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This paper describes how corrugated feed horns are designed for compact ranges with tight pattern control. Both the amplitude and phase of the horn pattern must be invariant over a wide frequency band. A horn synthesis computer program has been developed using the JPL HYBRIDHORN computer program as the analysis module which is driven by a Harris developed synthesis code (OPTDES). This paper also discusses launching techniques used to generate the HE(11) hybrid mode in the corrugated horn as well as design methods to eliminate ringing effects observed in both the input waveguide circuits and corrugated horns when used for RCS measurements.
The utility of absorber-lined tunnels to control the sidelobe levels of horns has previously been demonstrated. The use of such a tunnel gives the designer the option of designing a broadband feed, for example, and later tailoring the sidelobe level to meet a given specification. In this paper, a technique for calculating the radiation characteristics of a horn in an absorber-lined tunnel will be presented. The analysis is based on an absorbing phase screen approximation which has been used by one of the authors in analyzing the diffraction of signals around rocket plumes. Propagation through the tunnel is treated as if the wave travels through a sequence of layers in which the absorption depends on the transverse coordinates. The absorbing phase screen model will be developed, and then applied to the analysis of a Narda standard gain horn in a square tunnel which is lined with wedge absorbing material. For the determination of E and H-plane pattern cuts, a two dimensional model can be utilized. In order to determine the radiation pattern over the full range of theta and phi as is required for illuminating a reflector, a three dimensional model is needed. All calculations were implemented in Fortran on an IBM personal computer.
For the past two years the National Bureau of Standards (NBS) has been developing the capability to perform on-axis gain and polarization measurements at millimeter wave frequencies from 33-65 GHz. This paper discusses the error analysis of antenna measurements at these frequencies. The largest source of error is insertion loss measurements. In order to make accurate insertion loss measurements, flanges on antennas need to be flat and perpendicular to the waveguide axis to within approximately 0.001 cm (0.0005 in). In addition, waveguide screws need to be tightened with a device that supplies constant torque. For antennas with gains less than about 25-30 dB (probes) we can measure on-axis gains within an uncertainty of 0.14 dB in the 33-50 GHz frequency band and within 0.16 dB in the 55-65 GHz frequency band using the three-antenna technique on the extrapolation range. For antennas with larger gains we can measure on-axis gains within an uncertainty of 0.21 dB in the 33-50 GHz frequency band and within 0.24 dB in the 55-65 GHz band using the planar near-field technique. NBS in continuing development of its measurement capabilities, including measuring probe correction coefficients required in planar near-field processing, in order to provide accurate pattern measurements at these frequencies.
A roof-top antenna range has been installed at the Bellcore facility in Red Bank, New Jersey. This facility is used as a far field range to measure highly directive antennas at millimeter wave frequencies. Theoretical and experimental studies were performed to characterize the range environment and identify reflections. Two computer programs were used to analyze the strength and location of interfering signals at both UHF and millimeter wave frequencies. These programs use Geometrical Optics and the Geometrical Theory of Diffraction to predict the location and strength of diffracted and reflected energy from the surrounding structures. Both singly and doubly diffracted interferences were considered. A bi-static radar, with an 850 MHz carrier, bi-phase modulated by a 40 Mbit/s pseudonoise code, was used to measure the impulse response of the environment. The antenna range measurements are compared with the analysis done at 850 MHz and calculated results are printed for the behavior of the range in the millimeter wave regime.
The direct far field pattern measurement of an aperture antenna becomes more difficult as the size of the aperture increases. Recent measurements on reflector antennas with 2D2/? =1500’ at The Ohio State University ElectroScience Laboratory have demonstrated the usefulness of the compact range in obtaining the complete far field pattern of antennas with large far field distances.
This paper presents a test method showing it is practical to bench-test antennas to uncover gain-related deficiencies. Design considerations for the small chamber are given along with a brief error analysis.
Narrow band RCS measurements are usually presented as RCS versus target aspect angle in either a rectangular or polar format. Wide band measurements are not normally analyzed in the frequency domain. The normal procedure is to perform either a one or two-dimensional Fourier transform of wide band data or obtain high resolution information on the location of scattering sources. In this paper, we investigate the possible uses of the wide band data directly. In particular, we show that a natural coordinate system for analysis of these data is a polar format with frequency taking on the polar distance parameter and aspect angle taking on the polar angle parameter. This format is not coincidentally, an intermediate step in the production of fully focused two-dimensional radar images. The polar format frequency domain plots are shown to be effective at categorizing the nature of the physical scattering. This is especially true when combined with image domain filtering to isolate scattering regions of interest. In addition, it can be useful in determining anomalies in the radar measurement system performance, and in assisting the analyst to explain unexpected image domain results.
