Antenna Beamwidth Research Articles

Efficient Beamforming Technique Based on Sparse MIMO Array and Spatial Filter Bank

Spatial diversity gained through different beamforming techniques in antenna array is one of the main advantages over the single antenna. Antenna complexity and beamwidth broadening at the scanning angles other than broadside are downsides of antenna arrays that prevent its practical implementation from some applications. In this letter, we propose an efficient beamforming method based on the sparse multiple-input–multiple-output (MIMO) array and spatial filter bank (SFB). The sparse MIMO array produces narrow beams while significantly reduces the number of array elements without compromising system performance. Multiple main beams are chosen from grating lobes by SFB. By combining sparse array geometry and SFB, we can achieve a narrower beamwidth with less antenna elements, multiple beams, and constant beamwidth. The burden of system will be transferred from the frontend hardware to the signal processing back end.

Wideband Wide Beamwidth Full-Wavelength Sectorial Dipole Antenna Under Dual-Mode Resonance

In this article, a novel design approach to wide beamwidth dual-resonant, wideband sectorial dipole antennas is advanced. At first, a 1-D, full-wavelength dipole is evolved into a 2-D, sectorial dipole, so as to determine its two usable resonant modes. Then, both wideband and wide beamwidth characteristics are simultaneously attained under dual-mode resonance. Next, dual-resonant sectorial dipole antennas with flared angle of 270° and 240° are designed and studied. As experimentally validated, the proposed antenna exhibits an omnidirectional pattern with its impedance bandwidth over 70.4%. A few prototypes mounted above a ground plane are further investigated, so as to achieve a broad H-plane half-power beamwidth (HPBW) to over 120°. In addition, the antennas exhibit stable gain frequency response with fluctuation less than 2.2 dB within the entire impedance bandwidth. Thus, the advanced design approach based on 2-D dual-resonant, full- wavelength dipole leads to the formulation of novel wide beamwidth antennas with low frequency dispersion and simple configuration within a wide radiation bandwidth over 53.3%. Finally, a dual-polarized dipole antenna with port-to-port isolation higher than 34.5 dB and available radiation bandwidth of over 49% is implemented to further validate its potential for practical applications.

On Connectivity of UAV-Assisted Data Acquisition for Underwater Internet of Things

Underwater exploration activities have grown significantly due to the proliferation of underwater Internet of Things (UIoT). However, to transmit sensor data from UIoT to remote onshore data processing center requires a huge cost of deploying and maintaining communication infrastructures. In this article, we propose an unmanned aerial vehicles (UAVs)-assisted underwater data acquisition scheme by placing multiple sink nodes on the water surface to serve as intermediate relays between underwater sensors (IoT nodes) and UAVs. In our scheme, the sensor data are first transmitted via an acoustic-signal link to a buoyant sink node, which then forwards the data to a UAV via an electromagnetic link. In particular, we adopt two sink-node-deployment methods, i.e., grid placement and random placement of sink nodes. Since the path connectivity from an underwater sensor node to the UAV is crucial to guarantee reliable data acquisition tasks, we establish a theoretical framework to analyze the path connectivity via the intermediate sink node for both grid and random sink-node-deployment methods. Extensive simulation results validate the accuracy of the proposed analytical model. Moreover, our results also reveal the relationship between the path connectivity and other factors, such as sink node placements, antenna beamwidth of UAVs, and wind speed. We also further extend our UAV-assisted data acquisition to other scenarios with the consideration of trajectories of UAVs, movements of sink nodes, interference of both underwater acoustic and terrestrial radio links, and integration with edge computing.

Performance Modeling Framework for IoT-over-Satellite Using Shared Radio Spectrum

