Far-field Radiation Characteristics Research Articles

Method for vibration and acoustic radiation analysis of underwater stiffened plates with acoustic coatings

Based on the effective medium theory as well as the three-dimensional viscoelastic theory, a semi-analytical model of the three-dimensional underwater vibration and acoustic radiation with cavity-type stiffened plate structures covered with acoustic coatings is established to solve the issues related to underwater vibration and acoustic radiation calculation of the stiffened plate and shell structure with complex acoustic coatings. By comparing the far-field acoustic radiation characteristics of the proposed semi-analytical model and the finite element numerical model, this research verifies the validity and accuracy of the proposed model. On such a basis, this research preliminarily investigates the coupling effect exerted by stiffeners and parent plates in stiffened plates as well as the vibroacoustic characteristics of acoustic coatings, thereby providing a valuable idea for the prediction of vibroacoustic characteristics concerning underwater structures.

A Compact Novel Quad Patch High Gain Triple Band Microstrip Antenna for 5G/6G mm Wave Applications

This paper presents a compact, novel, quad patch and triple band single substrate microstrip patch antenna for 5G/6G mm wave applications. The aim is to design an antenna within the K-band with three resonance frequencies at 24, 29, and 34 GHz. The antenna is designed on a volumetric dimension of 11×12.7×1.6 mm3. The substrate used is FR4 (dielectric constant 4.4), having a loss tangent of 0.0022. A microstrip line of width 1 mm for a 50 Ω impedance line is used to match with the load antenna, which has four rectangular connected patches. Patch dimensions come from standard antenna equations and simulation done on Ansys High-Frequency Structure Simulator software. Validation of simulated results is done through measurements on the prototype antenna. A substantial good agreement is found between the simulated and measured results. The gain of the proposed antenna is 6.16 dBi, with return loss being ≤-10 dB. Bandwidths are 1.1 GHz (23.8 - 24.9 GHz), 0.9 GHz (28.6 - 29.5 GHz), and 0.8 GHz (33.7 – 34.5 GHz), respectively. The far-field radiation characteristics of both E-plane and H-plane are also reported. The proposed design is suitable for mm wave applications, including smart vehicles, global positioning systems, radio frequency identifications, etc.

Radiation-enhanced acoustically driven magnetoelectric antenna with floating potential architecture

A magnetoelectric (ME) antenna driven by a high-overtone bulk acoustic resonator (HBAR) can play a potentially positive role in the bandwidth enhancement benefit from its narrow harmonic frequency interval, in which radiation characteristics remain to be explored. HBAR ME antennas with floating potential architecture (FPA) and grounded are fabricated and demonstrated separately. The measured far-field radiation characteristics show that the FPA can significantly enhance the gain and radiation efficiency of the HBAR ME antenna by more than 10 dB compared to the grounded setup. Meanwhile, the time domain amplitude sweep demonstrates the high-power tolerance (>23.2 dBm) of the HBAR ME antenna. Two-dimensional finite element method analysis reveals that the FPA-induced electric field excites additional longitudinal-wave resonance, resulting in the coupling of dual longitudinal and shear waves, which is the intrinsic mechanism of its radiation enhancement from the perspective of acoustic excitation. Not only limited to HBAR antennas, the mechanism of FPA described here is also a promising candidate for radiation enhancement in acoustically driven antennas.

Source decomposition and reduced-order modeling of an installed F404-GE-103 engine using the optimized-location virtual reference method

Principal component analysis-related methods (i.e., proper orthogonal decomposition or partial field decomposition) are used widely in aeroacoustic applications for source characterization and reduced-order modeling. A previous paper [A. T. Wall et al., J. Acoust. Soc. Am. 144, 1356 (2018)] developed a coherence-based, virtual-reference method for performing physically meaningful PFD known as the optimized-location virtual references (OLVR) method. This paper performs a source decomposition using the OLVR method on acoustical holography data from an installed GE F404 engine. The OLVR-derived partial fields are compared with far-field radiation characteristics and partial equivalent sources are fitted to analytical wavepackets. Characteristics of this reduced-order model are discussed as a function of frequency and engine condition. [Work supported ONR Grant No. N00014-21-1-2069.]

