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This paper describes the nature of the errors introduced by amplitude and phase corruptions in the detection process of a classical quadrature mixer and a means for on-line hardware correction of those errors. The discussion defines the nature of the signal corruption produced by first order circularity errors, describes the hardware correction technique, and presents test results that demonstrate the effectiveness of the technique. The method had to meet the requirements for high precision and high speed sampling. The configuration described provides the correction with direct digital processing at the output of the in-phase and quadrature analog-to-digital converters on a pulse-by-pulse basis. The processor operates to pulse rates greater than 3 MHz and has demonstrated corrections with residual errors of approximately 0.01 dB.
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.
In near field antenna measurements, knowledge of the the [sic] probe antenna’s pattern, polarization and gain are of vital interest. To calibrate a probe for near field measurements is a delicate task, especially if the probe is small, i.e. low gain. The near field probe and the parameters general to a probe calibration are presented. The delicate task of obtaining an accurate gain for small aperture antennas as well as the problem of transfering [sic] the calibration from the facility where the probe is calibrated to the facility where it is to be used are focussed [sic] upon For a small aperture, the pattern is that of the radiating aperture. The unwanted scattering may be removed by filtering in the spherical mode domain thus obtaining the true aperture radiation. The gain derived from this may however be of little use in reality since the aperture always needs some form of mounting. Such a mounting may be covered with absorber which may reflect and diffract and thus affect the gain value.
Under the scope of the Spanish satellite programme, named HISPASAT, Casa-Space Division has undertaken the design, development, manufacture and test of the D.B.S. antenna. For the final test campaign, mechanical and electrical activities has to be completed. The D.B.S. antenna operates in Ku-band in both transmit and receive, giving coverage over Spain for five TV channels. The antenna is composed of a CFRP 2.2 m diameter reflector and a multibeam feed, which components are all waveguide mechanized. This paper gives a short technical description of the antenna, and presents the procedure and the major results obtained from the electrical test campaign. It comprised the R.F., Multipaction and Passive Intermodulation Product (PIMP) measurements at component level and the final R.F. tests at feeder and antenna levels.
Antenna specifications for space applications are very stringent in most cases requiring that antenna measurement facilities be validated before testing can proceed. One method by which this validation can be achieved is by means of antenna test range intercomparisons which entail the measurement of a suitable test antenna at several ranges wherein one range acts as a control laboratory. The problems of such an intercomparison manifest themselves in the availability of suitable validation antennas as well as a clear definition of test parameters and the standardization of comparison procedures to ensure accuracy, reliability and consistency. The several test range intercomparisons carried out by the Technical University of Denmark (TUD) under contract from the European Space Agency (ESA) provide the basis for the current effort under ESA contract to define a suitable validation antenna, design and acquire an antenna for 12 GHz operation as well as defining a Verification Test Plan.
In the present work, different configurations of reflector systems for indoor antenna and RCS measurements have been studied and compared. These include the Single Offset reflector, Dual Parabolic Cylinder configuration, Shaped Cassegrain, Front-fed Cassegrain and Dual Chamber Gregorian. The above comparison between the different systems is made in terms of: Configuration efficiency; Cross Polar level introduced by the reflector configuration; Scanning capability; ratio of the configuration equivalent focal length to main reflector aperture diameter and ratio of subreflector area to main reflector area; RCS background levels; phase errors due to reflectors surface roughness as a function of the frequency. In order to illustrate the above discussion, several examples of commercially available compact ranges (S.A., March, Harris) are examined, as well as some recently developed European facilities (MBB, ESTEC, RYMSA). As it will be shown, each configuration is best suited to satisfy different user requirements. For example Shaped Cassegrain/Gregorian configurations seem to be the most efficient for RCS measurements whereas the Front-fed Cassegrain quiet zone can be scanned with low degradation.
In this paper, an antenna measurement technique based on modified cylindrical NF/FF transformation will be presented. In conventional cylindrical near-field scanning techniques, the near fields are probed on a cylindrical surface surrounding the test antenna. This required extensive data acquisition and processing time which can be reduced substantially if the antenna under test is illuminated by a cylindrical wave. In this hybrid approach, cylindrical wave illumination is generated using a single parabolic reflector in combination with a (point) source. The far-field pattern is then computed by a powerful one-dimensional NF/FF algorithm. It is concluded that this alternative approach combines the attributes of the compact-range technique and the classical NF/FF transformation.
New results of wideband polarimetric radar-cross-section-(RCS-) antenna measurements are presented. A special antenna network description including polarization information and multiport feeding offers new insight in antenna behavior. The procedure omits the utilization of a standard gain antenna for absolute gain determination and no RF-feedline is necessary to the antenna under test. Antenna radiation, scattering and feed characteristics are all obtained with one measurement setup. Theory as well as measurements on different dual-polarized antenna types demonstrate the efficiency and uniqueness of this technique.
