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Far Field
Estimation of the size, location, and powerdensity of the 'bright spot' in a compact antenna range
When performing farfield testing on largeaperture 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 nearfield of the reflector. Also, for many antennas of interest, the reflector is likewise in the nearfield 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 farfield range of the same length would suffice.)
Estimation of the size, location, and powerdensity of the 'bright spot' in a compact antenna range
When performing farfield testing on largeaperture 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 nearfield of the reflector. Also, for many antennas of interest, the reflector is likewise in the nearfield 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 farfield range of the same length would suffice.)
Far field pattern correction for short antenna ranges
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.
Design of a multipurpose antenna and RCS range at the Georgia Tech Research Institute
The design of a multipurpose Antenna/RCS range at GTRI is described. A novel approach to design of the farfield antenna range utilizes the bottom 40foot section of a 130foot windmill tower. The top 90foot section is used as the main support for a slant RCS measurement range offering a maximum depression angle of 32º. A 100tom capacity turntable, capable of rotating an M1 Tank, is located 150 feet from the 90foot tower. The rigidity and stability of the tower should allow accurate phase measurement at 95 GHz for wind speeds up to 10 mph. In addition, a 500foot scalemodel range uses the ground plane effect to enhance target signaltonoise and is designed to be useful at frequencies up to 18 GHz. Initially, the radar instrumentation to be utilized with the ranges includes several modular instrumentation systems and associated digital data acquisition equipment at frequency bands including C, X, Ku, Ka, and 95 GHz. The properties of these systems, which include coherence, frequency agility, and dual polarization, are discussed.
Pulsed, computercontrollable receiver and exciter having wide instantaneous bandwidth for testing activeelement phased arrays
This paper describes a receiver and exciter built by Texas Instruments for automated testing of electronicscan antennas. The equipment is suitable for both nearfield and farfield testing, and is programmable through a GeneralPurpose Interface Bus (GPIB) conforming to IEEE Standard 488. A twochannel design is described, but the technology is equally applicable to receivers from one to three (or more) channels. The receiver outputs are digitized as 10bit I and Q (Inphase and Quadrature) components.
RADARSAT SAR antenna testing requirements and facility
The Radarsat synthetic aperture radar (SAR) antenna is baselined to be a large slotted waveguide planar array, with a rectangular aperture of dimensions 1.5m x 15m. At the nominal frequency of 5.3 GHz, the dimensions in terms of wavelengths are approximately 26.5 lambda x 265 lambda. The usual 2D(squared) divided by lambda formula yields a farfield range length of at least 7.96 Km, which is far beyond the range lengths currently available to the program. A more conservative design would at least double that number, rendering a farfield measurement concept all but impracticable.
(*) This work was carried out for the Radarsat Project Technical Office of the Communications Research Centre, Canadian Department of Communications, under DSS contract OSR8400175, funded by the Canadian Department of Energy, Mines, and Resources.
Reduction of nearfield techniques duration
Nearfield measurement techniques are widely used today for antenna farfield pattern characterization. Since the 60's, much has been done concerning accuracy. The three main coordinate systems, planar, cylindrical, and spherical have been investigated. probe corrections have been introduced [1]  [6].
Improving the accuracy of the planar nearfield farfield transformation by a proper choice of integration algorithm and grid
The planar scanning system is commonly used in the near field testing of high gain antennas, where the rectangular measurement grids are used. The polar grids are also used, which are more convenient when the antenna aperture is circular. In the planar scanners the measurements are carried out in the xy plane in increments of both x and y. The result of the measurement is an mxn matrix of the near field data consisting of m cuts with n data points per each cut. The far field patterns may then be calculated, using the near field data, by the aperture field integration or the modal expansion methods [1]. In this paper the aperture field integration method is studied, where the far field components can be calculated from [1]  [2].
Improving the accuracy of the planar nearfield farfield transformation by a proper choice of integration algorithm and grid
The planar scanning system is commonly used in the near field testing of high gain antennas, where the rectangular measurement grids are used. The polar grids are also used, which are more convenient when the antenna aperture is circular. In the planar scanners the measurements are carried out in the xy plane in increments of both x and y. The result of the measurement is an mxn matrix of the near field data consisting of m cuts with n data points per each cut. The far field patterns may then be calculated, using the near field data, by the aperture field integration or the modal expansion methods [1]. In this paper the aperture field integration method is studied, where the far field components can be calculated from [1]  [2].