A compact four port MIMO antenna for millimeterwave applications

A novel compact microstrip MIMO antenna with high isolation and low envelope correction coefficient has been proposed and presented in this paper. The proposed antenna is compact in size with 3.22x4.86 mm2, operating over the frequency band of 60GHz. The MIMO antennas have been designed andsimulated using electromagnetic design and verification platformIE3DTM. Two ports MIMO antenna with the size of 3.22x1.93 mm2 resonates at 58.1 GHz covering a band of 57-59.3 GHz, with the bandwidth of 2.3 GHz, gain of 5.2 dBi, and directivity of 8.67 dBi. It also provides aninput reflection coefficient of -18.41 dB with isolation of -19.98 dB. Proposed four port MIMO antenna resonates at 58 GHz covering a range of 56.9 GHz to 59.2 GHz, with a bandwidth of 2.3 GHz, gain of 5.44 dBi, and the directivity of 9.75dBi. It provides goodisolationranging from -19 dB to -30 dB with input reflection coefficient of -18.09 dB. The envelope correlation coefficient (ECC) of the proposed four-port MIMO antenna is below 0.06 in far-field radiation characteristics. The proposed MIMO antenna has been analyzed for its diversity performance in terms of ECC, mean effective gain, and diversity gain.

Far-Field Radiation Characteristics of Folded Monopole Antennas over a Conducting Ground Plane

Folded monopole structures have been used for many applications, including low-frequency electromagnetic wave transmission and reception. However, the literature on these antenna types is quite limited. Folded monopole antennas are mathematically complex compared to conventional monopole or dipole antennas since every fold introduces a new set of design parameters. This work studied the far-field radiation characteristics of multi-folded monopole antennas operating at 75 MHz in terms of their radiated power concerning the frequency, the far-field directivity of the electric field, and the effect of each design parameter on the far-field radiation power. According to the results, folding a monopole antenna multiple times increases its effective length, making this antenna a suitable candidate for applications where the antenna height is restricted. Additionally, the ground-to-wire separation has the biggest effect on radiated power. In both single-fold and two-fold cases, doubling the ground-to-wire separation increased the radiated power by 0.2 W compared to the other models with the same number of folds. As for the challenges, the impedance mismatch between the source and antenna causes a significant amount of power reflection; hence, suitable impedance matching is required to reduce reflected power.

Eigth-Port Orthogonally Dual-Polarized MIMO Novel Antenna with Non-Contact Feed for 5G Smartphone

In this paper, an eight-port orthogonally dual-polarized MIMO novel antenna using a non-contact feed for 5G smartphone applications in the 3.5-GHz band (3.3–3.6 GHz) is presented. The antenna consists of a 2*2 array with (eight-port Orthogonally dual-polarised with non-contact feed), which are symmetrically distributed in the inner of the smartphone frame. The dimension of the system circuit board is (25*25*1.6 mm3) with epsilon and loss tangent are 4.3 and 0.025, respectively. The proposed MIMO array is simulated, and a prototype is fabricated and tested. The results show that all the elements can cover the desired band of 3.3–3.6 GHz under the condition of −6-dB impedance bandwidth. The isolations are enhanced to 17 dB by combining the inverted-I ground slots with a neutralization line (NL) structure. In addition, the envelope correlation coefficient (ECC) via any two elements is below 0.15 which shows good independence in far-field radiation characteristics. The measured efficiencies of the elements in the operating band are higher than 40%. Moreover, the array ergodic channel capacity is also calculated based on the correlation matrix method to be about 35 bps/Hz with a 20-dB signal-to-noise ratio. In addition, the effects of the user’s hand and the head has been analyzed as well. Based on the above, the proposed eight-port dual-polarized MIMO antenna using a non-contact feed is a prospective candidate for future 5G smartphone applications.

