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ESA’s Compact Antenna Test Range at ESTEC has been relocated which has given the chance to improve the alignment of the reflectors. Based on measure-ments of the reflector surfaces the best-fit positions and orientations of the reflectors have been deter-mined. It turned out that the choice of parameters to describe the reflectors and their position had impor-tant impact on the optimization process: The parame-ters shall – as far as possible – be orthogonal in the sense that a change in one parameter must not influ-ence the final value of the other parameters.
Compact test ranges are worldwide used for real-time measurements of antenna and payload systems. The Compensated Compact Range CCR 75/60 and 120/100 of Astrium represent a standard for measurement of satellite antenna pattern and gain as well as payload parameter due to its extremely outstanding cross-polar behavior and excellent plane wave field quality in the test zone. The plane wave performance in the test zone of a compact test range is mainly dependent on the facilities reflector system and applied edge treatment as well as on the RF performance of the range feed. To provide efficient and economic testing and maintaining the needed measurement accuracy the existing standard set of high performance single linear feeds covering the frequency range from 1 - 40 GHz had been extended to operate simultaneously in dual linear polarization. In addition several customer specific range feeds had been developed and manufactured and validated. More detailed information and achieved test results for the new high performance range feeds will be presented.
ORBIT/FR has recently delivered several high performance millimeter wave antenna systems for use in compact range and direct illumination chambers. These systems utilize the latest Agilent Technologies millimeter wave modules used in conjunction with the PNA-X vector network analyzer. These systems offer the following features: . Integration of the transmit and receive modules at the AUT and source/feed antenna for a low loss implementation . Integral range reversibility for AUT transmit or receive capability . Full integration with a baseline 2-50 GHz system capability . Full and automatic harmonic selection for all measurement bands . Optimized RF equipment placement in the chamber The systems are integrated with the 959Spectrum Antenna Measurement Software to provide a fully automatic antenna measurement capability from 2-110 GHz. Patch panels were used to avoid any re-cabling form the microwave bands to millimeter wave bands. Greater than 70dB dynamic range was demonstrated at W band. Performance results are shown, and optimized layout considerations are discussed that demonstrate a design that results in high performance as well as operator convenience is setting up measurements over all the microwave and millimeter wave bands.
A broad band interferometer antenna was designed and manufactured by Saab Avitronics. Saab Aerotech has installed a test facility for calibration of the interferometer antenna. The main purpose of the facility is to measure the interferometric function of the antenna. The interferometric function of the antenna can be measured directly but this method puts very high demands on the test range performance. An alternative method where each element is centered on a short far-field range is evaluated and compared by measurement with a large compact range at Saab Microwave Systems. The paper also describes the design aspects when measuring broad band, broad beam interferometer elements together with the actual design of critical components such as positioners, RF-system and absorber treatment.
RF guided missile developers require flight simulation of their target engagements to develop their RF seeker. This usually involves the seeker mounted on a Flight Motion Simulator (FMS) as well as an RF target simulator that simulates the signature and motion of the target. Missile intercept engagements are unique in that they involve highly dynamic relative motion in a short period of time. This puts demanding requirements on the RF target simulator to adequately present the desired phase slope, amplitude, and polarization to the seeker antenna and electronics under test. This paper describes a newly installed RF Target Simulator that addresses these requirements in a unique fashion. The design utilizes a compact range reflector, dynamically rotated in two axes as commanded by the flight simulation computer, to produce the desired changing phase slope and an RF feed network dynamically controlled to produce the desired changing polarization and amplitude. Physical optics analysis establishes an accurate correlation between reflector physical rotation and resulting angle-of-arrival of the wave front in the quiet zone. The RF Target Simulator is self contained in a two-man portable anechoic chamber that can be disengaged from the FMS and rolled to and from the FMS as needed. Measurements are presented showing the performance of the RF Target Simulator.
A compact antenna test range has been analysed for stray signals. The analysis is based on GTD ray trac-ing, i.e. obeying the reflection law in the chamber walls and assuming straight edges of reflectors and walls. Comparisons to an RCS as well as a time-domain measurement of the quiet-zone performance show good agreements with respect to identification of the ray paths of the stray signals. Rough estimates of the power loss at reflections and diffractions show acceptable agreements with the measured levels.
