Hemispherical Coverage Research Articles

A Pattern-Reconfigurable Aircraft Antenna With Low Wind Drag

This article presents a pattern-reconfigurable saber-like antenna with low wind drag for the onboard communication application, under the requirement of upper hemispherical coverage. The compact antenna mainly consists of a segmented loop and a $\Pi $ -shaped polygon, which are closely integrated for compact size. By controlling the OFF/ON states of a p-i-n diode embedded in the segmented loop, the proposed antenna can be operated at dipole/monopole modes. An upper hemispherical coverage area can be achieved since broadside and omnidirectional patterns are obtained at dipole and monopole modes, respectively. To validate the design strategy, a prototype was fabricated and tested. A good agreement between the simulated and measured results is achieved. The measured −8 dB reflection coefficient common bandwidth of two modes is from 2.16 to 2.63 GHz with the relative bandwidth of 19.6% while keeping a smaller size of $30.5\times 32.5\times 0.6$ mm3 ( $0.24\,\,\lambda _{0} \times 0.26 \lambda _{0}\times 0.005 \lambda _{0}$ , $\lambda _{0}$ is the free-space wavelength at the center frequency). We portend that the proposed design scheme, with merits of low wind drag, metal ground compatibility, and upper hemispherical coverage, has the potential for airborne application.

An Intelligent Deep Learning-Based Direction-of-Arrival Estimation Scheme Using Spherical Antenna Array With Unknown Mutual Coupling

Spherical antenna array (SAA) has become highly attractive where hemispherical scan coverage is required as it can provide uniform directivity in all the scan directions. Various direction-of-arrival (DoA) estimation methods suffer from different problems, such as low accuracies in mismatched conditions, high computational complexity and poor estimation in a harsh environment. Another critical concern is mutual coupling (MC) characteristics between the array elements. These problems affect the quality of the navigation signal in harsh environments. This paper presents a robust DoA estimation and mutual coupling compensation technique based on convolutional neural network (CNN) for Spherical Array. Spherical harmonic decomposition (SHD) is used to facilitate feature extraction in two sets, which contains different features about the elevation and azimuth of the source for DoA estimation. The features serve as input to the learning technique for separate estimation of elevation and azimuth, which consequently reduce computational complexity as against the joint estimation of DoA. Learning methods for DoA estimation with few frames and dense search grids within the spherical array configuration are presented. To solve the MC error, the DoA estimation scheme is also used to obtain accurate spectrum peak in the multipath scenario with unknown MC and sharper spectrum peak via the unique structure of the MC matrix and spatial smoothing algorithms. In all, experimental results, which is the ground truth to test any procedure, show the effectiveness, validity, and potential practical application of the proposed technique.

A Compact Hemispherical Beam-Coverage Phased Array Antenna Unit for 5G mm-Wave Applications

A compact low-profile phased array antenna unit with unidirectional hemispherical beam-coverage for 5G mm-wave applications is proposed in this paper. A four-subarray configuration is used for the proposed structure to achieve unidirectional hemispherical coverage in the boresight direction normal to the substrate. An artificial magnetic conductor (AMC)-backed slot antenna array with an optimal separation distance of 1.9 mm (= 0.31 λ at 28 GHz) is proposed as a subarray. The proposed antenna has increased H -plane beamwidth with the measured peak gain of 11.62 dBi and provides the desired wide inclined beam pattern in the elevation plane. The proposed antenna also offers steered beams over the range within ±45° in the azimuth plane. The hemispherical-coverage, phased array antenna unit composed of the four designed subarrays has overall dimensions of 80.8 mm × 80.8 mm × 2.4 mm. The coverage efficiencies of the proposed phased array antenna unit are 0.82, 0.71, and 0.61 for threshold gains of 5 dBi, 8 dBi, and 10 dBi, respectively, where the maximum solid angle is 2π steradians.

Analysis of phased array antenna system via spherical harmonics decomposition

Spherical phased-array antenna has hemispherical scan coverage for transmission of satellite imagery data at high bit rates to the ground station. Different conditions have been assigned based on their effects on the overall performance of the communication link. Reliability analysis consequently becomes an important requirement of any system onboard a satellite. Although the phased array and some connected algorithms have been presented in the literatures; however, there is no extensive systematic and theoretical performance evaluation framework formulated. In this work, the authors present new method that efficiently and effectively analyses the statistical performance of phased-array antenna systems using spherical harmonics expansion approach. Specifically, the errors caused by limited antenna element number, measurement noise of antenna, imprecision in phased-array antenna elements positioning, and spatial aliasing are systematically and theoretically benchmarked via simulations. Spatial sampling mechanisms for the positioning of array antenna elements on a sphere are presented and evaluated. This study proposed design guide and analysis for spherical phased-array antenna systems, and antenna arrays that do not employ spherical harmonics explicitly.

