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In this article a compact sinusoidal tapered slot Vivaldi linear antenna array is designed for X and Ku band applications is presented. Printed Vivaldi antennas are extensively used for broadband applications because it gives high gain and broad bandwidth. The proposed antenna consists of two circular stubs, one rectangular slot and sinusoidal tapered lines on both sides of the antenna structure. These two tapered lines separated by circular slots and rectangular slot. The bandwidth of the antenna is improved with two circular stubs before the tapering. A rectangular slot is included before the two stubs to reduce the aperture width of the antenna. The feed line is then terminated with sectorial stub to have better coupling to the slot. The profile of the tapering of slot is designed as sinusoidal variation to have good end fire radiation for the entire frequency range. The simulated single antenna has return loss less than− 10 dB in between the frequencies 8.2–20 GHz. A five-element linear array is designed, simulated and prototype model is fabricated. The simulated and experimental results show return loss is less than − 7.5 dB for the frequency range of 8.2–20 GHz. The maximum gain of single element and array is 4.6 dBi and 7 dBi respectively. The Co and cross polarization radiation patterns are measured. The designed Vivaldi antenna array is used in X, KU band, electronic warfare and phased array applications. [ABSTRACT FROM AUTHOR]

In order to increase the radiation performance of aperture-type antennas, this paper demonstrates a low-profile, planar, single-layer, three-dimensional (3-D) printable metastructure. The proposed hybridized metastructure is highly transparent as it is made out of novel hybrid meta-atoms having transmission coefficient magnitudes greater than – 0.72 dB and fully complies with the near-field phase transformation principle. The hybridized design approach makes the metastructure planar, low-profile, light in weight, and compatible with additive printing technology. For the proof-of-concept, such metastructure is developed and numerically verified to enhance the radiation performance of a resonant cavity antenna (RCA). With the proposed metastructure, the peak directivity of the RCA is improved by 8.6 dBi (from 11.4 dBi to 20 dBi) at the operating frequency of 12.4 GHz. The aperture efficiency and 3-dB directivity bandwidth of the RCA with the metastructure are 41.46% and 16.5%, respectively. Using readily accessible thermoplastics or polymers and copper with cost-effective fused deposition modeling (FDM) 3-D printing technology, the proposed planar hybridized metastructure can be prototyped commercially. [ABSTRACT FROM AUTHOR]

A novel dual band tunable terahertz (THz) circularly polarized dielectric resonator antenna (CPDRA) is designed and numerically studied. Hybrid Silicon-Graphene materials are employed as radiator with cross-slot shaped aperture coupled feed, enabling tunable linearly and circularly polarized radiation. Silicon is a good material as dielectric resonator with its operation in the THz regime due to lack of absorption, cheaper to grow and machine. Cross shaped slots of appropriate dimensions are engraved in the centre of the ground plane to split the fundamental mode of the rectangular DR into two near degenerate orthogonal modes having quadrature phase difference. As a result, circular polarization is obtained in the upper passband. Introducing cross slot also helped to improve the impedance matching and dual band operation is achieved with linearly polarized response in lower band and circularly polarized response in the upper band. By adjusting the chemical potential of graphene, frequency tunability in the both the operating bands is obtained, without changing the physical geometry of the antenna. The proposed antenna operates with 10 dB impedance bandwidth of 4.24 \% (2.31–2.41 THz) and 12.1 \% (3.11–3.51 THz) and 3 dB axial ratio bandwidth of 3.54 \% (3.33–3.45 THz). The antenna parameters are calculated and gain of 6.11 dBi and 5.8 dBiC in lower and upper band, respectively and radiation efficiency of 96.5 \% in both operating bands is obtained. This hybrid radiator-based THz CPDRA shows great potential in the development of tunable THz devices and could pave a path for new researchers. [ABSTRACT FROM AUTHOR]