Delivering Internet-of-Things (IoT) connectivity over satellite is a promising solution for applications in remote and sparsely populated areas. These applications range from smart agriculture, logistics, asset tracking to emergency services. Using a shared radio spectrum with terrestrial services will facilitate a cost-effective and rapid deployment of IoT-over-Satellite since it reduces the administrative and financial hurdles of leasing a dedicated segment of the spectrum. Although IoT-over-Satellite communication provides larger service coverage, the vast number of IoT devices also increase the interference in the satellite uplink channel, and it becomes a significant challenge for the reliable performance of the IoT-over-satellite. In this paper, we propose a framework for modeling the performance of IoT-over-Satellite access systems when sharing the radio spectrum with terrestrial networks. We take into consideration several important aspects, namely; satellite orbit, terrestrial IoT devices uplink interference, atmosphere and gas absorption, and the probability of line-of-sight. The performance of the overall system is presented in terms of the uplink signal-to-interference-plus-noise ratio (SINR), and thus the time-availability of the satellite link during a typical pass. We focus on low earth orbit satellites due to their potential use in IoT applications, where we evaluate the framework using actual parameters of satellites located in 300–800 km orbits. Furthermore, the paper presents a numercial model to obtain the most suitable antenna beamwidth that maximizes the link-availability of the satellite link by the simultaneous reduction in the terrestrial interference and the boosting of the underlying IoT signal of interest.

Altitude and number optimisation for UAV‐enabled wireless communications

This study considers a downlink power consumption problem for unmanned aerial vehicles (UAVs)-assisted wireless communications, in which UAVs are used as aerial base stations to provide service for the ground users and equipped with a directional antenna of fixed beamwidth. Moreover, the on-board circuit power of UAV is taking into consideration. The authors derive a closed-form expression for the optimal flying altitude and number of UAVs by minimising the total power consumption under the users' rate requirements in the given coverage area. The numerical simulation and theoretical results show that the optimal flying altitude of UAVs depends on the beamwidth of the directional antenna at UAVs, the on-board circuit power of UAVs, and the rate constraint of each user.

Minimization of side lobe level of non-uniformly spaced concentric elliptical array antennas for a desired value of first null beam width in vertical and horizontal planes

ABSTRACT In this paper, the optimal reduction of side lobe level with constraints of a suitable first null beam width of a non-uniform concentric elliptical array antenna of uniformly excited isotropic elements is described. Three meta-heuristic optimization algorithms, namely, ant lion optimization, crow search algorithm, and moth fly optimization algorithms are used for the optimal synthesis of the considered array structure in vertical plane and in horizontal plane. Simulation result shows that the optimized side lobe level value is reduced compared to a uniform concentric elliptical array antenna of same size and same number of elements for both the planes.

Probabilistic Spatially-Divided Multiple Access in Underwater Acoustic Sparse Networks

Deploying Autonomous Underwater Vehicles (AUVs) is a necessity to enable a range of civilian/military underwater applications; yet, achieving a reliable coordination among the vehicles is a challenging issue due to the time- and space-varying characteristics of the acoustic communication channel. The design of a Medium Access Control (MAC) based on a probabilistic Space Division Multiple Access (SDMA) method for short/medium distances (less than $2\; \mathrm {km}$ 2 km ) is presented. This method considers the inherent vehicle position uncertainty due to the inaccuracies in models and the drift of the vehicles. It minimizes the acoustic interference statistically by considering the angular position of neighboring vehicles via a two-step estimation and by keeping the transmitter antenna's beamwidth of each vehicle at an optimal value. Such value is chosen considering three contrasting goals, i.e.: $(i)$ ( i ) spreading the signal beam towards the vehicle to combat position uncertainty using a coarse estimation; $(ii)$ ( i i ) focusing the beam to reduce acoustic energy dispersion through a fine estimation; and $(iii)$ ( i i i ) minimizing interference to other vehicles. Simulation results in a sparse underwater network show that this approach mitigates interference, reduces the probability of retransmission, and achieves higher data rates over conventional underwater MAC techniques.

Wide band ridge gap waveguide (RGW) fan beam antenna with low side lobes based on parabolic reflector principle

In this paper, a wide band ridge gap waveguide (RGW) fan beam antenna with low side lobe level (SLL) is presented making use of parabolic offset reflector concept in antenna geometry. In the proposed topology, in contrast to TEM based RGW horn, the amplitude distribution across the antenna aperture can be easily controlled. Furthermore, thanks to intrinsic feature of parabolic reflector in generating plane wave front, the phase distribution uniformity across the proposed antenna aperture is better than that of the RGW horn. These two facts allow the proposed topology to provide lower SLL compared to the RGW horn. A prototype of the proposed structure is designed and fabricated. Simulation and measurement results also show that wider operating bandwidth compared to the RGW horn can also be achieved using this topology. For the designed sample, the impedance bandwidth of 41% with -20 dB ≤ SLL ≤ - 15 dB and gain of 11.8-15.5 dBi is achieved. Results show that the proposed topology can be a good candidate for realization of high gain wide band RGW fan beam antennas with low SLL.