Design and Analysis of Broadband Ultrathin Reflective Linear-to-Circular Polarization Converter Using Polygon-Based Anisotropic-Impedance Surface

A broadband reflective linear-to-circular polarization converter (LCPC) is designed using a polygon-based single-layer anisotropic-impedance surface on an ultrathin (thickness is 0.053λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><b>0</b></sub> , where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><b>0</b></sub> is the wavelength corresponding to the mid operating frequency) ground-backed substrate. Using the admittance analysis of the equivalent circuit model (ECM) and extraction of the admittance through the area moment of inertia equations, simple and generalized design guidelines are presented. The proposed polarization converter produces left-handed circularly polarized (LHCP) and right-handed circularly polarized (RHCP) reflected waves, respectively, for the linearly polarized (LP) TE and TM incident waves. It offers 46% (7.62-12.16 GHz) 3 dB axial ratio bandwidth (ARBW) for normal incidences of both the TE- and TM-polarized waves. Moreover, for oblique incidences (up to 30°) of both the LP waves, the ARBW response remains quite stable. The far-field radiation characteristics, which are often not studied, are provided to show its usability as a dual-LP to dual-CP converting reflector for X-band communications. The measurement results show good agreement with the numerically simulated results.

Far-field noise radiation characteristics of an afterburning military jet aircraft

Because of the potential noise impacts of tactical jet aircraft, detailed far-field measurements are valuable in developing and validating models. This paper describes far-field measurements taken of the T-7A Red Hawk trainer aircraft. Data were taken at five microphone arcs, over six engine runups from idle to afterburner. The arcs were of varying resolution, but generally spanned 30 to 160 deg (relative to the jet inlet) at distances from 19 to 230 m. The spectra, sound pressure level, and skewness of the time derivative of the pressure waveform are analyzed according to microphone position and engine condition. Measurement consistency over the different runups and across all conditions validates the dataset for future analysis. [Work supported by AFRL.]

On near- and far-field acoustic radiation characteristics of ships in finite-depth water environment

A simplified calculation model is established to evaluate the acoustic radiation of the single-shell underwater ship structure considering typical ship mechanical excitation. The three-dimensional sono-elastic method of ships in Pekeris ocean-acoustic waveguide environment is used to calculate the acoustic radiation of the ship structure in three water environments. Variation of the ship's acoustic radiation, from the near field to the far field, is analyzed. In the near field, the value of the radiated acoustic pressure varies greatly with the changing of spatial coordinates (near-field acoustic waves exist). When evaluating underwater acoustic radiation of the ship quantitatively in the engineering, the locations of observation points (where the radiated noise is measured under water) are usually close to the ship. The distance of the observation point away from the hull is even smaller than the length of the ship taking into account the requirement of a sufficient SNR (Signal-to-Noise Ratio). At such a distance, it cannot guarantee that the converted acoustic source levels are basically stable and can effectively reflect the acoustic radiation magnitude in the far-field, that is, the condition of far-field investigation is not satisfied. This study will be helpful in answering two issues of concern in engineering: (1) How much near-field acoustic disturbance will be introduced if the distance from the hull to the observation point is less than the length of the ship? (2) How far does the observation point need to be away from the hull in order to exclude the near-field acoustic disturbance effectively?

An optimal circular antenna array design considering mutual coupling using heuristic approaches

This article shows the design of a non-uniformly excited single ring circular antenna array (CAA) for the synthesis of optimal far-field radiation characteristics. A recently proposed meta-heuristic based optimization algorithm called gray wolf optimization (GWO) and state-of-the-art swarm intelligence based evolutionary optimization technique known as particle swarm optimization with a distribution based update mechanism (PSOd) are individually applied to determine the optimum set of current excitation amplitude weights and the inter-element spacing among the array elements to reduce the side lobe level and 3-dB beamwidth considering the mutual coupling. The results obtained by employing PSOd and GWO are compared to those of the uniform radiation pattern and the recently published results of state-of-the-art literature having equal sets of elements to show the superiority of employed approaches. Three different design examples of 8, 10, and 12 elements CAA are reported in this article to study the performances of PSOd and GWO algorithm-based results over the results of other recently reported literature.

Computation of Near-Field and Far-Field Radiation Characteristics of Acoustic Transducers for Underwater Acoustic Imaging

This paper proposes a novel approach through analytical formulation for the determination of the radiation pattern of acoustic transducers at any arbitrary observation distance which covers both the near-field as well as the far-field. The proposed near-field/far-field analysis is generic and can be applied to a wide variety of acoustic apertures. The radiation pattern of the acoustic transducer at any arbitrary point of observation (both the near-field and far-field) is obtained by the vector summation of the fields radiated by the array of point sources located on the aperture of the acoustic transducer. The validity and novelty of the proposed approach have been proved by treating the far-field as a special case of near-field with the relevant distance criterion. The simulation studies show that near-field radiation patterns of the acoustic transducer exhibit changes in the profile of the amplitude patterns when the distance of observation is varied. The formation of a well-defined main beam of the radiation pattern occurs only after a distance of separation of about R=D2/λ from the radiating aperture. The presented analytical formulation has an attribute of wider generality because of its applicability to a variety of geometrical configurations of the aperture of an acoustic transducer.

