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A new implementation of the planar near-field back projection technique for phased array testing and aperture imaging is described. In the alignment of phased arrays, the aperture field is treated as a continuous distribution rather than using idealized array concepts. The continuous field is then sampled to obtain element excitations. In this way, nonrectangular arrays can easily be accommodated. The method also produces highly interpolated images of apertures that can offer much insight into their nature. Also, any polarization of the aperture field may be obtained if the probe pattern has been characterized. The technique uses large FFTs which are computed very quickly by a workstation located in the facility. Results from an iterative phase alignment of a 12x18 phased array are presented, as well as highly interpolated images of apertures and results which demonstrate the polarization selection.
A technique for aligning a phased array is described. Array element attenuation and phase commands are derived from far-field patterns measured without calibrations. The technique is based on iteratively forming mulls in the antenna pattern in the directions specified by a uniform array illumination. It may be applied in situations where array elements are not individually accessible, or where an array contains no build-in calibration capacity. The alignment technique was evaluated on a far-field range with a linear, 32-element array operating at L-band. The array containing transmit/receive modules with 12-bit amplitude and phase control. Insertion attenuation and phase measurements were comparable to those obtained by conventional techniques. However, the alignment procedure tends to compensate for the effects of nonuniform element patterns and range multipath. Thus, when used to implement other excitation functions, the array sidelobe performance with adaptive calibrations was substantially better.
Calibration is one of the most important activities to be performed during the assembly, integration and testing of a phased-array antenna. Space-based phased-array antennas, conceived for remote sensing applications and for satellite communications, are going to require both on-ground and on-orbit calibration techniques. The paper reviews on-orbit calibration methods being envisaged for an electronically steerable receiving array at S-band, to be embarked onto the forthcoming PSDE/Artemis satellite.
Electronically scanned phased array antennas typically have a large number of beam positions. Accurate on-line monitoring of phased array beam positions can be used to ensure proper antenna and total system performance. Bendix has developed and successfully implemented a beam-position monitoring technique designated the “RF Integral Monitor System”. Use of this on-line technique does not interfere with normal system operation and yields results that are comparable to results obtained on an actual far field antenna range. The RF Integral Monitor technique and specific hardware implementations, for both linear and circular electronically scanned phased arrays, will be described in this paper.
This paper presents an overview of the test and set-up requirements of active Synthetic Aperture Radar (SAR) antennas. The specific antennas under consideration are those that are intended to be used in the next generation of spaceborne SAR C-Band satellites. These antennas are typically 1m to 2m wide and 10m to 20m long, possessing between 3000 to 12000 radiating elements. The paper considers each unit of the active antenna in turn and identifies which tests are to be carried out where. In considering the test of the whole antenna some initial result of focussing techniques, to allow the antenna to be tested in real time at reduced distance, are presented.
To enhance the performance of existing near field techniques the new idea of far field pattern determination from only amplitude distributions of the near field is proposed. In this way the difficulties related to phase measurements are overcome. Some different algorithms are introduced and discussed. In particular, after recalling results for the planar geometry, cylindrical scanning surfaces are considered. The feasibility and the performances of the introduced algorithms are shown through numerical examples.
This paper deals with design and evaluation of Compact Range Antenna and RCS measurement systems. Reflector subsystem and feeders design as well as quiet zone evaluation and system performance qualification are considered. Acquisition, process and presentation software to control the whole system has been developed and successfully implemented. Two systems have been designed and are now at implementation stage. A Gregorian concept Compact Range is now been constructed at RYMSA (Spain). This facility has been fully designed by IRSA and will be operative by the end of 1990. Compact Payload Test Range (CPTR) at ESTEC (ESA) is now been tested. System Instrumentation and PAMAS (Payload and Antenna Measurement and Analysis Software) have been developed.
The reflective properties of a flat circular plate and a long thin wire are discussed in connection with the quality and calibration of the quiet zone (QZ) of a compact antenna test range. (CATR). The flat plate has several applications in the CATR. The first is simple pattern analysis, which indicated errors as function of angle in the QZ, the second uses the plate as a standard gain device. The third application makes use of the narrow reflected beam of the plate to determine the direction of the incident field. The vertical wire has been used to calibrate the direction of the polarization vector. The setup of an optical reference with a theodolite and a porro prism in relation to the propagation direction of the incident field is presented as well.
