AMTA Paper Archive

 

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The Effects of non-systematic instrumentation errors on measurement uncertainty
O.M. Caldwell (Scientific-Atlanta, Inc.), November 1990
The effects of non-systematic receiver instrumentation errors on precision antenna measurements are investigated. A simple uncertainty model relating dynamic range to random perturbation effects on amplitude measurements is proposed. Examples of measurement uncertainty versus both input level and measurement speed are presented using data taken on modern measurement receivers. Dara are compared with the model to estimate measurement uncertainty at various pattern levels and acquisition speeds. Equivalent dynamic range specifications are deduced from the measures data.
Global and local features of wideband RCS signatures
A. Bati (Pacific Missile Test Center),D. Mensa (Pacific Missile Test Center), R. Dezellem (Pacific Missile Test Center), November 1990
The utility of wideband RCS data for characterizing scattering mechanisms of complex objects has been established by wide-spread applications. The fundamental data from which the final products are derived consist of calibrated scattered fields measured coherently as a function of frequency and aspect angle. By processing these data, one-dimensional range or cross-range reflectivity profiles can be derived; by further processing, two-dimensional images can be derived. Modern RCS instrumentation systems capable of rapidly measuring and processing wideband data provide more object information than is conveyed by the RCS pattern, which has been the traditional descriptor of scattering behavior. The procedures of one- or two-dimensional imaging inherently involve integration processes, constituting many-to-one mappings in which data from a large set are collapsed to produce an individual pixel of the image. For example, a particular pixel of a range response is derived from the total object response “integrated” over a band of frequencies; similarly, a pixel of a two-dimensional image is derived from the object response “integrated” over frequency and angle. The exposure of a local feature of the object signature, obtained by collapsing the fundamental data, comes at the cost of obscuring the global descriptor. This paper explores techniques for presenting large amounts of information on single displays which retain both global and local features of the scattering process. These tools provide to the RCS analyst options for extracting and interpreting significant information from the measured data without arbitrary degrees of integration which can mask essential details represented in the data. The display methods utilize color coding to increase the amount of information conveyed by a single plot. Because color reproduction is not available for the proceedings, the paper is to be distributed at the conference.
An Economical system for RF antenna measurements
V. Autry (Hewlett-Packard Company),B. Coomes (Hewlett-Packard Company), November 1990
This paper examines antenna pattern measurements of RF frequency antennas (300 kHz-3 GHs) using an integrated source/receiver and measurement control software. Current microwave measurement systems provide sufficient measurement capability but are often too expensive to be used on ranges which require test frequencies of less than 3 GHz such as aircraft communications, cellular radio, GPS, and satellite telemetry antenna. Several system block diagrams based on the HP 8753 network analyzer will be examined with respect to system performance, measurement accuracy, and cost. System considerations for outdoor RF ranges such as RFI susceptibility will also be addressed.
A New implementation of the planar near-field back projection technique for phased array testing and aperture imaging
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.
Adaptive alignment of a phased array antenna
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.
New algorithms for enhancing the performance of near field techniques
O.M. Bucci (Universita’ di Napoli),G. D'Elia (Universita’ di Salerno), G. Leone (Universita’ di Salerno), R. Pierri (Universita’ di Napoli), T. Isernia (Universita’ di Napoli), November 1990
To enhance the performance of existing near field techniques the new idea of far field pattern determination from only amplitude distributions of the near field is proposed. In this way the difficulties related to phase measurements are overcome. Some different algorithms are introduced and discussed. In particular, after recalling results for the planar geometry, cylindrical scanning surfaces are considered. The feasibility and the performances of the introduced algorithms are shown through numerical examples.
Calibration techniques for compact antenna test ranges
J.A. Hammer (ESTEC), November 1990
The reflective properties of a flat circular plate and a long thin wire are discussed in connection with the quality and calibration of the quiet zone (QZ) of a compact antenna test range. (CATR). The flat plate has several applications in the CATR. The first is simple pattern analysis, which indicated errors as function of angle in the QZ, the second uses the plate as a standard gain device. The third application makes use of the narrow reflected beam of the plate to determine the direction of the incident field. The vertical wire has been used to calibrate the direction of the polarization vector. The setup of an optical reference with a theodolite and a porro prism in relation to the propagation direction of the incident field is presented as well.
Array antenna diagnosis and calibration
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.
