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In recent years different techniques have been developed for measuring large aperture antennas on smaller ranges. Problems still exist with these techniques, though, such as impracticality and size restrictions. This paper presents a new method for measuring a phased-array antenna at approximately one tenth the far-field distance. This method involves focusing the test array to a probe a certain distance away, then moving the probe along an elliptical path. Since different elliptical paths can be easily generated with the same test hardware, this new method promises to yield a measurement technique that can be readily adapted to different sized antennas. This paper also presents the results of computer simulations showing the validity and limitations of this technique.
When the planar near-field method is used for antenna characterization, two probes are required to measure an antenna under test (AUT). The receiving patterns (both amplitude and phase) of these probes, obtained from planar near-field measurements, must be utilized to accurately determine the far field of the AUT. This process is commonly called planar near field probe correction. When the AUT is nominally circularly polarized (CP), the measurements are more accurate and efficient if nominally circularly-polarized probes are used. Further efficiency is obtained when only one probe which is dual-polarized is used to allow for simultaneous measurements of both components. However, when using dual-port CP probes to measure the antenna, we must apply the probe correction even for on-axis measurements.
A novel technique has been devised that permits a length of cable to be measured in place and its transfer characteristic monitored as motion occurs. The scheme is to measure the cable in transmission as a member of a pair and to infer the characteristic of the cable from a set of three pair-wise measurements, in analogy to the well-known three-antenna technique. From the resulting knowledge of the signal cable's characteristic one can correct the measured data to account for the changes in the cable through which the signal of interest was passed.
The three cable method for removing the amplitude and phase variations of microwave cables due to temperature change and movement can offer a substantial improvement in antenna measurement accuracy. Implementation details of the method are provided for a planar near-field range. Items specifically addressed are range configuration, hardware requirements, data collection methodology, identification and assessment of error sources, and data reduction requirements.
Near field measurement techniques have become popular now a days (sic) and they are preferred for many applications to the conventional testing. In particular, for testing large planar arrays with a variety of parameters to measure, planar near field technique proves to be useful. The design of the planar near field measurement system varies with the needs of the measurements. This flexibility makes it suitable for somespecial (sic) tests on array antennas. The important design parametersinclude (sic) the type of scan, positional error limit, receiver and source instabilities, cabling, etc. It discuss (sic) in detail the type of scanning when large number of parameters like sum, azimuth and elevation difference patterns of an array antenna for various scan positions are to be measured. This paper describes a planar field system of size 2.5X2.5 metres (sic) and discusses its design details and in particular the type of scanning and the methods of correcting instability of the entire system.
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.
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.
A dual-linearly polarized probe developed for use in planar near-field antenna measurements is described. This probe is based upon Scientific-Atlanta's Series 31 Orthomode Feeds originally developed for spherical near-field testing. The unique features of this probe include dual orthogonal linear ports, high polarization purity, excellent port-to-port isolation, an integrated coordinate system reference, APC-7 connectors, and a thin-wall horn aperture to minimize probe AUT interactions. The probe was calibrated at the National Institute of Standards and Technology (NIST) and the calibration data consisting of the probe's complete plane-wave spectrum receiving characteristic s'02(K) were imported directly into the Scientific-Atlanta Model 2095/PNF Microwave Measurement System. This paper describes the dual-ported probe and its application in a planar near-field range.
A series of measurements to validate the performance of a Planar Near-Field (PNF) Antenna Test Range located at the Satellite and Aerospace Systems Division at Spar Aerospace Limited were made by Scientific-Atlanta during the month of February 1992. These measurements were made as a part of a contract to provide Spar with a Model 2095 Microwave Measurement System with planar near-field software options and related instrumentation and hardware. The range validation consisted of a series of self-tests and far-field pattern comparison tests using a planar array antenna provided by Spar that had been independently calibrated at another range facility. This paper describes the range validation tests and presents some of the results. Comparisons of far-field patterns measured on the validation antenna at both the Spar PNF facility and another antenna range are presented.
A novel planar near-field antenna measurement and diagnostic system is described. This bi-polar near-field system offers a large scan plane size with reduced "real estate" requirements and a simple mechanical implementation resulting in a highly cost effective antenna measurement system. A brief description of the bi-polar near-field range and its associated data processing methods are given. Measured results are compared with those obtained on a far-field range and a plane rectangular planar near-field range. It is shown that the UCLA facility produces highly accurate results which rival those of modern production antenna measurement facilities. Holographic images produced from measured data are provided to demonstrate the diagnostic capabilities of the antenna range and to provide electromagnetic field visualization for educational purposes.
