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A general challenge in drone localisation and navigation is the strong dependence on satellite positioning. Reconfigurable intelligent surfaces (RIS) offer a promising technology for global navigation satellite system (GNSS)‐free drone localisation and for the alleviation of the jammer effect by nulling the jamming signal. In this letter, we investigate how to optimise the nullification of the jammer while maximising the desired signal in a double RIS‐aided GNSS‐free drone localisation setup. The main objectives of the presented procedure are the maximisation of the desired signal received by the drone, minimisation of the jamming signal effect, accurate estimation of the angle of departure (AOD) from RIS to drone, and drone positioning in 3D. To address this challenge, we propose an alternating projection algorithm to perform jamming nullification by optimising the phase shift at each RIS element. Simulations show that by proper RIS element phase optimisation, the effect of the jammer is efficiently reduced, the AODs from RIS surfaces to drone are computed more accurately, and the drone 3D localisation accuracy is improved. This letter explores a double reconfigurable intelligent surfaces (RIS)‐aided global navigation satellite system‐free drone localisation setup to optimise jammer nullification while enhancing the desired signal. We propose an alternating projection algorithm to optimise the RIS phase shifts, achieving efficient jammer suppression and improved 3D drone positioning. Simulation results demonstrate that the proposed approach significantly enhances localisation accuracy and mitigates jamming effects.

Locating active radars in real environmental conditions is a very important and complex task. The efficiency of the direction finding (DF) of ground-based radars and other microwave emitters using unmanned aerial vehicles (UAV) is dependent on the parameters of applied devices for angle location of microwave emitters, and on the construction and modes of operation of the observed transmitting antenna systems. An additional factor having the influence on DF of the radar, when are used systems installed on the UAV, is the rotation of the antenna of a radar. The accuracy of estimation of direction of any microwave transmitter is determined by the terrain properties that surround the transmitter and the objects reflecting microwave signals. The exemplary shapes of the radar antenna patterns and the associated relationships with the probability of remotely detecting the radar and determining its bearings are described. The simulated patterns of the signals received at an emitter-locating device mounted on a UAV and the expected results of a monopulse DF based on these signals are presented. The novelty of this work is the analysis of the DF efficiency of radars in conditions where intense multi-path phenomena appear, and for various amplitudes and phases of the direct signal and multi-path signals that reach the UAV when assuming that so-called simple signals and linear frequency modulation (LFM) signals are transmitted by the radar. The primary focus is on multi-path phenomenon, which can make it difficult, but not entirely impossible, to detect activity and location of radar with a low-flying small UAV and using only monopulse techniques, that is, when only a single pulse emitted by a radar must be sufficient to DF of this radar. Direction of arrival (DOA) algorithms of signals in dense signal environment were not presented in the work, but relevant suggestions were made for the design of such algorithms.

More recently, the ability of the coprime array to yield large array apertures and high degrees of freedom in comparison with the uniform linear array (ULA) has drawn an enormous amount of attention. In light of this, we propose a low-rank matrix completion algorithm via minimization of the ratio of the nuclear norm and the Frobenius norm (N/F) to solve the two-dimensional (2D) direction finding problem for the L-shaped coprime array (LsCA). Specifically, we first interpolate the virtual co-array signal related to the cross-correlation matrix (CCM) and utilize the interpolated virtual signal for Toeplitz matrix reconstruction. Then, the N/F method is employed to perform low-rank matrix completion on the reconstructed matrix. Finally, exploiting the conjugate symmetry characteristics of the completed matrix, we further develop a direction-finding algorithm that enables 2D angle estimation. Remarkably, the 2D angles are able to be automatically paired by the proposed algorithm. Numerical simulation findings demonstrate that the proposed N/F algorithm generates excellent angular resolution and computational complexity. Furthermore, this algorithm yields better estimation accuracy compared to the competing algorithms.

This paper presents a method to design and optimize a mimetic, multi-band antenna for direction-finding applications based on multiple IoT mobile nodes for protecting sensitive areas. A set of 84 antenna configurations were selected based on possible resonant paths and simulated using a Method of Moments (MoM)-based tool to compute resonant frequencies, VSWR, and gain across three frequency bands centered on 433 MHz, 877.5 MHz, and 2.4 GHz. Compared to a brute-force approach requiring 814 full-wave simulations, our technique dramatically reduces computing time by performing only 84 simulations, followed by a fine-tuning procedure targeting the antenna segments with the highest contribution to the error figure. The final design provides good gain and VSWR figures over almost all the frequency ranges of interest.