Hemispherical Shifted Symmetry in Polar Cap Patch Occurrence: A Survey of GPS TEC Maps From 2015–2018

AbstractMuch theoretical and observational work has been devoted to studying the occurrence of F region polar cap patches in the Northern Hemisphere; considerably less work has been applied to the Southern Hemisphere. In recent years, the Madrigal database of mappings of total electron content (TEC) has improved in Southern Hemisphere coverage, to the point that we can now carry out a study of patch frequency and occurrence. We find that Southern Hemisphere patch occurrence is very similar to that of the Northern Hemisphere with a half‐year offset, plus an offset in universal time of approximately 12 hr. This is further supported by running an ionospheric model for both hemispheres and applying the same patch‐to‐background technique. Further, we present a simple physical mechanism involving a sunlit dayside plasma source concurrent with a dark polar cap, which yields a patch‐to‐background pattern very much like that seen in the TEC mappings for both hemispheres.

A 28 GHz 5G Phased Array Antenna with Air-Hole Slots for Beam Width Enhancement

In this paper, a 28 GHz fifth-generation (5G) phased array antenna with air-hole slots for beam width enhancement is proposed. The proposed antenna consists of eight dipole radiators on a mobile handset-sized ground with air-hole slots between the two adjacent elements for enhancing the half power beam width (HPBW) in the elevation plane. The dimensions of the proposed antenna are 130 mm × 42 mm × 0.127 mm. The proposed array antenna satisfies a −10 dB reflection coefficient in the frequency range from 27.2 to 29.2 GHz with a peak gain of 10.33 dBi and a side lobe level (SLL) of 13 dB. In addition to its good performance, the proposed antenna has a very wide HPBW (measured) in the elevation plane, up to 219 degree with a scan coverage of ±45 degree in the azimuth plane. The proposed antenna demonstrates excellent hemispheric beam coverage for 5G mobile handset devices and can enable cost-effective mass production.

Characterization and Performance of an Ultra-Wideband Wide-Coverage Multimode MIMO Antenna

A new ultra-wideband multimode (MM) antenna design that enables the detection/transmission of two orthogonal field components over a nearly hemispherical coverage area is presented in this paper. It integrates and colocates two perpendicularly oriented bow-tie dipole elements, a short convex monopole and four horizontally oriented tapered slot antenna (TSA) elements (formed by the dipoles) in order to produce four decoupled and complementary gain patterns. The antenna feeding structure includes four single-ended transmission lines supporting the desired set of individual excitation modes. Experimental verification confirms the predicted negligible coupling between the antenna operating modes and orthogonality of the corresponding radiated field patterns. These unique features can be exploited in applications where pattern and polarization diversity are of importance. In this study, we have evaluated the proposed antenna as a MIMO base station antenna and characterized it in two different propagation scenarios. For this example, it has been shown that the utilization of the additional monopole and TSA modes plays an important role in maximizing MIMO efficiency in line-of-sight (LOS) scenarios and at the same time provides additional independent data streams in rich scattering scenarios. In both considered scenarios, the antenna is shown to have a MIMO frequency bandwidth of 85%.

Extreme angle, tip-tilt MEMS micromirror enabling full hemispheric, quasi-static optical coverage.

Beam steering is essential for a variety of optical applications such as communication, LIDAR, and imaging. Microelectromechanical system (MEMS) mirrors are an effective method of achieving modest speeds and angular range at low cost. Typically there are a number of tradeoffs considered when designing a tip-tilt mirror, such as tilt angle and speed. For example, many mirrors are designed to scan at their resonant frequency to achieve large angles. This is effective for a scanning mode; however, this makes the device slow and ineffective as a galvo (quasi-static). Here, we present a magnetic MEMS mirror with extreme quasi-static mechanical tilt angles of ±60° (±120° optical) about two rotation axes. This micromirror enables full hemispheric optical coverage without compromising speed; settling in 4.5 ms using advanced drive techniques. This mirror will enable new applications for MEMS micromirrors previously thought impossible due to their limited angular range and speed.

