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The Electromagnetic Engineering Section of the National Research Council of Canada maintains a variety of pattern ranges and associated instrumentation to serve the needs of Canadian industry, government departments and universities. An extensive review of the facilities in 1983 revealed the need for significant modifications to maintain the current state-of-the-art level in antenna measurement technology.
In this paper we present a three-antenna measurement procedure which yields the polarization of an unknown antenna to an accuracy comparable to that of the improved method of Newell. The complete method is based on step-scan motion of the two polarization axes on which the antenna pairs are mounted. As a special case this step-scan procedure includes the usual single axis polarization pattern method of polarization measurement. This three antenna polarization measurement method can be readily automated and is carried out straightforwardly with the assistance of a minicomputer for data acquisition and data reduction. The data reduction method is based on conventional digital Fourier transform techniques and has the advantage of inherent noise rejection. It utilizes a large number of sample points which greatly overdetermine the parameters to be measured. The method has been verified experimentally with measurements made on multiple overlapping sets of three antennas, as is conventional for this kind of procedure. The data are presented for broad-beam antennas of the type used as near field probe horns.
Two alternative sampling techniques for planar near-field measurements are discussed. The first technique reduces the number of data points taken by 50% by measuring the field and its differential in one direction at each point. The second technique samples the field on a hexagonal lattice and allows reduction in the number of samples taken by up to 25%. Far-field patterns for an X-band antenna calculated from these alternative near-field sampling schemes are presented and compared with the far-field patterns calculated using conventional planar near-field techniques.
The compact range has been used for many years to measure directive antenna patterns. More recently, however, there has been increased interest to use the compact range for scattering measurements. In order to provide the proper field illumination for such measurements, the traditional designs must be improved in terms of the stray signals coming from the reflector termination. One attempt to improve the field quality in the measurement zone was to use a rolled edge structure added to the basic parabolic reflector. This improved the system performance but required excessively large structures to meet the system requirements. Thus, a novel blended surface was developed which satisfies the measurement requirements without adding large structures. This new design can provide ripple levels no larger that 1/10th of a dB across the target zone as will be shown in the oral presentation.
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.
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.
System-2000 instruments were created for pattern range applications. The SD-2000 Synchro Monitor was developed in 1983, the MC-2000 Motor Controller in 1984, and System-2000 Host Processor in 1985. Dual black and white video monitors are being used both for graphics and closed circuit television. A rigid body motion application written in FORTH includes graphic primitives to simulate range components. In this paper, a simple aircraft model is installed on a model tower. A square hole in the vertical stabilizer simulates where a probe or antenna is to be located. The hole is offset from the inter-section of model and tower rotation axes, for discussion. Raster and spiral scanning are examined. Spiral scanning required simultaneous control o two drive motors. Emphasis is placed on using System-2000 dual axis features for motor control and graphic imaging of successive model positions.
In this paper we describe the implementation of an antenna pattern recorder using a desktop digital computer to replace the conventional analog electro-mechanical element. This means that all pattern recorder front-panel controls and charts are displayed on and accessed via the computer’s CRT, keyboard and peripherals. It has all the regular features, e.g. choice of scales, pen up/pen down etc., plus a multitude of additional features, obtained owing to the use of a digital computer, which will later be outlined in detail. In spite of the numerous options available, the instrument is very easy to master, requires no preliminary knowledge of computer operation and programming. It is entirely menu-driven and designed to trap most operator errors while maintaining a user-friendly environment suitable for technician-level operation.
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.
Antennas are designed to operate with planar phase fronts, but are usually tested on finite length ranges that produce curved phase fronts. The result is a pattern error near the main beam. For conventional antennas the accepted range length requirement is R>2D2/? which produced a spherical phase error of 22.5 at the perimeter of a diameter D at wavelength ?. This, in turn, causes a 35 dB shoulder. For ultra low sidelobe antennas (ULSA) even longer ranges have been suggested. Such range sizes may be unavailable as well as undesirable, since the larger the range the more difficult it is to eliminate reflections.
Pulsed systems have been used for many years to eliminate unwanted clutter in RCS measurements, but have not been used much for antenna measurements, even though similar clutter problems are common to both. There are many reasons for this, such as cost, increased bandwidth requirements, lack of necessary hardware, etc. However, with the development of modern pin diode switches, one can construct a low cost pulsed measurement system that simply adds to existing CW equipment. Using the system design presented in this paper, one can eliminate unwanted clutter from antenna measurements simply by adjusting the transmit and receive pulse widths and the delay between them. For example, it can be used to range gate out the ground bounce for outdoor measurements or the backwall for an indoor facility so that one can accurately measure the backlobe of a high gain antenna. The pulsed system is presented along with several measured examples of its use.
A technique for improving the accuracy of G/T measurements of highly directive antennas is introduced. The technique presents was developed to overcome uncertainties in ephemeral information, antenna positioning, system gain stability, and other random and nonrandom phenomena. The particular application discussed uses Casseiopeia-A as a noise source but the technique can be adapted for use with other extraterrestrial noise sources.
Paper not available for presentation.
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.
This paper describes the relationship of probe polarization correction to probe-pattern corrected and non-probe-pattern-corrected spherical near-field measurements. A method for reducing three-antenna polarization data to a form useful for polarization correction is presented. The results of three-antenna measurements and the effects of polarization correction on spherical near-field measurements are 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.
End-to-end testing of electronic warfare (EW) equipment at the organizational or flight lines level is accomplished by use of an antenna coupler which is placed over the EW system antenna. The coupler is used to inject a stimulus signal simulating a signal emanating from a distant radar, and to receive and detect the EW system response (EW transmit) signal. The coupler is used to determine the EW receiver sensitivity over a swept frequency coverage and the EW transmit gain and effective radiated power (ERP) versus frequency characteristics, as well as to determine the operating integrity of the EW antenna and transmission lines.
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.
In recent years a new class of reflector antennas utilizing array feeds has been receiving attention. An example of this type of antenna is a reflector utilizing a moveable array feed for beam steering. [1]-[3]. Due to the circuitry required to adjust the weights for the various feed array elements, an appreciable amount of loss can be introduced into the antenna system. One technique to overcome this possible deficiency is to place low noise amplifiers with sufficient gain to overcome the weighting function losses just after each of the feed elements. In the evaluation of signal processing antennas that employ amplifiers the standard antenna gain measurement will not be indicative of the antenna system’s performance. In fact, by only making a signal measurement, the antenna gain can be made any arbitrary value by changing the gains of the amplifiers used. In addition, the IEEE Standard Test Procedures for Antennas [4] does not cover the class of antennas where the amplifier becomes part of the antenna system. There exists a need to establish a standard of merit or worth for multi-element antenna systems that involve the use of amplifiers. This communication presents a proposed figure of merit for evaluating such antenna systems.