Testing an active airborne phased-array military SATCOM antenna with ARAMIS
C. Renard (Dassault Electronique),G. Coutet (Dassault Electronique), G. Debain (Dassault Electronique), O. Silvy (Dassault Electronique), November 1990
The Dassault Electronique flexible near-field antenna test facility, ARAMIS, has been used for test and calibration of state-of-the-art active phased-array antennas which were designed for military SATCOM operation. The 14-month successful program dramatically emphasized the benefits of a flexible antenna test facility such as ARAMIS. These benefits are the following: • Flexibility o Far-field mode (test of radiating elements and modules) o Planar near-field mode (test of sub-arrays and complete antenna) o High-resolution field mapping mode o Array Element testing • Speed: quick mode switching, “on the fly” multiplexed acquisition • Versatility: calibration of a module, a sub-array and the antenna; radiation patterns; gain; faulty element detection • Productivity: a single indoor facility performing different types of measurements, integrated software Test results gathered during this program and showing the ARAMIS contribution are presented.
Evaluation of dual-port circularly polarized probes for planar near-field measurements
M.H. Francis (National Institute of Standards and Technology),K. MacReynolds (National Institute of Standards and Technology), November 1990
Accurate near-field cross-polarization measurements on circularly polarized (CP) antennas at millimeter-wave frequencies require well-characterized probes with low axial ratios. We have recently obtained and calibrated dual-port CP horns for use as near-field probes at frequencies of 40-50 GHz. These horns have axial ratios which are 0.3 dB or less over a 10% frequency bandwidth. With these good axial ratios the difference between vector and scalar probe correction is usually small. Additional advantages of the dual-port probes are the need for only a single alignment, more accurate knowledge of the relative phase between two ports of the same probe, and the ability to obtain both main and cross polarized data during one scan. The axial ratios of the dual port CP probes are also better than those of single-port CP Probes. In this paper we present some gain, axial ratio, and pattern measurements for these probes and show that they give accurate cross-polarization measurements.
A Spherical near field system with a scanning probe
S.S. Dhanjal (General Electric Company),M. Cuchanski (General Electric Company), November 1990
The near field technique has grown from experimental systems of the early 1960s to sophisticated accepted means of testing antennas. Several schemes have been employed, namely planar, cylindrical and spherical scanning. The spherical scanning system chosen for one of the near field ranges at GE Aerospace is different from most near field systems in that the test antenna remains stationary while the probe is made to scan over a surface of an imaginary sphere surrounding it. The sampled field is corrected for positional, phase and amplitude errors and transformed to the far field. Radiation patterns, gain, EIRP, group delay and amplitude response were measured for a shaped beam communications antenna.
The Effect of probe position errors on planar near-field measurements
J. Guerrieri (National Institute of Standards and Technology),S. Canales (National Institute of Standards and Technology), November 1990
Antenna engineers recognize that the planar near-field method for calibrating antennas provide accurate pattern and gain measurements. Bothe the pattern and gain measurements require some degree of probe position accuracy in order to achieve accurate results. This degree of accuracy increases for antennas that have structured near-field patterns. These are antennas in which the amplitude and phase change rapidly over a very small position change in the near-field scan plane. The National Institute of Standards and Technology (NIST) has recently measured an antenna with a very structured near-field pattern. This measurement was performed using a new probe positioning system developed at NIST. This measurement will be discussed and results will be presented showing how slight probe position errors alter the antenna pattern and gain.
Longitudinal translation at selected points - A measurement technique revisited
D.W. Hess (Scientific-Atlanta, Inc.), November 1990
The extraneous signals that perturb antenna patterns can be found and identified by a method known as “longitudinal translation at selected points”. The method is usually applied to certain selected angular points on the antenna pattern. With this technique the composite pattern – consisting of the direct-path signal and the reflection signal – is measured at a series of translation distances along the axis of the antenna range. By utilizing both the amplitude and phase of the received signal, one can remove the signal that results from stray reflection and retain the desired direct path signal. The result is an improved and more accurate version of the pattern. In this presentation I review this technique as specifically applied to compact range antenna measurements, and apply it to several patterns, to demonstrate the method.
Antenna range performance comparisons
E.H. England (Defense Research Agency),H. Hezewijk (TNO Labs) J. Bennett (University of Sheffield) N. Williams (ERA Technology Ltd.), November 1991
The radiation patterns of a low (40dB) sidelobe antenna have been measured on a variety of antenna test ranges including Near Field, Far Field and Compact versions. Originally intended to validate new Near Field Ranges, some of the early results will be presented and the variations examined. The need for some form of range validation is shown. There is also some explanation of the fundamental effects that various ranges have on results.