Global Travel Time Data Set From Adaptive Empirical Wavelet Construction

AbstractWe present a method for constructing the average waveform shape (hereafter called “empirical wavelet”) of seismic shear waves on an event‐by‐event basis for the purpose of constructing a high‐quality travel time data set with information about waveform quality and shape. A global data set was assembled from 360 earthquakes between 1994 and 2017. The empirical wavelet approach permits documentation of the degree of similarity of every observed wave with the empirical wavelet. We adapt the empirical wavelet to all pulse widths, thus identifying broadened (e.g., attenuated) pulses. Several measures of goodness of fit of the empirical wavelet to each record are documented, as well as signal‐to‐noise ratios, permitting users of the data set to employ flexible weighting schemes. We demonstrate the approach on transversely polarized SH waves and build a global travel time data set for the waves S, SS, SSS, Sdiff, ScS, and ScSScS. Onset arrival times of the waves were determined through a correlation scheme with best‐fitting empirical wavelets. Over 250,000 travel times were picked, from over 1.4 million records, all of which were human‐checked for accuracy via a Portable Document Format (PDF) catalog file making system. Many events were specifically selected to bolster southern hemisphere coverage. Coverage maps show that, while the northern hemisphere is more densely sampled, the southern hemisphere coverage is robust. The travel time data set, empirical wavelets, and all measurement metrics are publicly available and well suited for global tomography, as well as forward modeling experiments.

Dual CP Polarization Diversity and Space Diversity Antennas Enabled by a Compact T-Shaped Feed Structure

A compact T-shaped feed structure (TFS) is reported that enables the realization of two types of diversity antennas: a polarization diversity antenna (PDA) and a spatial diversity antenna (SDA). Both systems have a high potential for mobile wireless communication applications. The TFS includes four ports and two independent coaxial channels with effective isolation between them all. The PDA is a dual CP omnidirectional antenna. Its optimized prototype achieves measured impedance bandwidths of 16.4% and 15.28% in its LHCP and RHCP states, respectively, and realized gains in both between 4.8 and 6.46 dBic. The inner thin coaxial cable (ITCC) of the TFS directly drives its LHCP subsystem, facilitating its improved omnidirectional performance. This ITCC is also used to directly feed the SDA’s low-profile directional planar equiangular spiral antenna and its side port drives its omnidirectional RHCP antenna. Good hemispherical coverage is realized with a measured common impedance bandwidth larger than 14.35% with more than 40-dB isolation between its two ports. The corresponding measured realized gain of the SDA is between 4 and 7.8 dBic. The measured results for both optimized prototypes confirm their simulated performance characteristics.

Reliability Considerations of Spherical Phased Array Antenna for Satellites

Reliability is one of the most important aspects for any system onboard a satellite. This paper discusses different failure conditions and a fault-tolerant design of an active spherical phased array antenna (SPAA). This SPAA is having a hemispherical scan coverage for transmission of satellite imagery data at high bit rates to the ground station. Different failure conditions are identified and a criticality rank has been assigned based on their effects on the overall performance of the SPAA. Two entirely different configurations of the array are chosen to select the best one considering the failure effects. Based on these analyses, a rational margin is built such that the array can take care of even the most critical failure condition. This paper provides an insight toward the realization of a reliable phased array and thus useful for a practicing antenna engineer involved in designing antennas for the spacecrafts.

A SAR Reduced mm-Wave Beam-Steerable Array Antenna With Dual-Mode Operation for Fully Metal-Covered 5G Cellular Handsets

In this letter, a specific absorption rate (SAR) reduced 28 GHz beam-steering array antenna with dual-mode operation for a fully metal-covered fifth-generation (5G) cellular handset is proposed. The proposed antenna consists of two subarrays, each of which has eight rotated slot antenna elements, which are arranged on the upper frame and on the part of the back cover of the handset. The subarrays are selected according to the modes by using a switch. The proposed array demonstrates good reflection coefficients in the frequency band ranging from 27.2 to 28.2 GHz and the mutual couplings between antenna elements are less than –11.8 dB. The proposed antenna has good beam-steering properties and a hemispherical beam coverage for a millimeter-wave (mm-wave) 5G cellular handset. The calculated peak SAR values on the head phantom by the proposed structure, for the beam scan angles of 0° and 40°, are 0.53 and 0.88 W/kg, respectively, when the input power of each subarray is 24 dBm.

