Uniform Circular Antenna Array Research Articles

Experimental Evaluation of an SDR-Based UAV Localization System.

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).

Mode reconfigurable OAM helical array antenna for higher mode generation

AbstractIn this paper, an orbital angular momentum (OAM) mode reconfigurable antenna based on a uniform circular array (UCA) is presented. The phase superposition method is presented to overcome the limitation of the number of array units on the mode order in the conventional four‐element UCA antenna, which is limited to generating first‐order OAM beams. The unit phase is introduced by a bifilar helical antenna in this method, and the unit phase is superimposed with the feed phase of the UCA to enable the generation of 3rd‐order OAM beams from the four‐element UCA. At the same time, the DC signal‐controlled feed network assigns three distinct feed phases to the UCA, which realizes the reconfigurability of the three OAM beams. To achieve mode reconfigurability, 20 p‐i‐n diodes were integrated as switches in the feed network for controlling the ON/OFF status of p‐i‐n diodes in the feed network using DC signals. Finally, simulated and measured results show that three OAM beams (lz = −1, −2, and −3) have been generated in the frequency band from 10.6 to 11.8 GHz.

Distributed Sensitivity and Critical Interference Power Analysis of Multi-Degree-of-Freedom Navigation Interference for Global Navigation Satellite System Array Antennas.

Current research on the interference of GNSS (Global Navigation Satellite System) array antennas focuses on the single interference effect and the improvement of interference hardware capability, while the multi-degree-of-freedom (DOF) interference model and mechanism remain to be fully studied. Aiming at this problem, this paper analyzes the preconditions for the definition of anti-jamming degrees of freedom and the characteristics of super-DOF interference through formula derivation and simulation. First, by analyzing the influence of the number of interfering signals on the angular resolution, the prerequisite of the definition of anti-interference degrees of freedom in the airspace is proposed. Second, the definition of anti-interference degrees of freedom is used to calculate the change rule of the critical power of the interference under different numbers of interfering signals. Finally, the influence of super-DOF interference on the array antenna is analyzed. The results show that the prerequisite for the anti-interference freedom of the array antenna is that the distribution interval of the interfering signal is greater than 15°, taking a four-array element uniform circular array antenna as an example. The critical interference power of the array antenna decreases by about 15 dB when the number of interfering signals exceeds the degrees of freedom of the array antenna's interference immunity, provided that the interference resolution is satisfied. The conclusions of this paper give the critical power change rule of multi-DOF interference and the effect of super-DOF interference, as well as the prerequisites for the setting of interference signals, which can be used, for example, in the deployment of distributed interference sources and the development of anti-jamming algorithms.

Redefining uniform circular array’s limit by using square patch elements for higher order orbital angular momentum mode generation

This article proposes a technique to design the Uniform Circular Array (UCA) antenna for the generation of higher order of orbital angular momentum (OAM) modes using lesser number of antenna elements. Earlier, the highest possible OAM mode number (lmax) generated using conventional N-element UCA is limited by number of antenna elements N ≥ 2|lmax|. In the proposed design, a square patch element is placed between two antenna elements of conventional 4-element UCA to generate higher order OAM modes (0, ±1, ±2, and ±3 OAM modes) with lesser number of antenna elements. The proposed UCA is compact in size and requires less complex power dividing phase networks in comparison to conventional 8-element UCA to generate similar lmax. The proposed UCA with square patch is designed at 5.2 GHz and lmax of a N-element UCA with square patch is now limited by number of antenna elements as N ≥ |lmax|. The simulated and measured phase patterns for various OAM modes are in good agreement and supported by mathematical analysis. A comparison of the new structure with the conventional Uniform Circular Arrays available in the literature is also tabulated.

High Purity Orbital Angular Momentum Modes Reconfiguration Using Uniform Circular Array Antenna to Enhance Channel Capacity and Spectral Efficiency

Technology based on OAM (orbital angular momentum) has great potential for enhancing the bandwidth efficiency of telecommunication systems. Although OAM waves are orthogonal, it is possible to multiplex various modes within a single frequency channel. Significantly, the overall spectrum efficiency, as well as channel capacity, can be improved. Multiple users can share the same frequency channel by using orthogonal modes, which eliminates the requirement for extra resources like time and frequency. This research uses MATLAB code to derive a uniform circular array (UCA) antenna factor under the cylindrical coordinate system. This factor is used to illustrate the array antenna's electric field to generate OAM waves or radio waves that carry the OAM mode. OAM modes can be reconfigured for the no. of UCA elements (N) needed to generate a ripple-free radiation pattern based on the UCA antenna factor. Additionally, the significance of UCA radius and observational distance (the field plane-UCA plane gap) on the phase distribution and radiation pattern from OAM mode 1 to 5 is graphically evaluated and optimized. The MATLAB simulations compute the electric field phase distribution pattern (EFPDP) and normalized radiation pattern (NRP) at 76 GHz. The method predicts the peak, side lobes, and comparable radiation patterns of the radiation pattern, offering an effective means of optimizing OAM modes and analysing trade-offs.

