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In 1997 ORBIT/FR and Dornier Satellitensysteme (DSS), a corporate unit of Daimler-Benz Aerospace, agreed on strategic cooperation in the area of Compact Range products. This includes a licence agreement which allows ORBIT/FR to use the DSS developed reflector manufacturing technology utilizing steel castings to produce the highest precision reflectors machined for quiet zone sizes up to 8 x 12 ft. The standard product line includes both single reflector ORBIT/FR designs and the cross-polar compensated double reflector DSS design. Chelton (Electrostatics) Ltd. In Marlow, UK, is the first ORBIT/FR customer to receive a compact range using DSS technology. This radome measurement system uses a single reflector compact range with quiet zone of 4 x 6 ft. Other components include antenna, radome, and feed positioners, an HP 8530 based RF system, FR959 software and absorbers. Special software was developed to fully automate the entire radome acceptance test (up to 30 hours of acquisition and data evaluation) with a single command.
In a networked antenna measurement laboratory implementing Intranet technologies provides significant benefits. Some of the benefits include efficient data transfer, remote test setup, remote monitoring and control and ease of data analysis. This paper first summarizes some of the options available and considerations in incorporating an Intranet architecture in an antenna measurement laboratory. Relative merits and pitfalls of some of the solutions are discussed. Performance issues and tradeoffs are outlined. The David Florida Laboratory (DFL) RF Facility experience in implementing an Intranet based operation is presented.
Whether for speed or accuracy, it is often necessary to rapidly switch antenna beams during testing. Most current systems require a control line for each RF switch position or phase shifter bit [1,2]. Due to the need for slip rings, the number of bits that can be controlled by this method is limited. In addition, the voltage drop and interference over long lines limit the practical range lengths that can use these "wire-per-bit" techniques. A serial bit stream followed by a serial to parallel conversion is the usual approach to controlling a large number of switches with only a few lines. However, the serial bit stream approach is quite slow. This paper will present a high speed switch box that can control an arbitrary number of RF switches and phase shifters using only two control lines that can go very long distances. The electronic circuits and software interface of this box will be covered.
The objective of this research effort was to design, fabricate and test an RF and Infrared (IR) beam combiner for use at multiple missile simulation laboratories. The ideal combiner, in the transmission mode, should provide minimum attenuation to RF signals between 1 and 100 GHz (very broad band spectral coverage); in the reflective mode, the combiner will provide maximum reflection of infrared signals between 3 and 12 µm. These combiners will be used for the testing of multi-spectral missile systems at NAWC/ WD located at China Lake, CA. The innovative approach taken by MRC, for the development of the Dichroic Beam combiner, used practical implementations of Frequency Selective Surface (FSS) theory. The advantage of this technique over dielectric coatings or metallic coatings is that it optimizes RF throughput (attenuation is no longer a function of the thickness of the metal) while increasing reflectivity in the infrared. The approach taken resulted in the development of dichroic elements which are efficient at transmitting RF and reflecting IR; the delivered hardware was also manufactured having large physical sizes and odd dimensions.
During the design of spacecraft antennas a well defined geometrical configuration of antenna components is supposed. Also the requirements for the accuracy of the antenna integration normally will be given. The antenna alignment processes have to ensure, that the designed configuration with the required accuracy can be met. Additionally the antenna pointing has to be determined with respect to the RF measurement facility. In this paper the concepts are treated, how to determine the actual and the designed orientation and location of the components of the space antennas during subsystem and system level integration and tests. This includes also the definition of needed references for the antenna components, the creation and application of coordinates or orientation matrices at manufacturing or integration level, the used coordinate systems and the attainable accuracy for different methods. For the evaluation of the RF pattern performance, the correlation between the spacecraft coordinate system and the facility coordinate system has to be known. Basic principles of this pointing alignment and an error analysis of the measurement accuracy will be explained. The presented concepts are based on the experience at DSS' test facilities with various antenna types and agreed with different antenna manufacturers and customers.
Offset parabolic reflector Compact Ranges are limited for cross polarization measurements in comparison to compensated dual reflector systems. This means that, in some cases, the crosspolar measurements at low levels show a significant content of the compact range reflector cross polar. An investigation has been carried out at INTA to reduce the crosspolarization measurement errors levels to those of a compensated dual reflector system by the application of vector deconvolution techniques. Results are shown of the validation of the algorithm in a far-field range where a crosspolar field is introduced by depointing the transmitter antenna.
