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Antenna pattern measurements are dominantly influenced by the presence of extraneous fields in the test zone. A fast and simple way to recognize problems in pattern measurements provides the Antenna Pattern Comparison-technique (APC). This method usually consists of recording azimuthal patterns on different positions across the test zone. Differences in the amplitude data give a rough indication for the magnitude of the interfering signal. The "Novel APC-method" (NAPC) employs both amplitude- and phase-data so that it becomes possible to separate the direct and the extraneous signals from each other. It will be shown that this method is eminently suited to correct radiation patterns of high-gain and low-sidelobe antennas. For verification purposes corrected patterns are compared with time-dated ones and the resemblance is excellent. It is concluded that the NAPC-method is promising and powerful technique for accurate antenna pattern determination, mainly because it can be easily implemented for most applications.
S. Ohmori (Ministry of Posts and Telecommunications),H. Wakana (Ministry of Posts and Telecommunications), November 1992
A phased array antenna has been considered the favorite candidate and been developed for land mobile satellite communications. However, in communication experiments, a noise level in a receiving frequency band is found to be increased when a signal is transmitted. The amount of noise increase is found to depend on a scanning angle in azimuth directions to track the satellite, and the value is up to 20 dB in maximum and 5 dB in minimum. The noise increase was found to be caused by an nonlinear (sic) effect of a PIN diode, which are essentially used in phased array antennas.
S. Christopher (Electronics & Radar Development Establishment),A. Kaul (Electronics & Radar Development Establishment),
K.M. Balakrishnan (Electronics & Radar Development Establishment),
M.S. Easwaran (Electronics & Radar Development Establishment),
S.S. Rao (Electronics & Radar Development Establishment), November 1992
Despite their high cost, phased array antennas are becoming popular for radar applications because of their ability to provide reliable information even in a hostile environment. Evaluation of these antennas requires parameters like gain, radiation pattern, beam width, sidelobe (both near and far off) azimuth and elevation null depth, etc. to be tested over the entire range of frequency spots and scan angles. Typically, if the number of frequency spots are 24 and the number of beam positions for which the measurement has to be done are about 100, then the total number of measurements needed to generate the required data are 7200. In addition, phased arrays with a space feed have to be initially collimated at all the spot frequencies. The outdoor testing of these many parameters may not be convenient, and at times it may even be impossible. The planar near field measurement technique provides a systematic and accurate method of measuring large array antennas for all the required parameters.
M.H. Francis (National Institute of Standards and Technology),A. Repjar (National Institute of Standards and Technology),
D. Kremer (National Institute of Standards and Technology), November 1992
The National Institute of Standards and Technology (NIST) has written a certification plan to ensure that a proposed planar near-field facility is capable of measuring high-performance phased arrays. Generally for a complete plan, one must evaluate many aspects including scanner alignment, near-field probe alignment, alignment of the antenna under test, RF crosstalk, probe position errors RF path variations, the receiver's dynamic range and linearity, leakage, probe-antenna multiple reflections, truncation effects, aliasing, system drift, room multipath, insertion loss measurements, noise, and software verification. In this paper, we discuss some of the important aspects of the certification plan specifically written for the measurement of high-performance phased-array antennas. Further, we show how the requirements of each aspect depend on the measurement accuracies needed to verify the performance array under test.
J.H. Pape (Scientific-Atlanta, Inc.),A.L. Wilcox (Scientific-Atlanta, Inc.),
J.D. Huff (Scientific-Atlanta, Inc.), November 1992
Planar Near-Field scanning is becoming the method of choice for testing many types of antennas. These antennas include planar phased arrays, space deployable satellite antennas and other antennas either too large to move during the test or otherwise sensitive to the gravity vector. The planar scanner is a major component of the measurement system and must provide an accurate and stable platform for moving the RF probe across the test antenna's aperture.
This paper describes basic design requirements for a planar near-field scanner. Based on recent development activity at Scientific-Atlanta several design considerations are presented. Scanner parameters discussed include basic scanner concepts and geometry, scanner accuracy and stability, RF system including cabling and accuracy, load carrying requirements of the RF probe carriage, position and readout systems and drive and control systems. A scanner will be presented which incorporates many of the design features discussed.
C.B. Brechin (Scientific-Atlanta, Inc.),R. Kaffezakis (Scientific-Atlanta, Inc.), November 1992
This paper describes a novel planar near-field measurement system designed to test a beam-steered flat face phased array antenna. This system is unique in its ability to measure multiple beams during a single scan of the aperture. The system utilizes a very fast planar scanner with six foot by six foot of travel combined with fast beam-steering commands to significantly reduce the test time of multiple-beam phased array antennas. These features combined with software based on algorithms developed by the National Institute of Standards and Technology provide state of the art measurements of planar phased array antennas.
Rapid data acquisition is crucial in making comprehensive near-field scanning tests of electronically-steered phased array antennas. Multiplexed data sets can now be acquired very rapidly with high speed automatic data acquisition. To obtain high speed without giving up accuracy in probe position a feature termed subinterval triggering has been devised. To obtain simultaneously reliable thermal drift or tie scan data a feature termed block tie scans has been devised. This paper describes these two features that yield speed and accuracy in planar near-field scanning measurements.