Bandwidth improvement of planar antennas using a single-layer metamaterial substrate for X-band application

AbstractTo prevent far-field radiation characteristics degradation while increasing bandwidth, an attempt has been made to design and fabricate a microstrip antenna. An electromagnetic band gap (EBG) structure, including a layer of a metallic ring on a layer of Rogers 4003C substrate, is used. For a better design, a patch antenna with and without the EBG substrate has been simulated. The results show that the bandwidth can be improved up to 1.6 GHz in X-band by adding the EBG substrate. Furthermore, using this structure, a dual-band antenna was obtained as well. Finally, to validate the simulation results, a comparison has been done between simulation data and experimental results which demonstrate good agreement.

An optimal mutually coupled concentric circular antenna array synthesis using ant lion optimization

This paper presents an accurate design approach for concentric circular antenna array (CCAA) synthesis to improve the far-field radiation characteristics using a meta-heuristic optimization technique called ant lion optimization (ALO). The far-field radiation pattern is improved with lower side lobe level (SLL) which is essential for the reduction of interference in the entire side lobe regions. The ALO algorithm is a recently proposed evolutionary technique which is applied to determine the optimal sets of current excitation weights and to find the optimal inter-element spacing between the array elements in the 3-ring structure of the CCAA design. In this context, the design examples of two 3-ring CCAAs, one having the set of (4, 6, 8) elements and the other having the set of (8, 10, 12) elements, with and without the centre element, are presented by optimizing the array parameters. The results obtained by using the ALO algorithm–based approach show considerable improvement of SLL with respect to that of the uniform array pattern and those of the methods reported in the recent literature.

Antenna Design and Near-Field Characterization for Medical Microwave Imaging Applications

In medical microwave imaging (MMWI), the antennas usually operate at close distance from the body and are required to pick up weak echoes from the inside that are masked by high skin reflection. The near-field antenna behavior strongly determines how the received signals affect the effectiveness of the imaging algorithms. However, these usually simply assume the usual antenna far-field radiation characteristics. Here, we discuss three antenna effects that can deteriorate the overall imaging performance but are rarely addressed in the literature: antenna internal reflections, angular dispersion of the “near-field phase center,” and antenna frequency dispersive electric length. We propose dedicated methods to characterize these factors and present mitigation strategies to be integrated into the inversion algorithms. We demonstrate these effects for three frequently used broadband antennas, using signals from an experimental breast imaging lab setup. In fact, the antenna study and design cannot ignore that it operates in the near field of breast and interacts with its boundary. The methods and conclusions can be extended to other MMWI applications. To the best of our knowledge, this is the first systematic study of the above antenna factors in the context of MMWI.

Measurement and analysis of sound radiation from coherently vibrating shunt reactors

In parallel with the rapid development of ultra-high voltage (UHV) power transmission systems, noise contamination radiated from UHV shunt reactors is becoming an urgent concern. This investigation explored the distributed structural vibration of reactors and their near-field and far-field sound radiation characteristics based on a thorough on-site measurement and a combined numerical method. The proposed method could realize sound field reconstruction of on-site shunt reactors by directly measuring their surface vibration, thus avoiding complex modelling with fluid-structure interactions and multi-physics problems. Furthermore, the combined method was utilized to investigate the effect of acoustical environments upon reactors’ sound radiation. The results show that reflection boundaries composed of firewalls among reactor units could introduce a higher noise level in the parallel radiation region due to their influence on the sound source directivity. Finally, the sound power levels of the on-site reactors were derived from the constructed sound field, which could avoid on-site background noise concerns in the current executive standards.