This paper presents the initial field probe characterization results for an RF scattering compact range using a high precision calibration sphere. This approach uses an Inverted Stewart Platform to position the ultra-sphere through the target quite zone. The Inverted Stewert Platform and optical target tracking system provide a fast and efficient for performing a volumetric incident illumination field characterization of the compact range quite zone using a backscatter RF measurement. The Inverted Stewert Platform system uses six small diameter strings attached to the ultra-sphere to provide the ultra-sphere positioning over the entire quiet zone of the compact range. The inverted Stewart platform also offers increased stability of the target by damping out the torsional pendulum motion typically encountered in conventional string support systems. This presentation will discuss an in-house development of the sphere field probe and discuss advantages and disadvantages of the ultra-sphere volumetric field probe.
Measurement of radome beam deflection and/or Boresight shift in a compact range generally requires a complicated set of positioner axes. One set of axes usually moves the radome about its system antenna while the system antenna remains aligned close to the range axis. Another set of axes is normally required to scan the system antenna through its main beam (or track the monopulse null) in each plane so the beam pointing angle can be determined. The fidelity required for the beam pointing angle, combined with the limited space inside the radome, usually make this antenna positioner difficult and expensive to build. With a far-field range, a common approach to the measurement of beam deflection or Boresight shift uses a down-range X-Y scanner under the range antenna. By translating the range antenna, the incident field's angle of arrival is changed slightly. Because the X-Y position errors are approximately divided by the range length to yield errors in angle of arrival, the fidelity required of the X-Y scanner is not nearly as difficult to achieve as that of a gimbal positioner for the system antenna. This paper discusses a compact-range positioner geometry that approximates the simplicity of the down-range-scanner approach commonly used on far-field radome ranges. The compact-range feed is mounted on a small X-Y scanner so that the feed aperture moves in a plane containing the reflector's focal point. Translation in this 'focal plane' has an effect very similar to the X-Y translation on a far-field range, altering the direction of arrival of the incident plane wave. Measured and modeled data are both presented.
A large single reflector corner fed rolled edge compact range system, featuring an elliptical cylinder 12’ (H) x 16’ (W) x 16’ (L) quiet zone has been recently installed in a large anechoic chamber [1]. The Compact Range System parameters, such as reflector surface tolerance of better than 0.001” over the Quiet Zone section of the reflector and superior Quiet Zone field performance at frequencies down to 1.0 GHz were verified and validated. As a part of further studies of potential advantages delivered by the compact range system, the study of the compact range application to Antenna and RCS measurements at VHF/UHF frequencies was initiated. Though the reflector surface tolerance is not an issue at the VHF/UHF bands, successful compact range operation at these frequencies would be a significant expansion of the capabilities of the existing compact range system. In order to evaluate the system performance at VHF/UHF frequencies a number of challenging technical issues had to be resolved and performed. They include: Compact Range Quiet Zone Performance Analysis at the VHF/UHF bands Choice of a concept for a broadband feed suitable for the application and installation within the existing feed carousel Feed Design and Performance Validation Feed Installation in the existing feed carousel Quiet Zone Field Probing and Performance Verification All these issues were addressed in the development of a suitable low frequency feed, and are described in more detail below.
Orbit/FR has installed a new compact range for antenna measurements at ACE Antenna Corp. The measurement facility covers a frequency range from 0.8 to 40GHz with a Quiet Zone size of 3 m diameter x 3 m length. The design of the compact range is similar to the one already installed by Orbit/FR at Ericsson (Sweden) with some improvements in the mechanical design and in the system parameters. An intensive simulation of the reflector serrations had allowed for finding its optimal profile, thus improving the quiet zone parameters at entire frequency range, especially at low frequencies, at which a number of base-station and mobile antennas are expected for testing by ACE Antenna Corp. A new design of a feed positioner and a baffle house added more convenience for the compact range alignment and operation. The system was installed and qualified in March 2008. The field probing has been performed within the entire operating frequency range, which then allows for evaluation of the antenna measurement accuracy. A system description as well as results of simulation and excerpt of the qualification data is presented in the paper.
