K Band Radar Drone Signatures

A R T I C L E I N F O : RECEIVED: 23 JUNE 2020 REVISED: 27 AUG 2020 ONLINE: 23 SEP 2020 K E Y W O R D S : K band radar, drone signature, NI RIO, signal processing Creative Commons BY-NC 4.0 Introduction In recent years, the use of sensors with coherent signals, which use the changes of the reflected signal due to the Doppler Effect to identify the signatures of moving objects: machines, people, animals. The signature can be defined as a characteristic reflected signal-voltage, function of time and space, formed at the output of a receiving module generated by a radiating sensor: radar, laser, sonar. One advantage of coherent systems is the preservation of the phase of the reflected signal. In these systems, even a small vibration or rotation of the object causes a significant phase change. The term “micro-Doppler,” first introduced in coherent laser systems, has become popular in the literature. The micro-Doppler effect was first studied systematically by Victor Chen using a radar sensor. The micro-Doppler effect appears as Doppler frequency modulations in coherent laser or microwave radar systems induced by mechanical vibrations or rotations of a target or any part on the target. These Doppler modulations become a distinctive signature of a tar-get that incorporates vibrating or rotating structures, and provides evidence of the identity of the target with movement. N. Kolev, Y. Sivkov & E. Sirakov, ISIJ 47, no. 3 (2020): 349-354 350 The source of micromotion depends on the subject and can be a rotating propeller on a fixed-wing aircraft, the multiple spinning rotor blades of a helicopter, or an unmanned aerial vehicle (UAV); the vibrations of an engine shaking a vehicle; an antenna rotating on a ship; the flapping wings of birds; the swinging arms and legs of a walking person; and many other sources. Lately, the technology of Doppler radars for industrial applications and in the automotive field has been developing. There is a growing interest in the use of Doppler radars for drone detection. The aim of the present study is to develop a K band radar experimental setup and evaluate its capabilities for drone detection, distance to it and its speed measurement, to study the radar signature of a drone in the K band. K band radar experimental setup One of the possibilities for realization of a coherent radar setup is the use of a widespread low-power radar module with industrial application. One of the conventional radar low power front ends -IVS-465 is used in 24 GHz K band. This board has no preamplifier and custom conditioning board is used in the application. National Instruments data acquisition board MyRIO is used in the experiments. Provide a description of the methods that is sufficiently complete, so that a reader is able understand and eventually reproduce the methods and processing steps without referring to associated publications. The experiments were carried out in an enclosed space with drone motion in front of the radar antenna. Principles of Doppler radar signal processing application The radar circuit is built as an optimal receiver with coherent signal detection in a quadrature detector, which receives both part of the emitted and received Figure 1: Block diagram of K band radar experimental setup. K Band Radar Drone Signatures 351 Figure 2: Photos of drone and radar experimental setup. signal. After multiplying the two signals in the detector, a low-frequency signal with difference frequency is formed. In continuous transmission on a single frequency, the difference frequency is proportional to the speed of the radar target. The Doppler frequency as a difference between transmitted and received frequency due to target motion is given with the equation: (1) Where F0 is the frequency of the transmitted signal, Vt is radar target speed, θ is the angle between the target velocity vector and line of sight between transmitter and target, and c is the speed of electromagnetic wave. This radar front end allows estimation also of the target range. The difference frequency is proportional to the distance to the radar target if a linear frequency modulated signal is used during the transmission. It is necessary to supply the voltage-controlled oscillator of the module with a saw-tooth voltage with a given slope. After receiving the reflected electromagnetic wave and mixing it with the transmitted wave, there is a beat frequency – fb at the output which is linked with the target range: