摘要 :
An experiment was designed to study the effects of material type and configuration on Optical Cross Section (OCS) and spectrum. The experiment was conducted at an Air Force Research Laboratory (AFRL) far-field imaging facility, us...
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An experiment was designed to study the effects of material type and configuration on Optical Cross Section (OCS) and spectrum. The experiment was conducted at an Air Force Research Laboratory (AFRL) far-field imaging facility, using different diffuse and specular materials and various configurations and/or combinations of each. It was hypothesized that the OCS of certain combinations of materials is dependent on the diffuseness or specularity of the materials used, but the spectrum is independent of these factors and does not change. The objective of the experiment is to capture both OCS and spectra of different material configurations using different combinations of diffuse and specular materials in the bistatic illumination condition. OCS was calculated relative to the scattering of a Spectralon material that was in the scene during all data collects. Results show the accuracy of the above hypothesis and other effects that material type and configuration have on OCS and spectra.
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The TSAR EM code has contained far-field projection algorithms for some time. One drawback to previous versions of TSAR has been the necessity to run the field advancement routines each and every time to generate far-field data. A...
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The TSAR EM code has contained far-field projection algorithms for some time. One drawback to previous versions of TSAR has been the necessity to run the field advancement routines each and every time to generate far-field data. A change has been made to TSAR to allow tangential fields on the projection surface to be saved to a file. These fields can then be used with a new postprocessor, POSTFAR, to produce far-field points at any desired location without re-running the field advancement portion of TSAR. This will save large amounts of time in producing far-field calculations and allow calculation of other test point locations. If the tangential field data is saved to an 8mm tape, these calculations may be made at a much later date.
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Project Linear Chair is examining methods of measuring the near field and far field magnetic, electric, and electro-magnetic signatures of various underwater platforms. Initial hydro-mechanical mooring approaches which have been p...
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Project Linear Chair is examining methods of measuring the near field and far field magnetic, electric, and electro-magnetic signatures of various underwater platforms. Initial hydro-mechanical mooring approaches which have been proposed to position the sensor strings are depicted for the near field system and for the far field system. A stringent requirements of any proposed mooring system is the movement of the attached sensors in response to ocean currents. A sensor watch circle of 3 ft. radius is a desired goal to achieve.
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The measurement of radiation patterns is time consuming and expensive. Therefore, a novel technique that reduces samples required to measure radiation patterns is proposed where random samples are taken to reconstruct 2-dimensiona...
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The measurement of radiation patterns is time consuming and expensive. Therefore, a novel technique that reduces samples required to measure radiation patterns is proposed where random samples are taken to reconstruct 2-dimensional (2-D) or 3-dimensional (3-D) far-field radiation patterns. The proposed technique uses a compressive sensing algorithm based on sparse representations of radiation patterns using the inverse Discrete Fourier Transform (DFT) and the inverse Discrete Cosine Transform (DCT). The algorithm was evaluated by using 3 antennas modeled with the high-frequency structural simulator (HFSS): a half-wave dipole, a Vivaldi, and a pyramidal horn. The 2-D radiation pattern was reconstructed for each antenna using less than 44% of the total number of measurements with low-root mean square error (RMSE). In addition, the proposed reconstruction algorithm was evaluated using measured data obtained in an anechoic chamber. The 3-D radiation patterns of a pyramidal horn antenna was reconstructed by using only 13% of the total number of measurements. By using the proposed approach for radiation pattern reconstruction, the time required to take measurements in an anechoic chamber can be reduced up to 87%, therefore ensuring a good reconstruction with very low-RMSE in the case of a directive antenna such as the pyramidal horn.
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A commercially-obtained CO2 continuous-wave (c.w.) laser was used as the infrared (I.R.) emitting component in the construction of a 10.6 micrometer Laser Transmissometer. This report describes the construction and establishes the...
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A commercially-obtained CO2 continuous-wave (c.w.) laser was used as the infrared (I.R.) emitting component in the construction of a 10.6 micrometer Laser Transmissometer. This report describes the construction and establishes the performance of the transmissometer. It was found that the laser would oscillate unpredictably between the lower-order transverse electro-magnetic modes, and it was therefore necessary to try to predict pseudo-stationary points in the far diffracted field. Australia. (rh)
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The theory for calculating the transient far-field response of an antenna from planar near-field data in either the time domain or the frequency domain has been developed. A double integral must be evaluated if the authors begin w...
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The theory for calculating the transient far-field response of an antenna from planar near-field data in either the time domain or the frequency domain has been developed. A double integral must be evaluated if the authors begin with time-domain data, but a triple integral must be evaluated if they begin with frequency-domain data. However, the frequency-domain integrals are in a form that is suitable for three-dimensional FFT. Two idealized examples are studied, and identical results are obtained starting with frequency-domain or time-domain data. The main practical difficulty in determining the transient response is the large number of near-field samples that are required. If data are taken at only a few near-field points, then the singularity expansion method (SEM) presents a possible method of determining the complex resonances of the antenna under test.
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Systems are described for measuring the far- and near-field radiation patterns from optical fibers. Parameters which affect measurement precision, accuracy, resolution, and signal-to-noise ratio are discussed. Measurements using r...
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Systems are described for measuring the far- and near-field radiation patterns from optical fibers. Parameters which affect measurement precision, accuracy, resolution, and signal-to-noise ratio are discussed. Measurements using radiation patterns are covered; this includes radiation angle (numerical aperture), attenuation using mode filters, index profile, core diameter, and mode volume transfer function. Experimental examples are given in many instances.
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A new procedure is presented to develop multi-variable model-based parameter estimation (MBPE) model to predict far field intensity of antenna. By performing MBPE model development procedure on a single variable at a time, the pre...
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A new procedure is presented to develop multi-variable model-based parameter estimation (MBPE) model to predict far field intensity of antenna. By performing MBPE model development procedure on a single variable at a time, the present method requires solution of smaller size matrices. The utility of the present method is demonstrated by determining far field intensity due to a dipole antenna over a frequency range of 100-1000 MHz and elevation angle range of 0-90 degrees.
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The behaviors of the near- and far-field two-lobe radiation patterns from a circular-core two-mode fiber are studied by using both the mode and Kirchhoff diffraction theories. The electric field outside the output endface of the f...
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The behaviors of the near- and far-field two-lobe radiation patterns from a circular-core two-mode fiber are studied by using both the mode and Kirchhoff diffraction theories. The electric field outside the output endface of the fiber is derived from the electric field distribution of the LP sub 01 and LP sub 11 modes at the fiber endface using the Kirchhoff diffraction formula. Different phenomena are studied by solving this expression numerically at near-and far-fields. The Gouy phase shifts are quantitatively evaluated at cross-sections of the near field. The results reveal the distortion and dislocation of the far-field two-lobe pattern induced by an inclination angle of the fiber endface.
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