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Prony's method has been found useful in extracting the time domain response over extended time using data samples of limited time span. This paper describes results of studies underway to apply Prony's method to extracting the RCS time and frequency response from limited measured and computed data. The technique has been applied to characterize the RCS response of structures with inherent multiple resonances, e.g., a dielectric cube constructed using high-permittivity dielectric material. Implications of the technique to gated antenna and RCS measurements are discussed.
Prony's method has been found useful in extracting the time domain response over extended time using data samples of limited time span. This paper describes results of studies underway to apply Prony's method to extracting the RCS time and frequency response from limited measured and computed data. The technique has been applied to characterize the RCS response of structures with inherent multiple resonances, e.g., a dielectric cube constructed using high-permittivity dielectric material. Implications of the technique to gated antenna and RCS measurements are discussed.
A technique is presented for synthesizing a uniform plane wave at Fresnel zone distances. The method attempts to bridge the gap between compact range techniques and far field techniques, in the sense that one may potentially perform antenna or scattering measurements when a compact range reflector is electrically too small and the available far field range length is also too small. Similar to a far-field range, the distance to the test zone region generally varies with the side D of the test item and the frequency of operation being proportional to D2/X. Similar to a compact range, the test zone is confined to a localized region, and the quality of the test zone field does not improve with distance as it does for a far field range. The method is implemented by compensating the phase taper associated with a single radiator by employing a uniformly excited, concentric ring array. The quality and transverse extent of the test zone fields may be adjusted by varying the relative amplitude and phase excitation of the array. Syntheses of a test zone region characterized by a 1 dB amplitude ripple over 70% of the disk defined by the projected ring aperture is demonstrated.
A technique is presented for synthesizing a uniform plane wave at Fresnel zone distances. The method attempts to bridge the gap between compact range techniques and far field techniques, in the sense that one may potentially perform antenna or scattering measurements when a compact range reflector is electrically too small and the available far field range length is also too small. Similar to a far-field range, the distance to the test zone region generally varies with the side D of the test item and the frequency of operation being proportional to D2/X. Similar to a compact range, the test zone is confined to a localized region, and the quality of the test zone field does not improve with distance as it does for a far field range. The method is implemented by compensating the phase taper associated with a single radiator by employing a uniformly excited, concentric ring array. The quality and transverse extent of the test zone fields may be adjusted by varying the relative amplitude and phase excitation of the array. Syntheses of a test zone region characterized by a 1 dB amplitude ripple over 70% of the disk defined by the projected ring aperture is demonstrated.
The antenna analyzer is specifically designed to make use of measurement techniques that have been difficult to use until now The analyzer is an original vectorial receiver design, based upon the analysis of one of the sidebands of the marked RF measurement signal. Thanks to the RF marking process, the antenna analyzer is not the only equipment that allows characterization (in amplitude, phase or return loss) of all devices in a transmitting chain, including the high power elements, without cutting off the transmission. Originally introduced for the analysis of wired antennas in UHF-VHF bands, its use is now extended to microwave antenna measurements, especially printed circuit antennas. A special characteristic of the new analyzer, ESTAR 2110 is its capacity to measure the phase of RF signal with power levels as low as -120dBm. The analyzer is ideal for elaborate analysis of fundamental antenna parameters such as RF current distribution, close field, antenna pattern, impedance and phase balance of antenna network. The paper describes the marking principle and its use in making antenna parameter measurements.
The antenna analyzer is specifically designed to make use of measurement techniques that have been difficult to use until now The analyzer is an original vectorial receiver design, based upon the analysis of one of the sidebands of the marked RF measurement signal. Thanks to the RF marking process, the antenna analyzer is not the only equipment that allows characterization (in amplitude, phase or return loss) of all devices in a transmitting chain, including the high power elements, without cutting off the transmission. Originally introduced for the analysis of wired antennas in UHF-VHF bands, its use is now extended to microwave antenna measurements, especially printed circuit antennas. A special characteristic of the new analyzer, ESTAR 2110 is its capacity to measure the phase of RF signal with power levels as low as -120dBm. The analyzer is ideal for elaborate analysis of fundamental antenna parameters such as RF current distribution, close field, antenna pattern, impedance and phase balance of antenna network. The paper describes the marking principle and its use in making antenna parameter measurements.
