Uniform Circular Antenna Array Research Articles

Optimal Design of Uniform Circular Antenna Array in mmWave LOS MIMO Channel

The capacity of millimeter-wave (mmWave) line-of-sight (LOS) multiple-input multiple-output (MIMO) channel can be reduced due to the absence of rich scattering. However, the optimization of antenna array deployment can enable the maximum spatial multiplexing gain in the mmWave LOS MIMO channel, which can be applied to the long distance airborne data transmission. In this paper, we first establish the channel model of mmWave LOS MIMO based on a uniform circular antenna array (UCA) and derive the upper/lower bound of channel capacity. Aiming at achieving the maximum capacity of mmWave LOS MIMO channel, we propose the Newton-iterative method to obtain the optimal parameters of UCA. To simplify the optimization algorithm, the 2-D search can be transformed into 1-D search. Then, the analysis of bit error rate (BER) of the mmWave LOS MIMO system based on the UCA has been provided to quantify the mmWave LOS MIMO channel. Finally, numerical results demonstrate that the optimal parameters of UCA can be obtained by the Newton-iterative method and the BER of mmWave LOS MIMO communication system based on the corresponding optimized UCA can be minimized.

Orbital-Angular-Momentum Embedded Massive MIMO: Achieving Multiplicative Spectrum-Efficiency for mmWave Communications

By enabling very high bandwidth for radio communications, the millimeter-wave (mmWave), which can easily be integrated with massive-multiple-input-multiple-output (massive-MIMO) due to small antenna size, has been attracting growing attention as a candidate for the fifth-generation (5G) and 5G-beyond wireless communications networks. On the other hand, the communication over the orthogonal states/modes of orbital angular momentum (OAM) is a subset of the solutions offered by massive-MIMO communications. Traditional massive-MIMO-based mmWave communications did not concern the potential spectrum-efficiency-gain (SE-gain) offered by the orthogonal states of OAM. However, the highly expected maximum SE-gain for OAM and massive-MIMO communications is the product of SE-gains offered by OAM and multiplexing-MIMO. In this paper, we propose the OAM-embedded-MIMO (OEM) communication framework to obtain the multiplicative SE-gain for joint OAM and massive-MIMO-based mmWave wireless communications. We design the parabolic antenna for each uniform circular array antenna to converge OAM signals. Then, we develop the mode-decomposition and multiplexing-detection scheme to obtain the transmit signal on each OAM-mode of each transmit antenna. Also, we develop the OEM-water-filling power allocation policy to achieve the maximum multiplicative SE-gain for OEM communications. The extensive simulations obtained validate and evaluate our developed a parabolic antenna-based converging method, a mode-decomposition and multiplexing-detection scheme, and an OEM-water-filling policy, showing that our proposed OEM mmWave communications can significantly increase the SE as compared with the traditional massive-MIMO-based mmWave communications.

An Iterative Array Signal Segregation Algorithm: A method for interference cancelation and multipath mitigation in complex environments

A frequency-domain array signal segregation using an iterative approach (ASSIA) is developed to estimate the directions of arrival (DoAs), magnitudes, and phases of the signals' spectral components in a multipath environment. This is accomplished by using a uniform circular antenna array whose elements are individually connected to the radiofrequency (RF) front end of a neoteric radio. This technique is utilized to spatially and spectrally separate the communication signals of interest from the strong interfering signals without a priori knowledge regarding their DoAs. Through an extensive comparison with the other techniques reported in the literature, it is shown that ASSIA can detect the DoAs and signal levels of wide dynamic range (DR) much more accurately than what can be done with the existing techniques, provided that the signals' angular spacing is larger than the array beamwidth. Array calibration to capture the fabrication errors is essential to achieve the high level of the DR of signals that ASSIA can handle. The performance of the algorithm in the presence of strong jammers in complex multipath environments with Rayleigh fading characteristics is examined using numerical simulations based on an accurate ray-tracing propagation model. A statistical analysis based on Monte Carlo simulations shows that in such an environment, an ASSIA radio with a 12-element uniform circular array can improve the signal-to-jammer ratio (SJR) from -20 to at least +2 dB (minimum of 22-dB improvement) in more than 70% of occasions.