Large Compact Ranges for test zone sizes of 6 meters or can be used for both payload or advanced antenna and RCS testing. In order to determine the range accuracy, test zone field evaluation is required. For physically large test zone dimensions, scanning of the test-zone fields is difficult and impractical in most situations. Furthermore, the accuracy of planar or plane-polar scanners is usually not sufficient for applications above 10 GHz. An alternative approach is the RCS reference target method where the test zone field is derived from the RCS measurement of a flat plate. Such a target can be manufactured as a single sheet aluminium honeycomb structure with rectangular or circular cross section. Reference targets with large dimensions and high surface accuracy are available. Consequently, test-zone fields can be accurately determined for test zone diameters up to about 10 meters and frequencies up to 100 GHz. In this paper the application of this method will be demonstrated at the Compact Payload Test Range (CPTR) at ESA/ESTEC. Large rectangular plate has been used for field determination within a test-zone of 5.5 meters. A 2 meter diameter circular flat plate has been used to map the residual cross-polarization level within the test zone. It will be shown that valuable information about range performance (amplitude, phase and cross-polarization) can be accurately retrieved from the RCS measurements
ORBIT/FR designed and manufactured a plane wave scanner of unprecedented accuracy. It was delivered to Intespace in Toulouse, France, to verify the compact range quiet zone performance of the compact range system installed by Dornier Satellitensysteme GmbH. The design is of the plane polar type. The linear axis has an accurate travel range of 5.5 meters with additional acceleration and deceleration ranges. The polar axis has a travel range of over 180 degrees, so that a full circular plan of 5.5 meters in diameter can be evaluated. The mechanical overall planarity is better than ± 80 micrometers peak to peak. This is equivalent to ± 3.8° phase at 40 GHz. Special attention was given to the design of the RF cable track. A maximum phase variation equal to the mechanical accuracy was specified. However, no phase variation was noticed due to cable movements, even at 40 GHz. A new application for this scanner was to verify the actual boresight of the plane wave in both normal and so-called scanned boresight applications (compact range feed moved out of the focal point). For this purpose, the scanner was equipped with an optical mirror cube. Overall system alignment accuracies of 0.01° were typically achieved.
Diagnostic tools for the determination of the excitation coefficients of a multifeed antenna based on pattern measurements are extremely useful during a spacecraft antenna design. Due to the complexity of state of the art multifeed antennas, it is not straight forward to trace back to the location of possible error sources, if deficiencies or non-compliance's are detected during an antenna measurement campaign. Therefore a method was developed and tested at DSS which directly determines all effective excitation coefficients from pattern measurements. The method approximates the measured composite array pattern a set of computed element beam pattern, weighted by a set of unknown excitation coefficients. The resulting equation system is solved using the Method of Moments (MoM). The tool was extensively tested at DSS. The accuracy obtained for the calculations of the coefficients was in the 2% range beeing compareable to the accuracy of Beam Forming Network (BFN} measurements using a network analyser. In this paper the theoretical background of the method as well as some application cases will be described.
The effect of the platform in the radiation pattern of antennae on board satellites, aircraft or ships has to be taken into account in order to know the actual performance of antenna systems. To have an evaluation of this effect, software prediction codes are developed, providing a fast, cost efficient and comfortable solution compared to the usual measurement campaigns. Nevertheless, these codes have to be validated. Specific tests have been done in order to validate the prediction code FASANT, developed by the Universidad de Cantabria from Spain and based on the Uniform Theory of Diffraction (UTD). A description of the code is first done to follow with the measurement project that has been performed at the INTA facilities in Madrid. A mountable mock-up of the Hispasat satellite has been used to obtain different configurations. Special geometrical shapes have been added to the satellite platform to check for different scattering effects.
Most often when performing antenna and RCS measurements, integrating the results is performed with some type of computer generated simulation or model of the application scenario. In the case of Missile Engagements for Fuze Radars, there is an opportunity to engage full size targets in a near real engagement. The missile fuze antenna can be mounted on the test cart which is able to position the fuze antenna in azimuth, pitch and roll. For instrumentation the MESA Facility has available a PN coded BiPhase multi-range gate radar system. Various Full size targets are available for use in the arena. The target are positioned for a multitude of trajectories utilizing an overhead target positioning system. The Overhead Target Positioning System suspends and moves the targets using a multipoint string system that controls, Pitch, Roll, height, and azimuth positioning. The Overhead Target Positioning System (OTS) is also controlled in lateral movement. (across the range) This paper will show the verification of antenna patterns and RCS returns of full size targets using the MESA Radar system, and verification of these measurements using a hardware in loop fuze radar system simultaneously.