A Methodology for diagnostics and performance improvement for large reflector antennas using microwave holography
D.J. Rochblatt (California Institute of Technology), November 1991
Microwave holography has proven to be a powerful technique for various evaluations, diagnostics, and RF performance improvements for large reflector antennas. The technique utilizes the Fourier Transform relation between the complex far-field radiation pattern of an antenna and the complex aperture field distribution. Resulting aperture phase and amplitude distribution data can be used to precisely characterize various crucial performance parameters, including panel alignment, subreflector position, antenna aperture illumination, directivity at various frequencies, and gravity deformation effects. The methodology of the data processing presented in this paper was developed at JPL and has been successfully applied to the NASA/JPL Deep Space Network (DSN) 34m beam waveguide antennas. The performance improvement of the antenna was verified by efficiency measurements and additional holographic measurements. The antenna performance was improved at all operating frequencies of the antenna (wide bandwidth improvement) by reducing the main reflector “mechanical surface” rms error to 0.43 mm. At Ka-band (32-GHz) the estimated improvement is 4.1 dB, resulting in aperture efficiency of 52%.
Measurement techniques for cryogenic KA-band microstrip antennas
M.A. Richard (Case Western Reserve University),K.B. Bhasin (NASA Lewis Research Center) C. Gilbert (Ball Communications Systems Division) S. Metzler (Ball Communications Systems Division) P.C. Claspy (Case Western Reserve University), November 1991
The measurement of cryogenic antennas poses unique logistical problems since the antenna under test must be embedding in the cooling chamber. In this paper, a method of measuring the performance o cryogenic microstrip antennas using the closed cycle gas-cooled refrigerator in a far field range is described. Antenna patterns showing the performance of gold and superconducting Ka-band microstrip antennas at various temperatures are presented.
Ship mounted antenna measurements using GPS
Millington. T.A. (Southwest Research Institute),J.H. Nixon (Southwest Research Institute), R.W. Robinson (Southwest Research Institute), November 1991
Antenna amplitude and phase pattern measurements on combat ships and other large ships have typically relied on traditional methods which include circling a fixed buoy in the far field, tracking a shore-based transmitter with an optical device, or circling the subject ship with a smaller boat outfitted with a transmitter. These techniques required the measurement of many independent variables using less than precise methods to compute antenna patterns relative to the ship’s structure. Using the global positioning system to precisely locate the ship relative to the transmitter site location and combining this with the ship’s heading, antenna measurements can be accurately and quickly obtained. This paper will describe the traditional fixed buoy and optical follower techniques and contrast these against the more accurate and faster GPS antenna measurement technique.
Measurement receiver error analysis for rapidly varying input signals
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.
Calibration of large antenna measured in small quiet zone area
D-C. Chang (Chung Shan Institute of Science and Technology),M.R. Ho (Chung Shan Institute of Science and Technology), November 1991
Compact range systems have been widely used for antenna measurements. However, the amplitude taper can lead to significant measurement errors especially as the dimension of antenna is larger than quiet zone area. An amplitude taper removing technique by software implement is presented for compact range system. A 12 feet by 1.0 feet S-band rectangular slot array antenna is measured in SA5751 compact range system, which provides a quiet zone area with a 4 feet diameter. Results of corrected far-field patterns from compact range are compared with that taken by planar near-field range.
The Rafael radome measurement facility
A. Geva (RAFAEL),H. Katz (RAFAEL), M. Manela (RAFAEL), November 1991
The RAFAEL general purpose radome measurement range has been modernized and refurbished, maintaining its capability to accommodate all range of radome sizes up to 1.2 meters in diameter. It is based on a 3-axis positioner placed in an open anechoic chamber with a null seeker placed 20 meters away and about 10 meters above the ground. All the positioner’s axes are controlled by an automatic positioner controller. The receiver and source are based on a HP-8510B system. The X-Y null seeker serves for boresight error measurements. It has a 0.7m x 0.7m total motion span, which is about 2º. It is controlled by a dual-motor controller, so that the scanning antenna can be moved in any kind of motion. Instrumentation control and data acquisition and analysis is performed using a HP-330 UNIX controller. Present software handles monopulse antennas with or without a comparator, and can implement the comparator in software. There are two major measurement modes: One for BSE measurements and the other for radiation patterns.


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