Radar imaging using electromagnetic wave carrying orbital angular momentum

The concept of radar imaging based on orbital angular momentum (OAM) modulation, which has the ability of azimuthal resolution without relative motion, has recently been proposed. We investigate this imaging technique further in greater detail. We first analyze the principle of the technique, accounting for its resolving ability physically. The phase and intensity distributions of the OAM-carrying fields produced by phased uniform circular array antenna, which have significant effects on the imaging results, are investigated. The imaging model shows that the received signal has the form of inverse discrete Fourier transform with the use of OAM and frequency diversities. The two-dimensional Fourier transform is employed to reconstruct the target images in the case of large and small elevation angles. Due to the peculiar phase and intensity characteristics, the small elevation is more suitable for practical application than the large one. The minimum elevation angle is then obtained given the array parameters. The imaging capability is analyzed by means of the point spread function. All results are verified through numerical simulations. The proposed staring imaging technique can achieve extremely high azimuthal resolution with the use of plentiful OAM modes.

Impact of Beamforming on the Path Connectivity in Cognitive Radio Ad Hoc Networks.

This paper investigates the impact of using directional antennas and beamforming schemes on the connectivity of cognitive radio ad hoc networks (CRAHNs). Specifically, considering that secondary users use two kinds of directional antennas, i.e., uniform linear array (ULA) and uniform circular array (UCA) antennas, and two different beamforming schemes, i.e., randomized beamforming and center-directed to communicate with each other, we study the connectivity of all combination pairs of directional antennas and beamforming schemes and compare their performances to those of omnidirectional antennas. The results obtained in this paper show that, compared with omnidirectional transmission, beamforming transmission only benefits the connectivity when the density of secondary user is moderate. Moreover, the combination of UCA and randomized beamforming scheme gives the highest path connectivity in all evaluating scenarios. Finally, the number of antenna elements and degree of path loss greatly affect path connectivity in CRAHNs.

Stochastic Framework for Evaluating the Effect of Displaced Antenna Elements on DOA Estimation

We establish a statistical framework for investigating the influence of correlated random displacements of antenna elements in a uniform circular antenna array (UCA) on the distribution of direction-of-arrival (DOA) estimates. More specifically, we apply a stochastic collocation method for modeling the sparse UCA root-MUSIC-DOA estimates as polynomial expansions of the random displacements. Compared to Monte-Carlo simulations, this approach yields a speedup of about 40 for the case of a displacement of two antenna elements.

On Favorable Propagation in Massive MIMO Systems and Different Antenna Configurations

Asymptotic orthogonality of channel vectors, also called favorable propagation (FP), plays a key role in massive multiple-input multiple-output (MIMO) systems, allowing linear processing to achieve optimality and maximize the information rate. Much research on the FP condition emerges under different assumptions, most of which has been proved to satisfy the FP condition for some massive MIMO implementations. A generic channel model without mutual coupling is proposed to study more general implementations than previously investigated. Two theorems establish: 1) conditions on the steering matrix alone that are sufficient to guarantee the FP condition holds and 2) that a simple condition on the steering matrix alone is sufficient to guarantee FP for all practical massive MIMO implementations. Then the uniform linear array, uniform planar array (UPA), and uniform circular array (UCA) antenna configurations are studied. Theoretical analyses indicate how close and how fast the inner product of different steering vectors converges to zero for a finite number of base station (BS) antennas, and prove that the FP condition is satisfied for the antenna configuration considered for an unlimited number of BS antennas only if the antenna spacing is not proportional to the reciprocal of the number of antennas. The analysis shows that the UCA has the shortest distance from the FP condition among the three antenna structures, while the UPA is especially suitable for massive MIMO systems for 5G owing to its good FP performance and compact physical size. Simulation results validate the theory.

