Direction Finding Applications Research Articles

A compact broadband circularly polarized monopulse slot array antenna based on gap waveguide technology

ABSTRACT This paper presents a circularly polarized (CP) monopulse slot array antenna based on gap waveguide (GWG) technology. The proposed monopulse antenna is composed of a 4 × 4 array antenna fed by the monopulse comparator network in a compact three-layer structure. To achieve a broad axial ratio (AR) bandwidth of right-handed circular polarization (RHCP) in the sum radiation pattern, a septum polarizer is used in the radiating aperture. Based on this approach, horizontal transition structures are used to excite the radiating array from the WR-28 waveguide to the GWG, which helps to reduce the reflection loss and expand the impedance bandwidth. Experimental results show that the impedance bandwidth is 30.5 GHz to 40 GHz, which is 27.1%. The 3 dB AR bandwidth is 31%. The measured null depth is −40 dB, and the maximum measured gain in the sum pattern is 22 dBi at 34 GHz, while the antenna efficiency is greater than 86%. The advantages of low loss, broad bandwidth, and compact structure make the proposed antenna a competitive candidate for millimeter-wave (mmWave) monopulse direction-finding applications.

Generalized utilization of energy harvesting ability of TENG for concurrent energy storage and motion sensing application with effective external circuitry

Utilizing triboelectric nanogenerators (TENGs) for simultaneous mechanical energy harvesting and sensing applications is a crucial and challenging endeavor that can improve TENG-based self-powered sensing systems. However, this issue remains relatively underexplored and thus, it is the primary focus here. We propose a simple and generalizable external circuitry achieving simultaneous energy storage and sensing from the TENGs. Commonly available polydimethylsiloxane (PDMS) triboelectric film is dielectrically modified by loading synthesized sodium tantalate filler particles with high dielectricity. The fabricated films and aluminum tape are utilized as negative and positive triboelectric films. The electrical performance of the TENG operated in contact-separation mode is optimized based on the filler concentration in the PDMS film and the maximum electrical output of ∼ 195 V, ∼ 6.27 µA, and ∼ 44 µC/m2 is observed. Completely analyzed TENG with highly efficient and stable electrical output (for more than 10,000 operational cycles) is utilized for further experiments. Various fundamental voltage divider (VD) (capacitive, resistive, and inductive) electrical circuits are fabricated and their successful utilization for dividing the electrical output from the TENG is demonstrated. After a comprehensive analysis of the compatibility between the VD and TENG, it is determined that inductive and resistive VDs are the optimal choice. Owing to its simplicity, the resistive VD is further utilized to construct real-time vehicle speed sensing and approaching direction-finding applications. The proposed simple and generalized state-of-the-art process for simultaneous energy storage and sensing through the TENG could be revolutionary, potentially expanding its applicative scope significantly.

Wideband Antennas of Passive Seekers for Anti Radiation Missiles

Suppression of Enemy Air Defence (SEAD) is a fundamental element of Air Power application by means of in protecting friendly air attackers and destroying the enemy’s ability to defend against air attack. Most of the SEAD operation even today relies on Anti-radiation missile (ARM) which is an air-to-surface tactical missile designed to detect, seek, attack and destroy opponent’s radar. Passive seeker of ARM is a miniaturized ESM receiver which is capable of extracting the necessary angular data from the enemy radar emissions. Single head passive seeker covering wide frequency range from L to Ku band is the preferred choice. Wideband antennas have been designed and utilized for Direction Finding applications of ESM/ELINT receivers for ground, air and ship borne platforms. Unlike these platforms, there are several restrictions for passive seeker based compact ESM receiver for missile borne platform specially air to surface missile where lesser diameter is one of the preferred design parameter. This review paper mainly discusses the existing wideband antennas such as spiral, log-periodic, printed circuit vivaldi and all-metal vivaldi antennas and the comparison of their various parameters for passive seeker. The paper also suggests their suitability with respect to their placement on the missile for three configurations: concealed inside the radome, flush-mounted and conformal antenna based. The paper also brought about the specific test facility required for testing and evaluation of passive seeker to characterize it with missile radome which is the most challenging and time consuming task. Among the three passive seeker configuration discussed, conformal antenna based passive seeker using all-metal Vivaldi is the best option avoiding radome aberration correction which is being utilized in the present third generations of ARM. The second commonly and established passive seeker configuration is concealed inside the radome using spiral antennas where handling radome aberration correction is a limitation.

Effects of hydrogen sulfide on grass traits and water-gas transport in grass-planted unsaturated soil

Vegetation has been found to improve the hydrological performance of landfill cover. However, existing studies ignore the effects of hydrogen sulfide (H2S), which forms the toxic odour generated from municipal solid wastes. Hydrogen sulfide is a potential signalling molecule in regulating plant-stomata aperture, but how the plant–hydrogen sulfide interaction affects the water–gas transport in soil remains unknown. This aim of this study was to investigate the effects of hydrogen sulfide on Bermuda grass growth and its influence on water–gas transport in unsaturated soils. Soil columns, with and without vegetation, were prepared and fumigated with different hydrogen sulfide concentrations. These columns were subjected to controlled drought and rainfall sequentially. The results showed that grass leaves almost wilted without hydrogen sulfide fumigation due to the Pythium diseases caused by the antecedent waterlogged conditions. In contrast, hydrogen sulfide fumigation promoted grass growth because of the fungicidal effects of hydrogen sulfide. In drought, hydrogen sulfide fumigation caused stomata closure, which resulted in a lower matric suction in the vegetated soil than that without hydrogen sulfide fumigation. Accordingly, hydrogen sulfide concentration reduced because of oxidation by metal oxides in soil. Upon subsequent rainfall, more infiltration but lower matric suction was observed in vegetated soils than was found in the bare case, whereas hydrogen sulfide concentration decreased continuously due to gas dissolution in the pore water. Direct application of laboratory findings herein to field cases should be used with caution, because the applied continuous lighting and low evapotranspiration rate of the soil column tests may not be representative of field conditions.

Angle-of-Arrival Sensing Using a Machine Learning Enhanced Amplitude-Only System

A low-cost, low-complexity amplitude-only angle-of-arrival (AoA) sensor system is experimentally demonstrated. The sensor embeds a machine learning (ML)-in-the-loop procedure as the processing algorithm to extract both azimuth and elevation AoA information from a planar circular array. This has not been demonstrated in the open literature with the traditional AoA approaches, the same sensor’s dimensionality, field-of-view, or with as low system complexity. A four-channel receiver is designed, built, and assembled behind a simple four-element monopole array. The sensing components and ML algorithm are integrated to experimentally validate the hypothesis that both azimuth and elevation information can be determined from this simple, low-cost sensor. Moreover, a systematic procedure is introduced for the design of a deep neural network for the amplitude-only direction-finding application. Following this approach, major system complexity reductions are found—over 99% for the azimuth network and 98% for the elevation network, while still achieving 0.75° root mean square error (RMSE) in azimuth and 1.1° RMSE in elevation. Experimental results show up to 20% accuracy improvement in azimuth estimation, and 93% accuracy improvement in elevation, when compared to a lookup table-based method.

Design of a UWB Antenna with Multiple Ports on a Single Circular Radiator for Direction-Finding Applications

This paper proposes a single circular radiator with a multi-port (SRMP) antenna that can estimate the direction-of-arrival (DoA) in the azimuth and elevation directions. The proposed SRMP antenna is designed to minimize the size of the ultra-wideband system by using only one patch radiator. To verify the feasibility, the proposed antenna is fabricated, and the reflection coefficient and boresight gain are measured (-13.3 dB and 3.4 dBi at 8 GHz). Then, to observe the direction-finding performance, the DoA estimation results using the Bartlett beamformer are compared with the typical array. At all incident angles, a root-mean-square error of less than 1° is observed when the signal-to-noise ratio is higher than 6 dB.

Antithrombotic Therapy After AcuteCoronary Syndromes or Percutaneous Coronary Interventions inEast Asian Populations.

