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Compact ranges have found wide application for antenna measurements, RCS measurements, and, most recently, for spacecraft payload measurements. Each of these ap plications requires certain special features of the range optics, positioning systems, electronics, and software. The system design of a compact range measurement sys tem for making all these types of measurements presents a number of challenges. This paper will discuss the system aspects of the design of a multi-purpose compact range facility. Items of inter est include the RF electronics design, the positioning sys tem design, the optimization of the reflector and feeds and the specialized software design.
Forming radar images from large fractional bandwidth data can often lead to unusual artifacts or resolutions degraded from "expected" theoretical point-target values. The frequency dependencies of typical scatter ing mechanisms, such as diffractions, surface waves and speculars, can be significant over processing apertures when data are collected using large fractional bandwidth measurement systems. For example, it is well known that resonant scatterers exhibit blurring in the downrange direction of an image. Other scattering mechanisms have linear or quadratic amplitude dependencies which can also alter the impulse response from that of an ideal point scatterer. This paper will first provide a brief description of the frequency dependencies of various scattering mechanisms. The paper will then describe the corresponding effects seen in the impulse response, primarily in the range profile domain. Impulse response plots will be compared for data with large and small fractional bandwidths. Lastly, the effects of frequency dependent scattering on the impulse response will be shown using images generated from data collected in indoor compact ranges.
Image editing, a post measurement data processing technique, is an established method for the identification and reduction of non-target measurement artifacts like the target support system. The Environmental Research Institute of Michigan has applied this technique to data collected at the OSU "BIG EAR" VHF-UHF wideband compact range in order to remove or reduce target sup port interference and to extract selected target feature contributions to the RCS. In this paper, the application of the method to some BIG EAR measurements data is described and examples are shown which demonstrate the improvement in data quality and usability afforded by support contamination reduction and feature extraction techniques.
In an earlier paper ("System Engineering for a Radome Test System," John R. Jones, et al, AMTA, October 1994) the system level design of a compact range enhancement for the testing of the Triband Radome was presented. This paper will discuss the installation and testing of the radome measurement system in the compact range. The purpose of the radome measurement system is to determine (within close tolerances) boresight shift, transmission loss, antenna pattern changes and polarization effects caused by the radome. Unique features include novel coordinate transformation and correction by means of a laser autocollimator and data reduction algorithms. Also featured is the tracking subsystem which consists of a specially designed two-axis track pedestal, an autotrack controller, and three five-horn compact range feed arrays operating at X, K, and Q-bands. The performance of the triband radome measurement system in the compact range setting will be presented.
Far-field patterns obtained from planar near-field measurements of a prototype of the AMSU-B radiometer antenna by phase retrieval at 94 GHz are presented in this paper. Comparison with results from a compact range facility show good agreement within the main beam A modified algorithm takes into account any misalignments of the two intensity data sets so that the RMS near-field error metric comparing retrieved and measured values converges to < -30 dB. Phase retrieval is revealing itself as a useful technique to be applied to electrically large antennas at frequencies extending into the millimetre and sub millimetre bands.
Daimler-Benz Aerospace AG (Dasa) in Munich, Germany designed, developed, build and tested most of the INTELSAT VIII antennas. RF test requirements and results are presented for the Hemi/Zone antennas. These tests cover the Beam Forming Networks (BFN), the feed array in the cylindrical near field facility at ambient temperature and in a temperature range from -61 to +85 deg centigrade, and finally the complete antenna sub system, without and with satellite mock-up, in the large Compensated Compact Range. Dasa and TICRA software was used to calculate the far field results from the measured BFN coefficients and from the feed array results measured in the near field facility. Also alignment aspects are considered.
