High Harmonic Suppression Research Articles

Optimization of active microwave frequency multiplier performance utilizing harmonic terminating impedances

A primary factor affecting optimum performance of microwave multipliers employing nonlinear devices is the proper termination of the fundamental and other harmonic frequency components. The objective of this paper is to present a quantitative analysis leading to the assessment of optimum terminating impedances in the design of active frequency multipliers with special attention given to harmonics other than those desired. The analysis includes computer modeled HEMT data and supporting measured data for corresponding circuit realizations. Circuit designs are presented utilizing HEMT transistors as the active element to verify modeled results. Based on available literature, the results demonstrate, for the first time, the quantitative effects of harmonic termination on active multiplier conversion gain and fundamental and higher harmonic suppression. An experimental design reveals an improvement in multiplier gain of 124% over the conventional approach and data is presented which quantitatively illustrates the advantages of impedance termination considerations under optimal bias conditions.

Spectroscopy beamline at the Advanced Photon Source for the photon energy region from 0.5 to 3 keVa)

Interest in the 0.5 to 3 keV, intermediate x-ray, energy region has recently intensified as this spectral region covers, among others, the important L and M edges of transition-metal and rare-earth magnetic materials, respectively. Third-generation synchrotron facilities with their inherent high brightness have the unique potential to cover this energy region with high-resolution, high-flux x-ray beams ideal for spectroscopic studies. A 5.5-cm-period, planar undulator to be installed on the 7-GeV Advanced Photon Source will produce a high brightness source of intermediate-energy x rays. The 0.5- to 3-keV spectroscopy beamline is based on the spherical grating monochromator design that has already been shown to yield high resolution and throughput in the soft-x-ray region, below 1 keV. The beamline has been designed to cover the entire region with a peak resolving power of 6000–10 000. Photon flux at the sample is calculated to be in the range from 1011 to 1013 photons/s into a spot size of 1 mm2. A refocusing mirror will be used to further demagnify the image size at a second experimental station. As a second phase to the spectroscopy program, an elliptically polarized insertion device will be used. The polarization preserving nature of the grazing incidence optical elements in the SGM is crucial to obtain x rays of well-defined polarization. The beamline layout, together with calculations of resolution, throughput, power loading, and high harmonic suppression, will be presented. The photoemission experimental end stations for the spectroscopy station will also be briefly described.

Spectroscopy beamline at the Advanced Photon Source for the photon energy region from 0.5 to 3 keV (abstract)

Interest in the 0.5–3 keV, intermediate x-ray, energy region has recently intensified as this spectral region covers, among others, the important L and M edges of transition metal and rare-earth magnetic materials, respectively. Third-generation synchrotron facilities with their inherent high brightness have the unique potential to cover this energy region with high-resolution, high-flux x-ray beams ideal for spectroscopic studies. A 5.5 cm period, planar undulator to be installed on the 7 GeV Advanced Photon Source will produce a high brightness source of intermediate energy x-rays. The 0.5–3 keV spectroscopy beamline is based on the spherical grating monochromator design that has already been shown to yield high resolution and throughput in the soft x-ray region below 1 keV. The beamline has been designed to cover the entire region with a peak resolving power of 6000–10 000. Photon flux at the sample is calculated to be in the range from 1011 to 1013 photons/s into a spot size of 1 mm2. A refocusing mirror will be used to further demagnify the image size at a second experimental station. As a second phase to the spectroscopy program, an elliptically polarized insertion device will be used. The polarization preserving nature of the grazing incidence optical elements in the SGM is crucial to obtain x rays of well-defined polarization. The beamline layout, together with calculations of resolution, throughput, power loading, and high harmonic suppression will be presented. The photoemission experimental end stations for the spectroscopy station will also be briefly described. This research was supported by the U.S. Department of Energy, BES Materials Sciences under Contract No. W-31-109-ENG-38.

Suppression of DC line current oscillation of HVDC transmission system using voltage source forced commutation converter

AbstractThe conventional converter used in an HVDC system requires line voltage to turn off the current flowing through a thyristor or a mercury‐arc valve. Hence, the HVDC system cannot supply electric power to the system which has no ac source, such as a generator or a synchronous condenser. Thus, the HVDC system has some difficulties in operating with the weak system.The conventional solution to avoid these problems is to install large‐capacity synchronous condensers which require considerable construction costs and maintenance. Another solution is the application of a forced commutation converter.The recent development of high‐power and high‐frequency semiconductor devices with fast gate turn‐off ability (e.g., GTOs and SI thyristors) suggests the application of a voltage‐source‐type forced commutation converter (VSFC) to an HVDC system. To ensure the promising characteristics of the overall system, further investigation is of course necessary.The performance of dc transmission into a remote load‐only system without ac source has been investigated by means of computer simulation. In many runs of a simulation program of the HVDC system using VSFC, we noticed that long sustaining oscillation of dc line current and dc voltage occurs when a large disturbance is applied. The performance is worse when series dc reactance (DCL) is installed to suppress higher harmonics of dc line current. To improve the performance of the HVDC system using VSFC, an attempt was made to install the L‐R parallel damper circuit in series of dc transmission line. Simulation results when DCL and L‐R damper are installed in series show that suppression of higher harmonics is as effective as the installation of DCL only, and the damping of oscillation also is substantial to improve the dynamic performance of the whole system.

