A Brief History of the Development of the Near-Field Measurement Technique at the Georgia Institute of Technology

The activity of the Georgia Institute of Technology in the development of the near-field measurement technique is reviewed. The work conducted during the years 1967-1973 is given primary importance, and the major near-field developments in the 1973-1980 time period are also briefly described. HE GEORGIA Institute of Technology has historically T had a strong interest in antenna measurement techniques. Scientific-Atlanta, Inc. is a Georgia Tech spin-off company formed in the mid-1950’s to produce instrumentation for antenna measurements. The reflector compact antenna measurement technique was developed at Georgia Tech in the mid1960’s under the leadership of Richard C. Johnson. Georgia Tech was awarded a patent for the compact antenna measurement range in 1967 [l] . Also in the mid-l960’s, Demetrius T. Paris became interested in the near-field behavior of antennas in his study of radomes, which are often located in the radiating near field of an antenna. He showed that greater accuracy in far-field pattern calculation of an antenna can be achieved using the vector formulation of the diffraction equation which requires knowledge of both the electric and magnetic aperture fields versus the scalar formulation which requires knowledge of only one. These results were published in 1968 [2]. He likewise formulated a radome analysis technique which required knowledge and manipulation of both the electric and magnetic near fields of an antenna, as presented in a 1970 J . Searcy Hollis and Larry Clayton, Jr., of ScientificAtlanta had envisioned the practicality of planar surface nearfield measurements and had performed amplitude and phase near-field measurements of a Ku-band antenna, compared the calculated far-field patterns to measured far-field patterns and published these results as early as 1960 [4]. They used the scalar diffraction integral of the planar surface aperture fields to calculate the far-field pattern of the antenna. The scalar diffraction integral reduces to a Fourier transform of the planar surface aperture fields for far-field determination. Toward this end, Scientific-Atlanta had developed a 100-in by 100-in planar scanner, a phase-amplitude receiver, and a Fourier integral analog computer by 1961. paper ~31. Manuscript received January 1988. The author is with the School of Electrical Engineering, Georgia Institute of Technology, Atlanta, GA 30332. IEEE Log Number 8821098. Paris approached Scientific-Atlanta in his search for research support for his graduate student, the writer of this paper, in 1967. The topic of mutual interest was the theory and practical implementation of planar surface near-field measurements. Scientific-Atlanta provided a three-year research assistantship for the writer and donated a 100-in by 100-in planar scanner and associated manual position control unit to Georgia Tech. Over the course of the following three years, Hollis educated the writer in the state of the art in antenna measurement techniques including the pioneering work conducted at Scientific-Atlanta in near-field antenna measurements. The planar scanner was assembled in the basement of the Electronics Research Building of the Georgia Tech Engineering Experiment Station. The basement floor had to be lowered by 4 ft to accomodate the 14-ft height of the scanner. This area of the basement was known as the “swimming pool” and was next to the area where development of the compact range was taking place. H. Allen Ecker, then Chief of the Radar Division of the Engineering Experiment Station (now called the Georgia Tech Research Institute), was also interested in nearfield measurement technology [ 101 and supported this effort, which included housing and instrumenting the range. The writer determined that four key ingredients for modern near-field measurements were missing. The four were theory, near-field probe characterization, automation, and data processing. Scientific-Atlanta had previously provided two key ingredients: fast phase measurement apparatus in their Series 1750 Wide Range Phase/Amplitude Receiving System and an amplitude and phase stable scanner for positioning a near-field probe over a planar surface. The plane-wave spectrum theory of Booker and Clemmow [5] was chosen over the Kirchoff vector diffraction theory as the plane-wave spectrum theory allowed complete characterization of planar surface fields with knowledge of only the tangential components of the electric field. The scattering matrix approach of Kerns and Dayhoff [6] was used to compensate the plane-wave spectrum of the nearfield measurements for the plane-wave spectrum of the nearfield probe assuming no multiple scattering between the probe and the antenna under test. The writer restated the Kerns coupling equation in terms of band-limited spectra, and calculated bounds for the band-limiting process as a function of distance between the antenna under test and the measurement plane. The result was a near-field sample spacing requirement with an upper bound of one-half wavelength, 0018-926X/88/0600-0740$01 .OO