Because guidelines and recommendations in response to multiple randomized clinical trials (RCTs) of new therapies undergo rapid changes, antithrombotic therapies for patients after acute coronary syndrome, or percutaneous coronary intervention, are becoming more complex in daily clinical practice. The proportion of Asian populations enrolled in landmark RCTs is substantially low, which limits the direct application of trial findings into clinical practice in Asian countries. Moreover, compared with Caucasian patients, East Asian patients are considered to have a different ischemia/bleeding propensity in response to antithrombotic therapy, known as the "East Asian paradox" (ie, more bleeding events but fewer thromboembolic events). Coincident with consecutive RCTs in Western populations to optimize antithrombotic strategies, several such studies have now been conducted in East Asian cohorts. Herein, we provide a comprehensive summary of the key RCTs in this regard and propose future directions and perspectives for optimal antithrombotic therapies in East Asian patients.

Optimized Algebraic Algorithm for Ambiguity Resolution and DOA Computation in Baseline Interferometer

Background: Interferometer is the most preferred technique for high accuracy direction finding. For broadband direction finding (DF) applications, multiple antennas forming a number of baselines are used to achieve better accuracy in measuring the direction of arrival (DOA). Ambiguity resolution in multi-element interferometers is a crucial algorithm for the computation of DOA. Objective: This paper introduces a fast, algebraic Common Minimum Modulo Search (CMMS) algo-rithm for ambiguity resolution and DOA computation. LabVIEW-based tool for Monte Carlo simula-tion of the algorithm over various parameters is described. Method: The CMMS is a computationally efficient algorithm, where the longest baseline phase difference is used for accuracy, and the phase difference data from all other baselines are used for resolving the ambiguities in the longest baseline. A hybrid approach using correlation and minimum algebraic search is used to determine the best fit set of ambiguities to the measured phase difference data. Results: Case studies have been presented in the literature and the performance of the CMMS algo-rithm was validated against established algorithms. This paper discusses the FPGA implementation as well as its simulation results. Analysis is performed on the 6-18 GHz frequency band. Moreover, the sources of errors and resulting limitations regarding the applicability of the algorithm are also discussed. Conclusion: Simulation results establish the algorithm's effectiveness in ambiguity resolution and applicability to diverse array configurations. The short nine-clock cycle processing latency in FPGA is demonstrated by the simulation results.

Low energy availability in female athletes: From the lab to the field

ABSTRACT Decades of laboratory research have shown impairments to several body systems after only 4–5 days of strictly controlled consistent low energy availability (LEA); where energy availability (EA) = Energy Intake (EI) − Exercise Energy Expenditure (EEE)/Fat-Free Mass. Meanwhile, cross-sectional reports exist on the interrelatedness of LEA, menstrual dysfunction and impaired bone health in females (the Female Athlete Triad). These findings have demonstrated that LEA is the key underpinning factor behind a broader set of health and performance outcomes, recently termed as Relative Energy Deficiency in Sport (RED-S). There is utmost importance of early screening and diagnosis of RED-S to avoid the development of severe negative health and performance outcomes. However, a significant gap exists between short-term laboratory studies and cross-sectional reports, or clinically field-based situations, of long-term/chronic LEA and no definitive, validated diagnostic tests for RED-S exist. This review aims to highlight methodological challenges related to the assessment of the components of EA equation in the field (e.g. challenges with EI and EEE measures). Due to the uncertainty of these parameters, we propose the use of more chronic “objective” markers of LEA (i.e. blood markers). However, we note that direct extrapolations of laboratory-based outcomes into the field are likely to be problematic due to potentially poor ecological validity and the extreme variability in most athlete’s daily EI and EEE. Therefore, we provide a critical appraisal of the scientific literature, highlighting research gaps, and a potential set of leading objective RED-S markers while working in the field. Highlights Direct application of short-term laboratory-based findings in the field is problematic. Calculation of energy availability (EA) in the field is methodologically challenging and prone to errors. The use of several biomarkers may allow the detection of early exposure to low EA in the female athlete.

