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This paper reports on a study conducted by the Georgia Institute of Technology for the U.S. Army Electronic Proving Ground, Fort Huachuca, Arizona to determine the feasibility of a large (50-foot quiet zone) outdoor compact range located at Fort Huachuca. The range is to be operated over the frequency range from 5 to 100 GHz. The main function of the range would be to measure patterns of low gain antennas mounted on military vehicles and aircraft, to determine whether antenna/vehicle interactions were degrading system performance. The paper presents both the electromagnetic and mechanical rational used as a basis for feasibility. The feasibility study considered many possible compact range configurations including the center fed paraboloidal reflector, the offset fed paraboloidal reflector (both prime feed and subreflector feed) and the dual crossed parabolic cylinder (DCPC) reflectors.
The Compact Range RCS Measurement System is comprised of the Harris Shaped Compact Range and the Hughes Short Pulse Coherent RCS Measurement System. The range offers a 10 foot spherical quiet zone with less than ±0.25 dB amplitude ripple, 0.2 dB amplitude taper, and ±2 degrees phase ripple. The short pulse system offers a pulse width as small as 5 nsec with range gate increments of 100 psec minimum. The system has a sensitivity of –70 dBsm without integration and –120 dBsm with 50 dB of coherent integration. System linearity is better that ±0.5 dB over the 70 dB instantaneous dynamic range. The Shaped Compact Range offers nearly 98 percent illumination efficiency with negligible spillover which minimizes the required anechoic chamber size and the amount of absorbing material necessary. The block diagram of the system is shown in Figure 1.
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.
When performing far-field testing on large-aperture antennas, the range length 2D2/? (that is needed to achieve a ‘flat’ phase front at the test plane) is sometimes inconviniently long. In these instances, the compact range of Figure 1 may be used as an alternate. In this range, the spherical wave radiated by the range source antenna is converted to an approximately plane wave by a large parabolic reflector. The antenna to be tested is immersed in this plane wave, at a location that is well within the near-field of the reflector. Also, for many antennas of interest, the reflector is likewise in the near-field of the test antenna, although this is not a requirement. (For those cases where the reflector is in the far field of the test antenna, there is little motivation to use a compact range, since a conventional far-field range of the same length would suffice.)
The Ohio State University (OSU) ElectroScience Laboratory (ESL) utilizes a parabolic reflector as part of the compact range system [1]. It is necessary to probe the plane wave zone of this reflector in order to measure the purity of the plane wave that is generated. Variations in the amplitude or the phase of the signal received by a probe antenna as the probe is moved linearly across the plane wave region indicate deviations from a pure plane wave in the test zone.
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.
This paper describes the new antenna test facility now in operation at General Electric Space Systems Division in Valley Forge, PA. The antenna test facility is located in a new building 155’ x 74’ x 53’ high. It consists of a shielded anechoic room 60’ x 56’ x 35’ high which contains both a Compact Range and a Spherical Near Field Range, instrumented over the Frequency Range 1-100 GHz to perform automatic and manual measurements of antenna characteristics. In addition it provides for a 700’ boresight range accessible through large doors with an RF trans-parent window. A 3-axis positioner can accommodate antenna apertures up to 20’. The facility is used for both, testing of antenna systems and testing of entire spacecraft for electromagnetic compatibility and interference.
Millimeter wave antenna measurements are hampered by a lack of cost effective automated test equipment and the necessity of using unwieldy waveguide set-ups. This paper describes some practical considerations in using readily available test equipment to perform accurate, repeatable antenna measurements. Experimental results of gain, polarization and sidelobe level measurements will be discussed and compared with calculated results.
A dual offset shaped reflector compact range is described. Improvements over the traditional single reflector, apex-fed compact range are outlined and discussed. A design plan for a dual offset shaped reflector compact range for EHF antenna measurement is presented.
This paper describes a horizontal, cylindrical surface, near-field measurement facility which was designed and constructed in 1984 and is used for the determination of far field patterns from near field measurement of UHF television transmitting antennas. The facility is also used in antenna production as a diagnostic and alignment tool.
A dual offset shaped reflector compact range is described. Improvements over the traditional single reflector, apex-fed compact range are outlined and discussed. A design plan for a dual offset shaped reflector compact range for EHF antenna measurement is presented.
The complete sequence of RF tests required to evaluate the electrical performance of a broad band UHF helix antenna to be used in the zero gravity environment of space is described. The development of an adequate structure which would support the antenna and yet cause no pattern perturbation is mentioned. The test range configuration used, with the UHF antenna inside and anechoic chamber and the source antenna illuminating it through a polyfoam window in one side, is discussed. The problems encountered in taking radiation pattern plots and in making gain measurements using a gain standard near the low frequency limit, 250 MHz, of the antenna test range and the methods utilized to minimize their effect are given in some detail.
