After a brief history of near-field antenna measurements with and without probe correction, the theory of near-field antenna measurements is outlined beginning with ideal probes scanning on arbitrary surfaces and ending with arbitrary probes scanning on planar, cylindrical, and spherical surfaces. Probe correction is introduced for all three measurement geometries as a slight modification to the ideal probe expressions. Sampling theorems are applied to determine the required data-point spacing, and efficient computational methods along with their computer run times are discussed. The major sources of experimental error defining the accuracy of typical planar near-field measurement facilities are reviewed, and present limitations of planar, cylindrical, and spherical near-field scanning are identified.

An overview of near-field antenna measurements

Significant progress has been made in recent years on planar near-field measurements for antenna calibrations. Such measurements are also useful in the alignment and evalnation of compact ranges because they provide more information than a limited number of analogue plots in one dimension. Contour plots of amplitude and phase data obtained from more complete two-dimensional measurements precisely and accurately locate sources of problems in the range reflector, with phase contour plots being more useful as diagnostic tools.

https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=31162

Accurate evaluation of a millimeter wave compact range using planar near-field scanning

The electromagnetic field radiated by paraboloidal and hyperboloidal reflector antennas excited by an azimuthally independent, linearly polarized source is considered. The electromagnetic field is sampled on a spherical surface in order to numerically generate a set of spherical wave mode coefficients which, in turn, are used to compute antenna patterns. Patterns are produced in the near- and far-field regions based on both full and partial, or truncated, near- and far-field data as a function of the antenna parameters and the truncation angle location. The similarity of the patterns obtained from truncated field data to the untruncated patterns is found to depend on the pattern level at the truncation point, the location of the truncation point, the antenna parameters, and the radial distance between the spherical surfaces on which the electromagnetic field is sampled and produced. >

Application of spherical wave expansions to reflector antennas using truncated field data

Spherical wave expansions (SWEs) for focus-fed symmetric paraboloids and hyperboloids using truncated field data have been investigated. The input field data for obtaining the SWE coefficients of a symmetric reflector have been determined in terms of numerical single integrals using the formulation given by A.W. Rudge et al. (1986). Patterns obtained for a hyperboloidal reflector are shown. These patterns indicate that the on-axis accuracy of the patterns produced from truncated field data is determined by the pattern intensity at the truncation angle. Truncation at a point of relatively high field intensity results in an appreciable ripple level for the on-axis field amplitude as a function of distance from the reflector. >

Spherical wave expansions for reflector antennas with truncated field data

The general receiving antenna is represented as a linear differential operator converting the incident field and its spatial derivatives at a single point in space to an output voltage. The differential operator is specified explicitly in terms of the multipole coefficients of the antenna's complex receiving pattern. When the linear operator representation is applied to the special probes used in spherical near-field measurements, a probe-corrected spherical transmission formula is revealed that retains the form, applicability, and simplicity of the nonprobe-corrected equations. The new spherical transmission formula is shown to be consistent with the previous transmission formula derived from the rotational and translational addition theorems for spherical waves.

/pdf/the-receiving-antenna-as-a-linear-differential-operator-vqsvksnzq5.pdf

The receiving antenna as a linear differential operator: Application to spherical near-field scanning

Results of spherical near-field measurements on narrow-beam antennas

/pdf/results-of-planar-near-field-measurements-on-a-compact-range-2a8lo6vp55.pdf

Results of planar near-field measurements on a compact range at 18 and 54 ghz

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Results of spherical near-field measurements on narrow-beam antennas

Results of planar near-field measurements on a compact range at 18 and 54 ghz