Experimental spherical nearfield antenna test facility. Volume 8: Spherical nearfield measurements from a compactrange viewpoint
Abstract
A procedure is described in which the local plane wave field required for measuring the far field antenna pattern is generated by an array of sources distributed over the surface of a sphere. The probe weighting factors used in spherical near field measurements, by reciprocity, may be used as excitations for a spherical array, and the results must be a plane wave field inside a central portion of the sphere. Any deviations from a perfect plane wave indicate measurement errors, on a basis independent of the antenna under test. A computer program has been written to calculate this plane wave field, and the SNIFTC program has been modified to provide the excitation factors. Several cases have been run showing that a virtually perfect plane wave field is achieved, confirming the theory and validating both programs. Phase deviations less than 0.04 deg and amplitude variations less than 0.003 dB have been found theoretically within a spherical quiet zone. Several cases have been run to evaluate the effects of truncating the array. It is shown that the size and the quality of the quiet zone is independent of the array radius for a full spherical array. For a truncated array the quiet zone becomes smaller when the array radius is decreased. Also very small arrays have been investigated and a case is treated where a 3 x 3 array at 1/3 of the Rayleigh distance produce a phase which is less than for a single element at the full Rayleigh distance.
 Publication:

Final Report Technical Univ. of Denmark
 Pub Date:
 April 1979
 Bibcode:
 1979tudl.rept.....L
 Keywords:

 Antenna Radiation Patterns;
 Computer Programs;
 Plane Waves;
 Antenna Arrays;
 Far Fields;
 Fortran;
 Near Fields;
 Spheres;
 Test Facilities;
 Communications and Radar