The techniques of near-field antenna pattern measurement can be extended to near-field RCS measurement. The motivation for doing so is precisely the same as that for near-field antenna measurements; i.e., the convenience of an indoor antenna range, and an improvement in accuracy. Although the near-field measurement problem is solvable in principle in a manner analogous to the near-field antenna problem, it requires a significantly larger amount of time to take the necessary data, and to subsequently process the data to obtain useful quantities. BDM is currently involved in an on-going program to evaluate the feasibility of near-field bistatic RCS measurements. At the time of this writing, a complete set of mathematics has been formulated to handle the probe correction and data processing. The hardware has been built, software development is near completion, and the analysis of canonical scattering objects has been completed. Experimental data soon to be taken for these objects will be presented. It is hoped that the technique will prove to be a practical approach to RCS measurements.
March Microwave Systems B.V. is manufacturer of the dual cylindrical reflector Compact Antenna Test Range (CATR) that was designed by Vokurka [1] (see Fig. 1). The analysis of the test-zone fields of such a design is necessary to be able to optimize the geometry.
Over the last five years a considerable attention has been paid to further developments of Compact Antenna Test Ranges for both antenna and RCS measurements. For many applications, these devices proved to be more attractive than outdoor ranges or near-field/far-field transformation techniques. On the other hand, accurate operation at very low or very high frequencies can cause considerable difficulties. It is the aim of this paper to describe the theoretical limitation of collimating devices, in particular for low frequencies. For this purpose, an idealized collimator will be defined. Using the spectral components analysis a comparison of achievable accuracy will be made between collimators and outdoor ranges. Theoretical limits in the accuracy for RCS measurements will be computed for all applicable frequencies. Finally, a comparison will be made between the experiments on a dual-reflector Compact Antenna Test Range and theoretically achievable limits. Representative targets, like cylinders and rectangular plates have been used for experimental investigation. These data will also be presented.
In recent years automatic antenna test ranges have become more commonplace. This has created new particle problems related to the software and data stored. The problems are further pronounced if several test ranges are operated in parallel within the organization and nearfield tests are included.
This paper describes the computer system interfaces and hardware additions which provide engineers enhanced capabilities and greater flexibility from their antenna measurement systems. RCA Astro-Electronics has built three outdoor antenna ranges, each equipped with Scientific-Atlanta Antenna Analyzers. Two Series 2020 and one Series 2080 Analyzer are used to perform data acquisition and preliminary data processing for the three antenna ranges. Both S-A 2020 system computers have direct interface capabilities with two remote computer systems, which are primarily used for antenna design and analysis. The S-A 2080 system is interfaced indirectly via one of the S-A 2020 range computers. Direct line and modem interfaces provide user access to remote computer software and allow up and down loading of measured or computed data files. Using RCA software resident in each range computer, measured data files are unpacked, reformatted and downloaded for off-line processing. This process accelerates test schedules and allows analysis software to process data files from three antenna ranges in a single data format. Other enhanced system features include access to remote analysis software, requiring large disc storage space, for real-time evaluation at the antenna analyzer location.
The calibration of gain standards for antenna measurements requires path loss measurements between three antennas if the assumption of identical antennas is not made. The equipment finds the insertion loss for pairs of antennas as if the combination of the antennas and the free space between them were a two port network. The usual setup uses a network analyzer to measure the insertion loss. The Scientific Atlanta 2020 system can be operated as a network analyzer and used for these measurements. Part of the system is a synthesized signal source which allows frequency stepping, and along with leveling, enables the repetition of both amplitude and phase of the signals. The computer control of the equipment provides for rapid stepping through the frequencies, control of the receiver, ability to read amplitude and phase, and means of data storage for off-line analysis.
