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The backtransformation in (planar) Near Field processing is often claimed to be a very powerful tool for antenna diagnostics. Less known is a kind of defocusing effect which is introduced by the processing. Selecting the visible space in the Far-Field domain has a similar effect as a bandfilter in the frequency domain of an electric signal. In that analogous case it is better known that after the transform to the time domain, one has to deal with sin(x)/x behavior, limiting the resolution. The mathematics and convolution effects of both the onedimensional time-frequency transform as the two dimensional Near-Field Far-Field transform will be explained. Some measurement procedures are proposed, including S/N requirements. It turns out that the back transformation technique has some nasty properties which limit the use for alignment purposes. Some alternatives are discussed.
The backtransformation in (planar) Near Field processing is often claimed to be a very powerful tool for antenna diagnostics. Less known is a kind of defocusing effect which is introduced by the processing. Selecting the visible space in the Far-Field domain has a similar effect as a bandfilter in the frequency domain of an electric signal. In that analogous case it is better known that after the transform to the time domain, one has to deal with sin(x)/x behavior, limiting the resolution. The mathematics and convolution effects of both the onedimensional time-frequency transform as the two dimensional Near-Field Far-Field transform will be explained. Some measurement procedures are proposed, including S/N requirements. It turns out that the back transformation technique has some nasty properties which limit the use for alignment purposes. Some alternatives are discussed.
The Sirius 2 telcommunication satellite was build in France by Aerospatiale. As a subcontractor Saab Ericsson Space (SES) developed the telecommunication antenna for direct television broadcast. The satellite was successfully launched November 13, 1997. Three antennas were manufactured by SES: a quality model (QM), a flight model (FMl) and a flight spare (FM2). Each antennas consists of a 1.4 meter in diameter shaped main reflector fed by a shaped subreflector and a dual polarized feed horn. For the test of the antennas, spherical near-field antenna test ranges located at Ericsson Microwave System (EMW)/SES in Sweden and at the Technical University of Denmark (DTU) were used. Each of the three antennas was measured twice. Between the two measurements mechanical and thermal tests were performed. The paper presents the measurements on the satellite antennas together with a discussion of the advantages of using the spherical near-field technique for this type of measurements. Compared to a far-field range the advantages are evident: At both SES and DTU a measurement distance of ten and six meters respectively were used on the indoor ranges. On a far-field range a measurement distance in the excess of 250 meters must be applied. To decrease the measurement time the near fields were only measured in a certain region on the near field sphere. The influence of this truncation will be discussed. Coordinate systems for the antennas were defined using mirror cubes. The RF measurements as well as the optical measurements on the cubes were performed without dismounting the antenna from the antenna positioner. The radiation patterns are therefore precisely decined with respect to the coordinate systems of the cubes.
The Sirius 2 telcommunication satellite was build in France by Aerospatiale. As a subcontractor Saab Ericsson Space (SES) developed the telecommunication antenna for direct television broadcast. The satellite was successfully launched November 13, 1997. Three antennas were manufactured by SES: a quality model (QM), a flight model (FMl) and a flight spare (FM2). Each antennas consists of a 1.4 meter in diameter shaped main reflector fed by a shaped subreflector and a dual polarized feed horn. For the test of the antennas, spherical near-field antenna test ranges located at Ericsson Microwave System (EMW)/SES in Sweden and at the Technical University of Denmark (DTU) were used. Each of the three antennas was measured twice. Between the two measurements mechanical and thermal tests were performed. The paper presents the measurements on the satellite antennas together with a discussion of the advantages of using the spherical near-field technique for this type of measurements. Compared to a far-field range the advantages are evident: At both SES and DTU a measurement distance of ten and six meters respectively were used on the indoor ranges. On a far-field range a measurement distance in the excess of 250 meters must be applied. To decrease the measurement time the near fields were only measured in a certain region on the near field sphere. The influence of this truncation will be discussed. Coordinate systems for the antennas were defined using mirror cubes. The RF measurements as well as the optical measurements on the cubes were performed without dismounting the antenna from the antenna positioner. The radiation patterns are therefore precisely decined with respect to the coordinate systems of the cubes.
