Amplitude Direction Finder of Radio Frequency Emitters for Unmanned Aerial Vehicle

The detection and localization of low-power radio frequency emitters (RFE) in populated areas using stationary spectrum sensing (SS) equipment is ineffective due to the lack of line of sight in shadowing effect. To solve this problem, it is advisable to place the SS equipment on a small unmanned aerial vehicle (UAV). The limitations of this solution are low time for data collection and processing and the low computing power of SS device. This leads to a decrease in search capabilities of SS both in terms of spatial coordinates and frequency, which is critical in conditions of high density of RFE. The aim of this article is to increase the speed of RFE searching using a UAV-mounted SS device under time, weight, and energy constraints by using a system of broadband directional antennas and multichannel sequential signal processing. The amplitude direction finding method was chosen to estimate the direction of radio wave arrival, taking into account the mass and computational limitations of the SS device placed on the UAV. The proposed structure of the antenna system contains six log-periodic antennas spaced in a circle by 60°. To process the received signal, a multichannel sequential analysis scheme is proposed, in which one scanning receiver is alternately connected to each of the antennas. It is shown that for this scheme, the parameter to be optimized is the flight speed of the UAV. A generalized expression for calculating this value is obtained. An expression for approximating the main lobe of the antenna radiation pattern in form of a Gaussian function is obtained. A procedure for calculating the direction on RFE by comparing the amplitudes of the received signals by two neighboring antennas is developed. Recommendations to avoid ambiguities in calculation angle of arrival for the case of several RFE are given. Compared to existing solutions, when a single receiving channel with a single directional antenna is used and space scanning is performed by rotating the UAV, the proposed approach with a multi-antenna system will reduce the time for azimuthal directions scanning.