The Georgia Tech Research Institute (GTRI), under contract to the U.S. Air Force 46 Test Group, Radar Target Scattering Division (RATSCAT), at Holloman AFB, NM, has designed and developed a fully polarimetric, bistatic coherent radar measurement system (BICOMS). It will be used to measure both the monostatic and bistatic radar cross section (RCS) of targets, as well as create two-dimensional, extremely high-resolution images of monostatic and bistatic signature data. BICOMS consists of a fixed radar unit (FRU) and a mobile radar unit (MRU), each of which is capable of independent monostatic operation as well as simultaneous coherent monostatic and bistatic operation. The two radar systems are coherently locked via a microwave fiber optic link (FOL). This paper discusses the key system features of the BICOMS.
Responses in turntable imagery are properly focused if they behave as fixed point scatterers in the focal plane chosen for polar formatting. Other responses, be they generated by more complicated back- scattering or by fixed point scatterers outside the focal plane, have a curved phase. This curved phase can be used to recognize responses due to reflection between separated scatterers, and to determine the locations of the contributing scatterers, whether the scatterers are located on the target, its mount, or the turntable. For nonzero depression angles, the phase curvature can also be used to measure the height of a point reflector.
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.
Considerable attention has been given recently to the problem of properly calibrating RCS measurements. Traditionally accepted approaches utilize aluminum spheres for ease of placement (insensitivity to orientation) and availability of computationally accurate (Mie series) solutions. In many situations, however, it can be shown that spheres fail as calibration devices. Past AMTA presentations [1, 2, 3] have shown that required mechanical tolerances for spheres are stringent, and can be difficult to achieve. Furthermore, energy can be bistatically reflected from spheres into column or pylon target supports, adding to calibration contamination. One solution may be a more wide-spread introduction of squat cylinders as calibration devices. Outdoor ranges have utilized squat cylinders for years for many of the aforementioned reasons. Advantages and disadvantages exist as always. The reduction of target support interaction and improved mechanical tolerances may be offset by difficulty in providing computationally accurate cylinder predictions and proper cylinder orientation. This work attempts to straightforwardly illustrate how these considerations come into play to assist the range engineer in determining how best to proceed to calibrate his or her data.
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.
In the process of relocating an RCS range from Sycamore Canyon, Poway, CA to the Raytheon Systems Company plant site in Tucson, AZ, the very important question of measurement validation had to be addressed. This relocation has to be accomplished on a very aggressive schedule in order to keep the impact to measurement schedules at a minimum. A high standard of measurement capability had to be retained. The aggressive relocation schedule poses risks to site selection and subsequent range validation. We will present an outline of our validation plan and our relocation plan from a technical point of view, and discuss our various procedures for measurement and range validation. The philosophy and methodology of the proposed site selection and measurement for the validation of the Tucson test facility will also be presented. This paper will also present the resolution of encountered risks and problems.
BICOMS (Bistatic Coherent Measurement System) is a RATSCAT radar cross section (RCS) range at Holloman AFB, NM. BICOMS includes a Mobile Radar Unit (MRU), Fixed Radar Unit (FRU), and an Automated Field Probe (AFP). The MRU's antenna positioner system moves eight antennas using single pivot elevation/azimuth positioners and screw jack and cable hoist height actuators. The Automated Field Probe (AFP) raster scans a 40 x 40-foot aperture in front of the target under test. A 4- wheel drive scissors lift provides mobility and vertical axis travel. A cable drive moves a carriage horizontally along a 48-foot truss boom, mounted on the lift platform. The system computer controls both axes, as well as microwave data acquisition. All structures and systems feature minimum weight and wind resistance.
ORBIT/FR has recently designed an antenna measurement facility that combines a unique encoder based positioning system with the ability to test antenna systems in both transmitting and receiving modes of operation. This combination allows for the testing of high precision military, space borne, and commercial antennas and systems in their final, deliverable configuration. The system features a high precision roll over slide over azimuth positioning system, with angular precision of 0.001-0.002 degrees available. In addition, accurately located roll axes can be interchanged to accommodate various size classes of antennas. As part of the positioning system design, an extremely low profile AL- 060 roll axis provides for non-intrusive positioning of very small antennas. Automatic mode switching allows the antenna under test to be tested in either a transmit or receive mode of operation without operator intervention required. The system features the FR959 Automated Antenna Measurement Workstation and HP 8530 based RF instrumentation for data acquisition and control. The system is designed for operation over a frequency range of 800 MHz to 40 GHz. Band switching also allows for contiguous operation of the instrumentation, limited only by the available probe antennas utilized with the system.