A. O. Manichev – Ph.D. (Eng.), JSC «GSKB Almaz-Antey named after A.A. Raspletin», NTC “Altair”, Moscow. E-mail: email@example.com
A. N. Tuvaev – JSC «GSKB Almaz-Antey named after A.A. Raspletin», NTC “Altair”, Moscow. E-mail: Okean87@mail.ru
The phase direction-finding method is widely used in direction finding systems. It is based on the measurement of the phase difference between two (or more) signals at the output of different antennas. The essential disadvantage of this method is that the angular width of the bearing characteristic is determined by the distance between the antennas and can't be changed significantly in a given configuration of antenna system. At the same time, many practical applications require an extended bearing characteristic (for example, in the case when the method is realized at the base of the modules of a phased array antenna (PAA)).
The recently proposed phase method for formation of the extended bearing characteristic is free from this drawback. It is based on the comparison of the phase differences measured through the use of the classic phase method at two different frequencies. This paper considers the operation of this method in the presence of the random distortions of the amplitude-phase distribution (APD) in the aperture of a PAA and provides the experimental results confirming the efficiency of the method.
It is known from the statistical antenna theory that the random distortions of the APD usually result in a reduction of the directivity, an increase of the side lobe level, and "filling" nulls of the radiation pattern. But even more important factor (in relation to the considered method) is that the phase radiation pattern of a PAA is also changed. This reduces the accuracy of the method. The paper presents expressions for the bearing characteristic in the presence of the random distortions of the APD. At the basis of the formulae the impact of such distortions on the bearing characteristic of a real PAA is analyzed.
The operation of the method was tested experimentally. A rhombic PAA consisting of four 384-element modules with irregular (spiral) grid and uniform amplitude distribution was used for this purpose. The upper and the lower modules of the PAA (characterized by the largest distance between their centers) have been taken for the experimental verification. In order to obtain the extended bearing characteristic, the main beam of each module was broadened using a hyperbolic phase distribution, which proved to be efficient for this PAA.
The results of the experiment and the simulation showed high efficiency of the method and its ability to form a phase bearing characteristic with extended operating sector. The resulting operating sector of the bearing characteristic exceeds the operating sector of the classical phase method by more than 10 times. The developed statistical model taking into account the PAA's APD random distortions explain the difference between the theoretical and experimental bearing characteristics.