Direction finding and beamforming using cylindrical array of dipole antennas in the presence of cylindrical scatterer/reflector including the mutual coupling effect

Three-dimensional dipole arrays are normally used at the proximity of a reflective structure. Filamentary short-circuited dipoles are proposed to model the effect of the reflector structure. The computational burden is significantly reduced by using mutual impedance matrices. An analytical method of modelling the effect of the cylindrical reflector in a three-dimensional cylindrical geometry of dipole antenna arrays is introduced both for direction finding and beamforming applications in the presence of mutual coupling. The results of the implementation of the MUSIC (multiple signal classification) direction-finding algorithm show that the proposed model for accounting the cylindrical reflector, in the presence of a mutual coupling effect, has the required efficiency and reduced root-mean-square-error (RMSE). Monte-Carlo simulations for the beamforming algorithm are conducted to evaluate the signal-to-interference ratio (SIR) values in the presence of a cylindrical reflector and the results show that the model has the desired performance. The whole process of beamforming and pattern generation has been verified through high-frequency structural simulator (HFSS) simulation. The simplicity, adequate precision and low computational cost of this method can be appropriately used in the cylindrical reflector/scatterer in three-dimensional geometries, especially for base station applications.

Design of Dual-Polarized Pyramidal Log-Periodic Antenna with Integrated Feed for Additive Manufacturing

A dual-polarized log-periodic antenna with 5:1 bandwidth is considered for wideband, amplitude only direction-finding applications. The proposed system is comprised of two identical, orthogonal, sets of trapezoidal log-periodic arms. The arms’ inclination from planar facilitates reduced back lobe radiation to improve directivity and efficiency once absorber is introduced. One arm of each polarization set contains a variable radius coaxial shell to achieve impedance matching such that the system impedance at the base of the antenna is matched to 50 ohms. Analysis and design for the 3d printed direction-finding antenna system is accomplished using a commercial off the shelf (COTS) finite element method (FEM) solver.

Thinned Virtual Array for Cramer Rao Bound Optimization in MIMO Radar

By transmitting multiple independent waveforms at the transmit side and processing echoes of spatial targets at the receive side, Multiple Input Multiple Output (MIMO) radar enjoys virtual array aperture expansion and more degree of freedom (DOF), both of which favors the application of direction finding or estimation of direction of arrival (DOA). The expanded virtual aperture provides higher angular resolution which also promotes the precision of DOA estimation, and the extra DOF brought by waveform diversity can be leveraged to focus energy in certain spatial region for better direction-finding capacity. However, beamspace methods which match certain beampatterns suffer from deteriorated performance and complexity in implementation, and the advantage of virtual array aperture is limited by its virtual element redundancy. As an important performance indicator of DOA estimation, Cramer–Rao Bound (CRB) is closely connected to the array configuration of the system. To reduce the complexity of the system and improve CRB performance at the same time, in this paper, the virtual array of MIMO radar is designed directly by selecting outputs from matched filters at the receive side. For the sake of fair comparison, both scenarios with and without priori directions are considered to obtain optimized virtual array configuration, respectively. The original combinatorial problems are approximated by sequential convex approximations methods which produce solutions with efficiency. Numerical results demonstrate that the proposed method can provide thinned virtual arrays with excellent CRB performance.

Sparse planar arrays for azimuth and elevation using experimental data.

Sparse arrays are special geometrical arrangements of sensors which overcome some of the drawbacks associated with dense uniform arrays and require fewer sensors. For direction finding applications, sparse arrays with the same number of sensors can resolve more sources while providing higher resolution than a dense uniform array. This has been verified numerically and with real data for one-dimensional microphone arrays. In this study the use of nested and co-prime arrays is examined with sparse Bayesian learning (SBL), which is a compressive sensing algorithm, for estimating sparse vectors and support. SBL is an iterative parameter estimation method and can process multiple snapshots as well as multiple frequency data within its Bayesian framework. A multi-frequency variant of SBL is proposed, which accounts for non-flat frequency spectra of the sources. Experimental validation of azimuth and elevation [two-dimensional (2D)] direction-of-arrival (DOA)estimation are provided using sparse arrays and real data acquired in an anechoic chamber with a rectangular array. Both co-prime and nested arrays are obtained by sampling this rectangular array. The SBL method is compared with conventional beamforming and multiple signal classification for 2D DOA estimation of experimental data.