The new Compact Test Range at Dornier GmbH, operational since early 1990, is presented. The system is designed for both antenna and RCS measurements, for support of in-house projects as well as for third party measurement needs. Great emphasis has been on improving measurement through put to reduce effective measurement costs. The major system components are evaluated (anechoic chamber, compact range reflector system, RF instrumentation, positioner system, computer system and measurement software). System specifications, and where possible measured performance data are presented. Finally a typical antenna and RCS measurement are described to get an idea of possibilities together with required range time.
A method for measuring G/T of small gain active antennas has been developed. The measurement can be carried out inside an anechoic chamber with well controlled environment. The method has been validated by measurement of a simulated active antenna, whose G/T has been computed from the parameters measured by classical procedures.
The Concept of Compact Test Range has been recently much used for antenna testing facilities, its main characteristic of having far-field conditions in a small and closed place, for a very large frequency band, makes it very attractive. Antenna manufacturers are building them up when the millimetric waves and the spacecraft flight model antennas become part of their activities. The change of the point of view of the antenna characteristics – now, parameters like Gain and Radiation Patterns are replaced by EIRP, Flux Density or Coverage- modifies the classical test philosophy. It makes different the Test Procedures which, in addition, have to take into account the cleanliness and the quality control required for handling flight models, as well. The Compact Payload Test Range (CPTR) in ESTEC shows up a PWZ of 7 x 5 x 5 metres for a frequency range from 1.5 to 40 GHz.; it has been created for testing whole Spacecraft Payloads in space required cleanliness area. The particular properties of the CPTR as such as shielded room, feed scanning, multiaxis test positioner, etc. are used to improve its test possibilities.
The plane-wave spectral range probe technique introduced by Coblin can be used to locate multiple scattering centers on an antenna range. The x-y positioner presented by him is too costly for many applications. A plane-polar implementation of the technique provides a less costly alternative. A preliminary study of such an implementation is presented. The plane-polar positioner presented makes use of the roll-axis of a standard roll-over-azimuth positioner and the instrumentation of the range which was being used for this study.
Recently, super resolution techniques have been applied to image spurious signals in compact range measurement systems. These techniques include parametric modeling of the probe data as well as eigen-space based methods. In these techniques, in incident signals on the probed aperture are assumed to be planar, which may or may not be true. In general, if the separation between a signal source and the probed aperture is more than , where D is the size of the probed aperture, one can assume that the signal incident on the probed aperture is nearly planar. It is shown that this is not necessarily true for super resolution techniques. The signal level also affects the minimum distance requirements. The stronger the signal, the farther its source should be from the probed aperture to achieve the optimum performance.
The spherical probing technique for the angular location of secondary scatterers in antenna measurement ranges is demonstrated for an anechoic chamber far-field range. Techniques currently used for source location use measurements of the range field on a line or plane. A linear motion unit and possible a polarization rotator are necessary to measure the range field in this manner. The spherical range probing technique uses measurements of the range field over a spherical surface enclosing the test zone allowing existing range positioners to be used for the range field measurement. The spherical probing technique is demonstrated on an anechoic chamber far-field range with a known secondary reflection source. The plane wave spectrum of the measured range field is computed and used for source angular location. Source locations in the range correspond to the angular locations of amplitude peaks in the spectrum. The effects of the range field probe on this spherical probing is investigated by performing probe compensation.
Accurate scattering and antenna measurements require excellent plane wave purity in the target zone; however all measurement systems are contaminated by various stray signals which result in measurement errors. In this paper, a technique of evaluating the stray signal sources in a compact range using a diagonal plat plate as a test target is presented. The scattering cross section of the diagonal flat plate as a function of frequency and angle of rotation is first measured. Then the time domain response for each projection angle is processed to obtain a two dimensional ISAR image of the plate as well as the stray signals. From the stray signal images, the location and relative strength of the stray signals can be determined. Experimental results from the OSU/ESL Compact Range Facility are presented to demonstrate this stray signal imaging technique.
Much research has been done recently on the interpretation of measured field probe data in order to locate and quantify error sources present in the quiet zone of a compact range. This paper examines an alternative method of analyzing those data by applying spherical phase offsets to focus the field probe data to near-field distances. This method is applied to simulated field probe data for a large compact range. The technique yield the correct [x,y,z] coordinates of multiple scattering sources deliberately introduced into the simulated data.
Knowledge of the field character in a range is essential to the understanding of measurements performed. Field probe systems are commonplace for small compact ranges. Outdoor ranges have their systems and methods. A large compact range has unique needs. Available systems are not only fairly expensive, but normally time consuming to install. The McDonnell Douglas Technologies facility implemented a probe system designed to meet the particular needs of the facility.
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.
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.
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.