Modification of a planar undulator for the suppression of high radiation harmonics at zero angle

A simple modification of the planar undulator is suggested and tested to suppress higher odd harmonics of undulator radiation at zero angle by adding a profiled plate to some poles of the undulator. A possible application of such undulators is the reduction of the degradation rate of mirrors on storage ring FELs.

Suppression of DC Line Current Oscillation of HV DC Transmission System Using Voltage Source Forced Commutation Converter.

Conventional converter used in an HV DC system needs line volatge to turn off the current flowing through a thyristor or a mercury-arc valve. Hence HV DC system cannot supply electric power to the system which has no AC source, such as a generator or a synchronous condenser, or HV DC system has some difficulties to operate with the weak system. Conventional solution of avoiding these problems is installation of large capacity synchronous condensers, which needs considerable costs of construction and maintenance. Another solution is application of forced commutation converter. The recent development of high power and high frequency semiconductor devicees with fast gate turn-off ability (e. g. GTO's and SI thyristors) suggests the application of voltage source type forced commutation converter (VSFC) to an HV DC system. To ensure the promising characteristics of overall system, more investigation is, of course, necessary. We have been investigated performance of DC transmission into remote load-only system without AC source by means of computer simulation. In many runs of simulation program of HV DC system using VSFC, we noticed that long sutaining oscillation of DC line current and DC voltage occurs when large disturbance is applied. And the performance is worse when series DC reactance (DCL) is installed to suppress higher harmonics of DC line current. For improving the performance of HV DC system using VSFC, we investigated to install the L-R parallel damper circuit in series of DC transmission line. Simulation results when DCL and L-R damper are installed in series show that suppression of higher harmonics is as effective as installation of DCL only and the damping of oscillation is also substantial to improve the dynamic performance of whole system.

Quasiclassical calculation of magnetoresistance oscillations of a two-dimensional electron gas in an anharmonic lateral superlattice potential.

A classical approach, relating magnetoresistance oscillations of a two-dimensional electron gas (2DEG) in a weak lateral superlattice potential to the guiding-center drift of cyclotron orbits, is extended to periodic potentials of general shape, and justified from the quantum-mechanical Kubo formula. Several reasonable model potentials in a (gate) plane at some distance from the 2DEG are investigated in order to study two competing effects: (1) the suppression of higher harmonics with increasing distance according to Poisson's equation and (2) the relative enhancement of higher harmonics due to the (Thomas-Fermi) screening by the 2DEG itself. An experimental result by Winkler, Kotthaus, and Ploog, showing magnetoresistance oscillations with a rich structure, is closely reproduced by the calculations.

Synchrotron Radiation White Beam Topography with an Oscillating Monochromator

Drawbacks of white beam topography with synchrotron radiation, such as intense fluorescence background, thermal strain, and radiation damage, can be avoided by filtering the beam with an oscillating perfect crystal monochromator. The advantage of the white beam technique, namely the imaging of a sample of poor quality, is maintained. The image contrast is even improved due to the suppression of higher harmonics. Topographs of a LiF crystal demonstrate the feasibility of the method.

A Low-Noise VHF Frequency Synthesizer for Digital Modems

A compact design of a frequency synthesizer in 52 MHz to 88 MHz band with 12.5 kHz spacing is given. Quite high harmonic suppression with low-noise for use in wideband satellite modems has been achieved. By proper choice of components and using single loop, the synthesizer has been fabricated for use in digital modems for communication systems.

A Note on Dynamic Range of Quantizers

Based on the relationship between the inputand output correlation functions for a symmetric2N step optimum quantizer withGaussian noise inputs a computer programwas generated to obtain plots of the inputnumber of levels versus dynamic range of thequantizer. For it to be physically useful thedynamic range should be related to the distortionin the fundamental band and thedesired harmonic suppression. A definitionbased upon these considerations is suggestedand curves are plotted for two different fundamentaldistortion levels and three differentlevels of harmonic suppression. It is foundthat, for low levels of harmonic suppression(0-20 dB range), the dynamic range can beincreased by tolerating a higher level of fundamentaldistortion. In the medium range ofharmonic suppression (20-35 dB), any increasein the dynamic range due to higherfundamental distortion levels disappearsfor high level quantizers (typically 4 bitsor more). For still higher harmonic suppression(40 dB or higher), the dynamic range ofthe quantizer is independent of the acceptablefundamental distortion.