This paper reports on the measurements portion of an ongoing research program at the Georgia Institute of Technology into the design, analysis and measurement technologies of radomes. Specifically this paper reports on a technique for the near-field measurement of radome performance. The motivation for the development of the near-field measurement technique for radomes is to identify the types of interactions which take place between the radome and the transmitted electromagnetic field. It is postulated that such phenomena as coupling to the radome wall, tip scattering, internal reflections and bulkhead reflection would be easier to identify through near-field measurement than far-field measurement. * This work was supported by the Joint Services Electronics Program and Northrop Corporation
The ogival target-support pedestal as shown in Figure 1 is claimed to have a low radar cross section (RCS); yet, it can handle very large and heavy structures. This paper attempts to find out whether this claim is true through analysis as well as measurements. The pedestal backscatter is just one aspect of this study. Another more serious issue is associated with the bistatic scattering by the pedestal which influences the target illumination. * This work was supported in part by the National Aeronautic and Space Administration, Langley Research Center, Hampton, Virginia, under Grant NSG-1613 with The Ohio State University Research Foundation.
This paper describes the mechanical as well as electrical measurement of doubly curved reflector antennas. The techniques developed for measurement of the new Canadian RAMP Primary Surveillance Radar antenna are described. Instead of a conventional full size template fixture to measure the antenna contour accuracy, an optical twin-theodolite method is used. The problems of the method are discussed and a new simplified analysis for calculating reflector error of doubly curved antennas is presented. Reflector errors are calculated and displayed concurrent with the actual measurements. The measurement of primary and secondary patterns for such antennas are described. Included are brief descriptions of the improved Andrew pattern test range and anechoic chamber facilities.
This paper describes the computer system interfaces and hardware additions which provide engineers enhanced capabilities and greater flexibility from their antenna measurement systems. RCA Astro-Electronics has built three outdoor antenna ranges, each equipped with Scientific-Atlanta Antenna Analyzers. Two Series 2020 and one Series 2080 Analyzer are used to perform data acquisition and preliminary data processing for the three antenna ranges. Both S-A 2020 system computers have direct interface capabilities with two remote computer systems, which are primarily used for antenna design and analysis. The S-A 2080 system is interfaced indirectly, via one of the S-A 2020 range computers. Direct line and modem interfaces provide user access to remote computer software and allow up and downloading of measured or computed data files. Using RCA software resident in each range computer, measured data files are unpacked, reformatted and downloaded for off-line processing. This process accelerates test schedules and allows analysis software to process data files from three antenna ranges in a single data format. Other enhanced system features include access to remote analysis software, requiring large disc storage space, for real-time evaluation at the antenna analyzer location.
Compact range reflector systems have been previously used for far zone measurements in which case the feed is located at the reflector focus. It has been determined that near zone antenna pattern and backscatter measurements are feasible if the feed is appropriately located. Feed location information has been determined as a function of the radius of curvature of the near zone incident wavefront at the center of the measurement volume. Furthermore, numerous field quality data have been calculated. Field quality is defined as the closeness of the near zone field distribution in the measurement volume to the desired uniform spherical wavefront. The capability to measure near zone backscatter data was demonstrated with a 4-inch diameter cylinder, 4 feet in length. These measurements were made at 10 GHz, for a near zone range radius of 50 feet in the Ohio State University compact range facility. The near zone backscatter response for this cylinder was also calculated using a GTD analysis. A comparison of the calculations and measurements demonstrate the feasibility of the compact range for near zone backscatter measurements. This development leads to the consideration of compact range reflector systems for more general electromagnetic field simulations. For example, by employing an array feed, instead of a single feed element, the incident field in the measurement volume can be controlled in a rather flexible way. It is the purpose of this paper to explore some possible simulations.
This paper is a discussion of the upgrade of an automated antenna pattern data acquisition and analysis system located at the U.S. Army Electronic Proving Ground (USAEPG), Ft. Huachuca, Arizona. The upgrade was necessary as the existing facility was inadequate with respect to frequency coverage, data processing, and measurement speed and accuracy. The upgrade was also necessary in view of USAEPG long range plans to automate a proposed large compact range.
The design concept for outdoor antenna ranges operated at frequency 50 MHz is discussed. The antenna range is designed for test of VHF antennas mounted on a full-scale satellite mockup. Due to the large size of test objects, a tradeoff between cost and test accuracy among carious range configurations is addressed. Due to near-omni directional characteristics of test antennas, the multipath interference may be severe. The interference ground reflection, surface wave and multiple scattering are quantified and evaluated.