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1984 Vol. 6, No. 6
Display Method:
1984, 6(6): 425-434.
Abstract:
An adaptive transform coding method of image is presented, in which an image is devided into a number of image sub-blocks and two-dimensional symmetrie cosine transform is performed. And the bit-allocation map for adaptive quantization of transform coeffieients is obtained through estimation and transmission of some parameters of the sub-blocks. In the paper analytical and simulated experimental results of the method are given.
An adaptive transform coding method of image is presented, in which an image is devided into a number of image sub-blocks and two-dimensional symmetrie cosine transform is performed. And the bit-allocation map for adaptive quantization of transform coeffieients is obtained through estimation and transmission of some parameters of the sub-blocks. In the paper analytical and simulated experimental results of the method are given.
1984, 6(6): 435-449.
Abstract:
The discrete-time detection of narrowband coherent and incoherent pulse train signals in narrowband non-Gaussian noise is investigated. The structures of local-opti-mum(LO) detector are developed and found to be in the form of incorporating a local-optimum zero-memory nonlinearity (LOZNL) into the Neyman-Pearson optimum detector for narrowband Gaussian noise. Many practical detectors belong to the same class of structures of the LO detector. The expressions for the efficacies of the detectors are derived. In particular, Weibull and log-normal noise models are considered. The LOZNLs and the efficacies of the detectors are given, and the numerical results are presented graphically. It is shown that, in the sense of Pitman asymptotic relative efficiency (ARE), the asymptotic performance of many detectors whose nonlinearity can more effectively suppress the tail of the noise envelope distribution is apparently better than that of the Neyman-Pearson optimum detector for narrowband Gaussian noise.
The discrete-time detection of narrowband coherent and incoherent pulse train signals in narrowband non-Gaussian noise is investigated. The structures of local-opti-mum(LO) detector are developed and found to be in the form of incorporating a local-optimum zero-memory nonlinearity (LOZNL) into the Neyman-Pearson optimum detector for narrowband Gaussian noise. Many practical detectors belong to the same class of structures of the LO detector. The expressions for the efficacies of the detectors are derived. In particular, Weibull and log-normal noise models are considered. The LOZNLs and the efficacies of the detectors are given, and the numerical results are presented graphically. It is shown that, in the sense of Pitman asymptotic relative efficiency (ARE), the asymptotic performance of many detectors whose nonlinearity can more effectively suppress the tail of the noise envelope distribution is apparently better than that of the Neyman-Pearson optimum detector for narrowband Gaussian noise.
1984, 6(6): 450-460.
Abstract:
Based on the noice type of the digital characters and the requirements for the optical character recognition given by the authors, an algorithm of processing digital character noice is presented. The softwave and hardware of the algorithm are described.
Based on the noice type of the digital characters and the requirements for the optical character recognition given by the authors, an algorithm of processing digital character noice is presented. The softwave and hardware of the algorithm are described.
1984, 6(6): 461-472.
Abstract:
A technique of symmetry analysis for modal characteristics in uniform waveguides or resonators with ferrite rods is presented here. Symmetry analysis provides basic imformation coneerning modal characteristics, such as mode classification, mode degeneracies between mode classes, the azimuthal symmetries of the modal electromagnetic fields in each mode class, and specifying minimum waveguide sectors for each mode class which completely determine the modes of that mode class. After summarizaing of the basic points of symmetry analysis, some problems concerning symmetry operations are discussed, especially on modal electromagnetic fields in uniform waveguides containing ferrites. Then the given process of symmetry analysis is applied to the structures, i.e. uniform waveguides with Cn symmetry or Cnv symmetry and resonators with Dnh symmetry in which exist longitudinally magnetized ferriet rods. Finally, the analytical results are given in four tables.
A technique of symmetry analysis for modal characteristics in uniform waveguides or resonators with ferrite rods is presented here. Symmetry analysis provides basic imformation coneerning modal characteristics, such as mode classification, mode degeneracies between mode classes, the azimuthal symmetries of the modal electromagnetic fields in each mode class, and specifying minimum waveguide sectors for each mode class which completely determine the modes of that mode class. After summarizaing of the basic points of symmetry analysis, some problems concerning symmetry operations are discussed, especially on modal electromagnetic fields in uniform waveguides containing ferrites. Then the given process of symmetry analysis is applied to the structures, i.e. uniform waveguides with Cn symmetry or Cnv symmetry and resonators with Dnh symmetry in which exist longitudinally magnetized ferriet rods. Finally, the analytical results are given in four tables.
1984, 6(6): 473-480.