Common‐Volume Dual‐Frequency Radar Observations of 150‐km Echoes and Implications

AbstractWe present and discuss common‐volume dual‐frequency radar observations of 150‐km echoes made at 30 and 53 MHz from Gadanki by employing identical transmitter power and antenna beam width. These controlled experiments reveal that 150‐km echoes are stronger, broader in spectral width, and more frequent in their occurrence at 30 MHz than at 53 MHz. Echo intensities at 30 and 53 MHz are found to be consistent with the rocket‐borne observations of wave number spectrum of meter‐scale irregularities in the 150‐km region. The frequency dependence of spectral widths of the echoes while is found to be somewhat similar to that of electrojet type‐1 echoes it is opposite to that of electrojet type‐2 echoes and also to that of incoherent scattering in direction perpendicular to magnetic field. Spectral widths of the echoes observed by both radars are found to be independent of SNR. A detailed comparison of these observations with those made earlier suggests that instrument functions play an important role in manifesting SNR‐dependent/independent spectral width property of the 150‐km echoes. The narrow spectral properties and frequency dependence of echo intensity and spectral width clearly suggest that the irregularities responsible for the radar backscatter are linked with weak plasma turbulence and the meter‐scale irregularities responsible for radar echoes ought to be growing with direct injection of energy at the meter scale itself to overcome damping. We surmise the potential role of photoelectrons and atmospheric gravity waves in the underline plasma instability process.

An Improved CA-CFAR Method for Ship Target Detection in Strong Clutter Using UHF Radar

In this letter, the application of ultra-high frequency (UHF) radar for ship target detection over river is investigated for the first time. Due to the wide beam width of antenna, the ship detection of the UHF radar suffers from the broaden river clutters scattering from water waves. In addition, due to the high resolution, the ship echoes are seriously extended in both range and Doppler dimensions, which is different from the traditional point target signal. Extended target detection in strong river clutter is applied in this letter. Conventional constant false alarm rate (CFAR) detector is limited in this situation, which is applicable to the point target detection in clutter free background. An improved cell-averaging (CA)-CFAR method is proposed based on a joint estimation of threshold in range, Doppler and time serials of range-Doppler (R-D) spectra. Based on the time stationarity of clutter, this three-dimensional (3D) CA-CFAR combines several R-D spectra collected in continuous time to estimate the clutter threshold. The effectiveness of this improved method is validated using both simulated and field data.

Concurrent Respiration Monitoring of Multiple Subjects by Phase-Comparison Monopulse Radar Using Independent Component Analysis (ICA) With JADE Algorithm and Direction of Arrival (DOA)

While non-contact monitoring of human respiration has been demonstrated using Doppler radar, the concurrent monitoring of multiple equidistant subjects remains a significant technological challenge. Reported research has so far been limited to maintaining 1-m subject separation, based on the radar antenna beam-width. Proposed here is a hybrid method consisting of an SNR-based intelligent decision algorithm which integrates two different approaches to isolate respiratory signatures of two subjects within the radar beam-width separated by less than 1 meter. Using Independent Component Analysis with the JADE algorithm (ICA-JADE) and Direction of Arrival (DOA), this SNR-based decision algorithm works with an accuracy above 93%. In addition, angular location of each subject is estimated by phase-comparison monopulse and an integrated beam switching capability is demonstrated to optimally extract respiratory information. The proposed method coherently combines two separation methods to overcome multiple-subject monitoring limits which can lead to practical adoption for many respiration monitoring applications.

Maximum SNR Power-Delay Spectrum Propagation Models in Blocked 60-GHz Line-of-Sight Settings Inside Conference Halls

Models of the radio channel power delay profile are proposed for low-complexity 60 GHz communications systems that employ beam tracking capability in realistic indoor non-line-of-sight scenarios. A single-carrier transmission system that does not employ equalization, but only uses forward error correction is considered. The channel models were obtained from measurements done in a novel way in a conference room in which non-line-of-sight scenarios are created through a human-sized blocking object, and in which beamforming is applied at the receiver to track and obtain reflected paths. By deploying beamforming antennas and then switching to the best path when the LoS path is cut, it was found through measurements and models that very low delay spreads could be achieved. As a result, not only the new channel models are verified, but the proposed model could replicate the measured channel with narrow antenna beamwidth together with beam tracking and switching. The low delay spread performance could lead to low-power consuming devices and multi-gigabits-per-second transmission by a single carrier with simple FEC.