Analytical spatial correlation analysis based on the hierarchical angle model for uniform linear and circular antenna arrays

In this study, an analytical analysis of normalised spatial correlation based on a hierarchical angle model for uniform linear array (ULA) and uniform circular array (UCA) over clustered narrowband multiple-input multiple-output channels is presented. The clustered channel has independent multiple paths, each of which is a cluster consisting of a number of independent subpaths, constructing a hierarchical angle structure. Unlike most of existing analysis methods that employ various simplification to the hierarchical angle, in this study, the hierarchical angle is expressed as a function of bivariate random variables. This formulation can include the simplified models as special cases. Assuming the angle of departure and angle of arrival of each subpath are independent, a closed-form spatial correlation expression between transmit and receive antennas of ULA or UCA is derived. Simulation results show that the theoretical spatial correlation matches well with the simulated one with channel data generated from the 3GPP spatial channel model for different scenarios.

Design and Implementation of Dolph Chebyshev and Zolotarev Circular Antenna Array

Objectives: Uniform Circular Antenna arrays (UCAs) are most common in conformal antenna arrays with uniform excitation of elements. We targeted to design and synthesis UCAs with a high gain of >10 dB and a low sidelobe level of <20 dB. Methods: In this paper, the Uniform Circular Array (UCA) is presented with phase mode theory to extract the mode excitation using newly developed ARRAYTOOL. Along with phase modes, the magnitude distribution of elements is synthesized with Chebyshev and Zolotarev Polynomials whose resulting far-field patterns are desirable. Findings: It is observed that the Chebyshev and Zolotarev far-field pattern results a low sidelobe of 20 to 25 dB with fewer elements. It’s also observed that the elements spacing of more than λ/4 yields grating lobes with the visible region. This is one the design constrains for UCA with non-uniform excitation. Improvements: In comparison with uniformly excited UCAs, the Chebyshev and Zolotarev Polynomials show desirable radiation patterns with fewer elements. With sidelobe of less than 25 dB and minimum null points, the proposed microstrip array shows expected performance for RADAR system with high rotational symmetry.

Multi-objective optimization for UWB antenna array by APSO algorithm

In this paper, a uniform circular antenna array (UCAA) combining genetic algorithm (GA) or asynchronous particle swarm (APSO) for finding out global maximum of multi-objective function in indoor ultra-wideband (UWB) communication system is proposed. The algorithm is used to synthesize the radiation pattern of the directional UCAA to reduce the bit error rate (BER), to increase received energy and channel capacity in indoor UWB communication system. Using the impulse response of multipath channel, the BER of the synthesized antenna pattern on binary antipodal-pulse amplitude modulation system can be calculated. Based on topography of the antenna and the shooting and bouncing ray/image techniques, the synthesized problem can be reformulated into a multi-objective optimization problem which would be solved by the GA and APSO. Numerical results show that the fitness value and convergence speed by APSO is better than those by GA. The results also show that for multi-objective problem APSO compared to GA can reduce the BER substantially. Moreover, APSO can get better results for both line-of-sight and non line-of-sight cases.

Generation of OAM radio beams with modified uniform circular array antenna

A modified uniform circular array is analysed and configured to generate radio waves carrying orbital angular momentum (OAM). The relationship between OAM mode and array parameters is derived mathematically. Results show that the produced OAM mode can be altered arbitrarily by changing the exciting frequency when the array is fixed. Moreover, the OAM mode is associated with elevation angle, offering the potential of elevation resolution for radar imaging.

