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Far Field
G/T measurement of highly directive antenna systems
G.M. Briand (Harris Corporation), November 1984
A technique for improving the accuracy of G/T measurements of highly directive antennas is introduced. The technique presents was developed to overcome uncertainties in ephemeral information, antenna positioning, system gain stability, and other random and nonrandom phenomena. The particular application discussed uses Casseiopeia-A as a noise source but the technique can be adapted for use with other extraterrestrial noise sources.
A New antenna test facility at General Electric Space Systems Division in Valley Forge, PA.
R. Meier (General Electric Co.), November 1984
This paper describes the new antenna test facility under construction at General Electric Space Systems Division in Valley Forge, PA. The facility consists of a shielded anechoic chamber containing both a Compact Range and a Spherical Near-Field Range. In addition, it provides for a 700’ boresight range through an RF transparent window. The facility will be capable of testing antenna systems over a wide frequency range and will also accommodate an entire spacecraft for both system compatibility and antenna performance tests.
Cylindrical near field test facility for UHF Television Transmitting Antennas
J.A. Donovan (Harris Corporation),E.B. Joy (Georgia Institute of Technology), November 1984
This paper describes a horizontal, cylindrical surface, near-field measurement facility which was designed and constructed in 1984 and is used for the determination of far field patterns from near field measurement of UHF television transmitting antennas. The facility is also used in antenna production as a diagnostic and alignment tool.
Structural Design of a vertical antenna boresight 18.3- by 18.3-M planar near-field antenna measurement system
G. R. Sharp (NASA),P. A. Trimarchi (NASA) J.S. Wanhainen (NASA), November 1984
The near-field antenna testing technique is now an established testing approach. It is based on the work done over a twenty-year period by the National Bureau of Standards (Boulder, Colorado), The Georgia Institute of Technology and others. The near-field technique is used for large aperture, high frequency antennas where the antenna to probe separation necessary to test in the far-field of the antenna is prohibitively large.
Real time remote data gathering
D. Kadron (Westinghouse Electric Corporation), November 1984
The ability to gather real-time data from a remote site is of significant value in the far-field test of large scale non-reciprocal antenna arrays. With the advent of microprocessors, digitally controlled test equipment, and high speed data links, what was once impossible has not only become feasible but also economically realizable. This paper discusses the design of a remote data-gathering capability currently on-line at the Westinghouse Ridge Road Antenna Range. The system described is a computer-controlled phase and amplitude measuring technique remoted over a 1/3 mile range with a 56K baud fiber-optics data link. Considerations of system configuration, timing, protocol, error-detection and self-diagnostics are discussed.
Obtaining bistatic data utilizing a monostatic measurement system
P. Zuzolo (Fairchild Republic), November 1984
A monostatic radar measurement system at the U.S. Navy Pacific Missile Test Center (PACMISTESTCEN) located at Pt. Mugu, California was utilized to obtain incidence angle performance of radar absorbing structure (RAS) panels. The traditional methods of obtaining reflectivity data for absorptive materials over a range of incidence angles is a technique known as the NRL arch. Developed over 30 years ago by the U.S. Naval Research Laboratory, the technique utilizes moveable bistatic antennas on an arch equidistant from the test material panel in order to obtain incidence angle data.
Effects of the alignment errors on ahorn's crosspolar pattern measurements. Application to L-SAT propagation package antennas.
M. Calvo (Universidad Potitecnica de Madrid),J.L. Besada (Universidad Potitecnica de Madrid), November 1984
When low crosspolar pattern measurements are required, as in the case of the L-SAT Propagation Package Antennas (PPA) with less than -36 dB linear crosspolarization inside the coverage zone, the use of good polarization standards is mandatory (1). Those are usually electroformed pyramidal horns that produce crosspolar levels over the test zone well below the -60 dB level typically produced by the reflectivity of anechoic chambers. In this case the alignment errors (elevation, azimuth and roll as shown in fig. 1) can become important and its efects on measured patterns need to be well understood.
A Figure of merit for evaluating signal processing antennas
E. Jacobs (Aerospace Corporation), November 1984
In recent years a new class of reflector antennas utilizing array feeds has been receiving attention. An example of this type of antenna is a reflector utilizing a moveable array feed for beam steering. [1]-[3]. Due to the circuitry required to adjust the weights for the various feed array elements, an appreciable amount of loss can be introduced into the antenna system. One technique to overcome this possible deficiency is to place low noise amplifiers with sufficient gain to overcome the weighting function losses just after each of the feed elements. In the evaluation of signal processing antennas that employ amplifiers the standard antenna gain measurement will not be indicative of the antenna system’s performance. In fact, by only making a signal measurement, the antenna gain can be made any arbitrary value by changing the gains of the amplifiers used. In addition, the IEEE Standard Test Procedures for Antennas [4] does not cover the class of antennas where the amplifier becomes part of the antenna system. There exists a need to establish a standard of merit or worth for multi-element antenna systems that involve the use of amplifiers. This communication presents a proposed figure of merit for evaluating such antenna systems.