A wideband and circularly polarized hybrid ring CDRA is proposed for the applications of C, X and Ku-band. A small size two-headed drum-shaped aperture (Damaru shaped) inclined at 45° and microstrip line feed generates two orthogonal modes (HEMx11δ and HEMy11δ). The suggested ring CDRA of wideband characteristic is resonating between frequency band 6.96 to 14.12 GHz with 67.93% (7160 MHz) impedance bandwidth. oreover, dual-band circular polarization characteristics are also achieved from 8.22 to 9.53 GHz and 12.29 to 13.71 GHz with 3-dB axial ratio bandwidth (ARBW) of 14.76% (1310 MHz) and 10.92% (1420 MHz) respectively. The impact of various parameters of ring CDRA and aperture orientation on the functionality of the suggested antenna is also studied. The proposed radiator is fabricated on a 40 × 40 mm2 (0.93 × 0.93λ02 at lower cut-off frequency 6.96 GHz) FR-4 substrate of 1.6 mm thickness. Moreover, peak gain of 7.43 dB at frequency 12.66 GHz and radiation efficiency greater than 80% in the whole operating frequency is also achieved. [ABSTRACT FROM AUTHOR]

A design of high sensitivity Vivaldi antenna is introduced for detecting the low sugar and salt concentrations in water. The reason for selecting the Vivaldi antenna configuration is to provide two desired features; ultra-wideband and a high directivity so the surrounding clutter effect can be minimized. The prospective antenna embraces the ultra-wideband from 4 to 11 GHz. Two techniques are exploited to improve the antenna detectability; epsilon-near-zero (ENZ) metamaterial and antenna aperture amending. The ENZ metamaterial is very sensitive to the permittivity of the substrate, so any loading effect can easily alter the electric field distribution and hence affect the antenna phase properties. The aperture amending is used to improve substrate-air matching. An equivalent circuit model is scrutinized for further emphasis of the ENZ metamaterial operation, showing good agreement with EM simulation results. In terms of phase variation, the designed antenna is employed to sense sugar and salt in water. The amount of sugar and salt affects the material characteristics of the solution and, as a result, the reflected phases. Practical observations reveal that when the sugar and salt contents in the liquid increase, the phase falls. At 5 GHz the difference between the highest and lowest sugar concentrations is about 3° in the sugar case and 5° in the salt case, but at 8 GHz, the phase difference is about 30o in the sugar case and about 50° in the salt case. The sensitivity can be increased by operating at a higher frequency since the proposed antenna can detect very low levels (1%) of salt and sugar concentrations. The time-domain analysis is discussed, revealing low distortion of received pulses. [ABSTRACT FROM AUTHOR]

In this article, magnetically biased graphene is utilized to achieve a terahertz antenna capable of reconfiguring the polarization of the radiation pattern, transitioning between two states of linear and circular polarizations. The antenna is structured in a way that allows terahertz waves to enter through a slot aperture from a microstrip transmission line. These waves are then coupled to a silicon dielectric resonator, which has a graphene layer on top of it. Subsequently, the terahertz surface waves are launched within the silicon dielectric rod by the dielectric resonator. By applying a biased magnetic field perpendicular to the antenna, the conductivity tensor of graphene exhibits non-diagonal elements. This results in the production of circular polarization within the antenna. Furthermore, altering the direction of the applied bias magnetic field causes a shift in polarization from right-hand circularly polarized to left-hand circularly polarized. The modified relaxation-effect model is employed at terahertz frequencies to calculate the losses of silver metal, deviating from the accurate skin effect model used for microwave frequencies. Remarkable impedance matching is attained for linear and circular polarization within the range of 2.86 to 3.14 THz. The article provides detailed insights into the simulated reflection coefficient, axial ratio, gain, and radiation patterns. This device holds the potential for integration into diverse subwavelength terahertz systems. [ABSTRACT FROM AUTHOR]

A method of empirical evaluation of the transient response of an aperture-type antenna when it is excited by a video pulse has been proposed. The evaluation was carried out on the basis of comparing the excitation voltage of the antenna and the excitation voltage of the radiating aperture, which is calculated using the parameters of the emitted pulse. An evaluation of the energy efficiency of a given antenna as a converter of electrical energy into radiation energy has been given through variations in the antenna length and duration and shape of its excitation pulse. [ABSTRACT FROM AUTHOR]