O.M. Caldwell (Scientific-Atlanta Inc.), November 1991
An assessment of instrumentation error sources and their respective contributions to overall accuracy is essential for optimizing an electromagnetic field measurement system.
This study quantifies the effects of measurement receiver signal processing and the relationship to its transient response when performing measurements on rapidly varying input signals. These signals can be encountered from electronically steered phased arrays, from switched front end receive RF multiplexers, from rapid mechanical scanning, or from dual polarization switched source antennas.
Numerical error models are presented with examples of accuracy degradation versus input signal dynamics and the type of receiver IF processing system that is used. Simulations of far field data show the effects on amplitude patterns for differing rate of change input conditions. Criteria are suggested which can establish a figure of merit for receivers measuring input signals with large time rates of change.
A. Repjar (National Institute of Standards and Technology),D. Kremer (National Institute of Standards and Technology),
J. Guerrieri (National Institute of Standards and Technology),
N. Canales (National Institute of Standards and Technology), November 1991
The Antenna Metrology Group of the National Institute of Standards and Technology (NIST) has recently developed and implemented measurement procedures to diagnose faults on a flat phased-array antenna. First, the antenna was measured on the NISTplanar near-field (PNF) range, taking measurements on a plane where the multiple reflections between the probe and the antenna under test are minimized. This is important since the PNF method does not directly allow for these reflections. Then, the NIST PNF software which incorporates the fast Fourier transform (FFT) was used to determine the antenna’s gain and pattern and to evaluate the antenna’s performance. Next, the inverse FFT was used to calculate the fields at the aperture lane. By using this technique, errors in the aperture fields due to multiple reflections can be avoided. By analyzing this aperture plane data through the use of detailed amplitude and phase contour plots, faults in the antenna were located and corrected. The PNF theory and utilization of the inverse FFT will briefly be discussed and results shown.
P.R. Franchi (Rome Laboratory),H. Tobin (Rome Laboratory), November 1991
Problems exist with the measurement of large aperture antennas due to the far field requirement. This paper discussed a new method to measure a phased array at about 1/10 the normal far field. The basic idea involves focusing the test array at probe antenna a distance R away from the aperture. In the described measurement technique the probe antenna is placed on an arm that rotates 100º on the focal arc given by Rcos(?). This arc minimizes defocusing due to phase aberrations. To minimize the amplitude errors, the pattern of the probe antenna is carefully matched in order to compensate for the 1/R variation induced amplitude error. The application of this technique will enable arrays to be measured in anechoic chambers, allowing convenient classified testing, while avoiding the effects of weather, and will reduce the risks inherent in the high power testing on transmit. The results of a computer simulation is presented that characterizes the validity and limitations of the technique.
H.M. Aumann (Massachusetts Institute of Technology),F.G. Willwerth (Massachusetts Institute of Technology), November 1991
Beamspace techniques are usually employed to synthesize phased array antenna patterns of arbitrary shape. In this paper a beamspace method is used to calibrate the pattern of a 32-element linear array with a conventional array taper.
By measuring the antenna pattern in specific directions the beamspace technique permits the actually applied excitation function to be determined with little mathematical effort. Iterative corrections can then be made to the excitation function to maintain low sidelobe performance, or to compensate for element failures. Since local corrections to the array pattern result in global changes to the excitation function, explicit knowledge of where an element failure has occurred is not required.
The beamspace analysis was carried out using antenna patterns obtained by electronically scanning the array past a far-field source. Such pattern measurements offer the possibility of maintaining phased array performance in an operational environment.
L.D. Poles (Rome Laboratory),E. Martin (Rome Laboratory),
J. Kenney (Rome Laboratory), November 1991
Transmit – receive modules (T/R) utilizing GaAs monolithic microwave integrated circuit (MMIC) technology for amplifiers, attenuators, and phase shifters are becoming integral components for a new generation of radars. These components, when used in the aperture of a low sidelobe electronically steerable antennas, require careful alignment and calibration at multiple stages along the RF signal path. This paper describes the calibration technique used to measure the performance of an active aperture 64 element S-band phased array antenna that employs T/R modules at every element. RF component performance and phased array sidelobe characeristics are presented and discussed.
R.P. Heon (Texas Instruments),S. Sanzgiri (Texas Instruments), November 1990
The end-to-end G/T performance of an antenna system has typically been measured using celestial bodies. The technique requires high G/T performance ( 10 dB/K) to obtain accuracies of 0.5 dB. In addition, the measurement is dependent on several atmospheric and environmental conditions. This paper describes a technique for measuring the G/T performance of a low directivity, wide beamwidth antenna. The discussion details the measurements, extrapolation technique to demonstrate performance at specified atmospheric conditions, measurement uncertainties, and test results.