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.
Increasing demands on antenna design characteristics have led to corresponding increases in test requirements, particularly in the need for high speed multi-frequency or multi-beam measurements. Special steps are required in the data acquisition process to maintain synchronization of the data to insure accurate results are achieved. This paper will describe techniques used by NSI for a planar near-field measurement system using a Hewlett Packard 8530A with multiple frequencies and multiple beams acquired in the inner loop of the scan pattern.
This paper presents the feasability (sic) to explore the Focal Plane (FP) of a Compact Antenna Test Range (CATR). We first introduce the interest of getting very fast the Far Field Pattern of an antenna with a 2D modulated scattering array located at the focus of a CATR. Then, we discuss the geometric, electrical and optical constraints involved when using this technique. A comparison with a classical measurement performed at ESA-ESTEC is shown and we conclude by emphasizing the potentialities of this technique.
The idea of developing a large compact range with scanned quiet zone has been adopted by several international organizations (ESTEC, MBB, Ford Aerospace, etc.) and is expected to be an useful (sic) measurement tool. The Front-Fed Cassegrain configuration is likely to present good scanning capabilities due to its long equivalent focal length and the small curvature of both reflectors. However, some kind of degradation in the test zone is expected in the form of phase aberrations as a function of the lateral feed displacement and frequency, as well as an increase of the Xpolar level. In this paper, the phase aberration and the Xpolar component introduced by a non-centered Front-Fed Cassegrain configuration is analyzed in a GO-GO basis. It is found that the scanning concept can be applied up to a certain frequency limit in which a gradual reduction of the quiet zone dimensions is observed as the feed displacement (plane wave scanning angle) is increased.
A Planar Near Field to Far Field (PNF/FF) Transformation Program has been developed. This PNF/FF package includes probe correction, spectral filtering, position errors correction and sampled data expansion. In order to evaluate how measurement system errors affect PNF/FF transformation results, a whole set of simulation routines have also been implemented. In this paper, main modules of the PNF/FF package are discussed and error simulation models together with correction routines are described.
The measurements of an antenna at FM frequencies integrated in the bodywork of a terrestrial vehicle is a extremely (sic) delicated (sic) problem that will be larger if a ground plane must be simulated. An algorithm based on two measurements (magnitude and phase of the field components E() and E (1) on a scale model made in an anechoic chamber, has been developed to solve this problem. These measurements correspond to the value of the desired conical cut (only a narrow range of angles above the horizon is significant), and the associated cut needed to measure the specular reflection on the simulated ground plane.
A new near-field far-field transformation procedure, based on only amplitude measurement, is tested from both simulated and measured data. The measurements have been collected at Marconi Research Center and refers to a parabolic reflector working at 9 Ghz. This first experimental validation of the procedure fully support (sic) the feasibility of phaseless near field measurement in the antenna testing.
The measurement of modern low sidelobe antennas has brought a greater need for accurate site characterisation in order to quantify the effects of site scatterers. A multi-frequency Hankel function out-propagation technique is used to locate and identify site scatterers whose effects may degrade the patterns of antennas measured on the site.
The paper describes the high frequency measurements of the fields diffracted at the edges of an obstacle. The measurements are performed in an ordinary room, by using the time-domain filtering and frequency smoothing options of a vector network analyzer. The field distribution on a cylindrical arc is measured without the obstacle, and with the metallic obstacle present. The measurement approach in both cases proves to be rather different: without the obstacle, a modified calibration method should be used together with frequency smoothing, while in the presence of the obstacle, the same calibration set needs to be used in conjunction with time domain filtering. In the latter case, however, the use of frequency smoothing is not allowed. The results of the two measurements sessions can be condensed into one parametric curve expressing the additional attenuation of the radio signal, which is caused by the presence of the object on the propagation path. Practical and theoretical curves are compared for several object dimensions, and very good agreement is obtained in all cases.
The anechoic chamber housing the TUD-ESA Spherical Near Field Far Field Antenna Test Facility at the Technical University of Denmark dates back to 1967 while the present RF and data collection and control systems were designed and installed in several stages between 1978 and 1985. This paper undertakes to describe the definition and realization of a refurbished and upgraded radio anechoic facility for antenna measurements given as a starting point the already existing facility. In a parallel effort, both the RF and data collection and control subsystems are being renewed and upgraded.