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ACC has developed for the ESA-ESTEC CATR a compact but highly versatile 5-axis positioner. It is composed of a roll axis, upper azimuth, elevation, translation and lower azimuth axis. The clearance between the floor and the translation stage is designed to pass over a 12” walkway absorber while the roll axis height is only 155 cm (~5 feet). The standard configuration for medium or high gain antennas is the roll-over-azimuth or elevation-overazimuth configuration with a vertical interface for the AUT. For omni-directional antennas and RCS measurements, the positioner can be configured as a low profile azimuth positioner with a horizontal interface without a blocking structure behind the AUT. The positioner can also be configured for bistatic RCS measurements and Spherical Near Field. With the addition of a linear scanner, the Quiet Zone can be scanned in a polar way but also planar scanning is possible. Other key parameters are: angular accuracy: 0.01°, accuracy of the translation axis: 0.01 mm, load capacity 100 kg.
Modern day remote sensing spacecraft often feature multiple payloads sharing a common bus (spacecraft platform). RE02 emission testing (1, 2) characterizes the emission signature of a given payload in order to assess electromagnetic compatibility with respect to other payloads (i.e. “victims”) on the bus. Typically, a simple path loss model based on 1/r2 power variance (ref: Friis path loss equation) is used to account for the distance between the emitting and victim payloads using measured amplitudes taken during RE02 measurements. RE02 measurement technique (2) dictates that emissions testing take place at a fixed radial distance of one meter from the radiating instrument. At certain frequencies, however, this measurement takes place in the near field of the emitter. In general, power density amplitudes are greater in the near field than its far field counterpart. This paper investigates any potential error incurred by not accounting for this effect. A simple math model for a common mode radiator is developed to estimate this error and attempt to better understand the field relationships at lower frequencies where the near field predominates.
A new antenna diagnostics technique has been developed for the DTU-ESA Spherical Near-Field Antenna Test Facility at the Technical University of Denmark. The technique is based on the transformation of the Spherical Wave Expansion (SWE) of the radiated field, obtained from a spherical near-field measurement, to the Plane Wave Expansion (PWE), and it allows an accurate reconstruction of the field in the extreme near-field region of the antenna under test (AUT), including the aperture field. While the fundamental properties of the SWE-to-PWE transformation, as well as the influence of finite measurement accuracy, have been reported previously, we validate here the new antenna diagnostics technique through an experimental investigation of a commercially available offset reflector antenna, where a tilt of the feed and surface distortions are intentionally introduced. The effects of these errors will be detected in the antenna far-field pattern, and the accuracy and ability of the diagnostics technique to subsequently identify them will be investigated. Real measurement data will be employed for each test case.
Accurate antenna measurements at sub-millimeter frequencies are very challenging. Especially the phase measurement accuracy is usually limited by the mechanical accuracy of the measurement equipment. The measurement techniques used, and the measurement results of a dual reflector feed system (DRFS) at 650 GHz are presented in this paper. Planarity error compensation technique was used that enabled accurate correction to the measured phase pattern without accurate pre-existing information of the planarity error of the planar near-field scanner. The measured DRFS beam agrees well with the simulated and the achieved measurement accuracy is good.
Till recently, the testing of installed aircraft radars antennas and radomes required the dismantle of the units from the aircraft in order to measure theirs electromagnetic properties inside a classical anechoic chamber. Such operations were difficult, particularly time consuming and did not fully characterize the antenna within its operational environment. For these reasons, ELTA issued a request for an “in situ” spherical near-field test system that could be used for “on board testing of radars” located inside the nose of an aircraft. SATIMO responded with a solution based on its own proprietary rapid probe array technology already employed extensively worldwide for antenna testing. The facility was recently delivered to ELTA and “in-situ” measurement of a radar antenna and radome were performed (fig.1&2). This new generation of test system performs multi-beam, multi port and multi-frequency dual polarized complex measurements at a step of 3-degree in azimuth and elevation over a full hemisphere in a few minutes. It is fully autonomous and mobile so it can be used indifferently indoor or outdoor. Continuous wave or pulsed electromagnetic measurements are obtained thanks to an advanced software which allows the user to control the main radar parameters. Diagnostic of faulty elements in the radar is also possible through a special automated measurement mode. The antenna test system has been completed and validated through a detailed acceptance test plan including inter comparison with a traditional planar near field test range. This paper presents the general design consideration and a summary of the results of the extensive verification tests.