Accurate mechanical-to-electrical axis alignment (boresighting), gain, and pattern testing of radar antennae requires specialized tooling/fixturing. This requirement is often taken for granted and seldom discussed in the EE community. Particularly in a production environment, where rapid change of test configurations to accommodate multiple radar platforms are required, a convenient mounting scheme is mandatory. This paper describes and illustrates a method implemented at the Warner Robins Air Logistics Center to satisfy this demand. Drawings and/or photos of a three-point Universal Adapter fixture and several UUT Specific radar mounting fixtures are discussed. The paper discusses tolerances, materials, manufacturing processes, alignment, and antenna boresight methodologies.
NASA Langley Research Center built a compact range facility in 1990 with a dual rese,arch role. In addition to meeting measurement needs of the Electromagnetics Research Branch, the facility has been a test bed for compact range technologies. Initially, a Gregorian subreflector with untreated edges was used to feed the 16' x 16' blended rolled edge main reflector. The designed frequency range of the untreated subreflector was 6-18 GHz. In 1993 a new resistive card edge treated subreflector was built and installed enabling the frequency range to be extended on the low end down to 2 GHz. The subreflector performance was measured by probing the fields in the test measurement or quiet zone. A 14' linear composite prober was made to measure the fields out onto the rolled edge sections of the main reflector. Characteristics of the subreflector, main reflector, and the coupling aperture between the reflectors were identified. Of particular interest was the effect of the resistive card treatment on the nature of the caustic fields in the aperture. A surface distortion was also identified on the rolled edge portion of the main reflector.
Evaluation of serrated edge and blended rolled edge compact range reflectors is presented in this paper. An interactive approach is used to design the serrated reflectors. Several issues associated with the serrated reflectors are also discussed in this paper. Quiet zone fields for various serrated edge with an optimally designed blended rolled reflector are presented for comparison. In addition, simulations of a low sidelobe phased array measurement using serrated and blended rolled edge reflectors are shown to investigate their impact on the measurement accuracy.
A new technique for eliminating the desired planar wavefront (DPW) from the quiet zone fields of a compact range is described. In the technique, the probe data is modeled as a sum of a finite number of damped exponentials. A modified Prony's method is used to estimate the parameters of the damped exponentials. Next, the damped exponentials correspond ing to the DPW are identified and are subtracted from the probe data. Using simulated examples, it is demonstrated that at low frequencies the proposed technique performs much better than the other frequently used techniques for removing the DPW from the probe data. This, in turn, help in imaging the stray signals in a compact range.
High performance antennas require very accurate measurements which are difficult to meet in the conventional compact antenna test ranges. This measurement errors are produced by the non perfect plane wave synthesized by the compact range system. By the application of the reaction between the antenna under test true pattern and the compact range incident field, a closed form relation is found for the measured radiation pattern. Under certain conditions, this measured pattern can be approximated by the convolution of the two diagrams. In this paper it is presented the inverse procedure: the deconvolution to numerically calculate either the true radiation pattern of the antenna under test or the plane wave spectrum of the compact range incident field . The effectiveness and limitations of the method are discussed by numerical simulations and tested by measurements.
New results from complete scattering matric measurements on string-suspended simple geometric shapes - from the Boeing 9-77 compact range - are presented for the first time.
Earlier measurement results are reviewed to understand the result that cross -polarized patterns agree well when compared between a point-source compact range and spherical near-field scanning. By taking account of the symmetry of the aperture distribution, one can see how the cross-polarized pattern can be affected only moderately by the classic polarization feature of an offset reflector geometry.
The MSAT satellite payload [1] included the large L-Band Tx and Rx deployable reflector antenna subsystems, the Ku-Band downlink antenna, and the telemetry and command omni. The technical challenges associated with these antennas required a considerable amount of advanced testing for concept development and design, as well as for customer acceptance. The L-Band feed array breadboards were measured to quantify effects of mutual coupling. The L-Band antenna performance was verified by near-field measurement techniques and computer modelling. The Ku-Band shaped reflector antenna was tested in SPAR's compact range. A short summary is given of the omni antenna tests, and the PIM tests carried out on the L and Ku antennas.