In this work, a quad-port fractal MIMO antenna is configured, simulated, and experimented for ultra-wideband performance with the elimination of three interfering narrow bands. The antenna is assembled on dual 80 × 99.4mm2 FR-4 dielectric substrates wherein the top substrate comprises four 2nd iterative Sierpinski gasket fractal patches and the bottom substrate incorporates a feeding arrangement. The aperture-coupled feeding approach is employed to activate the fractal radiators. The multi-frequency response produced by fractal antenna elements is transformed into a wide working range by modifying apertures (clipped from the ground surface) into spiral-shaped structures and offsetting the feedlines toward the right. The designed array effectively radiates in the 3.07–11 GHz range with 112.7% fractional bandwidth while maintaining minimal inter-element isolation of 16.19 dB. Additionally, each feedline is amalgamated with circular split-ring resonators, U-slots, and rectangular split-ring resonators to eradicate the interference emerging from the C-band (downlink satellite), WLAN, and radio-location band, respectively. Several diversity operation attributes are analyzed and are found to inhere to their admissible standards. The measured performance of the fabricated antenna design (with and without band-stop structures) depicts an agreeable similitude with the simulation results, thus validating the real-world operability of the proposed MIMO antenna in ultra-wideband communication devices. [ABSTRACT FROM AUTHOR]

In this paper, a four-port graphene-dielectric resonator based MIMO radiator is structured and examined. The exclusive properties of designed radiating structure are: (i) designed aperture creates the circularly polarized (CP) waves in between 2.51 and 2.75 THz; (ii) proposed multiport aerial is structured so that every port is radiated in different direction; and (iii) change in the chemical potential of graphene creates the reconfigurable property in the designed antenna. The proposed antenna design works well between 2.49 and 2.85 THz with the isolation level approx. 20 dB among antenna ports. Radiator gain is about 4.5 dBi within the working band. The proposed antenna has stable far-field characteristics and a decent value of the MIMO parameter. All these features make the designed radiator employable for wireless communication systems at THz frequency. [ABSTRACT FROM AUTHOR]

A 10 Gbps Continuous Phase Frequency Shift Keying (CPFSK) modulation is proposed for a Free Space Optical (FSO) communication system. The system performance is analyzed by considering effects of atmospheric conditions, beam divergence, transmitter and receiver antenna aperture diameters for 1550 nm operation. In this paper, we evaluate the system maximum Quality-factor (Q-factor), Bit Error Rate (BER), and received power, where the system is greatly affected by th e mentioned parameters. This simulation is performed by using the Optiwave system software. The obtained simulation results show that CPFSK modulated FSO system with low beam divergence and high aperture diameter is upgrading maximum Q-factor and degrading minimum BER. [ABSTRACT FROM AUTHOR]

We designed a mesoscopic dielectric cuboid antenna connected to a flangeless WR-3.4 open-ended waveguide, and the antenna characteristics at 300 GHz were examined through simulations and experiments. Simulations confirmed that the flangeless design eliminated the flange-induced ripples in the radiation pattern, whose shape varied with frequency, and that the antenna operated in the full bandwidth of the WR-3.4 waveguide (220–330 GHz). Prototypes were then fabricated based on the simulation findings. A prototype with an antenna aperture area of 1.5 mm × 1.5 mm and an antenna length of 2.35 mm exhibited an antenna gain of 17.2 dBi at 300 GHz and a voltage standing wave ratio of less than 1.5 throughout the WR-3.4 waveguide bandwidth. The level of the side lobes at about ± 30 degrees in the E-plane pattern was approximately - 10 dB that of the main lobe. Therefore, the proposed antenna, connected to a flangeless waveguide, is a promising antenna for use in future short-range high-speed terahertz wireless applications such as kiosk downloads and board-to-board communication. [ABSTRACT FROM AUTHOR]

Manipulations of multiple carrier frequencies are especially important in a variety of fields like radar detection and wireless communications. In conventional radio-frequency architecture, the multi-frequency control is implemented by microwave circuits, which are hard to integrate with antenna apertures, thus bringing the problems of expensive system and high power consumption. Previous studies demonstrate the possibility to jointly control the multiple harmonics using space-time-coding digital metasurface, but suffer from the drawback of inherent harmonic entanglement. To overcome the difficulties, we propose a multi-partition asynchronous space-time-coding digital metasurface (ASTCM) to generate and manipulate multiple frequencies with more flexibility. We further establish an ASTCM-based transmitter to realize wireless communications with frequency-division multiplexing, where the metasurface is responsible for carrier-wave generations and signal modulations. The direct multi-frequency controls with ASTCM provides a new avenue to simplify the traditional wireless systems with reduced costs and low power consumption. The authors present a multi-partition asynchronous space-time-coding digital metasurface (ASTCM) to control multifrequency waves; they demonstrate its capabilities by sending eight pictures over distinct frequencies using this wireless transmitter. The proposed work shows potential in enhancing microwave systems with improved power efficiency and cost-effectiveness. [ABSTRACT FROM AUTHOR]