Analysis and Design of Broadband OAM Array Antenna

This paper presents a Uniform Circular Array (UCA) antenna of crossed-dipole that can excite vortex waves in a wide frequency range from 3.5 GHz to 8.4 GHz. In the design process, the theoretical derivation of the influence on the Orbital Angular Momentum (OAM) when the antenna elements are arrayed in Co-directional Antenna Array (CAA) and Rotational Antenna Array (RAA) is given respectively. The fixed mode of the dipoles CAA is achieved by feeding each element with equal amplitude and 90∘ phase difference produced by the broadband feeding network. Furthermore, the proposed broadband OAM array antenna has been fabricated and measured to verify the predicted properties. The vortex electromagnetic wave with +1 mode could be excited in the bandwidth of 82.35%. Simulated and measured results are in good agreement. The proposed OAM array antenna is simple in design principle, compact in structure and low in profile, making this array antenna an excellent candidate for broadband OAM communication systems.

Generation of highly azimuthal symmetric conical beam using the planar uniform circular array antenna for vehicular communication

Generation of highly azimuthal symmetric conical beam using the planar uniform circular array antenna for vehicular communication

A novel optimized conical antenna array structure for back lobe cancellation of uniform concentric circular antenna arrays

A novel optimized conical antenna array structure for back lobe cancellation of uniform concentric circular antenna arrays

Low-complex channel estimation in extra-large scale MIMO with the spherical wave properties

This paper investigates the low-complex linear minimum mean squared error (LMMSE) channel estimation in an extra-large scale MIMO system with the spherical wave model (SWM). We model the extra-large scale MIMO channels using the SWM in the terahertz (THz) line-of-sight propagation, in which the transceiver is a uniform circular antenna array. On this basis, for the known channel covariance matrix (CCM), a low-complex LMMSE channel estimation algorithm is proposed by exploiting the spherical wave properties (SWP). Meanwhile, for the unknown CCM, a similar low-complex LMMSE channel estimation algorithm is also proposed. Both theoretical and simulation results show that the proposed algorithm has lower complexity without reducing the accuracy of channel estimation.

Series-feed UCA antenna for generating highly azimuthal symmetric OAM Beam for unmanned aerial vehicles

This paper presents a new approach to producing a conical beam (CB) with highly azimuthal symmetry through a series-feed uniform circular array (UCA) antenna using circularly polarized (CP) elements and the orbital angular momentum (OAM) technique. Most previously proposed antenna designs for generating CB radiation patterns using mode-combining techniques have complex structures and high costs. The proposed antenna utilizes the inherent properties of OAM waves to generate a conical-shaped beam with simplicity and compactness. The UCA antenna utilizes CP elements, which are rotated to provide the desired far-field phase for generating the OAM beam. This design achieves extensive signal coverage and is highly efficient, with minimal spurious radiation and low insertion losses. The experimental measurements validate that the OAM beam produced by the UCA antenna has high azimuthal symmetry at 6GHz. The OAM beam generated exhibits high mode purity and a peak gain of 10dBi, with a divergence angle of ± 22°.

Optimized planar printed UCA configurations for OAM waves and the associated OAM mode content at the receiver

SummaryUtilization of planar printed uniform circular antenna arrays (UCA) to generate the orbital angular momentum (OAM) carrying waves in the millimeter‐wave (mmWave) frequency band is advantageous from the viewpoints of easy signal modulation and mode reconfiguration, low cost, low profile, and straightforward integration with the existing broadband wireless infrastructure. The OAM mmWave UCA are highly promising as the enablers of very high transmission data rates required by hybrid 5G/6G optical and wireless communication systems by complementing and enhancing other technologies currently in use. Therefore, we here contribute a detailed electromagnetic analysis of important constraints of such antenna arrangements aimed at short‐range multimode OAM wave transmission. We investigate (i) the required antenna array dimensions and optimized UCA arrangements for a particular link range and (ii) the corresponding mode structure of OAM waves in the plane of receiving arrays. Four relatively simple antenna configurations operating in the 60‐GHz band are compared. Theoretical assumptions based on ideal OAM modes are critically assessed and, using state‐of‐the‐art numerical electromagnetic analysis, compared to realistically generated OAM waves. The proposed “cyclic transmission setup” resulted in much lower unwanted field components in the region of receiving arrays. RMS magnitudes of unwanted modes are on average about 64% of the received mode, in comparison with 80% (up to 94%) for sequential transmission. The observed mode impurities and mode mixing effects at the receiver indicate the need to dedicate more attention to the system‐level design, the development of efficient receiving arrays, the MIMO processing, and the stream separation.

