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A multi-arrayed Navy shipboard direction finding antenna has been developed by Southwest Research Institute. New testing technique have provided substantial improvement in the antenna’s evaluation. The technique consists of transmitting a swept frequency signal using one array while receiving the coupled signal with a synchronized spectrum analyzer on the adjacent array. This provides an amplitude-frequency model of the arrays response to the transmitted signal. The received data from each frequency sweep is cross correlated with baseline data previously acquired from the particular installation when known to be operational. This paper presents the testing techniques and results.
As satellite systems continue to mature, the number of ground terminals and their complexity vastly increase. As new terminals develop, test techniques must be derived to assure compliance with system requirements. Specialized measurement techniques such as antenna measurements have been developed for portions of the required testing. While these specialized techniques are well described, a need exists to describe the overall testing of satellite ground terminals. Thus, this paper presents a system level discussion of the overall testing required by a typical ground terminal.
Most radomes are tested by measuring the antenna parameters without the radome, repeating the measurement after the radome is put into position and noting the changes introduced by its presence. In many cases this method is inapplicable to large ground based radomes. This paper presents a testing method based on a combination of individual panels (or rather, pairs of panels) measurements followed by analysis. Each procedure was separately established long ago. Most of the radome scattering which degrades antenna performance originates at the joints connecting the panels. Kay has shown how to predict the radome performance using the concept of induced field ratio (IFR) of the joints. Rusch et.al developed a method to measure this IFR. The combination approach came into use about five years ago and recently gained some general recognition.
We are carrying out research and development work on 23/26 GHz 5m-diameter solid-reflector deployable antennas for future satellites or platforms. For such large antenna systems, the thermal distortion arising from the severe space environment are the determining factors in their performance. To measure the thermal distortion we fabricated an antenna surface measurement system (ASMS) (1) that makes use of a laser beam. Using this measurement system we measured the thermal distortion of a partial model of the antenna placed in a constant-temperature chamber, and we also did a thermal distortion analysis in the test configuration and compared the two results. As a result, we verified the appropriateness of the mathematical model. Next we devised a mathematical model of the entire antenna in orbit and did a thermal distortion analysis. We found that using ultra-high-modulus CFRP material, the reflector-surface precision error meats the target precision.
Far-field pattern prediction of a mm wave reflector antenna from a scan of the near-field modulus is reported. The phase retrieval algorithm utilises minimisation and the generalized error reduction algorithm to retrieve both aperture amplitude and phase from a single planar intensity scan. The far-field pattern is calculated from the retrieved complex aperture. Experimental results from measurement of a 1.12m diameter reflector at 32 GHz are presented to illustrate the practicality of the algorithm for millimeter and submillimeter applications.
Phase relationships between the three dominant modes on a four armed spiral can be used to perform broad band, direction of arrival estimates, but this requires accurate estimates of the phase behavior of the antenna both in the design stage and for calibration purposes. Unfortunately, imperfections in range design make the measurement and interpretation of phase information extremely difficult. This paper describes an approach where the imperfections of the range and the behavior of the antenna are modelled, and range effects removed from antenna data through antenna motion, and frequency change. This technique obtained tremendous accuracy at the cost of large amounts of data processing.
A technique has been developed for calibrating a monostatic antenna, used for reflection measurements of a dielectric half space. The model is based on a one dimensional, spherical wave, scattering matrix theory. The scattering matrix coefficients are found by spatial integration of the eigenvectors. The system is deemed calibrated when the eigenvectors are linear. The spatial integration process works well enough that when a calibrated antenna is used as a reflection measurement tool, the surface of the half space can be as rough as the surface of coal and the correct dielectric constant and depth of the coal can be found.
Shaped beam illumination of a parabolic, circular aperture compact range reflector using a multi-ring planar array feed is investigated. Since no reflector edge treatment is employed, the entire parabolic surface is available for ray collimation. A technique is presented for the design of array feeds which result in a reflector illumination which is uniform with a specified ripple in the central portion, but zero at the rim in order to eliminate the first order edge diffracted field. Since the excitation coefficient of each element on a ring is constant and real-valued, no complex phase shifts are required, so that a simplified and cost-effective feed network implementation is possible. The quiet zone field is evaluated for arrays comprised of two, three, and four rings of elements. It is demonstrated that the quiet zone field amplitude taper and ripple can be optimized for a specific measurement application by adjusting the amplitude distribution among the rings. Performance is compared with that of a serrated reflector configuration. The array sidelobe level and physical size are examined with regard to overall system integration and implementation.
Multiple mechanisms for the generation of extraneous signals exist in a compact range. These include edge diffraction, scattering from surface imperfections, direct feed radiation, and scattering from absorber or other objects in the range. The field quality in the quiet zone is the resultant of the direct signal and these multiple scattering mechanisms. Since the scattering mechanisms are independent, their effects are often modeled independently and statistically combined to yield an estimate of quiet zone field quality. This paper examines the statistics of multiple independent extraneous signals in a compact range. It is shown that the amplitude ripple produced by an extraneous signal computed as the root sum of the squares (RSS) of the individual extraneous signals does not correctly predict the final quiet zone amplitude ripple. Theoretical results for scattering from multiple thin gaps in the surface of a compact range are presented and statistical computer models are used to demonstrate the computation of the resultant compact range quiet zone.