Fourth generation indoor range
K.S. Kelleher, November 1984
The measurement of microwave antennas indoors began with the advent of commercial absorbing material. The use of absorbers can be traced back to a 2 gHz material developed by the Dutch in the Thirties. During the Forties, considerable progress was made on absorbing materials, but even after World War II, security considerations limited the application. Some materials found use as indoor shields for antenna tests, but limited bandwidth limited the utility of these materials. When a broad band absorber was developed the antenna experts did not believe that this material would be made commercially because they presumed a limited market.
Using the HP 8510 network analyzer to measure the radiation patterm of a dipole antenna using time domain and gating to remove the effects of ground clutter
J. W. Boyles (Hewlett-Packard Company), November 1984
A classical problem encountered when measuring the far-field radiation pattern of an antenna in a medium-distance range is the degradation that occurs when undesirable reflections (from the ground or nearby objects) are present. To reduce this problem, the source and test antennas are often installed on towers to remove them from the reflective objects, RF absorptive materials are used to reduce the magnitude of the reflected signals, and often the reflective objects in the range are adjusted in order to null out the reflections and “clean up” the range. These solutions are often limited in their effectiveness and can be prohibitively expensive to implement.
Real time remote data gathering
D. Kadron (Westinghouse Electric Corporation), November 1984
The ability to gather real-time data from a remote site is of significant value in the far-field test of large scale non-reciprocal antenna arrays. With the advent of microprocessors, digitally controlled test equipment, and high speed data links, what was once impossible has not only become feasible but also economically realizable. This paper discusses the design of a remote data-gathering capability currently on-line at the Westinghouse Ridge Road Antenna Range. The system described is a computer-controlled phase and amplitude measuring technique remoted over a 1/3 mile range with a 56K baud fiber-optics data link. Considerations of system configuration, timing, protocol, error-detection and self-diagnostics are discussed.
Satellite near field test facility
R.D. Ward (Hughes Aircraft Company), November 1984
The paper describes a near field facility developed at Hughes Aircraft Space and Communications Group for the purpose of performing measurements on satellite antennas. The facility is designed for planar near field scanning with capability for adding cylindrical scanning. The facility has a scanner with a 21 foot square range and is capable of measuring large antennas with operating frequencies up to 15 GHZ. The measurement system is designed for testing multi-beam, multi-frequency antennas. Data collection, scan control and data analysis functions are all controlled by a single computer system. Growth plans include the addition of an array processor for the ability to perform Fast Fourier Transforms in near real time. Results for the antennas which have been measured will be shown along with far field range data for comparison.
Near field RCS measurements
E.B. Joy (Georgia Institute of Technology), November 1984
A planar surface, near-field measurement technique is presented for the near-field measurement of monostatic radar cross-section. The theory, system configuration and measurement procedure for this technique are presented. It is shown that the far field radar cross-section can be determined from the near field measurements. An associate near-field radar cross-section measurement technique is presented for the measurement of bistatic near field radar cross-section. The bistatic technique requires a plane wave illuminator in addition to the planar surface near field measurement system. A small compact range is used as the bistatic illuminator. Bistatic near-field measurements are presented for a simple target.
Software and hardware for spherical near-field measurement systems
D. W. Hess (Scientific-Atlanta, Inc.),C. Green (Scientific-Atlanta, Inc.), B. Melson (Scientific-Atlanta, Inc.), J. Proctor (Scientific-Atlanta, Inc.), J. Jones (Scientific-Atlanta, Inc.), November 1984
The following features have been added to the spherical near-field software set which is available for the Scientific-Atlanta 2022A Antenna Analyzer. Gain Comparison Measurement Probe Pattern Measurement and Correction Thermal Drift Correction Spherical Modal Coefficient Analysis Far-Field, Radiation Intensity, and Polarization Display The addition of the probe pattern correction permits antenna measurements to be made at range lengths down to within several wavelengths of touching. The addition of probe polarization measurement permits three antenna polarization measurements to be made and analyzed as well as two antenna polarization transfer measurements. Correction for phase and amplitude errors attributable to thermal drift is accomplished by the return-to-peak method. Reduction of antenna patterns to spherical modal coefficients is an essential feature of spherical near-field to far-field transforms and is offered as an augmentation to antenna design. Far field display features permit the far fields of antennas to be presented in both component and radiation intensity formats, in circular, linear and canted linear polarization components.