Exploring the effects of directional antennas on the secure connectivity and hop count of secure multi-hop ad-hoc wireless networks

Directional antennas can increase the received power in specific directions while reducing it in other directions. Utilizing this unique feature, we configure directional antennas at legitimate users to obtain twofold benefits for secure multi-hop ad-hoc wireless networks (AHWNs), i.e., enhancing the secure connectivity among legitimate users and lowering the hop count of the multi-hop paths. For the quantitative evaluation of these benefits, we first use a stochastic geometry graph to model the multi-hop AHWNs under the coexistence of eavesdroppers. Then, we introduce a simulation-based analysis method comprised of two algorithms: (a) the first algorithm provides the connectivity and the hop count of the shortest path between random source–destination pairs; (b) the second algorithm utilizes the results of the first one to return the average path connectivity, the probability mass function (pmf) of the hop count distribution, and the average hop count. This simulation-based analysis method helps to exhaustively study the behaviors of connectivity, hop count distribution, average hop count, and their mutual relationship in different scenarios. To the best of our knowledge, this paper is the first research work that studies the effects of directional antennas equipped at legitimate users on both secure connectivity and hop count of secure AHWNs in four combinations of two types of practical directional antennas, i.e., uniform circular array (UCA) antenna and uniform linear array (ULA) antennas, and two beamforming schemes, i.e., centralized and randomized beamforming. Moreover, comparisons with the case of using omnidirectional antennas are also provided. From the obtained simulation results, we demonstrate that using directional antennas does not always benefit the secure connectivity and hop count of secure AHWNs, i.e., only UCA-random gives higher secure connectivity and lower hop count than the omnidirectional antenna among four combinations of antenna type — beamforming scheme. Moreover, in the cases of high-density legitimate users and low-density eavesdroppers, lowering the average hop count is more remarkable than improving secure connectivity. The critical findings in this paper are valuable for deploying secure multi-hop AHWNs with directional antennas in practice.

Near-field formation of the UCA-based OAM EM fields and short-range EM power flux profiles

Orbital angular momentum (OAM) multiplexing is a recently considered solution for enhancing wireless and free-space optical communications channel capacity, whether implemented separately or in combination with existing multiplexing techniques. The theoretically infinite number of paraxially propagating and mutually orthogonal OAM modes is expected to increase the channel capacity. However, the orthogonality for different OAM modes has been shown to decrease for far link range distances, and the paraxiality of the OAM beams is not very good for small radiating sources. Based on the current knowledge, OAM beams are most likely to be used for short-range communications. Many models of the electromagnetic (EM) fields carrying the OAM neglect the fact that the OAM beam sources could be electrically large or introduce other approximations that are appropriate for far-field analysis only. An in-depth analysis of the short-range properties of OAM EM fields is still lacking. To address this problem, we propose the use of the infinitesimal (Hertz) dipole method customized for the analysis of the OAM EM fields. This technique can model the positioning and basic radiation properties of separate antennas or antenna sub-arrays that are the building blocks of OAM arrays exactly and efficiently. Similar modeling can represent the OAM sources for free-space optical communications. We focus here on the uniform circular antenna arrays and provide an in-depth analysis of what can and cannot be expected, in the best case, in their utilization. We assume low losses, which is a common assumption for many methods, except for computationally much more demanding full-wave simulations. The obtained results indicate the need to simultaneously optimize the transmission of all planned OAM modes and allow estimates of the link distances that could provide adequate OAM wave reception in various cases.

Direction of arrival estimation for BLE: Antenna array design and evaluation

The use of smart antenna arrays in wireless communication systems is becoming increasingly popular, as they improve the performance of the radio link and allow the integration of communication and sensing functions. In this paper, we present the design and performance evaluation of a uniform circular antenna array (UCAA) with 12 monopole antennas and RF switches to select the active antenna for the signal direction of arrival (DoA) estimation. The antenna configuration was optimized through simulations for a different number of antennas and antenna array radius. The frequency tuning of the antennas considered the coupling of the active antenna with adjacent antennas. The performance of the antenna array was evaluated by (1) simulations that examined the proximity of the antenna to the edge of the antenna array and the influence of adjacent antennas on the performance of the active antenna, and (2) measurements in outdoor and indoor environments. The results of the simulations show that antenna coupling can cause nulls in the radiation pattern, which affects the DoA estimation by reducing the signal-to-noise ratio. In a semi-controlled environment, we achieved a DoA estimation error of less than 1 degree by using the Bluetooth Low Energy (BLE) Angle of Arrival feature.