Steerable miniaturised printed quadrifilar helical array antenna using digital phase shifters for BGAN/GPS applications

A novel electronically steerable phased array antenna is developed for global positioning system/broadband global area network (GPS/BGAN) navigation applications. The array is composed of 2 × 2 printed quadrifilar helical antennas (PQHAs) integrated with digital phase shifters for beam steering over the transmit/receive bands. The feed network of each PQHA is based on a sequential rotation to achieve wideband circular polarisation (CP). An elegant control network with the embedded microcontroller is designed to provide driving bits to the phase shifters with reduced phase error. The meandered line design maintains high-performance CP radiation up to ±60° off-axis, within 1525 to 1660 MHz, and its size is 44% of the design with straight lines. The array gain is positive over 1450-1800 MHz beyond the BGAN band, with better than 13 dB return loss and <;2.2 dB axial ratio. The measured broadside gain of the array exceeds 8.5 dBi at 1600 MHz, and has a wide beam steering of ~±80° over the BGAN band. The developed antenna represents a significant technical advance to the design and manufacturing of PQHA array, it has a compact size, low cost and lightweight with a relatively large bandwidth and almost hemispherical coverage with excellent right-hand circularly polarized radiation.

Miniaturised multi‐beam‐controlled circular eight‐port beamforming network for long‐range UHF RFID hemispheric coverage

In this paper, a miniaturised multi-beam-controlled circular eight-port beamforming network for long-range ultra-high-frequency radio-frequency identification (UHF RFID) hemispheric beam-coverage systems (e.g. unmanned aircraft systems) is proposed. For multi-beam control and compact implementation, the proposed eight-port feeding network consists of an integrated beam-control block with a two-stage RF switch block, 12 quadrature hybrid couplers, and 12 90° phase shifters, and was designed and fabricated on a circular three-layer 1.2 mm FR-4 substrate. The diameter of the fabricated network is ~0.47 λ 0 at 915 MHz. The measured maximum insertion loss, and amplitude and phase imbalances of the fabricated network at the authorised UHF RFID frequency band (902-928 MHz) are ~4.5 dB, ± 1.3 dB, and ± 17.5°, respectively. An eight-element dipole antenna array with the proposed feeding network shows feasibility of hemispheric beam coverage by generating multiple beams simultaneously regarding port controls. Beam coverages, where the simulated realised gain is higher than 3 dBi, are ~180° and 130° at φ = 90 and 0°, respectively.

Dual-Band Circularly Polarized Antenna With Wide Axial Ratio Beamwidths for Upper Hemispherical Coverage

This paper presents a dual-band circularly polarized cross-dipole antenna with wide axial ratio beamwidths for full upper hemispherical coverage for GPS L1 and L2 bands. The antenna has curved radiating arms and a corrugated back cavity to enhance the beamwidth. A wideband hybrid coupler is used to feed the antenna at the two nearby frequency bands. Experimental results show that very wide 3-dB AR beamwidths of over 200° can be obtained, fully covering the upper hemisphere for the two GPS bands.

Radiation pattern optimisation of an antenna array on the spherical surface by using a varying number of optimisation parameters

This study presents an optimisation of antenna arrays on the spherical surface with new elementary antenna distribution using the particle swarm optimisation method. Many distributions of antenna elements on the sphere are known and processed, like icosahedral, spiral, Leopardi and so on, but neither of them is optimal. In this study, optimisation of the antenna array includes radiation pattern optimisation in order to achieve a radiation pattern with a narrow main lobe and very low side lobes. Although distribution of antenna elements is not uniform, optimisation is performed for two planes using the average fitness function. Different applications of antenna arrays require different parameters and different optimisation/process control procedures, too. Spherical antenna arrays with optimised placement of elements are capable of producing a desired radiation pattern, providing electronic scan coverage over the entire sphere and satisfying requirements for many applications in different branches of communications. An antenna array analysed in this study is a spherical array with very low grating lobes and a very narrow main lobe, and it could be used in hemispherical scan coverage.

