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UAV communications have seen a rapid rise in the last few years. The drone class of UAV has particularly become more widespread around the world, and illicit behavior using drones has become a problem. Therefore, localization, tracking, and even taking control of drones have also gained interest. Knowing the frequency of a target signal, its position can be determined (as the angle of arrival with respect to a fixed receiver point) using radio frequency-based localization techniques. One such technique is represented by the subspace-based algorithms that offer highly accurate results. This paper presents the implementation of the MUSIC algorithm on an SDR-based system using a uniform circular antenna array and its experimental evaluation in relevant outdoor environments for drone localization. The results show the capability of the system to indicate the AoA of the target signal. The results are compared with the actual direction computed from the log files of the drone application and validated with a professional direction-finding solution (i.e., Narda SignalShark equipped with the automatic direction-finding antenna). [ABSTRACT FROM AUTHOR]

The channel matrix of the commonly used uniform circular array-based orbital angular momentum (UCA-OAM) system reaches the full-rank state when the degree of freedom (DoF) is limited only by the number of UCA antenna elements. The rank of the channel matrix of the UCA-OAM system is equal to DoF under this condition. However, the practical DoF of the UCA-OAM system is always affected by other transmission factors, such as the transmission distance and the radius of the receiving antenna. Therefore, by exploiting the practical DoF of the UCA-OAM system affected by the transmission distance and the radii of the receiving antenna and transmission antenna, a novel channel capacity model of the UCA-OAM communication system with a deficient-rank channel (DRC) matrix is first proposed. Moreover, the formulas of the channel matrix and channel capacity for the DRC matrix are analytically derived. The results of numerical simulations indicate that when the practical transmission factors including transmission distance and radii of the receiving antenna and transmission antenna are considered, the UCA-OAM communication system with the DRC matrix has less channel capacity than that with the full-rank channel (FRC) matrix. These simulated results provide helpful guidance on the practical application of the UCA-OAM communication system. [ABSTRACT FROM AUTHOR]

This paper presents the generation of orbital angular momentum (OAM) vortex waves with mode +1 using dielectric resonator antenna (DRA) array. The proposed antenna was designed and fabricated using FR-4 substrate to generate OAM mode +1 at 3.56 GHz (5G new radio band). The proposed antenna consists of 2 × 2 rectangular DRA array, a feeding network, and four cross slots etched on the ground plane. The proposed antenna succeeded in generating OAM waves; this was confirmed by the measured radiation pattern (2D polar form), simulated phase distribution, and intensity distribution. Moreover, mode purity analysis was carried out to verify the generation of OAM mode +1, and the purity obtained was 53.87%. The antenna operates from 3.2 to 3.66 GHz with a maximum gain of 7.3 dBi. Compared with previous designs, this proposed antenna is low-profile and easy to fabricate. In addition, the proposed antenna has a compact structure, wide bandwidth, high gain, and low losses, thus meeting the requirements of 5G NR applications. [ABSTRACT FROM AUTHOR]

A reconfigurable ultra-wideband multimode terahertz OAM antenna array based on graphene and vanadium dioxide (VO 2) is presented in this paper. The uniform circular array (UCA) composed of circularly polarized (CP) antennas, which include a ring radiation patch, a parasitic patch, a perovskite substrate and an irregular VO 2 ground plane. The radiation patch is covered with a layer of graphene, by changing the chemical potential of graphene, the working bandwidth and axial ratio bandwidth of the antenna can be changed. By changing the phase state of VO 2 (metal state / insulation state) to control the working state of the antenna. The impedance bandwidth (IBW) of the CP antenna proposed is 115.09% (1.73–6.42 THz), the axial ratio bandwidth (ARBW) is 43.97% (2.36–3.69 THz). Using the CP antenna unit can simplify the complex feed network, and only feeding the equal amplitude and equal phase excitation can realize the vortex wave. Changing the number and rotation angle of the antenna unit can realize multimode vortex waves with the l = 0, ±1, ±2, ±3, the purity is approximately 1, respectively. The proposed UCA has excellent application prospect in the 6G communication. [ABSTRACT FROM AUTHOR]

In this paper, we propose a uniform circular array antenna with a simple feeding structure operating in the 5.2 GHz band for orbital angular momentum (OAM) mode multiplexing. The proposed antenna can generate simultaneously two types of OAM modes (l=±2) using eight radiating patches and a feed circuit consisting of one hybrid coupler and two concentric series-parallel feedlines. Because the two feedlines are designed concentrically with different radii, they do not intersect each other in the same plane, thus having the advantage of being spatially efficient. The successful creation of the two OAM modes was confirmed through the measured radiation pattern and helical phase distribution. The dual-mode OAM transmission test shows that the proposed antenna can be successfully employed for OAM mode multiplexing by obtaining >12.4 dB of isolation between the two OAM mode channels. [ABSTRACT FROM AUTHOR]

