Image matching using Hough transforms
Image matching using Hough transforms is discussed. Known objects in imagery are used as input to the transforms which allow prediction of similar objects in the imagery.
Davis, L. S.↗
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Helicopter rotor loads using discretized matched asymptotic expansions
The numerical practicality of a matched asymptotic expansion approach for the computation of unsteady three dimensional airloads on a helicopter rotor was improved. This effort utilizes a discretized repesentation of the doublet strength distribution and helical streamlines to decrease the computational requirements of the original analysis. The continuous variation of the doublet strength was approximated by piecewise constant or piecewise quadratic distributions, and the helical trajectory of a fluid particle was approximated by connected straight line segments. As a direct result of these simplified representations the computational time required for the execution of a typical flight condition was reduced by an order of magnitude with respect to the requirements of the original analysis. Airloads which were computed using the discretized method for a two bladed model rotor and a full scale four bladed rotor are in close agreement with measured results and airloads from the original asymptotic analysis. For conditions characterized by significant rotor/wake interaction the piecewise constant representation requires a reduced azimuth spacing to maintain acceptable accuracy.
Pierce, G. A.↗
Design considerations for high-power VHF radar transceivers: Phase matching long coaxial cables using a cable radar
The Poker Flat 49.92-MHz MST radar uses 64 phase-controlled transmitters in individual shelters distributed throughout the antenna array. Phase control is accomplished by sampling the transmitted pulse at the directional coupler of each transmitter and sending the sample pulse back to a phase-control unit. This method requires phase matching 64 long (256 meter) coaxial cables (RG-213) to within several electrical degrees. Tests with a time domain reflectometer showed that attenuation of high frequency components in the long RG-213 cable rounded the leading edge of the reflected pulse so that the cables could only be measured to within 50 cm (about 45 deg at 49.92 MHz). Another measurement technique using a vector voltmeter to compare forward and reflected phase required a directional coupler with unattainable directivity. Several other techniques were also found lacking, primarily because of loss in the long RG-213 cables. At this point it was realized that what was needed was a simple version of the phase-coherent clear-air radar, i.e., a cable radar. The design and operation of this cable are described.
Johnson, P. E.↗
Longitudinal-mode control in integrated semiconductor laser phased arrays by phase velocity matching
The spectrum of semiconductor-laser arrays with separate contacts is investigated. It is demonstrated that the individual laser currents can be selected such that the array operates in a single longitudinal mode, in contrast to the multimode nature of its individual constituents. Moreover, it is possible to tune the lasing frequency by varying the laser currents. Wavelength tuning range of about 50 A, with tuning rate of about 5 A per milliampere, is demonstrated. It is suggested that these spectral features, characteristic of lasers which are coupled in parallel, result from the strong frequency dependence of their spatial mode pattern near the phase-matching frequency of their coupled waveguides.
Kapon, E.↗
The determination of physical and dynamical parameters of Pluto/Charon and binary asteroids by least-square formation of a matched filter for a time series of images. I - The operational theory
A theory is derived for the determination of the masses, radii, and orbital elements of the Pluto/Charon, or similar, system based on the prediction of an image distribution over space and time and its comparison with observation. The comparison may be ultimately through the theory of least squares or the application of a matched filter to the observations as a three-dimensional signal stream at an initial or intermediate state. The theory is an approximation correct to fifth order in the diameters of celestial bodies. The theory of astronomical seeing that is used is based on Kolmogorov turbulence in the long-exposure limit. The images must be photometric. Linear tracking errors that can be removed are preferable to either automatic or manual guiding, in the collection of candidate observations.
Wildey, R. L.↗
Compensation of reflector surface distortions using conjugate field matching
The feasibility of compensating for reflector surface distortions has been investigated. The performance characteristics (gain, sidelobe level, null location, beamwidth, etc.) of space communication reflector antenna systems degrade as the reflector surface distorts due to thermal effects from a varying solar flux. The technique reported here will maintain the design radiation performance independently of thermal effects on the reflector surface. With the advent of monolithic microwave integrated circuits (MMIC), a greater flexibility in array-fed reflector system design can be achieved. MMIC arrays provides independent control of amplitude and phase for each of many radiating elements of the feed array. The conjugate field matching technique provide a basis for obtaining the required element excitations under surface distortion for maintaining the design radiation performance. It is assumed that the surface characteristics (x, y, z, first derivatives, and second derivatives) under distortion are known.
Acosta, R. J.↗
Matched asymptotic expansions to similarity solutions of shock diffraction
Formal asymptotic expansions with differently scaled variables are matched to obtain a uniform approximation to the similarity solution of the shock-wedge diffraction problem.
Harabetian, E.↗
An E-plane analysis of aperture-matched horn antennas using the moment method and the uniform geometrical theory of diffraction
The moment method and the uniform geometrical theory of diffraction are utilized to obtain two separate solutions for the E-plane field pattern of an aperture-matched horn antenna. This particular horn antenna consists of a standard pyramidal horn with the following modifications: a rolled edge section attached to the aperture edges and a curved throat section. The resulting geometry provides significantly better performance in terms of the pattern, impedance, and frequency characteristics than normally obtainable. The moment method is used to calculate the E-plane pattern and BSWR of the antenna. However, at higher frequencies, large amounts of computation time are required. The uniform geometrical theory of diffraction provides a quick and efficient high frequency solution for the E-plane field pattern. In fact, the uniform geometrical theory of diffraction may be used to initially design the antenna; then, the moment method may be applied to fine tune the design. This procedure has been successfully applied to a compact range feed design.