Software and hardware for spherical near-field measurement systems
D. W. Hess (Scientific-Atlanta, Inc.),C. Green (Scientific-Atlanta, Inc.), B. Melson (Scientific-Atlanta, Inc.), J. Proctor (Scientific-Atlanta, Inc.), J. Jones (Scientific-Atlanta, Inc.), November 1984
The following features have been added to the spherical near-field software set which is available for the Scientific-Atlanta 2022A Antenna Analyzer. Gain Comparison Measurement Probe Pattern Measurement and Correction Thermal Drift Correction Spherical Modal Coefficient Analysis Far-Field, Radiation Intensity, and Polarization Display The addition of the probe pattern correction permits antenna measurements to be made at range lengths down to within several wavelengths of touching. The addition of probe polarization measurement permits three antenna polarization measurements to be made and analyzed as well as two antenna polarization transfer measurements. Correction for phase and amplitude errors attributable to thermal drift is accomplished by the return-to-peak method. Reduction of antenna patterns to spherical modal coefficients is an essential feature of spherical near-field to far-field transforms and is offered as an augmentation to antenna design. Far field display features permit the far fields of antennas to be presented in both component and radiation intensity formats, in circular, linear and canted linear polarization components.
The Determination of near-field correction parameters for circularly polarized probes
A. C. Newell (Electromagnetic Fields Division),D. P. Kremer (Electromagnetic Fields Division), M.H. Francis (Electromagnetic Fields Division), November 1984
In order to accurately determine the far-field of an antenna from near-field measurements the receiving pattern of the probe must be known so that the probe correction can be performed. When the antenna to be tested is circularly polarized, the measurements are more accurate and efficient if circularly polarized probes are used. Further efficiency is obtained if one probe is dual polarized to allow for simultaneous measurements of both components. A procedure used by the National Bureau of Standards for determining the plane-wave receiving parameters of a dual-mode, circularly polarized probe is described herein. First, the on-axis gain of the probe is determined using the three antenna extrapolation technique. Second, the on-axis axial ratios and port-to-port comparison ratios are determined for both the probe and source antenna using a rotating linear horn. Far-field pattern measurements of both amplitude and phase are then made for both the main and cross components. In the computer processing of the data, the on-axis results are used to correct for the non-ideal source antenna polarization, scale the receiving coefficients, and correct for some measurement errors. The plane wave receiving parameters are determined at equally spaced intervals in k-space by interpolation of the corrected pattern data.
Using the HP 8510 network analyzer to measure the radiation patterm of a dipole antenna using time domain and gating to remove the effects of ground clutter
J. W. Boyles (Hewlett-Packard Company), November 1984
A classical problem encountered when measuring the far-field radiation pattern of an antenna in a medium-distance range is the degradation that occurs when undesirable reflections (from the ground or nearby objects) are present. To reduce this problem, the source and test antennas are often installed on towers to remove them from the reflective objects, RF absorptive materials are used to reduce the magnitude of the reflected signals, and often the reflective objects in the range are adjusted in order to null out the reflections and “clean up” the range. These solutions are often limited in their effectiveness and can be prohibitively expensive to implement.
The Coefficient file: a basic feature of spherical near-field software architecture
D.W. Hess (Scientific-Atlanta Inc.), November 1985
The matrix of scattering coefficients which describes the transfer of excitation between the port of an antenna and free space forms a fundamental description of that antenna. In carrying out the spherical near-field to far-field transforms for a probe-corrected measurement one is required to utilize the scattering coefficients of the probe antenna. An essential feature of any software system which supports probe-corrected measurements is the capability of analyzing and storing these coefficients.
Alternative sampling techniques for more efficient planar near-field measurements
L.E. Corey (Georgia Tech Research Institute),D.R. O'Neil (Georgia Tech Research Institute), November 1985
Two alternative sampling techniques for planar near-field measurements are discussed. The first technique reduces the number of data points taken by 50% by measuring the field and its differential in one direction at each point. The second technique samples the field on a hexagonal lattice and allows reduction in the number of samples taken by up to 25%. Far-field patterns for an X-band antenna calculated from these alternative near-field sampling schemes are presented and compared with the far-field patterns calculated using conventional planar near-field techniques.
Optimum near-field probing for improved low sidelobe measurement accuracy
J. Hoffman (Technology Service Corporation),K. Grimm (Technology Service Corporation), November 1985
A novel technique for improved accuracy of sidelobe measurement by planar near field probing has been developed and tested on the modified near field scanner at the National Bureau of Standards. The new technique relies on a scanning probe which radiates an azimuth plane null along the test antenna’s mainbeam steering direction. In this way, the probe acts as a mainbeam filter during probe correction processing, and allows the sidelobe space wavenumbers to establish the dynamic range of the near field measurement. In this way, measurement errors which usually increase with decreasing near field signal strength are minimized. The probe also discriminates against error field which have propagation components in the direction of mainbeam steering, such errors may be due to multipath or scanner Z-position tolerances. Near field probing tests will be described which demonstrate measurement accuracies from tests with two slotted waveguide arrays—the Ultralow Sidelobe Array (ULSA) and the Airborne Warning and Control System (AWACS) array. Results show that induced near field measurement error will generate detectable far field sidelobe errors, within established bounds, at the –60dB level. The utility of te probe to detect low level radar target scattering will also be described.


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