Recent research on space technology applications has revealed a growing demand for deployable structures with large apertures. Numerous deployable structures that can form a single closed loop have been developed with a total weight limitation. The main purpose of this paper is to present an equivalent parameterized mechanical modeling method that is appropriate for an annular tensegrity structure, which is a tensioned structure that is intended for antenna applications with an aperture range of 30–100 m. In this model, the solutions of geometrically nonlinear problems for the cables and beams of the hoop are presented. Both the kinetic energy and potential energy are identified, which are represented by the velocity of the node component and strain component, respectively, of the beam members in the hoop unit of the parameterized hoop structure. Then, the behaviors of the eigenvalues and vibration modes for this tensegrity structure based on dynamic analysis are also investigated. Additionally, the effect on dynamic performance is demonstrated when the structural parameters are changed. The sensitivity of the structural parameters to dynamic characteristics is separately analyzed. The priority approaches to improving the overall stiffness of the structure when employing different hoop configurations are proposed. [ABSTRACT FROM AUTHOR]

Integrating antenna elements from various bands within a limited area is a necessity in current base station antennas (BSAs). Among these elements, the antenna designed for the lowest frequency band is the largest, making its design the most challenging. This paper introduces a novel cross-dipole antenna element, referred to as the Palm antenna, designed to operate within the frequency range of 0.698–0.96 GHz. The Palm antenna aims to suppress cross-band scattering in dual-band dual-polarized antenna arrays commonly employed in cellular BSAs. The low-band (LB) elements achieve transparency in high-frequency bands (HB) by utilizing the radar cross-sectional reduction method. Additionally, a new figure of merit, the FLHB/FULB ratio, is introduced, which compares the lowest frequency of the HB antenna (FLHB) to the upper frequency of the LB element (FULB). This ratio is significantly lower in our designs (FLHB/FULB = 1.46), facilitating decoupling between the LB and HB elements. Experimental results demonstrate that inserting LB-pass HB-stop meanders into LB radiators enhances de-scattering across a broad frequency band, significantly reducing pattern distortion induced by LB elements. The array comprises two columns of HB antennas operating from 1.4 to 2.7 GHz, interleaved with a single column of LB antennas operating from 0.698 to 0.96 GHz. As a result of the proposed method, a de-scattering bandwidth of 66.8% has been successfully achieved. [ABSTRACT FROM AUTHOR]

Frequency-modulated continuous wave radar techniques typically have inadequate angular resolutions due to the limited aperture sizes of antenna arrays in spite of employing multiple-input multiple-output (MIMO) techniques. Therefore, despite the existence of multiple objects, angularly close objects with similar distances and relative velocities are recognized as one single object. Autonomous driving requires the accurate recognition of road conditions. This requirement is one of the critical issues to be solved to distinguish significantly close objects. This paper proposes a technique referred to as an antenna element space pseudo-peak suppressing (APPS) method to resolve angularly close targets. The proposed APPS method aims to identify closely spaced objects on roads. These angularly close targets cause a single peak in a spatial spectrum obtained by a beamformer-based angle estimation. The APPS considers this single peak as pseudo. The APPS radar cancels this pseudo peak from the spatial spectrum. Then, the obtained residual received signal is analyzed. With these procedures, the APPS identifies the number of targets. The APPS also estimates the target angles. The proposed APPS is experimentally validated using a typical single-chip MIMO-based radar evaluation board with three transmit (TX) and four receive (RX) antennas. The experimental results confirm that the proposed APPS successfully resolves angularly close pseudo targets with an angle difference of approximately 0. 5 ∘ . [ABSTRACT FROM AUTHOR]

