diffraction by the terrain may in most cases be essentially avoided for short and medium hop distances. The discussion also includes considerations on diversity operation for increased transmission reliability and a brief comparison of the advantages of millimeter waves over both microwaves and optical wavelengths for links with short and medium hop lengths. Experimental work is reported on point-to-point transmission at 90.5 GHz (or 3.3 mm wavelength) carried out over a period of more than one year. Operation with antennas exposed to precipitation and wind has been found feasible. Measured transmission losses under a wide range of weather conditions were found to stay well within the limits predicted. The need for more research on short-term signal fluctuations ("scintillations") and propagation-time fluctuations is pointed out. The theoretical and experimental results have established a considerable degree of confidence in the feasibility of millimeter-wave link systems with short to medium hop distances and low power requirements.     

Progress in millimeter-wave fiber-radio access networks

Future radio access networks operating at millimeter-wave frequencies have the capacity to offer broadband interactive services to a customer base requiring untethered access. Optical fiber-feed networks incorporating wavelength division multiplexing have been proposed as a backbone network providing full-duplex interconnectivity between multiple remote antenna basestations and a central office implementing a variety of switching and routing functions. Rapid developments in both lightwave and microwave enabling technologies have fuelled an intense effort into the research and development of these networks. In this paper, we present a review of the progress of millimeter-wave fiber-radio networks in the areas of the associated enabling technologies, sub-systems and system demonstrations.     

Silicon high-resistivity-substrate millimeter-wave technology

The application of molecular beam epitaxy (MBE) and X-ray lithography for the fabrication of monolithic integrated millimeter-wave devices on high-resistivity silicon has been investigated. Process compatibility and the retention of high-resistivity characteristics were measured using the spreading resistance method and Hall measurements after various process steps. Microstrip resonators of ring and linear geometry were fabricated on 10 000 Ω.cm silicon substrates. For linear microstrip resonators, the attenuation was found to be less than 0.6 dB/cm at 90 GHz. A 95-GHz IMPATT oscillator circuit and a planar microstrip antenna array have been fabricated on highly insulating silicon substrates. For the oscillator, a combined monolithic-hybrid integration technique was used to attach the discrete IMPATT diode to the resonator circuit. The oscillator does not require tuning elements. Preliminary experimental results are 8 mW of output power with 0.2 percent efficiency at 95 GHz.     

Integrated millimeter-wave corner-cube antennas

An integrated corner-reflector antenna has been designed, fabricated and measured at millimeter-wave frequencies. The structure consists of a traveling-wave antenna integrated on a 1.2-μm dielectric membrane, and suspended in a longitudinal cavity etched in a silicon wafer. A novel traveling wave antenna design, the modified-bend antenna, with an antenna length of 1.2 λ and spacing 0.96 λ from the apex, results in a wideband input impedance centered at 140 Ω and low cross-polarization levels. Measurements at 180-270 GHz show a well-defined pattern with low sidelobe levels, and a main-beam efficiency of 93% and 83% at 180 and 222 GHz, respectively. The monolithic approach allows the integration of a matching network and a Schottky-diode or SIS detector at the base of the antenna to yield a low-noise monolithic millimeter-wave receiver     

Performance study of iSCSI-based storage subsystems

iISCSI is emerging as an end-to-end protocol for transporting storage I/O block data over IP networks. By exploiting the ubiquitous Internet infrastructure, iSCSI greatly facilitates remote storage, remote backup, and data mirroring. This article evaluates the performance of two typical iSCSI storage subsystems by measuring and analyzing block-level I/O access performance and file-level access performance. In the file-level performance study, we compare file access performance in an NAS scheme with that in an iSCSI-based SAN scheme. Our test results show that Gigabit Ethernet-based iSCSI can reach very high bandwidth, close to that of a direct FC disk access in block I/O access. However, when the iSCSI traverses through longer distance, throughput relies heavily on the available bandwidth between the initiator and the target. On the other hand, the file-level performance shows that iSCSI-based file access (SAN scheme) provides higher performance than using NFS protocol in Linux and SMB protocol in Windows (NAS scheme). However, the advantage of using iSCSI-based file accesses decreases as the file size increases. The obtained experimental results shed some light on the performance of applications based on iSCSI storage.     

Designing communication subsystems for high-speed networks

Is shown that system structure and implementation of a communication subsystem are vital elements in high-throughput protocol implementation. A well-structured and carefully implemented subsystem can exploit high-speed transmission links and preserve their speed up to the application. The issues of memory management and organization are presented as examples. Support for data movement and processing overlap, and intelligent DMA, two alternatives for the communication subsystem to achieve higher performance and scale to higher-speed links, are discussed     

A millimeter-wave monolithic grid amplifier

A 36-element monolithic grid amplifier has been fabricated. The peak gain is 5 dB at 40.8 GHz with a 3-dB bandwidth of 1.4 GHz. The active elements are pairs of heterojunction-bipolar-transistor's (HBT's). The individual transistors in the grid have a maximum oscillation frequency,f _max , of 100 GHz. The grid includes base stabilizing capacitors which result in a highly stable grid. This is the first report of a successful monolithic grid amplifier.     

Optimization of millimeter-wave glow-discharge detectors

A simplified theory that provides the basis for determining the optimum gas composition and pressure which maximize the responsivity of millimeter and submillimeter glow-discharge detectors at a given spectral frequency is presented together with experimental verification.     

The Hat Creek millimeter-wave interferometer

A fixed-baseline millimeter-wave interferometer, operating initially at 13.5 mm, has been put into operation at the Hat Creek Observatory as the first step in the development of a two-element aperture synthesis telescope. The first system consists of a 3-m antenna and a 6-m antenna spaced 265 m apart. Large receiver bandwidths may be used at high frequencies, and this system employs an intermediate frequency bandwidth of about 400 MHz. It also has automatic gain control and a phase stabilized local-oscillator reference cable. Observations may be made either in the continuum or with a 128-channel spectrometer. The baseline vector has been obtained from observations of about 7 QSO's. The instrument has been used to derive accurate absolute positions of interstellar water vapor sources, to study Mercury, Venus, and Mars, and to make crude maps of a few complex continuum sources. Measurements of the interferometer phase fluctuations due to the atmosphere indicate that interferometer is possible under average weather conditions at Hat Creek at wavelengths as short as 2 mm. The synthesis telescope, the next stage, has two 6-m antennas which can be located at various stations on a T-shaped track. The east-west leg is 300 m and the north-south leg is 200 m, permitting full synthesis for sources on the equator and at declinations as low as -30° as well as at high declinations. Operation at wavelengths down to 2 mm will be possible with resolution of 1"-2".     

Mutual coupling between millimeter-wave dielectric-resonatorantennas

The mutual coupling between aperture coupled cylindrical dielectric-resonator antennas (DRAs) is analyzed using the finite-difference time domain method. The perfectly matched layer is used as absorbing boundary conditions. The voltage excitation source of microstrip structure is based on the Zhao's model, in which the source plane or the terminal plane can be moved very close to the discontinuity so that the computational domain can be reduced substantially. The numerical results are verified by measurements and reasonable agreement between theory and experiment is obtained. It is shown that this method is highly efficient for the analysis of DRAs     

A millimeter-wave geometric phase interferometer

A millimeter-wave interferometer operating purely on the geometric phase is presented. Like its optical counterpart described by Hariharan and Roy, this system uses two circular polarizers with a half-wave section in between. The geometric phase of each signal is determined by the orientation of the half-wave section.