Large Compact Antenna Test Range (CATR) reflectors are often made up of accurate individually fabricated panels which results in interpanel gaps. The electromagnetic scattering produced by these gaps may cause a degradation of the quiet zone performance. An analytical approach coupled with experimental determination of a key new parameter, the magnetic induced field ratio (MIFR), has been developed to evaluate the effect of the scattering from the interpanel gaps. Depending upon the gap scattering assessment, a decision has to be made whether or not to have the gaps filled. Furthermore, these panels are often painted for aesthetics and to protest against corrosion. Therefore, the effects of paint on the panel has to also be addressed. A novel technique of gap treatment and its evaluation is described.
Measurements in the compact range system are susceptible to errors. Some of these errors are caused by chamber stray signals illuminating the target such as sidewall, backwall, ceiling and floor scattering. One of the major source of these stray signals is the feed spillover or the feed/subreflector spillover in a dual reflector system where the feed/subreflector is not isolated from the main chamber. Due to the limited chamber size, some of these errors cannot be eliminated by either hardware gating or software processing. An alternative approach to reduce these errors is by use of a feed cover such that the spillover field is highly attenuated before it can reach the target or chamber clutter sources. The feasibility of using feed cover in a compact range system to reduce the feed spillover has been studied in this paper. The effectiveness and problems associated with using a feed cover have been investigated in terms of numerical simulation and experimental measurements.
A panelized 56 by 50 foot compact range reflector with a wrap-around rolled edge treatment was installed in an anechoic chamber. Good quiet zone performance required that the as-built surface precisely follow the theoretical cosine blended contour. Commercially available CAD/CAM software served as the design platform for development of the overall system layout, rolled edge panel designs and the CNC milling machine source code for contour machining the rolled edge panels. Formed aluminum and machined composite panel fabrication techniques are described, and resulting aggregate surface accuracies as good as 1.0mil rms are presented. The use of multiple triangulating theodolites, photogrammetric measurements with peak accuracies of 0.5 mils, and custom bestfitting software used in surface alignment are described.
A code based n Geometric Optics, but applicable to diffuse surface scattering, it is evaluated for prediction of downrange high range resolution (HRR) plots of signatures generated in a compact range. A description of the technique is given, including physical justification, underlying assumptions, and flexibility of implementation. Data collected at the Hughes Compact Range will be presented in support of the analysis. Usefulness of this code in generating tradeoffs for compact range designs is demonstrated. Variations in the performance of the compact ranges are shown as a function of various range design parameters, including horn performance, chamber length, and target/wall interaction. Results are analyzed and presented in space and time domains.
Performance trade-offs are investigated between the use of clustered waveguide bandwidth feeds and the use of one multi-octave bandwidth single aperture feed in a prime focus compact range for dual linear polarization. The results show that feed structure may be used for advantage for the particular test requirements of compact range systems for Radar Cross Section Measurement.
A compact antenna range has the potential capability of accurately testing antennas larger than the quiet zone specified by its manufacturer. This expansion of the quiet zone can be achieved by using an analytically derived “Gain Correction Factor (GCF)” for a specific antenna under test (AUT). This GCF should be added to the gain measured in the range. A validation testing of the GCF for a 90” antenna at 44.5 GHz was successfully conducted. The antenna gain, sidelobe and axial ratio were measured in a compact range with a 4’x4’ quiet zone and in a larger range with a 12’ x 8’ quiet zone. The difference in gain was compared to the derived GCF and excellent agreement was achieved. The differences between first sidelobes and axial ratios were negligible.
A comparative analysis of different geometries of dual compact antenna test ranges is done looking at the cross-polarization level and the scanning capability of the system. The analysis is based on a very simple and quick computation of the fields over the main refector [sic] projected aperture.
Advanced Radar Cross Section (RCS) Data Analysis, consisting of comparisons of measured RCS data to predictions, multiple plot overlays, imaging, etc., it is most often performed off-line. This causes a lag in data acquisition time by as much as several days. McDonnell Douglas Technologies Incorporated’s (MDTI) Radar Measurement Center, a large target (40 feet) indoor RCS measurement facility, used an advanced RCS data analysis system, based on a Tektronix XD-88 superworkstation, for on-line data processing. This system connects over a Local Area Network to the data acquisition computer. This allows the workstation access to each data file immediately after each measurement for processing, without affecting the data acquisition capabilities of the radar system. The hardware used for connections, capabilities of the MDTI-written software, and the capability to store plotted data on VHS videotape directly from the workstation, is described herein.
As millimeter wave antenna systems become increasingly popular, engineers are challenged to develop effective methods for testing them. A practical method of designing a millimeter wave antenna measurement instrumentation system is presented in which frequency range, accuracy, dynamic range, and speed are considered.
The Antenna Metrology Group of the National Institute of Standards and Technology (NIST) has recently developed and implemented measurement procedures to diagnose faults on a flat phased-array antenna. First, the antenna was measured on the NISTplanar near-field (PNF) range, taking measurements on a plane where the multiple reflections between the probe and the antenna under test are minimized. This is important since the PNF method does not directly allow for these reflections. Then, the NIST PNF software which incorporates the fast Fourier transform (FFT) was used to determine the antenna’s gain and pattern and to evaluate the antenna’s performance. Next, the inverse FFT was used to calculate the fields at the aperture lane. By using this technique, errors in the aperture fields due to multiple reflections can be avoided. By analyzing this aperture plane data through the use of detailed amplitude and phase contour plots, faults in the antenna were located and corrected. The PNF theory and utilization of the inverse FFT will briefly be discussed and results shown.
This paper describes a software based receiver post processor that corrects circularity and gain errors in coherent receivers. The receiver post processor additionally provides range gating capabilities, signal quality estimation, mixer non-linearity detection and various display functions. This paper will concentrate primarily on the identification of circularity errors by the receiver post processor.