The measurement accuracy of state-of-the-art RF test facilities like near-field or compact test ranges is influenced due to applied system hardware as well as operational facts which are influenced by human errors. The measurement errors of near-field test facilities were analyzed and published in the past times and are based on the 18-term error model of Newell [1]. For compact test ranges and especially for the cross-polar free compensated compact range a similar error model was established at Astrium GmbH within a study for the satellite service provider INTELSAT [2] in order to define possible facility performance improvements and maximum achievable values for the measurement accuracy. It has to be remarked, that test programs for space applications require very stringent adherence to procedures and documentation of process steps during a test campaign. Within this paper, recommendations for process optimizations and procedures will be presented to guarantee the adherence to the valid error budgets and to minimize the Human Factor. A description of main error contributions in the Compensated Compact Range (CCR) of Astrium GmbH will be performed. Furthermore, the error budgets for pattern and gain measurements and achievable performance improvements will be given.
Within the European Union network "Antenna Center of Excellence" – ACE (2004-2007), a first intercomparison campaign among different European measurement systems, using the 12 GHz Validation Standard (VAST12) antenna, were carried out during 2004 and 2005. One of the challenges of that campaign was the definition of the accurate reference pattern. This was the reason why a dedicated measurement campaign for definition of the accurate reference pattern was hold during 2007 and beginning of 2008. This second campaign is described in the companion paper “Dedicated measurement campaign for definition of accurate reference pattern of the VAST12 antenna”. This dedicated measurement campaign was performed by Technical University of Denmark (DTU) in Denmark, SAAB Microwave Systems (SAAB) in Sweden and Technical University of Madrid (UPM) in Spain. This campaign consisted of a large number of measurements with slightly different configurations in each of the three institutions (2 spherical near field systems and one compact range). The purpose of this paper is to show the process to achieve the reference pattern from each institution and the evaluation of the accuracy. The acquisitions were performed systematically varying in applied scanning scheme, measurement distances, signal level and so on. The results are analyzed by each institution combining the measurement results in near or far field and extracting from these measurements: a “best” pattern, an evaluation of possible sources of errors (i.e. reflections, mechanical and electrical uncertainties) and an estimation of the items of the uncertainty budget.
Some compact ranges use two orthogonal linear polarized feed horns for circular polarized antenna measurement. These two feed horns are symmetrically located along the vertical plane through the longitudinal axis (VPTLA). For accurate axial ratio measurement, the CP antenna under test (AUT) should also lie on the VPTLA. However, for some applications, the AUT has to be offset from the VPTLA during measurement. When this happens, rays from two feed horns reaching the AUT are out of phase. This extra phase error causes unwanted test error for the axial ratio measurement. This paper presents an analysis on the error cause, and provides a method to compute and correct the phase error, when the AUT is offset from the VPTLA. The method computes the extra phase difference from two feed horns to the AUT using geometrical optics method. This phase difference is then used to correct the tested data. This paper also shows a successful measurement example using this correction technique.
This paper presents a novel method to evaluate very small stray signals in compact range. The ripples of signals probed by an omni-directional antenna along the orthogonal direction of the bore sight could be treated as signals in time domain. Transforming the probed data with fast Fourier transform (FFT), the direction and amplitude (relative to the test signal) of each stray signal could be obtained. To improve the accuracy, time domain software gating should also be used in calibrating the measurement error of amplitude and phase. The presented method has the ability to measure very small stray signals with good angle resolution. The method has been tested by both simulation using MATLAB and experiment in the compensated compact range CCR120/100 in CAST using a monopole antenna centered on a circular ground plane as a probe. Good results were obtained.