Performance improvement of sound source direction finding is a critical acoustic task in target localization, tracking, and navigation as an NP problem that suffers from sound reflection and noise in passive or active methods. The accuracy of prediction increases by integrating more information about the signal specification, source position, sensor attributes, microphone array topology, characteristics of hardware architecture, dimension of distance, the status of environmental sounds, climatic conditions, effects of signal propagation, properties of barriers, and setting of initial estimation which is time-consuming. This paper presents a scalable method of sound source direction finding based on the time-difference-of-arrival approach to improve the accuracy of predictions of three-dimensional space in an outdoor environment. The real-time passive process is robust to sound reflection and ambient noise that decreases the running-time and increases the accuracy significantly through complexity reduction by proposing a novel Krill Herd algorithm based on successive unconstrained minimization technique. Experimental results of different actual and simulated datasets show the angle error amounts of Azimuth and Elevation are 0.7164∘ and 1.5054∘ in the near-field, and are 1.0260∘ and 0.2071∘ in the far-field, respectively. Performance evaluation of the passive proposed process shows that higher accuracy can be reached by using more parallel distributed sensor arrays.

The possibility of constructing a multi-position direction finding system for the case of a priori uncertainty, based on the application of the principles of multiplication of single marks of the location of the emitting target (multistructure principle) and their subsequent partition into classes (clustering principle) is considered. The criteria and algorithms for detecting the resulting cluster and for constructing the optimal estimation of target location stable to anomalous measurement errors are presented, taking into account the time costs of their computer realization. Practical recommendations and results of comparative analysis of different algorithms are given.

The phase interferometer is an effective direction finding (DF) method. It is widely utilized in various electronic reconnaissance systems due to its advantages of fast operation and high precision. In a wideband system, the combination of long and short baselines, or even multi-level baselines, is applied in an interferometer to solve the contradiction between accuracy and phase ambiguity for DF. In this paper, a novel analysis method is proposed to obtain the probability of successfully solving ambiguity based on mathematical statistics. According to the length ratio between short and long baselines, the joint density function of phase errors can be derived. Then, the probability can be achieved under different signal-to-noise ratios (SNRs) by integrating the joint density function in a specific interval. Furthermore, the formula of phase measurement error is adjusted by the least square method to improve computational accuracy in low SNR during the process. Under different baseline configurations, the strategy can provide the theoretical probability of successfully solving ambiguity, thus guiding the baseline design for obtaining a maximum probability without impacting the specified DF accuracy. Simulation results show that the mathematical model is efficient in some complex cases.

The application of direction finding location technology in electronic warfare is becoming more and more extensive. Aiming at the problem that the traditional location method will greatly affect the location accuracy when the measurement information of each observation station is disturbed, a dual-station direction finding location algorithm based on disturbance detection is proposed. The algorithm uses the least squares method to obtain the target’s position information at each moment, then designs an improved Kalman filter algorithm with disturbance detection to improve the location accuracy. The simulation results show that the algorithm can still accurately track the target when the measurement information is disturbed, which has practical application value.

Aiming at the application scenarios of underwater structure gas leakage detection in marine oil and gas development process, the power spectrum characteristics of underwater structure gas leakage radiation noise are analyzed. An new target direction finding algorithm is proposed, and the gas leakage detection-finding software is designed. Then, the test platform is built to complete the experimental study of underwater structure gas leak detection. The test results show that the new target direction finding algorithm used in this paper is compared with the conventional beam forming algorithm. The difference between the maximum beam energy value and the sub-maximum value is bigger, indicates that the target's resolving power is strong, which effectively improves the detection capability of gas leakage targets in underwater structures.

Direction finding (DF) using the uniform circular array composed of horizontal log-periodic dipole antennas (UCA-LPDA) is studied in this paper. One advantage of the UCA-LPDA is that it has a reasonable effective radius for broadband DF. Compared with the previous works which usually focused on isotropic antennas, the UCA-LPDA has higher gain and higher angular resolution for the direction of arrival estimation. The spatial response of the UCA-LPDA and the direction of arrival (DOA) estimation algorithms are discussed. The proposed polarized MUSIC (Pol-MUSIC) method can obtain the DOA of signals with any unknown polarizations while no search of the polarizations is required. Based on the theoretical analysis, the actual signal DF experiment which uses a UCA-LPDA with 24 elements was carried out. The DF experiments results demonstrate the effectiveness and accuracy of using UCA-LPDA with Pol-MUSIC method.