Phase Transforming Based on Asymmetric Spoof Surface Plasmon Polariton for Endfire Antenna With Sum and Difference Beams

An endfire antenna with sum and difference beams is designed based on phase transforming of a proposed asymmetric spoof surface plasmon polariton (SSPP) structure. The asymmetric arrays of grooves, with different groove depths, periods, and/or duty ratios, serve as transmission structure and transmit electromagnetic (EM) waves in SSPP modes. Due to the distinct phase constants for the EM fields on the two sides of the asymmetric structures, the transformation of phase difference for the EM waves is realized. Superposition in the endfire direction for the in-phase and out-of-phase EM fields forms the endfire radiations with sum and difference beams. A design procedure is proposed where operating frequencies of the endfire antenna are predicted with the dispersion curves of the asymmetric SSPP structures and allocated by phase transformation. A prototype is implemented to validate the proposed design principle. Sum beam operating frequencies of the endfire antenna are at 5.50, 6.60, and 7.09 GHz, while difference beams appear at 6.10 and 6.90 GHz. Good agreement of the results validates the feasibility of the proposed mechanism and design procedure. The proposed endfire antenna with sum and difference beams has broad prospect in direction finding, tracking, and anti-interference applications.

Low Gain Ripple and DC-Grounded Slant-Polarized Formulation With 360° Broadbeam Coverage

In this paper, a new slant-polarized slot antenna configuration is presented for direction finding and base station applications. The proposed antenna comprises enhanced size coaxial cables, slots, and feeding assemblies. The slant polarization is achieved by four angled slots etched around the outer cylinder of the oversized coaxial cable. An internal compact axis-symmetric feeding network connects primary apertures to form the omnidirectional antenna. Simulations and measurements demonstrate that the antenna maintains an omnidirectional pattern from 2.5 GHz to 2.8 GHz, having 11.3% bandwidth (measured return loss <−10 dB) and gain ripple of ±0.2 dB in the azimuth plane, which leads to the stable operational coverage. Another benefit of this structure is its polarization purity. The cross-polarization levels are below −14dB over the whole bandwidth. Move over; it is ruggedized DC short, self-supporting, and surface-mountable structure. Furthermore, compact and conformal shape reduces aerodynamic drag and makes this antenna a potential candidate for mounting vehicle systems too.

A Biomimetic Miniaturized Microphone Array for Sound Direction Finding Applications Based on a Phase-Enhanced Electrical Coupling Network.

In this research, we proposed a miniaturized two-element sensor array inspired by Ormia Ochracea for sound direction finding applications. In contrast to the convectional approach of using mechanical coupling structures for enlarging the intensity differences, we exploited an electrical coupling network circuit composed of lumped elements to enhance the phase differences and extract the optimized output power for good signal-to-noise ratio. The separation distance between two sensors could be reduced from 0.5 wavelength to 0.1 wavelength 3.43 mm at the operation frequency of 10 kHz) for determining the angle of arrivals. The main advantages of the proposed device include low power losses, flexible designs, and wide operation bandwidths. A prototype was designed, fabricated, and experiments examined within a sound anechoic chamber. It was demonstrated that the proposed device had a phase enhancement of 110 at the incident angle of 90 and the normalized power level of −2.16 dB at both output ports. The received power levels of our device were 3 dB higher than those of the transformer-type direction-finding system. In addition, our proposed device could operate in the frequency range from 8 kHz to 12 kHz with a tunable capacitor. The research results are expected to be beneficial for the compact sonar or radar systems.

Wideband Vector Antenna for Dual-Polarized and Three-Dimensional Direction-Finding Applications

A wideband and reconfigurable radiation pattern vector antenna is proposed for dual-polarized and three-dimensional direction-finding applications. Compared with the state of the art, this antenna achieves the accurate estimation of the direction of arrival of an incoming vertically or horizontally polarized electromagnetic field over a wider bandwidth (7:1). Measurement results are in good agreement with the simulated results obtained from full-wave electromagnetic simulations.