A planar surface, near-field measurement technique is presented for the near-field measurement of monostatic radar cross-section. The theory, system configuration and measurement procedure for this technique are presented. It is shown that the far field radar cross-section can be determined from the near field measurements. An associate near-field radar cross-section measurement technique is presented for the measurement of bistatic near field radar cross-section. The bistatic technique requires a plane wave illuminator in addition to the planar surface near field measurement system. A small compact range is used as the bistatic illuminator. Bistatic near-field measurements are presented for a simple target.
When low crosspolar pattern measurements are required, as in the case of the L-SAT Propagation Package Antennas (PPA) with less than -36 dB linear crosspolarization inside the coverage zone, the use of good polarization standards is mandatory (1). Those are usually electroformed pyramidal horns that produce crosspolar levels over the test zone well below the -60 dB level typically produced by the reflectivity of anechoic chambers. In this case the alignment errors (elevation, azimuth and roll as shown in fig. 1) can become important and its efects on measured patterns need to be well understood.
An innovative technique has been developed for accurately measuring very low Sidelobe Antenna patterns by the method of planar near field probing. The technique relies on a new probe design which has a pattern null in the direction of the test antenna’s steered bean direction. Simulations of the near field measurement process using such a probe show that -60dB peak side-lobes will be accurately measured (within established bounds) when the calibrated near field dynamic range does not exceed 40 dB. The desireable property of the new probe is its ability to “spatially filter” the test antenna’s spectrum by reduced sensitivity to main beam ray paths. In this way, measurement errors which usually increase with decreasing near field signal level are minimized. The new probe is also theorized to have improved immunity to probe/array multipath and to probe-positioning errors. Plans to use the new probe on a modified planar scanner during tests with the AWACS array at the National Bureau of Standards will be outlined.
The development of advanced spacecraft communication antenna systems is an essential part of NASA’s satellite communications base research and technology program. The direction of future antenna technology will be toward antennas which are large, both physically and electrically; which will operate at frequencies of 60 GHz and above; and which are nonreciprocal and complex, implementing multiple beam and scanning beam concepts that use monolithic semiconductor device technology. The acquisition of accurate antenna performance measurements is a critical part of the advanced antenna research program and represents a substantial antenna measurement technology challenge, considering the special characteristics of future spacecraft communications antennas.
This presentation will focus on the recently revised ANSI C95 RF Radiation Exposure Standard. Some of the research background for the new standard will be given, and its impact will be explained. Instrumentation guidelines for measuring potentially hazardous fields will be presented. The possible damaging effects of non-ionizing RF radiation is receiving increased attention in the public eye, and it behooves the practicing antenna engineer to be aware of the potential dangers to health and safety from exposure of RF energy.
The measurement of microwave antennas indoors began with the advent of commercial absorbing material. The use of absorbers can be traced back to a 2 gHz material developed by the Dutch in the Thirties. During the Forties, considerable progress was made on absorbing materials, but even after World War II, security considerations limited the application. Some materials found use as indoor shields for antenna tests, but limited bandwidth limited the utility of these materials. When a broad band absorber was developed the antenna experts did not believe that this material would be made commercially because they presumed a limited market.
A planar surface, near-field measurement technique is presented for the near-field measurement of monostatic radar cross-section. The theory, system configuration and measurement procedure for this technique are presented. It is shown that the far field radar cross-section can be determined from the near field measurements. An associate near-field radar cross-section measurement technique is presented for the measurement of bistatic near field radar cross-section. The bistatic technique requires a plane wave illuminator in addition to the planar surface near field measurement system. A small compact range is used as the bistatic illuminator. Bistatic near-field measurements are presented for a simple target.
The compact range is an electromagnetic measurement system used to simulate a plane wave illuminating an antenna or scattering body. The plane wave is necessary to represent the actual use of the antenna or scattering from a target in a real world situation. Traditionally, a compact range has been designed as an off-set fed parabolic reflector with a knife edge or serrated edge termination. It has been known for many years that the termination of the parabolic surface has limited the extent of the plane wave region or, more significantly, the antenna or scattering body size that can be measured in the compact range. For example, the Scientific Atlanta (SA) Compact Range is specified to be limited to four foot long antennas or scattering bodies as shown in their specifications. Note that the SA compact range uses a serrated edge treatment as shown in Figure 1. This system uses a parabolic reflector surface which is approximately 12 square feet so that most of the reflector surface is not usable based on the 4 foot square plane wave sector. As a result, the compact range has had limited use as well as accuracy which will be shown later. In fact, the compact range concept has not been applied to larger systems because of the large discrepancy between target and reflector size. In summary, the target or antenna sizes that can be measured in the presently available compact range systems are directly related to the edge treatment used to terminate the reflector surface.