The Precision Airborne Measurement System (PAMS) is a flight test facility at Rome Laboratory which is designed to measure in-flight aircraft antenna patterns. A capability which provides antenna pattern measurements for multiple VHF and UHF antennas, at multiple frequencies, in a single flight, has recently been demonstrated. A unique half space VHF/UHF long periodic antenna is used as a ground receive antenna. Computerized airborne and ground instrumentation are used to provide the multiplexing capability. The new capability greatly reduces time and cost of flight testing. The design, construction, and calibration of the half-space log-periodic ground receiving antenna is discussed and the ground and airborne segments of the instrumentation are described.
The Precision Airborne Measurement System (PAMS) is a flight test facility at Rome Laboratory which is designed to measure in-flight aircraft antenna patterns. A capability which provides antenna pattern measurements for multiple VHF and UHF antennas, at multiple frequencies, in a single flight, has recently been demonstrated. A unique half space VHF/UHF long periodic antenna is used as a ground receive antenna. Computerized airborne and ground instrumentation are used to provide the multiplexing capability. The new capability greatly reduces time and cost of flight testing. The design, construction, and calibration of the half-space log-periodic ground receiving antenna is discussed and the ground and airborne segments of the instrumentation are described.
The field present in the test zone of an antenna measurement range can be calculated from the range field measured on a spherical surface containing the test zone. Calculated test zone fields are accurate only within a spherical volume concentric to the measurement surface. This paper presents a technique for determining the probing radius necessary to create a volume of accuracy containing the test zone of the range. The volume of accuracy radium limit is caused by the spherical mode filtering property of the displaced probe. This property is demonstrated in the paper using measured field data for probes of differing displacement radii. This property is used to determine the volume of accuracy radium from the probing radius. This is demonstrated using measured far-field range data.
The field present in the test zone of an antenna measurement range can be calculated from the range field measured on a spherical surface containing the test zone. Calculated test zone fields are accurate only within a spherical volume concentric to the measurement surface. This paper presents a technique for determining the probing radius necessary to create a volume of accuracy containing the test zone of the range. The volume of accuracy radium limit is caused by the spherical mode filtering property of the displaced probe. This property is demonstrated in the paper using measured field data for probes of differing displacement radii. This property is used to determine the volume of accuracy radium from the probing radius. This is demonstrated using measured far-field range data.
This paper considers an electromagnetic field simulation of an anechoic chamber with experimental verification. The simulation is a Geometric Optics (Ray Tracing) mathematical model of the direct path between two antennas and interfering scattering. There are two separate models due to the frequency dependent nature of the pyramidal radar absorbing material (RAM). The model for the frequency range of 30 to 500 MHz was used to characterize the specular scattering. The specular scattering was modeled as a lossy, tapered, TEM transmission line in an inhomogeneous anisotropic tensor material. The frequency range from 500 MHz to 18 GHz was characterized by dominant tip diffraction of RAM patches and the model made use of a Uniform Theory of Diffraction code for a dielectric corner. The measurements and simulations were based on an azimuthal cylindrical scan. Diagnostic measurements were also performed by a cylindrical scan of a directional horn antenna to locate scattering sources in the chamber. A cylindrical wave, modal expansion of the diagnostic data which included a one dimensional Fast Fourier Transform with Hankel function expansions.