Design and Development of Circular Polarized Conformal Microstrip patch Antenna

This paper presents broadband circular polarized conformal antenna with a square patch for on-board applications. The substrate is located in between patch and the ground. A novel Circular polarized square patch with microstrip feed with two truncated corners with conformal structure is designed. Using a parametric study on the effect of the position of feed, the antenna parameters VSWR bandwidth, half power beam width and polarization of antenna are analysed. Finally fabrication of conformal square patch on 2.2 dialectic substrate and measured results are discussed.

On the Tradeoffs Between Coverage Radius, Altitude, and Beamwidth for Practical UAV Deployments

Current studies on unmanned aerial vehicle (UAV) based cellular deployment consider UAVs as aerial base stations for air-to-ground communication. However, they analyze UAV coverage radius and altitude interplay while omitting or over-simplifying an important aspect of UAV deployment, i.e., effect of a realistic antenna pattern. This paper addresses the UAV deployment problem while using a realistic three-dimensional directional antenna model. New tradeoffs between UAV design space dimensions are revealed and analyzed in different scenarios. The sensitivity of coverage area to both antenna beamwidth and height is compared. The analysis is extended to multiple UAVs and a new packing scheme is proposed for multiple UAVs coverage that offers several advantages compared to prior approaches.

Experimental Validation of GNSS Interferometric Radio Occultation

In this work, we present experimental results on the interferometric radio occultation (iRO) signal processing techniques, and compare the performance to the closed-loop and open-loop processing used in conventional radio occultation measurements. We also discuss the effects of antenna beam width to mitigate inter-satellite interferences, as well as how the local oscillator stability affects the obtained Doppler estimates. The required signal processing resources are less stringent for the iRO than for conventional RO techniques. In addition, the zenith iRO has a comparable performance to the well-established RO techniques.

Analysis of the Azimuth Ambiguity and Imaging Area Restriction for Circular SAR Based on the Back-Projection Algorithm.

Circular synthetic aperture radar (CSAR) has a 360° observation capability on the central observation scenario. A typical way to process CSAR imaging is to cut data into small sub-apertures because most targets are only coherent at a very small observation angle. There are many sub-aperture imaging methods after development in recent years. The back-projection algorithm is widely used because it is simple and can be applied to an arbitrary trajectory. Because of the limitation of the Nyquist sampling frequency and influence of the antenna sidelobe, azimuth ambiguity is a phenomenon that may occur in the radar imaging process. The existing researches typically choose the back-projection (BP) imaging area according to the SAR platform flight path and the antenna beam width. The limitation of the CSAR imaging area and its azimuth ambiguity region are rarely analyzed theoretically. This paper focus on the sub-aperture imaging of CSAR, based on the BP algorithm, which derives the relationship of azimuth ambiguity with CSAR parameters such as the pause repeat frequency (PRF), slant range angle, velocity of radar platform, etc. This paper proposes an equation for the calculation of the azimuth ambiguity region and analyzes the limitations, which provides theoretical support for CSAR parameter design, imaging area selection, and azimuth ambiguity analysis.

Wave-Height Mapping From Second-Order Harmonic Peaks of Wide-Beam HF Radar Backscatter Spectra

