Practical approach of measuring of angular bearing errors for radiotransparent radomes with complex shape in the “antenna – radome” system in the entire possible scanning ar-ea of the airborne radar antenna system

Abstract

A nose radiotransparent radome (RTR) plays the role of a dielectric lens of a complex shape, which can significantly affect the radiation characteristics of the airborne radar antenna of an aircraft located under it. Modern radars, as a rule, are built on the basis of antenna systems with electronic beam control – phased antenna arrays. The phasing of the array is carried out in the most different (available for a given phased array) spatial directions. One of the parameters that define the operation of the radar under the RTR is the error in determining the angular position of the targets found by the radar. With complex forms (with one plane of symmetry) of the nose RTR, the resulting angular bearing errors (ABE) depend significantly on the spatial position in which the radar antenna is currently phased. In some cases, bearing errors must be taken into account when operating the radar. This becomes especially important in direction finding and tracking of targets remote to the limit for radar aircraft. In this case, the data on the values of the ABE depending on the current coordinates of the array phasing become relevant. The aim of the article is to present a simple technique that makes it possible to practically measure the ABE in the system “antenna – RTR” in a significant area of electronic scanning by the antenna beam. The technique for measuring the ABE has been developed, which was tested on the basis of an antenna-measuring collimator complex (“compact test site”). Mathematical expressions have been given for calculating both components of ABE (in the phased antenna array angular coordinate system) based on the measured data. At the initial stage, the technique has been tested on the basis of a specially made quick-detachable model-simulator of the radome, which has the ability to introduce arbitrary ABE. With the help of this model, a comparison of the results of measurements obtained on the basis of the proposed method and the method associated with the measurement of dynamic spatial radiation patterns (RP) has been performed. A good correlation of data has been noted for different methods, but on one physical model-simulator of the RTR, which allows us to speak about the correctness of the chosen approach. Subsequently, the correctness of the proposed method has been confirmed by the data collected when working with the system “phased antenna array – RTR” (teardrop shape). In this case, the calculated components of the ABE have been compared with the results of direct measurements by the difference method, when each of the orthogonal components is calculated by measuring the angle of displacement of the minimum of the corresponding difference pattern, obtained before and after the installation of the RTR. The developed technique of preliminary measurement of angular bearing errors over a significant part of the surface of a real RTR makes it possible, if necessary, to compensate the measured ABE in aircraft radar computers, thereby increasing the accuracy of determining the spatial coordinates of targets in space.