This paper describes a new multi-purpose planar & cylindrical near-field antenna test facility installed at the Royal Netherlands Navy (RNN). In this paper an overview is given of the initial list of requirements that was generated and the process of selecting the best type of measurement facility to address these. A description of the facility is given and an outline of the accuracy of the planar/cylindrical near-field scanner is presented. The paper contains details of the extensive validation program and measured data demonstrating the performance of the system.
Nearfield Systems, Inc. (NSI) has delivered the world's largest vertical near-field measurement system. With a 30m by 16m scan area and a frequency range of 1GHz to 50GHz, the system consists of a robotic scanner, laser optical position correction, computer and microwave subsystems. The scanner and microwave equipment are installed in an anechoic chamber 40m in length by 24m in width by 25m in height. The robotic scanner controls the probe positioning for the 33m by 16m vertical scanner using X, Y, Z and polarization axes. The optical measurement package precisely determines the X and Y axes position, alignment errors along the X and Y axes, and Z-planarity over the XY scan plane.
Hughes Space & Communications Group uses near field measurement systems for satellite antenna qualification tests on many of its commercial satellites. Hughes contracted with Nearfield Systems Inc. for delivery of several large horizontal planar near-field scanners for these tests. A 40' x 22' system was commissioned in early 1997 and has since been used for numerous commercial satellite tests. Prior to satellite antenna range testing, this range was characterized for gain measurements, co-polarized and cross-polarized pattern measurements, and measurement repeatability at C-band frequencies. This paper will highlight some of the findings from the characterization effort for this particular test facility.
We are developing a new indoor bistatic measurement technique for scale model targets. This procedure will collect far-field data at bistatic angles from 60° to nearly 180° and near-field data over a 10' high, 10' radius cylinder surrounding the target. A stationary parabolic reflector illuminates the target while a duplicate parabolic reflector, rotated to its bistatic position, acquires far-field data. The independent, concentrically mounted near-field scanner gathers comparison data. Most compact range reflectors employ shaped edges to avoid edge diffracted signals entering the measurement volume. We report results of using shaped absorber material over otherwise unmodified reflector edges to reduce diffraction. High-resolution 3D images of sample structures demonstrate the practicality of this approach.
Due to the high cost of constructing anechoic chamber, the multi-usage of a chamber in various applications is very effective in terms of cost as well as space. In this paper, we describe an anechoic chamber, currently used at SK Telecom in Korea. This is designed for the measurements of both far/near field antenna and EMC/EMI in the identical chamber. This anechoic chamber and measurement system support antenna test in the frequency range of 150 MHz to 40 GHz and satisfy the requirement of ANSI C63.4 and CISPR16.1for EMC/EMI. The near field measurement system supports planar, cylindrical and spherical methods to test various types of antennas. For the far field and EMC/EMI measurement, the planner near field scanner is hidden by movable absorber wall. The AUT positioner is foldable and can be stored under the chamber floor. Brief description of the chamber and the measurement system with measured results are also provided.
The maintenance, test and repair workload for the Air Force MSQ-118 satellite ground-based The current MSQ-118 work requires the support of four maintenance shops and a planar near-field certification range. About one dozen employees maintain and test 148 phased-array antennas, each containing thousands of components, including radio-frequency (RF) stripline and microelectronics circuitry. This paper will detail the planning and start of the relocation of the antenna repair and test facilities.
The DREO-DFL Antenna Research Lab (DDARLing), contains far-field and planar near-field antenna measurement ranges. Measurements can be made on both ranges from 1.0 to 62.5 GHz. In the early implementation stages of our antenna measurement ranges, most of our energy was absorbed in mastering the mechanics of the positioners and the intracies of the operation of the software, and addressing component failures. To make useful measurements, it is necessary to minimize system errors. Early experience and frustration has led us to the development of an ordered series of standardized procedures that are aimed at careful set-up, calibration, and operation of the ranges. Within these procedures, attention is paid to the identification and minimization of errors due to alignment, equipment calibration, linearity, leakage, multipath, and drift. Following a brief description of the two ranges in the DDARLing facility, the paper provides details of one of these procedures.
The objective of this study is to evaluate the measurement errors of a near-field range at in order to develop some techniques to minimize them. Measurements were performed on a standard gain horn as references. The methodology presented demonstrates that it is feasible to calculate the far-field radiation from near-field measurement with one deconvolution that will include all the errors introduced by the instrumentation
A general approach for phase-retrieval is discussed. The representation is based on an advanced non-redundant sampling representation and is able to explicitly take into account geometrical characteristics of the source, like the overall dimension and the general shape, as well as a priori inforn1ation on the near-field and far-field.
