Yu. N. Kalinin - Ph.D. (Eng.), Leading Research Scientist, Scientific and Production Enterprise TRIM. E-mail: kalinin_yuri@mail.ru

Nowadays, a method of measuring antennas in the near field using a planar scanner is widely applied. Modern antenna measuring and computing complexes (AMCC) operating in the near field are known for their big sizes of scanning area (tens of meters) and a wide frequency band (over 50 GHz). A number of technical problems arising out of lengthy high-frequency links are encountered in designing these complexes, namely: high signal attenuation and phase drift caused by temperature variations in the course of continuous many-hour measurements of large-size antennas. Lengthy cable lines are to be laid because it is necessary to measure the field phase distribution of the generator branched reference signal. Frequency conversion applied in the vector network analyzers does not solve the problem in general since in this case a problem of attenuation and phase drift occurs for a heterodyne signal. In some cases it may be an obstacle in implementing the technical requirements for AMCC. In connection with it a study of possible ways for obtaining antenna directional patterns without direct measurements of field phase distribution is very relevant. The article reviews an iterative phase distribution retrieval algorithm by the results of field amplitude distribution measurements only on two adjacent parallel planes near the antenna aperture. This algorithm uses another algorithm for recalculating the field amplitude-phase distribution from one plane into another parallel plane being at a distance of several wavelengths. The field is recalculated both in the direction of electromagnetic wave distribution and antenna aperture. A kind of this algorithm is a phase retrieval algorithm with calculation of phase distribution in the antenna aperture plane and limitation of the calculated field by the aperture geometrical dimensions. This algorithm is used for antennas with a relatively low amplification factor (for example horn antennas), whose field phase distribution on the plane contains a vivid phase structure of spherical wave. The results of experimental measurements are provided for two types of antennas: X-range phased-array antenna about 30 in diameter and pyramidal horn antenna sized 913,5 cm at the frequency of 12 GHz. The directional patterns obtained using the phase retrieval algorithm are compared to the diagrams obtained following the results of complex amplitude-phase distribution measurements in a direct way.