A method for obtaining the individual element excitations of an array antenna from measured radiation patterns is presented. Applications include element failure diagnosis, phased array antenna calibration, and pattern extrapolation. The measured far-field information is restricted to visible space which does not always contain the entire Fourier domain. A typical example is phased array antennas designed for large scan angles. A similar problem arises during near-field testing of planar antennas in which case the significant far-field domain is restricted by the scanning limitations of the near-field test facility. An iterative procedure is then used which is found to converge to the required solution. The validity of the approach has been checked both using the theoretical radiation patterns and real test cases. Good results have been obtained.
A novel and very powerful measurement technique is presented which allows the determination of antenna radiation and scattering by radar-cross-section (RCS-_ measurements. The antenna under test is treated as a loaded scatterer using a polarization dependent network model that allows a complete antenna description in terms of scattered, radiated and absorbed waves. A load variation principle is used to determine the network model parameters and all commonly used antenna parameters like gain, antenna polarization, axial ratio, polarization decoupling, input impedance and also structural scattering can be derived from the backscatter measurement without using any additional standard antenna. With the antenna network description it is furthermore possible to examine the antenna behavior for arbitrary excitation or loading on their waveguide or radiation port.
In 1984 MBB has started the design and development of a compensated dual reflector Compact Antenna Test Range (CATR) with a quiet zone of 5.5x5.0m (w x h). Since early 1989 this test facility is fully operational and qualified for a frequency range from 2-204 GHz.
The quiet zone performance of the Harris 1606 compact Range Collimator has been reported in the literature for 2 through 35 GHz 1,2. This paper discussed our achievements in the past year with the 1606 at 95 GHz. We will summarize the improvements in our fabrication and alignment methods that have yielded excellent performance at these frequencies using an intermediate size multi-panel main reflector. Quiet zone performance data will be presented from recent measurements on the Millitech Corporation’s Millimeter Wave Antenna Test Range in South Deerfield, MA and from the Harris 1606 Capital test equipment range.
A 75 foot diameter offset paraboloidal outdoor compact range reflector was designed for operation up to 95 GHz and installed at Ft. Huachuca, Arizona. The need for high frequency operation required that a highly accurate reflector surface be maintained in the desert’s harsh thermal and wind environment. The use of thermal modeling to predict the temperature distribution in the structure, along with extensive finite element analysis to determine the structure’s distortions from thermal, wind and gravity loads were integral to the reflector design. Using the above tools, thermal isolation techniques were developed to minimize the harmful effects of the thermal environment on surface accuracy. A surface error budget based upon both calculations and measurements shows an overall rms error of 4.9 mils under optimal environmental conditions, degrading to only 6. Mils under the worst operating conditions.
As the need for taking antenna measurements moves indoors, the antenna engineer must begin to work with a variety of constraints. Many of these constraints are directly related to facilities considerations. Often the current chamber size is not possible due to the available spaces within one’s organization. Perhaps a new building or an addition onto an existing building is possible, but more often than not the antenna engineer is faced with a number of sites that are “close” to his/her ideal model. But how does one valuate the tradeoffs? What are the ramifications of changing the performance characteristics, the size of the Quiet Zone, or the frequency of operation? What would happen to the size and price of a facility if the performance changed from an 8 foot Q.Z. down to a 2 GHz to a 6 foot Q.Z. down to 1 GHz? Is there a model to help sort out some of these issues. This paper will present a model to help the engineer sort out these issues in an organized manner.
A major objective in the design of an RCS measurement facility is to obtain the greatest possible productivity (overall measurement efficiency) while maintaining the accuracy and sensitivity necessary for low radar cross section targets. This paper will present parameters affecting the total throughput rates of an indoor facility including instrumentation, target handling, and band changes-one of the most time consuming activities in the measurement process. Sensitivity and accuracy issues to be discussed include radar capabilities, feeds and feed clustering, compact range, background levels, and diffraction control.