The Plume Measurement Facility is a new outdoor facility providing the capability to characterize tactical rocket motor plumes. Radar cross section of the plume is measured by both a near field and a far field radar. Infrared/ultraviolet/visible (IR/UVNIS) charac teristics are measured by numerous instruments recording spacial, temporal, and spectral data. All instrumentation is calibrated and adjusted to realtime standard day meteorological data and all data is recorded on a common synchronized time base.
A sampling strategy for array diagnosis is discussed. The proposed strategy is able to obtain a minimum (i.e. equal to the number of array elements), and optimum (i.e. working as well as a uniform l/2 sampling rate) number of measurements in a given region of a plane in front of the array.
In a recent article in the October 1996 Antennas and Propagation Society Magazine, Milligan discussed the sampling that is required to achieve a desired antenna pattern coverage using planar near-field scanning. To ensure that this region of coverage is not corrupted we must also consider the effects of aliasing. Aliasing will occur if the near-field sampling does not contain at least two samples per period for the fastest near field variation. As a result, the periodically continued patterns begin to overlap, and the measured pattern will be the complex sum of the overlapping patterns. We show that the relation between the near-field sampling and the maximum angle of coverage is more restrictive when we also require that the effect of aliasing be negligible. We give some examples to show the consequences of not following the more restrictive requirements.
A comparison of three near-field position error correction techniques has been performed on simulated near-field data. The purpose of this study was to evaluate the allowable positional tolerances required for planar near-field scanners. Simple k-correction, extended k-correction, and Taylor series correction were applied to computed near-field data contaminated with various kinds of errors, including position errors in one and three dimensions, and random electrical noise. Ideal and error contaminated near-field data were computed for small-size, mid-size, and large-size arrays. Probe position errors up to one-quarter wavelength in each axis and one wavelength in a single axis were used. Probe position error correction was performed using all three methods, and the results were evaluated
Coherent processing using measurements on two probe scan planes with different antenna under test (AUT)-to-probe separations reduces the effects of coupling between the AUT and the probe or, alternatively, reduces the effects of room scatter. The results of these doublet scans can be coherently combined to mitigate one or the other (but not both) of these error terms. For either case, the extraneous signals cancel when the far field patterns from the two planes are coherently combined. The new "quadrille" scan technique coherently combines four separate scan planes which will cancel in one set of pattern measurements both the AUT-probe coupling error and the room scatter error. If either the coupling or the room scatter is much larger than the other, the error reduction attained by the quadrille may not merit the additional measurement time; however if the two terms are comparable the quadrille may be needed to attain precise measurements.
Measuring an antenna in a planar near field range has become a common method for characterizing an antenna's radiation properties. Planar near-field measurements are best suited for narrow beam antennas, such as large parabolic reflectors. However, it is often necessary to also measure a standard gain horn (SGH) to obtain an accurate gain level reference and the measurement of an SGH in a planar near-field range is difficult because the SGH has a broad beam. The most significant error that typically occurs when measuring an SGH is the scan plane truncation effect. In this paper, a scan data window function is de veloped for reducing the scan plane truncation effect that occurs when measuring an SGH. Applying a window function to the scan data from a near-field measurement is not a new idea, but the particular development of the window function in this paper provides the necessary physical insight to easily choose the proper window function for any given SGH and measurement configuration. A summary of the theory behind this new scan data window function is presented along with various measurement examples.
The adoption of planar near-field scanning techniques by many industrial organisations to meet their measurement requirements for large, directive antennas has led to a significant demand for calibrated probes. To compensate for the effects of the probe used in near-field scanning measurements one requires an accurate knowledge of the gain, axial ratio, tilt and pattern. While NPL has been measuring the gain of microwave antenna standards for over seventeen years, it is only in the last two years that facilities and techniques have been developed to measure the polarisation parameters and pattern of probes. For the gain and polarisation, three antenna techniques are employed and both linearly and circularly polarised probes can be calibrated. Since calibration data is required at each frequency at which the planar scanner is to be operated, the measurement techniques and software have been developed to allow measurements to be performed at a large number of frequencies simultaneously. This reduces the turn round time, cost and the need for interpolation between measurement points.