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For approximately 10 years the National Bureau of Standards has used the Extrapolation Technique (A. C. Newell, et al., IEEE Trans. Ant. & Prop., AP-21, 418-431, 1973) for accurately calibrating transfer standard antennas (on-axis gain and polarization). The method utilizes a generalized three-antenns approach which does not require quantitative a priori knowledge of the antennas. Its main advantages are its accuracy and generality. This is essentially no upper frequency limit and it can be applied, in principle, to any type of antenna, although some directivity is desirable to reduce multipath interence.
The ability to gather real-time data from a remote site is of significant value in the far-field test of large scale non-reciprocal antenna arrays. With the advent of microprocessors, digitally controlled test equipment, and high speed data links, what was once impossible has not only become feasible but also economically realizable. This paper discusses the design of a remote data-gathering capability currently on-line at the Westinghouse Ridge Road Antenna Range. The system described is a computer-controlled phase and amplitude measuring technique remoted over a 1/3 mile range with a 56K baud fiber-optics data link. Considerations of system configuration, timing, protocol, error-detection and self-diagnostics are discussed.
Rapid advances in digital and micro-computer technology have revolutionized automated control of most measurement processes and the techniques for analysis, storage and presentation of the resulting data. Present-day computer capabilities offer many “user-friendly” options for antenna instrumentation, some of which have yet to be exploited to their full potential. These range from vendor-integrated turnkey systems to innovative designs employing a multitude of subsystem components in custom-interfaced configurations. This paper reviews system and component choices keeping in mind their relative merits and trade-offs. Key design considerations are outlined with particular emphasis on: a) Integration and interfacing of different instrumentation, hardware and software subsystems. b) Upgrading and/or designing of completely new facilities. Various other problems, such as vendor package compatability, and those associated with the analysis and application of measured antenna data are discussed. In addition, suggestions are offered to promote the establishment of a mechanism to facilitate the interchange of data between different antenna measurement laboratories and analysis centres.
This paper presents a three-antenna plane-wave scattering-matrix (PWSM) formulation and a formal solution. An example will be demonstrated in which two of the three antennas are electromagnetically identical (the transmitter and the receiver) and the third (the scatterer) has arbitrary electromagnetic properties. A reduced reflection integral-matrix will be discussed which describes the transmit, scatter, receive (TSR) interaction. An antenna scatterer spectral tensor Greens function is identified. In this formulation the transmit spectrum will be scattered by the third arbitrary antenna (target) and this scattered spectrum may be considered to have originated from a transmitting antenna. Near-field antenna measurement techniques are applicable with determine the electric (scattered) field spectral density function.1, 2 If a second deconvolution is applied, a transmit probe corrected spectral density function or scattering tensor can be determined in principle. In either case, a near- or far-electric field can be calculated and a radar cross section determined.
One of the variables to be quantified when making antenna measurements is position. Without accurate and timely position information, the spatially dependent data cannot be correctly interpreted. Scientific-Atlanta’s 1885 Positioner Indicator and 1886 Position Data Processor offer several improvements in providing position information which can enhance an antenna measurement system. New position indicating techniques have been implemented to allow a higher degree of accuracy and speed than previously attainable. These have been combined with advanced features for automatic system flexibility to create a high performance instrument for many applications. This paper describes the capabilities of these two instruments and how they can be used to improve system performance.
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.
The paper describes a near field facility developed at Hughes Aircraft Space and Communications Group for the purpose of performing measurements on satellite antennas. The facility is designed for planar near field scanning with capability for adding cylindrical scanning. The facility has a scanner with a 21 foot square range and is capable of measuring large antennas with operating frequencies up to 15 GHZ. The measurement system is designed for testing multi-beam, multi-frequency antennas. Data collection, scan control and data analysis functions are all controlled by a single computer system. Growth plans include the addition of an array processor for the ability to perform Fast Fourier Transforms in near real time. Results for the antennas which have been measured will be shown along with far field range data for comparison.
The purpose of an instrumentation radar is to characterize the Radar Cross Section (RCS) of a target as a function of target aspect and radar frequency. In addition, an instrumentation radar may be used to produce a high resolution radar image of a target which is useful in target identification work and as a diagnostic tool in radar cross section reduction. These purposes differ from those of a conventional radar, in which the objective is to detect the presence of a target and to measure the range to the target. Several different radars are currently used to perform radar cross section measurements. Common instrumentation radars may be classified as CW, Pulsed CW (Low-Bandwidth IF), Linear FM (FM-CW), Pulsed (High-Bandwidth IF) and Short Pulse (Very High-Bandwidth IF). These radars accomplish the measurement task in distinct manners, and it is sometimes difficult to determine where the strength or weakness of each radar lies. In this paper, a set of performance criteria is proposed for RCS measurements. The proposed criteria can be applied uniformly to any instrumentation radar independent of the type of radar design employed. The criteria are chosen to emphasize those performance characteristics that relate directly to RCS measurements and thus are most important to the user. Two instrumentation radars which have been designed at Scientific Atlanta, namely the Series 2084 (Linear FM) and the Series 1790 (Pulse), are used to illustrate the application of the performance criteria.
A monostatic radar measurement system at the U.S. Navy Pacific Missile Test Center (PACMISTESTCEN) located at Pt. Mugu, California was utilized to obtain incidence angle performance of radar absorbing structure (RAS) panels. The traditional methods of obtaining reflectivity data for absorptive materials over a range of incidence angles is a technique known as the NRL arch. Developed over 30 years ago by the U.S. Naval Research Laboratory, the technique utilizes moveable bistatic antennas on an arch equidistant from the test material panel in order to obtain incidence angle data.
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.
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 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.
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.
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.
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.
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.