This paper will discuss the system level design of a radome test system implemented in a compact range. The system includes a tracking pedestal controlled by an autotrack controller, a measurement receiver, a unique five-feed arrangement for the compact range which accommodates both tracking and measurement functions, and a laser autocollimator for coordinate system referencing. Key elements of system design include the required coordinate system transformations, the mechanical design of the positioning system and its contribution to the system error budget, the dynamics of the tracking system, and the synchronization of the autotrack controller, the measurement receiver, and the system controller. These aspects of system design will be discussed and measurement and analysis results will be presented.
Traditionally the Compact Range is not considered a viable method for conducting low frequency (VHF/UHF) antenna or RCS measurements because of the limited electrical size of the collimating reflector system. Normally, compact range measurements are conducted in the extreme near-field or the collimating system where to reflector size is on the order of 25 to 30 wavelengths minimum with at least four wavelength edge treatments. This mode of operation limits measurements to the high UHF band (800 MHz) and above for typical sized reflector systems in use today. Recent research with compact range3s indicates that acceptable VHF.UHF measurements can be conducted in the quasi far-field region of the collimating system with reflectors as small as five wavelengths and with electrically short edge treatments. A good user knowledge of this mode of operation is required to maximize its utility. A qualitative measure of acceptable quiet zone performance must also be established. This paper addresses the theory of operation, practical implementation and inherent limitations of the non-conventional use of the indoor compact range for conducting low frequency measurements.
The Compensated Compact Range (CCR) has been proven to be a high performance test facility for payload and large satellite antenna measurements. To efficiently measure complete antenna farms with various types of antennas on the spacecraft in the same test campaign led to the growing demand for testing e.g. Global Horn antennas on the spacecraft in the CCR. As a matter of fact, medium gain antennas feature a small aperture simultaneously requiring larger test angles. Therefor, main interferer like "direct leakage" between the CCR feed and the antenna under test have to be quantified and their impact on the measurement accuracy have to be reconsidered. The presented paper will investigate theoretically the feasibility of testing high performance widebeam antennas in the Top-Fed-Cassegrain double reflector system. Qualified measurement results of INTELSAT Global Horn Antennas featuring medium gain and extreme crosspolarization purity will be presented.
A PTD (Physical Theory of Diffraction) code has been developed to analyze the quiet zone performance of serrated edge compact range reflectors. This PTD code utilizes a modified Ludwig's method to achieve fast convergence for the PO (Physical Optics) integration and the ILDC (Incremental Length Diffraction Coefficients) method to calculate the diffraction correction due to the edge current. In this paper, key formulations for this approach will be derived. Calculated results for an example range will be shown and compared with other published data.
The design, alignment and characterization of a compact range facility at the University of California at Los Angeles is summarized. The range is intended to operate from X-Band to 60 GHz, and to accommodate test items up to 3 feet in diameter. The compact range reflector is a circular aperture offset paraboloid which is devoid of edge treatment. Reduction of reflector edge diffraction effects is achieved using an array feed for narrowband test applications, or a horn feed for broadband test requirements. The array feed requires only one relative amplitude excitation coefficient and no phase shifters, so that a simple and cost-effective implementation using a radial transmission line beam-forming network is possible The array pattern displays a deep null at the reflector rim for diffraction reduction, and a flat-topped beam which results in minimum quiet zone field amplitude taper and high reflector aperture efficiently. Structures for support and alignment of the range reflector and feed are discussed, and alignment procedures are summarized. Range performance at X-Band using an array feed is determined using transverse and longitudinal pattern comparison methods.
One critical issue in designing absorber for an anechoic chamber is the bistatic scattering performance of the absorber and its effect to the quiet zone field quality. The bistatic scattered fields from the absorber side walls, floor and ceiling of the range result in undesired stray signals which can cause significant measurement errors. Consequently, it is very important to analyze the performance of the absorber from the overall system point of view; i.e., the performance of the absorber in the range environment. This paper will address this issue and present calculated results of absorber wall performance for a compact range with a blended rolled edge reflector.