This paper considers an electromagnetic field simulation of an anechoic chamber with experimental verification. The simulation is a Geometric Optics (Ray Tracing) mathematical model of the direct path between two antennas and interfering scattering. There are two separate models due to the frequency dependent nature of the pyramidal radar absorbing material (RAM). The model for the frequency range of 30 to 500 MHz was used to characterize the specular scattering. The specular scattering was modeled as a lossy, tapered, TEM transmission line in an inhomogeneous anisotropic tensor material. The frequency range from 500 MHz to 18 GHz was characterized by dominant tip diffraction of RAM patches and the model made use of a Uniform Theory of Diffraction code for a dielectric corner. The measurements and simulations were based on an azimuthal cylindrical scan. Diagnostic measurements were also performed by a cylindrical scan of a directional horn antenna to locate scattering sources in the chamber. A cylindrical wave, modal expansion of the diagnostic data which included a one dimensional Fast Fourier Transform with Hankel function expansions.
A technique for multipaction analysis based on finite element modeling of the electromagnetic fields within a device is demonstrated. A multipaction device is modeled with HFSS to determine the field solution for use in multipaction analysis. The resultant field magnitudes within the critical gap region were compared with the measured breakdown events for 4 different gap sizes of the device. The relationship between the scattering coefficient convergence and field solution convergence is examined, and some indicators of the latter are established. The correlation between the data and the predictions indicates that the technique represents s reasonable analytical tool for such analysis.
A technique for multipaction analysis based on finite element modeling of the electromagnetic fields within a device is demonstrated. A multipaction device is modeled with HFSS to determine the field solution for use in multipaction analysis. The resultant field magnitudes within the critical gap region were compared with the measured breakdown events for 4 different gap sizes of the device. The relationship between the scattering coefficient convergence and field solution convergence is examined, and some indicators of the latter are established. The correlation between the data and the predictions indicates that the technique represents s reasonable analytical tool for such analysis.
The interdependence of accuracy and speed should be considered when analyzing measurement requirements. Tradeoffs can be made to optimize the measurement when accuracy is of primary importance, or where speed is critical. Several different measurement modes of the HP 8530A Microwave Receiver are presented, each with different measurement speed and accuracy tradeoffs. Examples are given that illustrate which acquisition modes would be appropriate to optimize the acquisition speed and accuracy in a variety of applications
The interdependence of accuracy and speed should be considered when analyzing measurement requirements. Tradeoffs can be made to optimize the measurement when accuracy is of primary importance, or where speed is critical. Several different measurement modes of the HP 8530A Microwave Receiver are presented, each with different measurement speed and accuracy tradeoffs. Examples are given that illustrate which acquisition modes would be appropriate to optimize the acquisition speed and accuracy in a variety of applications
The Method of Cauchy has been used to extrapolate a desired parameter over a broad range of frequencies using some information about the parameter as a few frequency points. The approach is to assume that the parameter, as a function of frequency, is a ratio of two polynomials. The problem is to determine the order of the polynomials and the coefficients that define them. For theoretical extrapolation/interpolation the sampled values of the function and, optically, a few of its derivatives with respect to frequency have been used to reconstruct the function. This technique also incorporates the method of Total Least Squares to solve the resulting matrix equation.
The Method of Cauchy has been used to extrapolate a desired parameter over a broad range of frequencies using some information about the parameter as a few frequency points. The approach is to assume that the parameter, as a function of frequency, is a ratio of two polynomials. The problem is to determine the order of the polynomials and the coefficients that define them. For theoretical extrapolation/interpolation the sampled values of the function and, optically, a few of its derivatives with respect to frequency have been used to reconstruct the function. This technique also incorporates the method of Total Least Squares to solve the resulting matrix equation.
This presentation offers some examples of performance in accomplishing high volume testing under the rigorous technical constraints imposed by the satellite industry. As an example of a high speed system, the Scientific-Atlanta Model 2095 will be used to illustrate the capability offered by today's technology. This system has found applicatio0n in the facilities of five satellite manufacturers constructed within the past three years and is proven by its demonstrated application in satellite programs.
This presentation offers some examples of performance in accomplishing high volume testing under the rigorous technical constraints imposed by the satellite industry. As an example of a high speed system, the Scientific-Atlanta Model 2095 will be used to illustrate the capability offered by today's technology. This system has found applicatio0n in the facilities of five satellite manufacturers constructed within the past three years and is proven by its demonstrated application in satellite programs.