Directivity Pattern Of Antenna Research Articles

A Link Quality Estimation-Based Beamforming Training Protocol for IEEE 802.11ay MU-MIMO Communications

The multi-user multiple-input-multiple-output (MU-MIMO) beamforming training (BFT) enables an access point (AP) and multiple stations (STAs) to determine appropriate directional antenna patterns; to this end, the AP transmits multiple action frames to the STAs during the MU-MIMO BFT. However, if the antenna weight vectors (AWVs) are determined to transmit the action frames inefficiently, this could lead to unnecessary transmissions, which could increase the BFT time. To mitigate the signaling overhead, the schemes used in our previous work employed AWVs, which use multiple beams simultaneously to transmit the action frames. Nevertheless, these existing schemes are still adversely affected by redundant transmissions because these schemes overlook the transmit diversity gain obtained from multi-beam concurrent transmission. Therefore, in this study, we propose a novel transmit antenna configuration scheme that mitigates the signaling overhead by considering the transmit diversity of the inter-symbol interference (ISI) channel incurred when multiple beams are used simultaneously. Our proposed scheme determines each candidate antenna weight vector (AWV) using multiple beams and efficiently identifies the STAs within reach of the corresponding multi-beam concurrent transmission. The numerical and simulation results demonstrate that our proposed scheme shortens the BFT time in comparison with existing schemes.

Fundamental Limits on Detection of UAVs by Existing Terrestrial RF Networks

Detection of drones carries critical importance for safely and effectively managing unmanned aerial system traffic in the future. Given the ubiquitous presence of the drones across all kinds of environments in the near future, wide area drone detection and surveillance capability are highly desirable, which require careful planning and design of drone sensing networks. In this paper, we seek to meet this need by using the existing terrestrial radio frequency (RF) networks for passive sensing of drones. To this end we develop an analytical framework that provides the fundamental limits on the network-wide drone detection probability. In particular, we characterize the joint impact of the salient features of the terrestrial RF networks, such as the spatial randomness of the node locations, the directional 3D antenna patterns, and the mixed line of sight/non line of sight (LoS/NLoS) propagation characteristics of the air-to-ground (A2G) channels. Since the strength of the drone signal and the aggregate interference in a sensing network are fundamentally limited by the 3D network geometry and the inherent spatial randomness, we use tools from stochastic geometry to derive the closed-form expressions for the probabilities of detection, false alarm and coverage. This, in turn, demonstrates the impact of the sensor density, beam tilt angle, half power beam width (HPBW) and different degrees of LoS dominance, on the projected detection performance. Our analysis reveals optimal beam tilt angles, and sensor density that maximize the network-wide detection of the drones.

Формирование расширенных провалов в диаграмме направленности адаптивного пространственного фильтра с плоской антенной решёткой

The adaptive antenna array beamforming is used to suppress jammers by placing antenna directional pattern nulls in the directions of the jammer sources. The performance of the beamformer is known to degrade in rapidly moving jammer environments. This degradation occurs due to the jammer motion that can bring the jammers out of the sharp nulls of the adaptive directional pattern. The directional pattern nulls broadening is an effective means to settle this problem. To broaden the nulls, the first derivative of the pattern in the directions of the jammer sources is set equal to zero. Being applied to the beamformer with a linear array, this technique allows producing broaden nulls in the directional pattern. However, in the case of a two-dimensional planar antenna array, the nulls will broaden only in one angular plane. In order to equally broaden the nulls in all angular directions and in this way to make them symmetrical, some additional constraints on the second partial derivatives of the directional pattern should be imposed. To set these constraints, it is necessary to include additional transformed steering vectors of jammers in the basis of the jammer subspace. These new transformed steering vectors are calculated in accordance with the expressions for the second partial derivatives of the directional pattern. In this paper, the expressions for the transformed steering vectors are derived and a novel beamforming algorithm based on them is proposed. In the adaptive beamforming algorithm based on such an approach unknown steering vectors of jammers are replaced by the eigenvectors of the sample covariance matrix corresponding to the largest eigenvalues. The effectiveness of the proposed method is verified by the computer simulation results. The computational complexity of this algorithm is estimated.

Statistical treatment of signal power measurements under identification of the distant radiator antenna directional pattern

Based on the use of the least squares method and the fastest gradient descent algorithm, the procedure for approximation of measurements of the radiation power of the transmitting antenna has been developed. This procedure involves an average power pattern of a linear type antenna with random amplitude and phase deviations on the assumptions of their normal distribution, consistency of average amplitude and phase dispersion along the antenna, Gaussian form of the correlation coefficient of deviations. As an approximation quality criterion, the minimum of the sum of the squared deviations of radiation power estimates at points of measurement from theoretical values of a random function that determines the shape of the radiation pattern is used. Given the nonlinearity of the function, the numerical approximation procedure based on the fastest gradient descent method has been proposed. The direction of descent at the next iteration is selected on the basis of the current value of the gradient of the criterion function. The criterion for the completion of the process is the achievement of a stationary, in a statistical sense, area of the function.