This new G/T measurement technique offers advantages over the existing technologies. Measurements are limited to the output port of the antenna so as to include all interactions between components within the system. This allows for accurate characterization of phased array performances. In addition, testing can be performed on indoor antenna ranges under environmentally controlled conditions.
D. Garneski (Hughes Aircraft Company, Radar Systems Group), November 1990
A new implementation of the planar near-field back projection technique for phased array testing and aperture imaging is described. In the alignment of phased arrays, the aperture field is treated as a continuous distribution rather than using idealized array concepts. The continuous field is then sampled to obtain element excitations. In this way, nonrectangular arrays can easily be accommodated. The method also produces highly interpolated images of apertures that can offer much insight into their nature. Also, any polarization of the aperture field may be obtained if the probe pattern has been characterized. The technique uses large FFTs which are computed very quickly by a workstation located in the facility. Results from an iterative phase alignment of a 12x18 phased array are presented, as well as highly interpolated images of apertures and results which demonstrate the polarization selection.
H.M. Aumann (Massachusetts Institute of Technology),F.G. Willwerth (Massachusetts Institute of Technology), November 1990
A technique for aligning a phased array is described. Array element attenuation and phase commands are derived from far-field patterns measured without calibrations. The technique is based on iteratively forming mulls in the antenna pattern in the directions specified by a uniform array illumination. It may be applied in situations where array elements are not individually accessible, or where an array contains no build-in calibration capacity.
The alignment technique was evaluated on a far-field range with a linear, 32-element array operating at L-band. The array containing transmit/receive modules with 12-bit amplitude and phase control. Insertion attenuation and phase measurements were comparable to those obtained by conventional techniques. However, the alignment procedure tends to compensate for the effects of nonuniform element patterns and range multipath. Thus, when used to implement other excitation functions, the array sidelobe performance with adaptive calibrations was substantially better.
J.H. Acoraci (Allied-Signal Aerospace Company), November 1990
Electronically scanned phased array antennas typically have a large number of beam positions. Accurate on-line monitoring of phased array beam positions can be used to ensure proper antenna and total system performance. Bendix has developed and successfully implemented a beam-position monitoring technique designated the “RF Integral Monitor System”. Use of this on-line technique does not interfere with normal system operation and yields results that are comparable to results obtained on an actual far field antenna range. The RF Integral Monitor technique and specific hardware implementations, for both linear and circular electronically scanned phased arrays, will be described in this paper.
M. Johansson (Ericsson Radar Electronics AB, Antenna Systems),B. Svensson (Ericsson Radar Electronics AB, Antenna Systems), November 1990
A method for obtaining the individual element excitations of an array antenna from measured radiation patterns is presented. Applications include element failure diagnosis, phased array antenna calibration, and pattern extrapolation.
The measured far-field information is restricted to visible space which does not always contain the entire Fourier domain. A typical example is phased array antennas designed for large scan angles. A similar problem arises during near-field testing of planar antennas in which case the significant far-field domain is restricted by the scanning limitations of the near-field test facility. An iterative procedure is then used which is found to converge to the required solution.
The validity of the approach has been checked both using the theoretical radiation patterns and real test cases. Good results have been obtained.
A.J. Fenn (Massachusetts Institute of Technology), November 1990
Airborne or spaceborne radar systems often require adaptive suppression of interference and clutter. Before the deployment of this adaptive radar, tests must verify how well the system detects targets and suppresses clutter and jammer signals. This paper discusses a recently developed focused near-field testing technique that is suitable for implementation in an anechoic chamber. With this technique, phased-array near-field focusing provides far-field equivalent performance at a range distance of one aperture diameter from the adaptive antenna under test. The performance of a sidelobe-canceller adaptive phased array antenna operating in the presence of near-field clutter and jamming is theoretically investigated. Numerical simulations indicate that near-field and far-field testing can be equivalent.
M. O'Brien (Loran Randtron Systems),R. Magatagen (Loran Randtron Systems), November 1989
This paper describes the techniques applied to a fully automatic computer controlled, HP8510 based, range gated digital data acquisition system used to provide scale modeled large aperture synthesis, evaluation of aircraft blockage effects, array patterns, element cancellation ratios, as well as providing a large accurate data base for radar simulation exercises.
H.M. Aumann (Massachusetts Institute of Technology),F.G. Willwerth (Massachusetts Institute of Technology), November 1989
Performance verification of an adaptive array requires direct, real-time sampling of the antenna pattern. For a space-qualified array, measurements on a far-field range are impractical. A compact range offers a protected environment, but lacks a sufficiently wide field of view. Conventional near-field measurements can provide antenna patterns only indirectly.
This paper shows how far-field antenna patterns can be obtained in a relatively small anechoic chamber by focusing a phased array in the near-field. The focusing technique is based on matching the nulls of far-field and near-field antenna patterns, and is applicable to conformal or nonuniform phased arrays containing active radiating elements with independent amplitude and phase control.
The focusing technique was experimentally verified using a 32-element, linear, L-band array. Conventionally measured far-field and near-field patterns were compared with focused near-field patterns. Very good agreement in sidelobe levels and beamwidths was achieved.
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