Abstract:
The proximity focused microchannel plate (MCP) image intensifier can be used as a fast optical shutter, due to its high temporal and spatial resolution, large spectral and input intensity range, high gain, and possibility of transient recording of single-shot events.A microchannel plate image intensifier combining with a gating pulse generator constitutes the simplest image converter camera with high gain and fast response. Three different gating manners for a typical second generation converter tube (18 mm,ITT-F4111 type) are compared. A new control circuit for gating the photocathode of the image intensifier is developed, and it generates high amplitude nanosecond pulses. The experimental result shows that a camera exposure time of about 2 ns has been obtained with this gating generator. The matching of the gating generator with the image intensifier is also discussed. a simple and efficient method is presented to eliminate the multi-exposure effect which must be avoided in single-shot photography.
The proximity focused microchannel plate (MCP) image intensifier can be used as a fast optical shutter, due to its high temporal and spatial resolution, large spectral and input intensity range, high gain, and possibility of transient recording of single-shot events.A microchannel plate image intensifier combining with a gating pulse generator constitutes the simplest image converter camera with high gain and fast response. Three different gating manners for a typical second generation converter tube (18 mm,ITT-F4111 type) are compared. A new control circuit for gating the photocathode of the image intensifier is developed, and it generates high amplitude nanosecond pulses. The experimental result shows that a camera exposure time of about 2 ns has been obtained with this gating generator. The matching of the gating generator with the image intensifier is also discussed. a simple and efficient method is presented to eliminate the multi-exposure effect which must be avoided in single-shot photography.
1984, 6(6): 481-489.
Abstract:
Starting from fluid mechanics-Maxwell coupled equations, a gain formula of free electron laser with an axial magnetic field is obtained by use of Laplace transform. The numerieal calculations and the analyses of the dispersion relation indicate that when the electron cyclotron frequency approaches to i-p(i is the frequency of the incident pump wave and p is the electron plasma frequeney), there is a marked drop in the gain and the position of the peak of gain-pump signal mismatch curve shifts downwards from p. We can use the phenomenon of zero-gain to calculate p.
Starting from fluid mechanics-Maxwell coupled equations, a gain formula of free electron laser with an axial magnetic field is obtained by use of Laplace transform. The numerieal calculations and the analyses of the dispersion relation indicate that when the electron cyclotron frequency approaches to i-p(i is the frequency of the incident pump wave and p is the electron plasma frequeney), there is a marked drop in the gain and the position of the peak of gain-pump signal mismatch curve shifts downwards from p. We can use the phenomenon of zero-gain to calculate p.
1984, 6(6): 490-494.
Abstract:
A new PM-focusing system with two regions of uniform magnetic field, suitable for gyrotron is proposed and studied with computer. In the calculation, a radial system made of Sm-Co magnets is used. The maximum magnetic energy-products (BH)max of the magnets are about 20MGOe. In order to adjust the magnitude of the magnetic field, some small coils are inserted into the two regions so that about five percent field change can be obtained.As a computed example a 40-50 kg Sm-Co PM-focusing system for an 8 mm band H02 mode gyromonotron operating at secondary harmonic of the cyclotron frequency is needed to obtain an intense magnetic field of 6500-7000 Gs. This is very atteractive for the development of 8 mm band gyrotrons and near-centimetre band ones. In the last part of the paper some problems such as the extension of the uniform region and increasing the efficiency of magnetic circuit are briefly discussed.
A new PM-focusing system with two regions of uniform magnetic field, suitable for gyrotron is proposed and studied with computer. In the calculation, a radial system made of Sm-Co magnets is used. The maximum magnetic energy-products (BH)max of the magnets are about 20MGOe. In order to adjust the magnitude of the magnetic field, some small coils are inserted into the two regions so that about five percent field change can be obtained.As a computed example a 40-50 kg Sm-Co PM-focusing system for an 8 mm band H02 mode gyromonotron operating at secondary harmonic of the cyclotron frequency is needed to obtain an intense magnetic field of 6500-7000 Gs. This is very atteractive for the development of 8 mm band gyrotrons and near-centimetre band ones. In the last part of the paper some problems such as the extension of the uniform region and increasing the efficiency of magnetic circuit are briefly discussed.
1984, 6(6): 495-502.
Abstract:
A method of measuring the pattern axis-ratio and the direction of an elliptieally polarized wave of UHF omnidirectional antenna on satellite is presented. The experimental results shows that the method is applicable.
A method of measuring the pattern axis-ratio and the direction of an elliptieally polarized wave of UHF omnidirectional antenna on satellite is presented. The experimental results shows that the method is applicable.
1984, 6(6): 503-504.
Abstract:
A grid control pulsed TWT with depressed collector and PPM focusing system is reported in this paper. It operates at X-band and delivers peak output power of 1 kW with saturation gain of 47 dB. The duty cycle is 3%. The electron beam transmission is 95% with RF output at saturated condition. The efficiency is not less than 30% (excluding the heater power).
A grid control pulsed TWT with depressed collector and PPM focusing system is reported in this paper. It operates at X-band and delivers peak output power of 1 kW with saturation gain of 47 dB. The duty cycle is 3%. The electron beam transmission is 95% with RF output at saturated condition. The efficiency is not less than 30% (excluding the heater power).