Adjustable circuits on semiconductor switching elements as a matching device in radar stations for outer space monitoring

Formulation of the problem. When scanning in space by a phased array antenna (PAA), which consists of a large number of emitters, there is an interaction between them in the form of impedance. It affects the matching quality of the receiving-transmitting module of the PAA with the emitter and leads to significant losses of power and detection range of the radar station.Objective. Improving the quality of the PAA emitters matching when changing the position of the antenna directional pattern beam in space due to the use of adjustable super high frequency (SHF) matching circuits on the switching elements.Results. The article substantiates an increase in the functional capabilities of the development of adjustable matching circuits of super-high frequencies due to the use of switching elements in the device, which allow reducing the influence of factors caused by a change in the input impedance of the radiating element in phased antenna arrays. Based on the presented mathematical model, the change in the input resistance of the radiating elements is taken into account, which arises due to their mutual influence, and makes it possible to research the potential characteristics of controlled circuits when their structure and parameters change. The method of choosing the structure and parameters allows the device to be adjusted to the change in the input complex load resistance and ensure the minimum voltage standing-wave ratio.Practical significance. The proposed device allows for the calculation of implemented adjustable matching circuits, which, with existing materials and manufacturing technologies, provide a decrease in losses and an increase in range. An experimental model of microstrip design was developed based on the proposed device and a field experiment was carried out, which confirmed the correctness of the approach to the developed device.

STUDY OF THE INFLUENCE OF INTENSIFYING ADDITIVES ON LOW-TEMPERATURE SYNTHESIS OF SLAVSONITE AND CELZIAN IN THE CREATION OF RADIOTRANSPARENT CERAMIC MATERIALS

The studies carried out concern the development of structural radiotransparent ceramic materials based on the four-component system BaO–SrO–Al2O3–SiO2. Due to the widespread use of radar equipment at modern aviation facilities, the development of radiotransparent fairings for them is a rather important and urgent task.The purpose of the fairings is to protect the antenna devices of radar stations from environmental influences during flight. Based on this, the fairings must meet a complex set of requirements for aerodynamic, thermal, radio engineering and mechanical properties. These requirements at supersonic flight speeds of modern objects increase significantly, since the improvement of the aerodynamic shape, the increase in the mechanical strength and thermal stability of the fairings contradicts the interests of radio engineering, leading to a significant deterioration in their radiotransparency and to distortions of antenna directional patterns. The consequence is a decrease in the range of radar stations and serious deterioration in their accuracy characteristics.The aim of the research was to obtain, on the basis of the BaO–SrO–Al2O3–SiO2 system, crystalline phases of slavsonit and celsian at low temperatures and times of synthesis, by introducing sintering intensifiers with fluxing and modifying action.The influence of a number of additives on the intensification of the low-temperature synthesis of slavsonit and celsian is investigated. The positive effect of the eutectic additive of the SnO2–Li2O system on the preparation of a densely sintered ceramic material based on solid solutions of slavsonit and monoclinic celsian is shown. It has been established that, according to its dielectric properties, the obtained ceramic material can be classified as structural radio-transparent materials.

Virtual Sensing Directional Hub MAC (VSDH-MAC) Protocol with Power Control

Medium access control (MAC) protocols play a vital role in making effective use of a multiple access channel as it governs the achievable performance such as channel utilization and corresponding quality of service of wireless sensor networks (WSNs). In this paper, a virtual carrier sensing directional hub (VSDH) MAC protocol incorporating realistic directional antenna patterns is proposed for directional single hub centralized WSNs. While in most instances, MAC protocols assume idealized directional antenna patterns, the proposed VSDH-MAC protocol incorporates realistic directional antenna patterns to deliver enhanced link performance. We demonstrate that the use of directional antennas with a suitable MAC protocol can provide enhanced communication range and increased throughput with reduced energy consumption at each node, compared to the case when only omnidirectional antennas are used. For the scenarios considered in this study, results show that the average transmit power of the sensor nodes can be reduced by a factor of two, and at the same time offer significantly extended lifetime.