Mechanical and environmental considerations for outdoor operation of an inflatable column are discussed in the context of a 30-ft-high column. The column is designed to support a 900-lb load in a 30-knot wind. Column RCS is less than -40 dBsm below 1 GHz for both horizontally and vertically polarized illumination. Designs using Mylar and Teflon-coated Kevlar as skin materials are compared. The primary concerns are wind loading, pressure regulation, and solar heating. Wind effects include static loading, gusting, and vortex shedding. In addition, wind-driven particulates, such as sand or stones propelled by passing vehicles can puncture the column. A pneumatic control system maintains a constant internal support pressure in the presence of leaks or pressure fluctuations due to changes in solar illumination.
This system provides improved techniques for controlling positioning axes, and secure transmission of position data from remotely located control systems. Advancements in controls technology have allows more complex configurations for use in the manipulation of RCS targets in indoor ranges. This paper will discuss a unique system design that provides automated testing and positioning of RCS test bodies. The current system uses seven axes of motion, and allows for simultaneous motion as well as synchronous motion of any axis pairs in the system. These axes include Target azimuth and elevation, Pylon azimuth and elevation, Upper and Lower turntable azimuth, and carriage linear drives. In addition, the concepts of secure data transmission through the use of specialized fiber optics are addressed. Finally, a complex set of safety interlocks and man and machine protection is discussed. The entire system is currently implemented and running in the Boeing range.
The Hughes Aircraft Company recently completed the design, development, and construction of a new engineering facility that is dedicated to providing state-of-the-art Radar Cross Section Measurements. The facility is located at the Radar Systems Group in El Segundo, California and consists of two secure, tempest shielded anechoic chambers, a secure high bay work area, two large secure storage vaults, a secure tempest computer facility, a secure conference room, and the normal building support facilities. This RCS measurement test facility is the result of Hughes committing the time and money to study the problems which influence user friendly RCS measurement facility design decisions. Both anechoic chambers contain compact ranges and RCS measurement data collection systems. A description of the facility layout, instrumentation, target handling capability, and target access is presented.
There are two main parts to an antenna or RCS measurement system: the measurement instrumentation, and the measurement environment or “range”. Performance of the measurement system is dependent upon both the instrumentation and the range. Developing a successful measurement system requires understanding both parts of the system. This paper describes a Compact Test Range that has been designed and built for the purpose of demonstrating antenna and RCS measurement performance of a complete measurement system. Additionally the Compact Test Range will serve as a development platform for future antenna and RCS products and systems. The purpose of the chamber, design objectives, design techniques, expected and measured performance are all discussed.
Lockheed’s Advanced Development Company (LADC), located in Burbank, California, has recently completed construction of a state-of-the-art indoor Antenna/RCS test facility. This facility is housed in a dedicated 40,000 square foot building which is a maximum of 80 feet high. This building contains three anechoic chambers providing Antenna/RCS measurement capability from 100 Mhz to 100 Ghz. The largest chamber, with dimensions of 64 feet by 64 feet by 97 feet is configured as a compact range. This chamber utilizes the largest collimating reflector that Scientific-Atlanta has ever constructed. Primary test usage of this chamber is for RCS measurements in the frequency band of 700 Mhz to 100 Ghz. The second chamber is configured as a tapered horn test range. Its dimensions are 155 feet long with a 50 foot by 50 foot by 55 foot volume measurement zone. This chamber is utilized for RCS tests in the VHF, UHF, and L frequency bands and antenna tests from 100 MHz and up. The third chamber, with dimensions 14 foot by 14 foot by 56 foot, is a far field chamber designed to check out and evaluate small items up to 100 GHz. The entire facility has been designed to maximize efficiency, minimize the cost of operation, and produce outstanding quality data from Antenna/RCS measurements. A number of innovative techniques in model handling, model access, and model security were incorporated into the facility design. These features, as well as utilization of unique Lockheed designed and built pylons, allowed achievement of all these goals.