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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.
A classical problem encountered when measuring the far-field radiation pattern of an antenna in a medium-distance range is the degradation that occurs when undesirable reflections (from the ground or nearby objects) are present. To reduce this problem, the source and test antennas are often installed on towers to remove them from the reflective objects, RF absorptive materials are used to reduce the magnitude of the reflected signals, and often the reflective objects in the range are adjusted in order to null out the reflections and “clean up” the range. These solutions are often limited in their effectiveness and can be prohibitively expensive to implement.
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.
RCA-Astro Electronics in Princeton, N.J. designs, develops and tests multiple-beam offset reflector antenna systems in the C and Ku frequency bands for satellite communications. Antenna measurements are performed at the antenna subsystem and the system level and on the complete spacecraft to demonstrate that alignment and performance meet their specification. This paper discussed the antenna range designs and test techniques involved in data acquisitions for contour patterns, cross-polarization isolation and antenna gain characterization. A description of the software required to obtain, analyze and present the data will be included in addition to typical test results.
Wideband RCS instrumentation systems can provide a high degree of range resolution. By combining wideband RCS data with a synthetic-aperture or Doppler processing, the spatial distribution of radar reflectivity can be determined. These systems provide diagnostic capabilities which are useful for locating scattering sources on complex objects and for assessing the effectiveness of modifications. The Proceedings of the 1983 meeting included a paper which described a linear-FM system operating over a 3 GHz bandwidth capable of measuring RCS vs range, cross range, and frequency using a single measurement set-up. This paper analytically demonstrates a procedure for extracting CW RCS patterns from the wideband data obtained using the linear-FM system. By combining the latter and the former processing, it is possible to obtain from a single data array both wideband responses showing the spatial distribution of scatterers and narrowband responses which are the traditional CW RCS patterns. The paper includes experimental verifications of these assertions by comparing results of CW measured data with data extracted from wideband RCS measurements.
The following features have been added to the spherical near-field software set which is available for the Scientific-Atlanta 2022A Antenna Analyzer. Gain Comparison Measurement Probe Pattern Measurement and Correction Thermal Drift Correction Spherical Modal Coefficient Analysis Far-Field, Radiation Intensity, and Polarization Display The addition of the probe pattern correction permits antenna measurements to be made at range lengths down to within several wavelengths of touching. The addition of probe polarization measurement permits three antenna polarization measurements to be made and analyzed as well as two antenna polarization transfer measurements. Correction for phase and amplitude errors attributable to thermal drift is accomplished by the return-to-peak method. Reduction of antenna patterns to spherical modal coefficients is an essential feature of spherical near-field to far-field transforms and is offered as an augmentation to antenna design. Far field display features permit the far fields of antennas to be presented in both component and radiation intensity formats, in circular, linear and canted linear polarization components.
In order to accurately determine the far-field of an antenna from near-field measurements the receiving pattern of the probe must be known so that the probe correction can be performed. When the antenna to be tested is circularly polarized, the measurements are more accurate and efficient if circularly polarized probes are used. Further efficiency is obtained if one probe is dual polarized to allow for simultaneous measurements of both components. A procedure used by the National Bureau of Standards for determining the plane-wave receiving parameters of a dual-mode, circularly polarized probe is described herein. First, the on-axis gain of the probe is determined using the three antenna extrapolation technique. Second, the on-axis axial ratios and port-to-port comparison ratios are determined for both the probe and source antenna using a rotating linear horn. Far-field pattern measurements of both amplitude and phase are then made for both the main and cross components. In the computer processing of the data, the on-axis results are used to correct for the non-ideal source antenna polarization, scale the receiving coefficients, and correct for some measurement errors. The plane wave receiving parameters are determined at equally spaced intervals in k-space by interpolation of the corrected pattern data.
Recent construction of RCS ranges has involved paraboloidal reflectors ranging from a few feet to sixty feet in diameter. These reflectors have required broad band feeds because the typical radar illuminator-receiver is capable of operating over an octave in frequency. This paper will describe a series of feeds which cover any octave in frequency from 100 mHz to 8 gHz, with coaxial line inputs. In addition waveguide-port feeds will be described which cover all of the standard waveguide bands up to 18 gHz. The four basic requirements for all of these feeds are: a) capable of handling the radar power, b) VSWR less than 2 to 1, c) orthomode operation with a 30 db isolation between the two linear polarizations and d) a radiation pattern which is constant with frequency. A fifth problem, for the reflectors which are truncated, is that of providing an elliptical cross section beam over the frequency band.