Interference Characterization and Power Optimization for Automotive Radar With Directional Antenna

Wide deployment of radar sensors on automotive vehicles can potentially lead to a severe interference problem. Such interference has been characterized without considering directional antenna patterns, which could lead to results significantly larger than the actual ones. In this paper, we study the mean power of effective echo signals and interference, by considering both front- and side- mounted radars equipped with directional antennas. We employ the stochastic geometry method to characterize the randomness of vehicles and hence radars in both two-lane and multi-lane scenarios, and derive closed-form expressions for the mean interference by approximating the radiation pattern by Gaussian waveforms. Simulation results are shown to match the analytical results very well, and insights are obtained for the impact of radar parameters on interference. Based on the interference analysis, we aim to minimize the total transmission power of each vehicle with constraints on the required signal to interference and noise ratio. An optimal solution is obtained based on linear programming techniques and corroborated by simulation results.

On Over-the-Air Testing for Devices With Directional Antennas

This paper investigates the impact of devices under test (DUTs) with directional antennas on the recreated channel in the over-the-air (OTA) testing for massive multiple-input multiple-output (MIMO) devices using prefaded signal synthesis (PFS) technique. Assuming the uplink in real radio environments, the directional receiver (Rx) antenna patterns would affect the gains in different incoming directions, thereby affecting the spatial characteristics of the target channel. A typical multi-probe anechoic chamber (MPAC) setup for massive MIMO base stations (BSs) is studied, where a limited number of probe antennas are distributed over the probe wall to emulate the target channel by proper probe weighting. The directional antenna patterns would have nonnegligible effects on the emulated spatial characteristics which may become inaccurate for DUTs with directional antennas and thus need to be re-examined. Therefore, the reconstructed channel with the PFS technique will be investigated under the MPAC setup in this paper, with particular focus on the DUTs with directional antennas. The deviations between the covariance matrix of the Rx antennas under the target channel and the covariance matrix under the reconstructed channel are used as the metric to evaluate the performance of the reconstructed channel, and the optimal probe weights are also re-determined. Furthermore, given beamforming capability of massive MIMO BSs, the impact of the BS antenna patterns on angular spectrum is investigated as well. In addition, since the reconstructed channel needs to not only reflect the spatial characteristics of Rx antennas but also reflect the spatial characteristics of transmitter antennas and propagation environment, the end-to-end channel capacities are evaluated. Simulation results under various scenarios show that the accuracies of the reconstructed channel in terms of spatial correlation, angular spectrum and channel capacity can be improved by using the re-optimized probe weights when directional antenna patterns of the DUTs are taken into account.

Additively manufactured trapezoidal grooves for wideband and high gain Ku‐band antenna

Grooves around aperture antennas are known to be instrumental in obtaining directive antenna patterns. The shapes of the grooves are often restricted to rectangular or triangular due to manufacturing difficulties in traditional metal machining, and because of this reason, the effect of groove shape on antenna performance is often overlooked. The aim of this study is to analyze different groove shapes with the help of additive manufacturing. Waveguide slot fed, dual cavity aperture antenna with grooves is designed and the effect of groove shapes on antenna performance is studied at Ku band. Two antennas with and without grooves are built using 3D printing technology. Measured antenna performance reveals 5 GHz bandwidth covering 10 to 15 GHz for Ku-band satellite communications and part of the X-band applications. Proposed antenna achieves 13.25 dBi peak gain at 14 GHz and the gain is better than 11.25 dBi over the entire Ku-band uplink and downlink frequency bands.

Wideband Circularly Polarized Applications: Design of a compact, traveling-wave-fed loop antenna

A novel compact wideband circularly polarized (CP) directional loop antenna is presented in this article. The antenna is formed by an inner loop with periodic capacitive loading and an outer concentric loop, both of which are placed on the top side of a dielectric substrate and fed by nonradiating slots. A traveling-wave feed network is adopted to excite the slots, thereby providing the loops with currents of the same magnitude and appropriate phase delay. Thus, stable symmetrical directional CP radiation is achieved. In addition, the feed network is wrapped on the lower cylindrical dielectric substrate, so the size of the antenna can be made very compact. A prototype is implemented to verify the design concept. The measured results indicate that the antenna reaches a compact size e of O0.11l0 t 0.075l0 (l0 is the wavelength corresponding to the lowest CP operating frequency), an available bandwidth of 31.3% (1.375-1.875 GHz), maximum broadside gain of 5.03 decibel above the gain of a isotrope antenna (dBic) and stable wide-beam directional radiation patterns covering the whole CP passband.

