A.R. Bestugin1, M.B. Ryzhikov2, Yu.A. Novikova3, I.A. Kirshina4

1−4 SUAI (Saint Petersburg, Russia)

The prospects for the growth of cases of technical implementation of AFAR in small-sized airborne radar stations on small aircraft intended for the development of hard-to-reach territories are associated with the need to provide autonomous information support when solving complex tasks to ensure take-off and landing in difficult conditions, the delivery of passengers and cargo to hard-to-reach settlements, rescue operations. At the same time, the issue of flight safety is a key one. In difficult weather conditions, often characteristic of hard-to-reach territories, and when flying at a relatively low altitude, airborne radar stations are indispensable in detecting formations dangerous to flight in the atmosphere, other aircraft in the air that pose a potential collision hazard, high-altitude terrain areas.

In active phased antenna arrays, in order to determine the flight paths of aircraft on opposite or intersecting courses when using radar data, it is necessary to ensure accurate measurement of the angular spatial position, for which the monopulse direction finding method is actively used. The paper considers a method for achieving unambiguity of direction finding characteristics in an on-board radar by comparing the signals of the total and difference reception channels by azimuth and elevation angle.

Simulation results are presented that determine the conditions for reducing the number of angular directions of possible arrival of third-party signals that can lead to ambiguity of the direction finding characteristics in a multichannel active phased array antenna. Narrowing the area of unambiguity to the interval of angles in which the main beam of the radiation pattern is located is based on varying the parameters of the amplitude distribution and comparing the signals coming through the total and two difference channels. Using the example of the implementation of amplitude distributions in the form of a cosine function raised to a given degree, it is shown that under certain conditions it is possible to achieve either a small number of angular directions in which there is an ambiguity of the direction finding characteristic or completely solve this problem. The advantages and disadvantages of the method are indicated. The main disadvantage is the nonlinear nature of the dependence of the number of angular directions in which there is no unambiguity of the direction finding characteristic on the degree of decay of the amplitude distribution to the edges of the radiating surface of the antenna. This makes it difficult to find the amplitude distribution at which both the requirements for radiation characteristics and the unambiguity of angular measurements are satisfied. Numerical results are obtained and an approach is described for choosing one or another amplitude distribution to implement the proposed method for increasing the efficiency of single-digit measurement of angular directions.

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