Heedy, D. J.↗
An aperture-matched compact range feed horn design
The moment method and the uniform geometrical theory of diffraction are used to obtain two separate solutions for the E-plane far field pattern of an aperture-matched horn antenna. This particular horn antenna consists of a standard pyramidal horn with the following modifications: a rolled edge section attached to the aperture edges and a curved throat section. The resulting geometry provides significantly better performance in terms of the pattern, impedance, and frequency characteristics than normally obtainable. The moment method is used to calculate the E-plane pattern and voltage standing-wave ratio (VSWR) of the antenna. However, at higher frequencies, the moment method requires large amounts of computation time. On the other hand, the uniform geometrical theory of diffraction provides a quick and efficient high frequency solution for the E-plane field pattern. This procedure has been successfully applied to design a compact range feed horn.
Heedy, D. J.↗
Matching Network For Microwave Preamplifier
Stable operation and broadband, optimum noise performance achieved. Amplifier designed by new method of matching input impedance for optimum noise figure and stability. Output more nearly constant over wider frequency range.
Sifri, Jack D.↗
A comparison of the radiation tolerance characteristics of multijunction solar cells with series and voltage-matched configurations
The effect of series and voltage-matched configurations on the performance of multijunction solar cells in a radiation environment was investigated. It was found that the configuration of the multijunction solar cell can have a significant impact on its radiation tolerence characteristics.
Gee, J. M.↗
High effectiveness contour matching contact heat exchanger
There is a need in the art for a heat exchanger design having a flexible core providing contour matching capabilities, which compensates for manufacturing tolerance and distortion buildups, and which accordingly furnishes a relatively uniform thermal contact conductance between the core and external heat sources under essentially all operating conditions. The core of the heat exchanger comprises a top plate and a bottom plate, each having alternate rows of pins attached. Each of the pins fits into corresponding tight-fitting recesses in the opposite plate.
Blakely, Robert L.↗
Rapid code acquisition algorithms employing PN matched filters
The performance of four algorithms using pseudonoise matched filters (PNMFs), for direct-sequence spread-spectrum systems, is analyzed. They are: parallel search with fix dwell detector (PL-FDD), parallel search with sequential detector (PL-SD), parallel-serial search with fix dwell detector (PS-FDD), and parallel-serial search with sequential detector (PS-SD). The operation characteristic for each detector and the mean acquisition time for each algorithm are derived. All the algorithms are studied in conjunction with the noncoherent integration technique, which enables the system to operate in the presence of data modulation. Several previous proposals using PNMF are seen as special cases of the present algorithms.
Su, Yu T.↗
Three-dimensional atmospheric entry problem using method of matched asymptotic expansions
The analysis of a three-dimensional atmospheric entry problem using the method of matched asymptotic expansions is considered. A composite solution is formed in terms of an outer solution, an inner solution and a common solution. The outer solution is obtained from the gravitationally dominant region, whereas the aerodynamically dominant region contributes to the inner solution. The common solution accounts for the overlap between the outer and inner regions. In comparison to previous work, this simplified methodology yields explicit analytical expressions for various components of the composite solution without resorting to any type of transcendental equations to be solved only by numerical methods.
Naidu, D. S.↗
A comparison of the radiation tolerance characteristics of multijunction solar cells with series and voltage-matched configurations
The effect of series and voltage-matched configurations on the performance of multijunction solar cells in a radiation environment was investigated. It was found that the configuration of the multijunction solar cell can have a significant impact on its radiation tolerance characteristics.
Gee, James M.↗
Structural stereo matching of Laplacian-of-Gaussian contour segments for 3D perception
The stereo correspondence problem is solved using Laplacian-of-Gaussian zero-crossing contours as a source of primitives for structural stereopsis, as opposed to traditional point-based algorithms. Up to 74 percent matching of candidate zero crossing points are being achieved on 240 x 246 images at small scales and large ranges of disparity, without coarse-to-fine tracking and without precise knowledge of the epipolar geometry. This approach should prove particularly useful in recovering the epipolar geometry automatically for stereo pairs for which it is unavailable a priori. Such situations occur in the extraction of terrain models from stereo aerial photographs.
Boyer, K. L.↗
A moment method solution of a volume-surface integral equation using isoparametric elements and point matching
Three integral equations for TE (transverse electric) scattering by dielectric cylinders having large values of permittivity are examined. A moment-method solution of the volume-surface integral equation is developed employing isoparametric elements and point matching. The solution is shown to be more accurate and stable than the traditional solutions using pulse basis, particularly in the case of scatterers having large refractive indices.
Jin, Jian-Ming↗
Holographic matched filter for full-field in-line signal processing of optical-fiber sensor outputs
A holographic matched filter is used to measure the changes in the output of a dual-mode fiber undergoing axial strain. The hologram is formed by interfering collimated light from a single-mode reference fiber and an unstrained dual-mode sensor fiber on a small piece of holographic material. When the hologram is illuminated by the strained sensor fiber, the cross-correlation field comparing the dual-mode output and its previous state, as recorded in the hologram, is collected, focused into a pick-up fiber, and sent to a photodiode. This arrangement allows for a compact, in-line method for full-field processing of the strain-induced changes in phase and amplitude in the sensor fiber. Other uses of such fiber-based correlators are suggested.
Indebetouw, Guy↗