A modeling framework for supporting and evaluating connectivity in cognitive radio ad hoc networks with beamforming

In this paper, we present an analytical modeling framework for supporting and evaluating the impact of shadowing and beamforming on the topological connectivity of cognitive radio ad-hoc networks (CRAHNs) where primary users (PUs) are equipped with omnidirectional antennas while secondary users (SUs) are equipped with directional antennas such as uniform linear array (ULA) antenna and uniform circular array (UCA) antenna. The main features and contributions in this paper are as follows. First, we derive a formula for calculating effective coverage area of a node in secondary network by taking the effect of path loss, antenna model, and beamforming scheme into consideration. Second, we mathematically analyze the expected number of neighbors and communication probability of a SU based on the effective coverage area of SU and the spatial---temporal existence of PU's operation. We also derive the expression of the upper bound of path connectivity between two arbitrary SUs in the networks. Third, we point out that UCA antenna is the most suitable antenna for CRAHNs. We find the optimal number of elements corresponding to each type of directional antenna at which the highest connectivity can be achieved. The validity of our analysis is verified by comparing with simulations. The results in this paper provide efficient guidelines for system designers to characterize and optimize the connectivity of CRAHNs with beamforming.

A novel hybrid IWO/WDO algorithm for nulling pattern synthesis of uniformly spaced linear and non-uniform circular array antenna

This paper introduces a new, fast, efficient and global optimization algorithm called hybrid invasive weed optimization (IWO) and wind driven optimization (WDO). The hybrid algorithm is verified with six standard benchmark functions and implemented to the nulling pattern synthesis of a uniform linear array (ULA) and non-linear circular array (NUCA) antenna having a minimum side lobe level (SLL), and beam width to minimize the interference effect by optimizing the parameters of array elements. Two examples of ULA pattern synthesis with broad null at desired direction are considered to illustrate the efficacy of the proposed algorithm. The results are compared with those obtained by BEES, PGSA, BFO, WDO and MTACO algorithms. Further, one design example of NUCA antenna is considered and the results obtained by hybrid algorithm is compared with those obtained by other evolutionary algorithms such as GA, PSO, CS, FA, BBO, COA, and MIWO. Simulation studies demonstrate the improved performance of hybrid IWO/WDO algorithm in terms of synthesizing broad null, minimum SLL, beam width control and the rate of convergence for nulling pattern synthesis of ULA and NUCA antenna compared to other twelve reported algorithms.

Analysis of MIMO antenna array based on 3D Von Mises Fisher distribution

A three-dimensional (3D) Von Mises Fisher (VMF) distribution model was derived in multiple-input and multiple-output (MIMO) antenna communication environment. The azimuth of arrival and elevation of arrival are distributed for VMF distribution instead of the uniform or other traditional distributions. In particular the MIMO uniform Y-shaped array (UYA) and the uniform circular array (UCA) antenna topology are considered at mobile station and base station. The developed spatial fading correlation of the VMF model is determined by parameters of the concentration parameter, antenna spacing, mean azimuth of arrival, mean elevation of arrival. Using the channel model, the effects of the concentration parameter and the mean elevation angle on the capacity of MIMO antenna systems was analyzed. It is shown that the mean elevation of arrival must be taken into account in 3D MIMO communication environment.

SIR 향상 다중 노드용 UCA 빔 형성 전력 할당 방법

본 논문에서는 원형 배열 안테나를 사용한 무선 메쉬 네트워크 LOS 환경에서 다중 노드 빔 형성을 위한 SIR 향상 빔 형성 전력 할당 기법을 제안한다. 제안된 방법은 다중 노드 접속을 위한 다중 노드 빔 형성 시 존재하는 전력 제한 조건을 만족시키며 송신 전력이 최대화되는 다중 빔 전력 할당 기법이다. 전산 모의 실험을 통하여 제안 한 빔 형성 전력 할당을 적용하였을 때 UCA 안테나에서 기존의 방법보다 다중 노드의 SIR이 향상됨을 확인하였다. This paper proposes a power allocation method for multiple node beamforming with uniform circular array antennas to increase SIR of nodes in wireless mesh network. The proposed method calculates beamforming power allocation vectors that maximizes SIR satisfied with power constraint of HPA. The simulation results demonstrate the proposed method achieves the enhanced SIR of nodes than that of beamforming method.