Cloud and Sun‐glint statistics derived from GOES and MODIS observations over the Intra‐Americas Sea for GEO‐CAPE mission planning

AbstractKnowledge of cloud cover, frequency, and duration is not only important to study cloud dynamics, but also critical in determining when and where to take ocean measurements from geostationary orbits such as the Geostationary Coastal and Air Pollution Events (GEO‐CAPE) mission due to the challenges in achieving complete hemispheric coverage of coastal oceans, estuaries, and inland waters at hourly frequency. Using GOES hourly measurements at 4 km nadir resolution between 2006 and 2011, the number of cloud‐free hourly observations per day (Ncf) for solar zenith angle θo &lt; 80° was estimated for each 0.1° location of the Intra‐Americas Sea. The number of Sun‐glint‐affected hourly observations per day (Nsg) was also calculated based on the planned GEO‐CAPE observation geometry and realistic wind speed. High‐latitude and equatorial oceans showed the lowest Ncf (&lt;2.4) in all climatological months, and highest Ncf was observed in the Gulf of Mexico (GoM) and Caribbean (&gt;4.5). Different regions showed differences in seasonality of cloud‐free conditions and also showed differences in the hour of a day at which the satellite observations would have the maximal cloud‐free and glint‐free probability (Tmax). Cloud cover from Moderate Resolution Imaging Spectroradiometer (MODIS) 1 km measurements are &gt;10% higher than those from the MODIS 250 m measurements, supporting ocean color missions at subkilometer resolutions to enhance both spatial coverage and temporal frequency. These findings provide valuable information for GEO‐CAPE mission planning to maximize its science value through minimizing the impacts of clouds and Sun glint.

Intracranial Electrophysiology of Auditory Selective Attention Associated with Speech Classification Tasks.

Auditory selective attention paradigms are powerful tools for elucidating the various stages of speech processing. This study examined electrocorticographic activation during target detection tasks within and beyond auditory cortex. Subjects were nine neurosurgical patients undergoing chronic invasive monitoring for treatment of medically refractory epilepsy. Four subjects had left hemisphere electrode coverage, four had right coverage and one had bilateral coverage. Stimuli were 300 ms complex tones or monosyllabic words, each spoken by a different male or female talker. Subjects were instructed to press a button whenever they heard a target corresponding to a specific stimulus category (e.g., tones, animals, numbers). High gamma (70–150 Hz) activity was simultaneously recorded from Heschl’s gyrus (HG), superior, middle temporal and supramarginal gyri (STG, MTG, SMG), as well as prefrontal cortex (PFC). Data analysis focused on: (1) task effects (non-target words in tone detection vs. semantic categorization task); and (2) target effects (words as target vs. non-target during semantic classification). Responses within posteromedial HG (auditory core cortex) were minimally modulated by task and target. Non-core auditory cortex (anterolateral HG and lateral STG) exhibited sensitivity to task, with a smaller proportion of sites showing target effects. Auditory-related areas (MTG and SMG) and PFC showed both target and, to a lesser extent, task effects, that occurred later than those in the auditory cortex. Significant task and target effects were more prominent in the left hemisphere than in the right. Findings demonstrate a hierarchical organization of speech processing during auditory selective attention.

A Compact Circularly Polarized Antenna for 5.8-GHz Intelligent Transportation System

A compact circularly polarized antenna suitable for applications of an intelligent transportation system (ITS) is presented. The antenna consists of a disc patch operating in modal degeneration, which is gap-coupled with multiple annular sectors. The use of parasitic resonators coupled to the degenerated modes of the patch enhances the realized gain and the polarization purity, at the cost of only a modest increase in the area. Despite the small size of $35\times 35$ mm $^2$ (0.46 $\lambda _0^2$ at the central frequency of 5.8 GHz), the experimental validation of the best prototype confirms a hemispherical coverage with a half-beam power of 80°, a maximum left-hand gain of 7.16 dB, a cross-polarization discrimination of 21 dB, and a 10-dB return-loss bandwidth exceeding 900 MHz, a performance suitable for ultracompact tag reader realized in cost-effective single-layer technology.

Source Geometry Optimization for Hemispherical Radiation Pattern Coverage

Single beam patterns radiated by linear sources degrade as their maxima points toward endfire direction. Different source geometries are, therefore, to be investigated and compared to achieve better angular coverage. We choose to perform this by analyzing the characteristics of the linear operator connecting the current source to the far field in a simplified two-dimensional (2-D) geometry through its singular value decomposition (SVD). Two indexes are introduced and found useful to achieve geometry optimization. First, the case of continuous sources is examined and then the results are extended to discrete (array) sources. It is found that, while the best solution is a conformal semicircumference source, linear sources arranged at angles provide nearly identical single beam patterns pointing in different directions to provide a hemispherical coverage.