Impact of antenna directivity on compressed sensing-based DOA estimation employing UCA antenna

This letter investigates the impact of the antenna element directivity on compressed sensing (CS)-based direction of arrival (DOA) estimation employing the uniform circular array (UCA) antenna. In the CS-based approach, the reconstruction accuracy of sparse signals is determined by a sensing matrix, which depends on the array antenna configuration in the DOA estimation. In our study, we analyze the cross-correlation between column vectors of the sensing matrix and clarify the estimation accuracy for various antenna element radiation patterns.

Generation of OAM Waves and Analysis of Mode Purity for�G燬ub-6燝Hz燗pplications

This article presents the generation of Orbital Angular Momentum (OAM) vortex waves with mode 1 using Uniform Circular Array (UCA) antenna. Two different designs, namely, UCA-1 (4-element array antenna) and UCA-2 (8-element array antenna), were designed and fabricated using FR-4 substrate to generate OAM mode 1 at 3.5 GHz (5G mid-band). The proposed antenna arrays comprised rectangular microstrip patch elements with inset fed technique. The elements were excited by a carefully designed feeding phase shift network to provide similar output energy at output ports with desired phase shift value. The generated OAM waves were confirmed by measuring the null in the bore sight of their 2D radiation patterns, simulated phase distribution and intensity distribution. The measurement results agree well with the simulation results. Moreover, a detailed mode purity analysis of the generated OAM waves was carried out considering different factors. The investigation found that the greater the number of elements, the higher the purity of the generated OAM wave. Compared with other previous works, the proposed antenna design of this paper is very simple to design and fabricate. In addition, the proposed antennas are compact in design even at lower frequency band with very wide bandwidth to meet the requirements of 5G mid-band applications.

Single-slice microwave imaging of breast cancer by reverse time migration.

Microwave imaging of breast cancer is considered and a new microwave imaging prototype including the imaging algorithm, the antenna array, and the measurement configuration is presented. The prototype aims to project the geometrical features of the anomalies inside the breast to a single-slice image at the coronal plane depending on the complex dielectric permittivity variation among the tissues to aid the diagnosis. The imaging prototype uses a solid cylindrical dielectric platform, where a total of 24 optimized Vivaldi antennas are embedded inside to form a uniform circular antenna array. The center of the platform is carved to create a hollow part for placement of the breast and the multistatic, microwave scattering parameters are collected with the antenna array around the hollow center. The dielectric platform further enhances the microwave impedance matching against the breast fat tissue and preserves the vertical polarization during the measurements. In the imaging phase, a computationally efficient inverse electromagnetic scattering method-reverse time migration (RTM)-is considered and adapted in terms of scattering parameters to comply with the actualmeasurements. The prototype system is experimentally tested against tissue-mimicking breast phantoms with realistic dielectric permittivity profiles. The reconstructed single-slice images accurately determined the locations and the geometrical extents of the tumor phantoms. These experiments not only verified the microwave imaging prototype but also provided the first experimental results of the imagingalgorithm. The presented prototype system implementing the RTM method is capable of reconstructing single-slice, nonanatomical images, where the hotspots correspond to the geometrical projections of the anomalies inside the breast.

Favorable Propagation for Massive MIMO With Circular and Cylindrical Antenna Arrays

Massive MIMO systems with uniform circular and cylindrical antenna arrays are studied. Favorable propagation property is rigorously shown to hold asymptotically in LOS environment for a fixed antenna spacing and under some mild conditions. The analysis is based on a novel method using a Bessel function expansion, a new bounding technique and a simplified representation of inter-user interference for array geometries obeying Kronecker structure.

이중 모드 OAM 통신을 위한 간단한 급전 구조를 가진 균일 원형 배열 안테나

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.

Generation and numerical simulation of the focused OAM beams

The generation of the focused orbital angular momentum (OAM) beams using concentric uniform circular array (CUCA) is proposed in this paper. Since the ring shaped beams of the traditional electromagnetic (EM) vortex wave diverge along the propagation axis, only part of the beam is utilized for target detection, leading to a low efficiency. In this paper, two schemes are proposed to generate the focused OAM beams using concentric uniform circular antenna array (CUCA). Different from the traditional beam convergence method by reducing the divergence angle using parabolic reflector or lens, the proposed method employs a group of OAM beams with same divergence angle so that the superposed beam is focused at a certain azimuth angle. The feed amplitudes and phases of the elements of CUCA are firstly designed and validated using array factor multiplication. Then full wave simulations are conducted based on multilevel fast multipole algorithm (MLFMA) to calculate the radiation patterns and near field distributions of CUCA consist of micro strip patch antenna to further validate the proposed schemes. Simulation results indicate that the focused OAM beam can be achieved and the phase of the radiated field keeps the vortex property.