Synthesis of Circular Array Antenna for Sidelobe Level and Aperture Size Control Using Flower Pollination Algorithm

Sidelobe level suppression is a major problem in circular array antenna (CAA) synthesis. Many conventional numerical techniques are proposed to achieve this which are time consuming and often fail to handle multimodal problems. In this paper, a method of circular array synthesis using nature inspired flower pollination algorithm (FPA) is proposed. The synthesis technique considered here adapts one and two degrees of freedom, namely, amplitude only and amplitude spacing. The effectiveness of the FPA is studied by comparing the results with genetic algorithm (GA) and uniform circular array antenna (UCAA) with uniform spacing. Also the effect of additional degree of freedom on the aperture size and the computational time is analyzed. A relative side lobe level (SLL) of −25 dB is achieved using the algorithm under both no beam scanning (0°) and beam scanning (15°) conditions for 20 and 40 elements of CAA.

High Performance Direction Finding Algorithm Based on Phase Locked Loop

Using Phase Locked Loop based single channel Direction Finding (DF) system to estimate the bearing angle or the coordinates of an incoming radio signal(s) has much more advantages than multiple receiver system does in many practical scenarios such as mobile communication. This method utilizes a bank of Phase Locked Loops (PLLs) to calculate the differential phase of signal received by an M-element uniform circular antenna array with a commutative switch followed by single channel Software Defined Radio (SDR) receiver. One important factor when using conventional phase locked loop is the requirement of the small convergence rate of the algorithm compared to the switching cycle. In order to achieve small convergence rate, we propose a method for DOA estimation with low computation complexity that improves significantly the performance of conventional PLLs system. An analysis of the challenges of computation complexity in this algorithm is presented. The simulation results for DOA estimation using the proposed structure with low complexity are shown to verify the performance of the system.

Millimeter Wave Communications With Symmetric Uniform Circular Antenna Arrays

This letter is concerned with the singular value char- acterization of fixed point-to-point millimeter wave channels with symmetric uniform circular antenna arrays (UCAs) at both the transmitter and receiver. We model the channel as a line-of-sight (LoS) multiple-input multiple-output (MIMO) one and derive an explicit expression for all channel singular values. The asymptotic analysis when the end-to-end distance or the number of antenna elements goes to infinity is then developed. Numerical examples are provided to verify the validity of our discussions. The results in this letter show that the achievable multiplex gain is limited under such a system setting, regardless of the numbers of antennas at the transmitter/receiver. This observation provides benchmarks for the practical performance of UCA-based gigabits wireless communications over millimeter wave channels. Index Terms—Millimeter wave, line-of-sight, multiple-input multiple-output, uniform circular antenna arrays.

DESIGN OF LINEAR AND CIRCULAR ANTENNA ARRAYS USING CUCKOO OPTIMIZATION ALGORITHM

Cuckoo optimization Algorithm (COA) is employed for the optimization of linear and non- uniform circular antenna arrays. COA is a novel nature inspired computing algorithm which is motivated by the life of Cuckoo. Like other nature-inspired algorithms, COA is also a population-based method and uses a population of solutions to proceed to the global solution. The method of COA is used to determine a set of parameters of antenna elements that provide the required radiation pattern. The efiectiveness of COA for the design of antenna arrays is shown by means of numerical results. Comparison of results of COA is made with that obtained using other popular methods. The results reveal the superior performance of COA as compared to other techniques both for design of linear and circular antenna arrays.

Synthesis of Thinned Concentric Ring Array with Dipole Radiators Using Firefly Algorithm

The application of new metaheuristic approach, Firefly algorithm, for the thinning of large multiple Concentric Circular dipole arrays is presented. A nine-ring Uniform Circular antenna array with central element feeding is considered. To analyze the effect of thinning, optimization is carried out with and without pre fixing the percentage value of thinning. The performance of the array in terms of sidelobe level and beam width is discussed in four cases. The numerically simulated patterns are obtained and compared with those of concentric circular isotropic arrays.