Offshore Electromagnetic Spectrum Distribution Prediction Algorithm Based on Ray Tracing Method

The detection and management of electromagnetic spectrum resources is becoming more and more important. It is difficult to predict the electromagnetic spectrum distribution accurately in complex maritime environment. In this letter, the offshore environment model is described in conjunction with the Pierson–Moskowitz (PM) wave spectrum and antenna attitude. Then, we establish the offshore electromagnetic spectrum distribution prediction model. The offshore electromagnetic wave propagation is divided into the sight straight-line ray propagation and rough sea surface reflecting-line ray propagation. Combined with the antenna directional pattern, we propose the effective angle to accelerate effective rays distribution estimation. In the simulation, the ray distribution is obtained based on the instantaneous PM wave spectrum data, and the final field strength of the effective ray at the receiving point is calculated. The experimental results show that the prediction model based on ray tracing method can accurately estimate the offshore electromagnetic spectrum distribution.

5G Massive MIMO Architectures: Self-Backhauled Small Cells Versus Direct Access

In this paper, we focus on one of the key technologies for the fifth-generation wireless communication networks, massive multiple-input-multiple-output (mMIMO), by investigating two of its most relevant architectures: 1) to provide in-band backhaul for the ultra-dense network (UDN) of self-backhauled small cells (SCs), and 2) to provide direct access (DA) to user equipments (UEs). Through comprehensive 3GPP-based system-level simulations and analytical formulations, we show the end-to-end UE rates achievable with these two architectures. Differently from the existing works, we provide results for two strategies of self-backhauled SC deployments, namely random and ad-hoc, where in the latter SCs are purposely positioned close to UEs to achieve line-of-sight (LoS) access links. We also evaluate the optimal backhaul and access time resource partition due to the in-band self-backhauling (s-BH) operations. Our results show that the ad-hoc deployment of self-backhauled SCs closer to the UEs with optimal resource partition and with directive antenna patterns, provides rate improvements for cell-edge UEs that amount to 30% and tenfold gain, as compared to mMIMO DA architecture with pilot reuse 3 and reuse 1, respectively. On the other hand, mMIMO s-BH underperforms mMIMO DA above the median value of the UE rates when the effect of pilot contamination is less severe, and the LoS probability of the DA links improves.

Adaptive Antenna Pattern Notching of Interference in Synthetic Aperture Radar Data Using Digital Beamforming

Radio Frequency Interference (RFI) is a growing problem in Synthetic Aperture Radar (SAR) systems as scientific motivations push the radars to lower frequencies and as more wireless services share the frequency spectrum. New, advanced SAR instruments, such as NASA’s EcoSAR, DBSAR and DLR’s Tandem-L mission, employ a multichannel architecture capable of Digital Beamforming (DBF). Radars with DBF are capable of notching the antenna pattern in specific directions, which can be utilized to suppress RFI on board or in post-processing. A well-researched beamformer for this purpose is the Minimum Variance Distortionless Response (MVDR) Beamformer. However, the number of interferers that can be removed through notching is limited by the number of receive channels. It is therefore essential to adaptively change the antenna pattern notching throughout the image in time and frequency for the best results with a given number of receive channels. In this paper, we present several methods to achieve this notching by making use of the spatial SAR signal distribution in range time, range frequency, azimuth time and azimuth Doppler that is inherent to the SAR imaging geometry. Because this distribution is time-variable and yet predictable, it can be used to improve the angle of arrival estimation of the RFI and the adaptive notching. The presented methods can be applied to a Digital Beamforming (DBF) SAR signal with multiple channels in elevation and/or in azimuth. Simulations show that the proposed methods increase the ability to notch out-of-swath interference from multiple directions and lessen the impact on in-swath interference. The improvement of the interferometric coherence for a single-pass interferogram acquired by NASA’s EcoSAR system (capable of DBF in elevation) is demonstrated. The removal of periodic RFI artifacts is achieved.

Improving the navigation spacecraft radio visibility with signal processing algorithms usage

The article deals with topical issues of spacecraft external design for the global navigation satellite system (GLONASS). The development and analysis of data processing algorithms are considered a part of the external design phase. Data for processing algorithms was obtained from real orbital grouping spacecraft. Mathematical modelling was performed based on real data to analyse navigation signals propagation conditions from GLONASS satellites. Implementation of mathematical modelling approach included such aspects as finding the optimal antenna pattern and filtering radio frequency signals. Theoretically optimal antenna directivity patterns were implemented taking into account available data about satellite orbital parameters. Bessel, Butterworth, Chebyshev and elliptic filters were used as standard filtering methods. Modified low-pass filtering algorithm was considered as an improved filtering algorithm. Application of the modified filtering method allowed to reduce geometric dilution of precision value in the consumer positioning case. Obtained results are applicable to design possible options for improving the existing GLONASS orbital group.