Barriers to the use of integrated project delivery (IPD): a quantified model for Malaysia

PurposeThe purpose of this paper is to quantify the barriers to the use of integrated project delivery (IPD), as assessed by 115 construction professionals in Malaysia.Design/methodology/approachBarriers recording highest citation amongst researchers worldwide were collated in the form of a conceptual model. This model was validated via a partial least squares structural equation modelling technique.FindingsFindings advance the body of knowledge on IPD by providing original insights into the nature of key barriers, quantifying the relative importance of each barrier.Research limitations/implicationsDespite the above-mentioned contributions, and before drawing any conclusion, it is prudent to acknowledge limitations, particularly the chosen research approach in focusing on the Malaysian context. Therefore, caution must be exercised in direct application of findings to other contexts; research findings should be seen through the lens of moderatum generalisations (see Payne and Williams, 2005).Practical implicationsApart from contributions to the body of knowledge, for the world of practice, conditions impacting a transition to IPD are discussed, with a recommendation for change management through a tested mechanism like the European Corporate Sustainability Framework.Originality/valueBeing the first empirical study undertaken to quantify the relationship among the identified barriers and IPD, the present study contributes to the field by addressing the gap in IPD research in Malaysia, as an exemplar of a developing country; it creates knowledge to inform further improvements in project performance through facilitating IPD use. The study also offers insight to construction stakeholders in other developing countries for tackling issues that hinder the adoption of an IPD approach, and it also points to major barriers such that resources for tackling barriers may be allocated properly.

Predictors of Nurses' Research Use in Canadian Long-term Care Homes

ObjectivesWe examined the influence of individual characteristics and organizational context features on nurses' self-reported use of research evidence in long-term care (LTC) homes. DesignA cross-sectional analysis of survey data collected in the Translating Research in Elder Care program. Setting and participants756 nurses (registered nurses and licensed practical nurses) from 89 LTC homes in Western Canada. MethodsGeneralized estimating equation modeling was used to identify which individual characteristics and organizational context features significantly predicted (P < .05) 3 kinds of self-reported research use by nurses: instrumental (the direct application of research findings), conceptual (using research findings to change thinking), and persuasive (using research findings to convince others). ResultsNurses reported a moderate to high level of research use. There were no significant differences in mean research use scores by nursing role. Only 2 variables were associated with all 3 kinds of research use: having a positive attitude toward research, and availability of structural and electronic resources. Additional variables associated with instrumental research use were problem-solving ability, engaging in formal interactions (eg, education sessions), and better perceptions of organizational slack–staff (the availability of sufficient staff). Additional variables associated with conceptual research use were self-determination and job efficacy. Finally, additional variables associated with persuasive research use were belief suspension (the ability to suspend previously held beliefs), organizational citizenship behavior (one's voluntary commitment to the organization), self-determination, job efficacy, evaluation, and better perceptions of organizational slack–time (perceived availability of extra time). Conclusions and implicationsConceptual and persuasive research use were most strongly influenced by individual characteristics, whereas instrumental research use was predicted equally by individual and organizational variables. Nurses working in LTC are positioned in leadership roles; by targeting both the individual- and organizational-level predictors of nurses' research use, they can improve conditions for individuals living in LTC.

Sparsity based off-grid blind sensor calibration

Compressive Sensing (CS) based techniques generally discretize the signal space and assume that the signal has a sparse support restricted on the discretized grid points. This restriction of representing the signal on a discretized grid results in the off-grid problem which causes performance degradation in the reconstruction of signals. Sensor calibration is another issue which can cause performance degradation if not properly addressed. Calibration aims to reduce the disruptive effects of the phase and the gain biases. In this paper, a CS based blind calibration technique is proposed for the reconstruction of multiple off-grid signals. The proposed technique is capable of estimating the off-grid signals and correcting the gain and the phase biases due to insufficient calibration simultaneously. It is applied to off-grid frequency estimation and direction finding applications using blind calibration. Extensive simulation analyses are performed for both applications. Results show that the proposed technique has superior reconstruction performance.