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In this paper, the performance of a two-dimensional (2D) Massive MIMO angle parameter system with a uniform circular array (UCA) topology at base station is studied based on the field measurements in indoor line-of-sight (LOS) scenario at a frequency of 4.45 GHz. Many spatial parameters are extracted, including angle information and correlation characteristic. It is shown that correlation lies between antenna elements and users. It is illustrated in the envelope correlation coefficient which goes on a downward trend while the antenna spacing is increasing in the measurements. [ABSTRACT FROM AUTHOR]

The performance of the source enumeration with the uniform circular array (UCA) is deteriorated considerably by the colored noise. This effect becomes more obvious especially when the total number of the sources is lower and closed to that of the array sensors. To address this problem, this paper proposes a source enumeration modeling based on a UCA having M antennas (M-UCA). The M-UCA is operated in a narrow band far field environment with the arbitrary azimuth and elevation angles. First, the Hilbert Huang transformation is employed to derive the phase sequence of each selected intrinsic mode function (IMF) of the signal acquired by each antenna of the M-UCA. Then, the phase sequences of the selected IMFs of the signal acquired by all the antennas of the M-UCA are employed to construct an instantaneous phase covariance matrix (IPCM) among the antennas in the UCA. An IPCM is constructed for each order of the selected IMFs. After performing the eigenvalue decomposition of the all IPCMs, a set of eigenvalues carrying useful information for the estimation of the total number of the sources is acquired. This set is served as the training set. Finally, the training set is used to derive the mathematical model via the support vector machine. The trained model can be used to perform the sources number detection. Both the computer numerical simulations and the radio frequency anechoic chamber experiments validate that the source estimation accuracy of the constructed M-UCA mathematical model based on our proposed method has a high robustness to the incident angles variations, the SNR variations, and the snapshot number variations in the colored noise environment in the determined case, especially in the case of that the total number of the signal sources is only one less than the number of the antennas in the UCA. [ABSTRACT FROM AUTHOR]

Based on the rank reduction theory (RARE), a decoupled method for 2D direction of arrival (DOA) estimation in the presence of elevation-dependent mutual coupling is proposed for compact uniform circular arrays (UCAs). Using a new formulation of the beamspace array manifold in the presence of mutual coupling, the azimuth estimates are decoupled from the elevation estimates and obtained with no need for the exact knowledge of mutual coupling. For the elevation estimation, a 1D parameter search in the elevation space for every azimuth estimate is performed with the elevation-dependent mutual coupling effect compensated efficiently. Though the computational load for the elevation estimation is increased compared to that of the original UCA-RARE algorithm, the 1D parameter search in our method overcomes most of the inherent shortcomings of the UCA-RARE algorithm. This enables unambiguous and paired 2D DOA estimation with the elevation- dependent mutual coupling effect being compensated for effectively. Numerical examples are presented to demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In a beamforming system, mutual coupling among the elements can significantly degrade the system performance. However, the mutual coupling effects can be compensated if an accurate model of mutual coupling is available. This paper utilizes a mutual coupling matrix model to compensate mutual coupling in the beamforming of a uniform circular array. In addition, a circular array of dipoles was built and measurements were performed. The predictions are compared with measurements, and verified with results from full-wave simulations [ABSTRACT FROM PUBLISHER]

For smart antenna systems, the space-time correlation of received signals at an antenna array is a crucial parameter in most adaptive beamforming techniques. In this paper, we experimentally investigate the variation of spatial and temporal fading correlations and the eigenspread of a space–time correlation matrix for a seven-element uniform circular array (UCA) under the line-of-sight (LOS) and the non-line-of-sight (NLOS) urban propagation conditions. A space-time fading correlation model for the UCA, which depends on angular distribution of multipaths, array geometry, Doppler shift, and time offset, is also proposed. The results show that spatial correlations between any pair of antenna elements in the NLOS propagation are less than those in the LOS propagation, and temporal correlations are approximately the same for both propagation conditions. The NLOS propagation causes larger eigenspread for the space-time correlation matrix, as compared to the NLOS propagation. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 40: 61–65, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11285 [ABSTRACT FROM AUTHOR]