Offshore Electromagnetic Spectrum Distribution Prediction Model Based on Ray Tracing Method and PM Wave Spectrum

Electromagnetic spectrum distribution prediction is the basis for the development of wireless communication technology. Due to the high randomness of the rough sea surface, it is difficult to accurately predict the offshore electromagnetic spectrum distribution. We present a prediction model of offshore electromagnetic spectrum distribution based on ray tracing method and Pierson-Moskowitz (PM) wave spectrum model. Based on the antenna attitude and the antenna directional pattern, the field strength calculation formulas of the electromagnetic wave sight line ray (SLR) propagation and the electromagnetic wave reflecting line ray (RLR) propagation off the sea surface are established. As the sea surface and the antenna attitude change, the effective rays from the transmitting antenna to the receiving antenna also change. This paper focus on the electromagnetic spectrum distribution prediction by calculating the effective angle (EA) of the transmitting antenna. We relate the EA to the antenna tilt angle and the antenna directional pattern, and combine the PM wave spectrum to establish the offshore electromagnetic spectrum distribution prediction models. Finally, we simulated the electromagnetic spectrum distribution prediction based on specific PM wave spectrum data.

Efficient MU-MIMO Beamforming Protocol for IEEE 802.11ay WLANs.

IEEE 802.11ay supports multi-user multiple-input-multiple-output (MU-MIMO). However, the MU-MIMO beam-forming training (BFT) is a time-consuming process for finding appropriate directional antenna patterns, and inefficient BFT results in a long training time. Thus, in this letter, we propose an algorithm that configures the transmit antenna with the aim of reducing the number of redundant transmissions during MU-MIMO BFT. Both analytic and simulation results show that our proposed algorithm can significantly reduce the training time.

Determination of spacecraft antenna directivity pattern with the use of an Earth-based station

The problem of defining characteristics of the spacecraft antenna directivity pattern is considered in the paper. The solution of the problem will make it possible to estimate changes of antenna parameters with time. A method of defining the spacecraft antenna directivity pattern with the use of the earth-based data receiving stations is proposed for solving the problem. The results of simulation modeling of distribution of electromagnetic radiation over the Earth's surface for different routes of flight are presented in the paper. These results show the possibility of using an earth-based data receiving station for the construction of the spacecraft antenna directivity pattern. An algorithm of calculating parts of the direction characteristic with their subsequent integration is given in the article. The conditions limiting the accuracy of the proposed method as well as the ways of speeding up the construction of the spacecraft antenna directivity pattern are determined. Approbation of the proposed method through the example of the antenna of the small spacecraft AIST-2D is discussed. The directivity pattern of the antenna of the radio data link for transmitting target information of the satellite was constructed for this purpose and characteristic parts of the antenna directivity pattern are defined. The results of the comparative experiment with changes in the antenna radiation direction and definition of changes in information reception characteristics are presented.

Analysis of the Potential Precision of Measurement of Angular Coordinate

A comparative analysis of the potential precision of measurements of the angular coordinate of a radar target in discrete and linear scanning of an antenna beam is performed. A formula for determining the variance of an estimate of the angular coordinate based on the likelihood function for two positions of the antenna beam and the Kramer–Rao expression is obtained. An approximation of the form of the antenna directional pattern is proposed. Based on the results of the calculations, it is established that the precision of a measurement of the angular coordinate is higher in discrete scanning than in linear scanning.

Limited Feedback Channel Estimation in Massive MIMO With Non-Uniform Directional Dictionaries

Channel state information (CSI) at the base station (BS) is crucial to achieve beamforming and multiplexing gains in multiple-input multiple-output (MIMO) systems. State-of-the-art limited feedback schemes require feedback overhead that scales linearly with the number of BS antennas, which is prohibitive for 5G massive MIMO. This paper proposes novel limited feedback algorithms that lift this burden by exploiting the inherent sparsity in double-directional MIMO channel representation using overcomplete dictionaries. These dictionaries are associated with angle of arrival and angle of departure that specifically account for antenna directivity patterns at both ends of the link. The proposed algorithms achieve satisfactory channel estimation accuracy using a small number of feedback bits, even when the number of transmit antennas at the BS is large-making them ideal for 5G massive MIMO. Judicious simulations reveal that they outperform a number of popular feedback schemes and underscore the importance of using angle dictionaries matching the given antenna directivity patterns, as opposed to uniform dictionaries. The proposed algorithms are lightweight in terms of computation, especially on the user equipment side, making them ideal for actual deployment in 5G systems.