Compact high-frequency surface wave radar has been widely applied to the measurement of sea surface current, but its accuracy and direction resolution of wave parameter estimation are always limited due to the wide beam of the antenna. In this article, a novel wave-height mapping method based on the second-order harmonic peak (SHP) of radar Doppler spectra is proposed to address this concern. The characteristic of the SHP at the Doppler frequency of $\sqrt {2}$ times the Bragg frequency is studied through the theoretical derivation and numerical simulation. A relationship between the ratio ( $R$ ) of the SHP power to the Bragg peak power and significant wave height ( $H_{s}$ ) is derived. Furthermore, the $R$ – $H_{s}$ model is improved by incorporating influences, such as background noise and antenna beamwidth. With this improved model, a wave-height mapping algorithm based on the direction finding technique is presented. This approach enables the significant wave-height map extraction using a broad-beam radar. Finally, wave-height maps obtained at different sea states are depicted and analyzed, and the wave heights appearing on the maps are compared with buoy data over a one-month experiment to verify the validity and robustness of the algorithm. During this period, the significant wave height varies from about 0.5 to 4.5 m, and the radar measured wave heights at different range/distance bins show an overall root-mean-square error (RMSE) of 0.33–0.77 m and a correlation coefficient (CC) of 0.78–0.94, with respect to the buoy measurements.

Wide Angle Beam Steerable High Gain Flat Top Beam Antenna Using Graded Index Metasurface Lens

This paper presents a beam steerable low-profile lens antenna with a flat top wide beam and a high gain operating at 10.10 GHz. It consists of a graded index metasurface (GIMS) lens placed on the top of a microstrip patch antenna (MPA) radiator. An ultrathin linear graded index metasurface (LGIMS) and a radial graded index metasurface (RGIMS) lens were designed for the magnitude and phase transformation of the radiated beam from the microwave radiator. First, an LGIMS lens antenna was designed by placing an LGIMS on the top of an MPA radiator at an optimum height. A maximum measured gain of 16.37 dBi indicating a maximum gain enhancement of 11.50 dB with beam steering in a conical plane with a vertex angle of 84° was observed. Next, a flat top beam (FTB) antenna with a stable gain band was designed by placing an RGIMS on top of an LGIMS lens antenna. The measured peak gain of 14.82 dBi with an FTB pattern having a 1 dB gain variation range of about 96° is observed. Furthermore, the movement of the LGIMS and the RGIMS on top of the radiator results in continuous beam scanning with a maximum gain variation of 1 dB in a conical plane with a vertex angle of about 100°. A maximum gain of 14.82 dBi with a maximum gain enhancement of 10.30 dB at 10.15 GHz was obtained due to the linear and angular movement of the LGIMS and the RGIMS in the FTB antenna. The simulated and measured results are in good agreement.

Broadband Low-RCS Phased Array With Wide-Angle Scanning Performance Based on the Switchable Stacked Artificial Structure

A novel and simple switchable stacked artificial structure (SAS) is proposed and studied in phased arrays to realize a smart integration of broadband radar cross section (RCS) reduction and scanning range expansion. The proposed SAS is composed of a frequency selective surface (FSS) and a metamaterial absorber (MA). The lower part of the SAS can be switched between an FSS and a surface-waveguide (SWG) high-impedance surface (HIS) hybrid structure which can be used for wide-beam antenna design and array mutual coupling reduction. The upper part of the SAS can be seen as an MA. A linear phased array is presented and investigated based on the proposed switchable SAS. When the phased array is switched to its working mode, the SWG-HIS hybrid structure plays an important role to support a wide-angle scan from −75° to +75° with low sidelobes. When the phased array is shut down, the FSS-MA stacked structure can realize a low-RCS design in the frequency range of 0–11.2 GHz. An array prototype which operates at 4.6 GHz is fabricated and measured. The measured results have validated the radiation and scattering performance of the designed phased array.

Analyzing the Tradeoffs in Using Millimeter Wave Directional Links for High Data-Rate Tactile Internet Applications

Ultra-low latency and high reliability communications are the two defining characteristics of Tactile Internet (TI). Nevertheless, some TI applications would also require high data-rate transfer of audio-visual information to complement the haptic data. Using Millimeter wave (mmWave) communications is an attractive choice for high datarate TI applications due to the availability of large bandwidth in the mmWave bands. Moreover, mmWave radio access is also advantageous to attain the airinterface-diversity required for high reliability in TI systems as mmWave signal propagation significantly differs to sub-6GHz propagation. However, the use of narrow beamwidth in mmWave systems makes them susceptible to link misalignment-induced unreliability and high access latency. In this paper, we analyze the trade-offs between high gain of narrow beamwidth antennas and corresponding susceptibility to misalignment in mmWave links. To alleviate the effects of random antenna misalignment, we propose a beamwidth-adaptation scheme that significantly stabilize the link throughput performance.