Multiple reflection effects on a nearfield range
The NBS has developed a test for estimating the effects of multiple reflections between the probe and antenna on the far field using a nearfield measurements. The essence of this test is to take nearfield data at more than one separation distance. For each separation distance the far field is obtained using a Fourier transform. The different far fields are then averaged in a complex manner. The difference between the average far field and each of the other far fields is due to multiple reflection effects.
Nearfield measurement of radome performance
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 nearfield measurement of radome performance. The motivation for the development of the nearfield 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 nearfield measurement than farfield measurement.
* This work was supported by the Joint Services Electronics Program and Northrop Corporation
Displaced phase center antenna measurements for space based radar applications
An investigation of the use of array mutual coupling measurements, to evaluate displaced phase center antenna (DPCA) performance, is made. The details of a subscale space based radar (SBR) DPCA phased array and the array mutual coupling technique are discussed. DPCA results are quantified experimentally under a number of test conditions. It is shown that the test array beam decorrelation computed from array mutual coupling data, is in good agreement with both theoretical predictions, planar near field measurements and direct far field measurements.
Methods for the calculation of errors due to wall effects in an RCS measurement compact range
A method for the calculation of the errors induced through targetwalltarget interactions is presented. Both nearfield and farfield situations are considered. Farfield calculations are performed both with Fraunhoffer diffraction theory and target antenna analogies. Absorber is considered as both a specular and a diffuse scatterer. The equations developed permit trade studies of chamber size versus performance to be made.
Farfield pattern measurements and time domain analysis of reflector antennas in the compact range
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.
Experimental study of interpanel interactions at 3.3 GHz
A general theoretical approach is formulated to describe the complex electromagnetic environment of an Nelement array. The theory reveals the elementtoelement interactions and multiple reflections within the array. To experimentally verify some features of the theory, measurements on experimental array panels in various configurations were made. These array panels consisted of 256 microstrip radiating elements. In each of the configurations both the nearfield and portside signals were measured to study the interactions between these panels. In particular, the effects of opencircuited array panels on the radiation pattern of a single panel are observed both in the near field and in the far field. It is found that internal scattering is the main mechanism of interaction between panels, rather than reradiating of signals received from adjacent panels. The effects of scattering are observable at the 50 dB level.
Farfield pattern measurements and time domain analysis of reflector antennas in the compact range
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.
Antenna pattern correction for range reflections
When performing antenna pattern measurements on farfield antenna test ranges or in anechoic chambers, one of the main problems concerning the pattern accuracy is range reflections. Previous works dealing with this have been limited to the onedimensional case.
Quiet zone characterization using Fourier transform technique
A technique has been developed to characterize the illuminating signal present within an antenna test zone. Information of angular multipath distribution as well as relative signal amplitudes of various paths can be ascertained by transforming phase and amplitude data measured at numerous intervals across the lineal aperture probe apparatus. An experiment was carried out to test the technique using a tenfoot linear aperture probe installed to probe an antenna test zone located at one end of a onehalf mile range. During the experiment several measurements were carried out at two different locations within the farfield antenna range and at two different frequency bands. This paper discusses the results of the experiment as well as the practical aspects of this technique.
NADC low sidelobe farfield measurement range
This paper describes a novel technique for acquisition of farfield antenna patterns from a very low sidelobe antenna.
The low sidelobe requirement imposes stringent multipath restrictions on the measurement range and to accommodate this requirement a vertical range configuration is employed rather than the more conventional range which is parallel to the earth's surface. To assure accurate measurement of sidelobe levels, multipath levels were specified at minus seventy dB (70 dB) relative to the directpath, peakofthebeam level.
In this novel range configuration, an Antenna Under Test (AUT) is oriented to face skyward and operated in a receive mode with EField illumination provided from an airborne source. An optical tracker provides data of airborne source location and timedivision multiplexing of both frequency and antenna beam position enable optimization of data acquisition efficiency. Postacquisition processing provides deinterleaving of the desired beam(s)/frequency(s).
This paper will present a discussion of the problems encountered and the techniques employed to overcome them in the design of this range. A description of the range will also be presented.
Time gating of antenna measurements
The principle of timegated antenna measurements is differentiation of signals by timeofarrival. On a farfield antenna range, all reflected stray signals arrive later in time than the direct path signal. A pulsemodulated waveform from the source antenna can be gated at the receiving antennaundertest to produce a response to the wanted signal only.

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