Serrations are often applied at the edges of compact-range reflectors in order to reduce the scattering from the edges into the quiet zone. At low frequencies the serrations show different scattering of the field at the two polarisations: parallel to and perpendicular to the serration teeth. This has been verified by modelling a range by the Method of Moments (MoM). The size of the range reflectors is about 7.5 m by 10 m which make the re-flectors difficult to handle by MoM even at a fre-quency which is low for the range, viz. 1.7 GHz, in which case the reflectors are each 2400 wavelengths squared. A narrow strip, horizontal or vertical, across the re-flector and closed by a single serration tooth at each end is shown to give a good prediction of the field along a line parallel to the strip in the quiet zone. By this simple model of the range it has been demon-strated that the quiet-zone field depends highly on the polarisation. When the polarisation is parallel to the teeth the quiet-zone field has ripples which are 0.3 dB peak-to-peak, but for the perpendicular polarisation the field variations are 0.8 dB peak-to-peak. The results are compared to quiet-zone fields deter-mined by Physical Optics (PO).
Indoor RCS measurement facilities are usually dedicated to the characterization of only one azimuth cut and one elevation cut of the full spherical RCS target pattern. In order to perform more complete characterizations, a spherical experimental layout has been developed at CEA for indoor near field monostatic RCS assessment. The experimental layout is composed of a motorized rotating arch (horizontal axis) holding the measurement antennas. The target is located on a polystyrene mast mounted on a rotating positioning system (vertical axis). The combination of the two rotation capabilities allows full 3D near field monostatic RCS characterization. Two bipolarization monostatic RF transmitting and receiving antennas are driven by a fast network analyser : - an optimised phased array antenna for frequencies from 800 MHz to 1.8 GHz - a wide band standard gain horn from 2 GHz to 12 GHz. This paper describes the experimental layout and the numerical post processing computation of the raw RCS data. Calibrated RCS results of a canonical target are also presented and the comparison with compact range RCS measurements is detailed.
If an acquired RF field data set captures all the radiated energy, transformations will have minimal errors. However, it is sometimes impractical to capture the complete radiated field. In this case, some sort of edge treatment is required before transforming the data set. Usually, a function such as a cosine taper is added to the edge to minimize transformation errors. Unfortunately, these functions may be discontinuous to the measured data and its’ derivatives. This paper will present a method of truncation which matches the measured data and its’ derivatives. It will then transform the RF field data to the compact range reflector surface and compare the results of several truncation methods.
In order to ensure proper measurements in the compact range, the reflector needs to be aligned within the range. Unfortunately, the reflector does not have any direct method of leveling or locating such as straight edges or fiducials at known locations. The only known reference is the ideal point cloud. As the point cloud is given, it is oriented correctly in the range. So by centering the point cloud in the range, the compact range reflector can be aligned to the range by minimizing its deviation from the ideal point cloud. This paper will go through the mathematics used to accomplish this alignment in the translation along and rotation about the three primary axes. In addition, it will give a method of determining reflector twist. The method is sufficiently generic that it can be applied to other shapes and figures of merit.
Conventional compact ranges use a reflector antenna’s near field to produce the plane wave illumination needed to measure a second antenna under test (AUT). The quasi-compact range described here uses a conventional reflector antenna at a greater range separation than conventional compact ranges, but still within the reflector’s near field. Its illumination allows the antenna evaluations at smaller range separations than the AUT’s far-field distance and allows modification of a current far-field range with a reflector range antenna to measure larger test articles than normally acceptable. This approach preserves many advantages of a standard compact range including reduced multipath and high measurement sensitivity that result from the collimated near field of the illuminating reflector antenna. Additionally, a conventional reflector antenna is used without requiring edge treatments. Experience with a four-foot prime focus parabola operating at 18 GHz illustrates this technique. The measured quiet zone fields compare favorably with calculated values using the GRASP codes. Likewise, measurements of a 20”-diameter offset reflector antenna compare favorably with GRASP results.
This paper describes the motivation and major issues related to the design of an RCS radar instrumentation system for use in a compact range. The high degree of sophistication implemented in commercially-available radar systems renders them subject to significant MTTR (mean time to repair) with corresponding losses in range productivity. The objective of the design effort was to develop a system of minimal complexity, maximally suited to troubleshooting and repair by laboratory personnel, while retaining the operational efficiency normally provided by the commercial systems.