Till recently, the testing of installed aircraft radars antennas and radomes required the dismantle of the units from the aircraft in order to measure theirs electromagnetic properties inside a classical anechoic chamber. Such operations were difficult, particularly time consuming and did not fully characterize the antenna within its operational environment. For these reasons, ELTA issued a request for an “in situ” spherical near-field test system that could be used for “on board testing of radars” located inside the nose of an aircraft. SATIMO responded with a solution based on its own proprietary rapid probe array technology already employed extensively worldwide for antenna testing. The facility was recently delivered to ELTA and “in-situ” measurement of a radar antenna and radome were performed (fig.1&2). This new generation of test system performs multi-beam, multi port and multi-frequency dual polarized complex measurements at a step of 3-degree in azimuth and elevation over a full hemisphere in a few minutes. It is fully autonomous and mobile so it can be used indifferently indoor or outdoor. Continuous wave or pulsed electromagnetic measurements are obtained thanks to an advanced software which allows the user to control the main radar parameters. Diagnostic of faulty elements in the radar is also possible through a special automated measurement mode. The antenna test system has been completed and validated through a detailed acceptance test plan including inter comparison with a traditional planar near field test range. This paper presents the general design consideration and a summary of the results of the extensive verification tests.
Comparisons of the far-field results from two different ranges are a useful complement to the detailed 18 term uncertainty analysis procedure. Such comparisons can verify that the individual estimates of uncertainty for each range are reliable or indicate whether they are either too conservative or too optimistic. Such a comparison has recently been completed using planar and spherical near-field ranges at Nearfield Systems Inc. The test antenna was a mechanically and electrically stable slotted waveguide array with relatively low side lobes and cross polarization and a gain of approximately 35 dBi. The accuracies of both ranges were improved by testing for, and where appropriate, applying small corrections to the measured data for some of the individual 18 terms. The corrections reduce, but do not eliminate the errors for the selected terms and do not change the basic near-to-far field transformations or probe correction processes. The corrections considered were for bias error leakage, multiple reflections, rotary joint variations and spherical range alignment. Room scattering for the spherical measurements was evaluated using the MARS processing developed by NSI. The final results showed a peak equivalent error signal level in the side lobe region of approximately -60 dB for both main and cross component patterns for angles of up to 80 degrees off-axis.
As new antenna designs reach higher frequencies and smaller sizes, traditional large scale antenna chamber systems become ill-suited for measurement. External mixing, room-sized chambers, and expensive test equipment add large costs and burden to antenna measurement systems. A smaller, more cost effective system is proposed. Using the bipolar planar scanning technique developed at UCLA, a portable and movable millimeter-wave antenna chamber is currently under development. The chamber is being designed to fit on the end of a standard optical table and enjoys the space-saving and accuracy inherent to the bipolar planar configuration. Simple construction of the chamber will allow relatively easy assembly and disassembly and allow movement of the chamber from one table to another, if needed. Antenna of diameters up to 40cm can be accommodated and scan planes of up to ~160cm can be measured. Millimeter-wave frequencies from around 30GHz to 67GHz can be measured. Antennas measured will use planar near-field to far-field techniques. In particular, the post-process will follow the OSI/FFT method and will incorporate the phase retrieval techniques developed for the bipolar configuration. These phase-less measurements will allow the use of scalar millimeter-wave test equipment with much lower cost than comparable vector test equipment.
The polarization extraction in the phaseless near-field measurement is investigated. Sensing the antenna polarization based on the implementation of phase-retrieval methods like IFT (Iterative Fourier Technique) will not result to a unique solution. It is shown how a single extra point measurement can provide the complete vectorial representation of the field in a two-component representation. This means for the first time by the application of phaseless methods, one not only can get an understanding of the dominant polarization of the antenna in terms of linearity, ellipticity or circularity but also the true representation of the co- and cross polarized components in the far-field based on any definition (like Ludwig’s definitions). The applicability of the method is shown through a near-field measurement of a right-hand elliptically polarized antenna array in UCLA bi-polar near-field facility.
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.
Reflections in anechoic chambers can limit the performance and can often dominate all other error sources. NSI’s MARS technique (Mathematical Absorber Reflection Suppression) has been demonstrated to be a useful tool in the fight against unwanted reflections. MARS is a post-processing technique that involves analysis of the measured data and a special mode filtering process to suppress the undesirable scattered signals. The technique is a general technique that can be applied to any spherical near field or far-field range. It has also been applied to extend the useful frequency range of microwave absorber down to lower frequencies. This paper will show typical improvements in pattern performance, and will show results of the MARS technique using data measured on numerous antennas.