Strong effect of outer plasma layers of femtosecond laser-induced plasma-channel antenna and its metallic counterpart on their radiation

The effect of various radially inhomogeneous distributions of plasma conductivity and dielectric permittivity on the far-field radiation characteristics are studied for the femtosecond laser-induced plasma-channel Vee antenna and compared to that of the radially homogeneous conductivity distribution, frequently used as a rough approximation. The radiation characteristics of the antenna are affected mainly by the outer boundary plasma layer due to skin effect and are fairly different from that of the cross-sectional averaged homogeneous conductivity distribution, and it is preferable to modulate a laser beam intensity to have radially increasing or annular distribution. The inner part of an antenna channel beyond the skin depth does not have an essential effect on its radiation characteristics, even though the inner is a highly conductive metal, as the current can hardly flow through it. The outer plasma layer can produce a complicated phenomenon, such as the signal attenuation or blackout, when it is formed around the solid metal antenna in a sufficiently fast-flow field. The simultaneous action of the radiation absorption and current flow benefiting to the radiation in the plasma layer can vary the antenna radiation characteristics in a complicated manner. The effect of plasma sheath existing between the metal antenna surface and the plasma layer on the radiation characteristics is also considered. It is also shown that the negativity of plasma permittivity does not have a great effect on the far-field radiation characteristics due to its insignificance in the radiation absorption and the irrelevance to the current.

A Heuristic Approach to Design Linear and Circular Antenna Array for Side Lobe Reduction

This paper presents a heuristic approach-based design of a symmetric linear antenna array (LAA) and a non-uniformly excited single-ring circular antenna array (CAA) to improve the far-field radiation characteristics. The far-field radiation pattern improves with lower side lobe level (SLL) which is essential for the reduction in interference in the entire side lobe regions. A recently proposed evolutionary algorithm called social spider algorithm (SSA) is applied to determine the optimum sets of current excitation weights and the inter-element spacing among the array elements to reduce the SLL. In this context, 10-element and 16-element LAA and 8-element, 10-element and 12-element CAA design examples are presented by optimizing the array parameters. The simulation results obtained by using SSA-based approach confirm a considerable improvement in SLL and some restricted improvement in half-power beam width with respect to the uniform array pattern and those of the recently reported literature.

Concentric circular antenna array synthesis for side lobe suppression using moth flame optimization

This paper presents an accurate approach for Concentric Circular Antenna Array (CCAA) synthesis to improve the far-field radiation characteristics of the antenna using a meta-heuristic optimization technique called Moth Flame Optimization (MFO). The far-field radiation pattern improves with lower Side Lobe Level (SLL) which is essential for the reduction of interference in the entire side lobe regions. MFO algorithm is a recently proposed evolutionary algorithm which is applied to determine the optimum sets of current excitation weights and to find the optimal inter-element spacing between the array elements in the 3-rings structure of CCAA design. In this context, the design examples of two 3-ring CCAAs, one having the set of 4, 6, 8 elements and the other having the set of 8, 10, 12 elements, with and without centre element, are presented by optimizing the array parameters. The results obtained by using MFO algorithm based approach show a considerable improvement of SLL with respect to that of the uniform array pattern and those of the approaches reported in the recent literature.

A Multifeed Antenna for High-Efficiency On-Antenna Power Combining

This paper presents a multifeed antenna structure that synthesizes the desired far-field radiation characteristics with on-antenna power combining and increases the total radiated power of a wireless transmitter. The driving signals at the multiple antenna feeds are scaled properly in amplitude and phase, so that they collectively synthesize the desired on-antenna current/voltage distribution and achieve the resulting desired far-field radiation pattern. The proposed multifeed antenna offers flexibility to optimize the antenna driving impedances based on the locations of the feeds. It also simplifies the passive impedance matching and power-combining networks between the antenna feeds and the transmitter outputs, substantially increasing the total transmitter power efficiency. Most importantly, the proposed multifeed antenna achieves on-antenna low-loss power combining, which, compared with antenna array-based spatial power combining, does not suffer from narrowed beamwidth or enlarged antenna panel size. As proof of concept, multifeed slot antennas and a multifeed square loop antenna are designed and characterized at 10.3 GHz. Conventional single-feed slot antennas and a single-feed square loop antenna are also implemented as reference designs. Well matched antenna gains and radiation patterns between the proposed multifeed antennas and the conventional single-feed antennas are achieved in the measurements, demonstrating the on-antenna power combining of the proposed multifeed antennas without distorting the far-field radiation patterns.