This paper discusses design aspects related to a tiltable lightweight near-field scanning system for use at sub-millimeter frequencies. It addresses design issues as they relate to accuracy and scanner distortions from multiple causes. Calibration methods to measure and correct for anticipated and unanticipated errors are briefly addressed. Actual test results are presented. The tiltable scanner being discussed was designed for the Atacama Large Millimeter/submillimeter Array (ALMA) [1] and is being used by the National Radio Astronomy Observatory (NRAO) [2]. It has many other applications by virtue of its light weight (approx. 120 lbs) and ability to be oriented at different angles. These include flight-line testing and other in-situ antenna test applications.
In this paper we present a direct optimization procedure which utilizes phase-less electric field data over arbitrary surfaces for the reconstruction of an equivalent magnetic current density that represents the radiating structure or an antenna under test. Once the equivalent magnetic current density is determined, the electric field at any point can be calculated. Numerical results using experimental data are presented to illustrate the applicability of this approach for non-planar near field to far field transformation as well as in antenna diagnostics.
In this paper we present a direct optimization procedure which utilizes phase-less electric field data over arbitrary surfaces for the reconstruction of an equivalent magnetic current density that represents the radiating structure or an antenna under test. Once the equivalent magnetic current density is determined, the electric field at any point can be calculated. Numerical results using experimental data are presented to illustrate the applicability of this approach for non-planar near field to far field transformation as well as in antenna diagnostics.
The planar near-field antenna measurement system at KRISS has been upgraded to V-band (50 GHz – 75 GHz). This paper describes the upgraded planar near-field antenna measurement system that consists of a planar near-field scanner, a microwave subsystem and an extrapolation range, and shows the uncertainties in gain for a rectangular near-field probe and a Cassegrain antenna at 65 GHz.
A wide range of wireless services are being installed in modern vehicles. Applications including radio reception (FM), navigation systems (GPS), satellite radio, keyless entry, future data services (IEEE 802.11) and mobile telephone are increasingly installed in modern vehicles. Integration of these technologies in cars and trucks has generated a need to accurately determine the performances of the antenna devices when mounted on the vehicle.
Spherical near field measurement techniques combined with probe array technology offer a fast and accurate way to measure antenna performances. The use of increasingly higher frequencies and reduced testing time in all modern antenna applications has increased the need for probe array based measurement systems at higher frequencies.
Spherical near field measurement techniques combined with probe array technology offer a fast and accurate way to measure antenna performances. The use of increasingly higher frequencies and reduced testing time in all modern antenna applications has increased the need for probe array based measurement systems at higher frequencies.
The CTIA (The Wireless Association – www.ctia.org) were the first to publish a widely accepted test plan for antenna performance testing of “live” mobile phones[1]. The test plan describes the use of phantom heads and involves recording transmitted power and receiver sensitivity information over a full sphere to derive parameters such as Total Radiated Power (TRP) and Total Integrated Sensitivity (TIS). The test plan, has until now, assumed that testing is performed in the far-field at test distances greater than 2D2/.. For typical mobile phone frequency and device test diameters (assumed 300mm in the CTIA test plan), this has not been a constraint. However, as such testing evolves to include the various versions of IEEE 802.11 combined with new devices such as larger laptops and other consumer electronics, a far-field test requirement would lead to very large test facilities. Using experiments and rigorous simulations, this paper will show that for the commonly accepted performance criteria, the far-field requirement is unnecessarily strict. A minimum distance requirement based on the geometry and probe pattern is proposed which will ensure that the performance parameters (TRP, TIS, and others) are obtained with insignificant loss of accuracy.
In this paper we have revisited the phase retrieval problem for planar near-field antenna measurements. It will be shown that the complexity of retrieval procedures is function of not only the independency of different sets of measurements but also the characteristics of the antenna under test (AUT). Features of antenna like its beam direction will have profound effect on the success of phase reconstruction algorithms. The failure of a well known phase retrieval method, Iterative Fourier Transform (IFT), is investigated for a case where the antenna has a scanned beam. It is found that this is due to the non-judiciary choice of the initial guess. To alleviate the deficiency of the IFT a simple but effective initial guess is sought by Differential Evolutionary Algorithm (DEA). DEA tries to find the best initial phase guess which minimizes an error criterion. Subsequently this best guess will be fed to the phase retrieval IFT routine for further phase refinements. Having done this the far-field can subsequently be constructed. The improvement in the phase reconstruction algorithm is examined, through a series of simulations and measurements.