We consider technical aspects of using quadrature amplitude modulation in modern microwave active phased antenna arrays. A necessity of improving the accuracy of phase adjustment for realizing complex types of the amplitude-phase distribution of signals in the antenna aperture, which is required for forming the directional patterns with a low level of side lobes, is substantiated. Special attention is paid to experimental studies of the parameters of the beamforming elements of the transceiving units based on quadrature modulators. A possibility of significant (over an order of magnitude) improvement of the accuracy of setting the specified phase of a microwave signal compared with that ensured by discrete phase shifters is discussed. Conclusions are made on the expedience, especially in the millimeter-wave range, of developing the beamforming circuits based on quadrature amplitude modulation of the carrier for modern high-quality active phased antenna arrays. [ABSTRACT FROM AUTHOR]

Calculation relations are derived for analyzing the possibility of detecting local inhomogeneities by the method of reflected waves when carrying out acoustic investigation of the ground layer. The amplitude value of the total response at the receiving antenna output is represented as a two-dimensional terrain—a function of two arguments: delay time of the back-reflected pulse echo signal and the aperture center displacement during spatial scanning relative to the place of the intended localization of the inhomogeneity. Based on a graphical representation of the total response of the receiving antenna in the form of a two-dimensional space–time terrain, the feasibility of the proposed method for detecting local inhomogeneities proposed method of detection local inhomogeneities in the probed medium is demonstrated. The illustrations of the results of mathematical and numerical modeling clearly show that this approach helps in obtaining information about the actual profile or nature of the horizontal spatial distribution of the anomaly. The influence of the duration of the probing pulse and the aperture of the receiving antenna, the size and depth of the local inhomogeneity, as well as the dissipation factor, during the propagation of seismic-acoustic waves on the resolution in probing and remote diagnostics of inhomogeneity parameters is analyzed by mathematical and numerical modeling. The field of application of the developed technique is engineering seismic exploration of karst cavities, breccias, caverns, and other types of local inhomogeneities. [ABSTRACT FROM AUTHOR]

The effect of intermodal correlations on the efficiency of the spatial processing of a signal in oceanic waveguides with a perturbed surface is studied. An algorithm of calculating the correlation matrix of a signal on the aperture of a horizontal antenna array with allowance for the interferential structure of an acoustic field in the sound channel is proposed. The antenna gain factor is analyzed for three spatial-processing methods, such as the standard phased antenna array, optimal linear processing, and optimal quadratic optimization techniques. The results of numerical modeling for the hydrological conditions of the Barents Sea in the winter period are given. Particular attention is paid to interferential oscillations in the gain factor of an antenna array and the dependence of its values "smoothened" at the scale of the interferential structure of an acoustic field in a waveguide on the problem parameters. [ABSTRACT FROM AUTHOR]

An aperture coupled two element metamaterial antenna suitable for multiple input multiple output applications in the frequency band of 7.525–9.1 GHz is proposed. This three-layered structure utilizes a vertical array of rectangular complementary split ring resonators between the contiguously placed circular non-bianisotropic complementary split ring resonator radiating elements for enhancement of isolation. This antenna achieves a maximum of 47 dB isolation through this Mu Negative structure insertion in the frequency band for 0.11 λ0 separation of the two antenna elements. The proposed antenna achieves a fractional − 10 dB impedance bandwidth of 18.94% and has a peak gain of 8.15 dB. The efficiency of the antenna is 84.14% and the envelope correlation coefficient is less than 0.03 in the operating band. The antenna is low profile with an overall size of 0.85 λ0 × 0.45 λ0 × 0.133 λ0 and is suitable for X-band military applications. [ABSTRACT FROM AUTHOR]

In this article, we have proposed a novel miniatured two element circular antenna array operating at 28 GHz suitable for 5G wireless communication system. Each element has three circular sections embedded over an FR4 substrate. High isolation and good gain are the key requisites when the miniaturized antennas at very close proximity are employed. The paper has designed an antenna element consisting of three circular sections with two auxiliary feeds at 28 GHz. The mushroom-like EBG unit cell has been designed to obtain zero reflection phase at 28 GHz. Five such electromagnetic band-gap (EBG) unit cells, along with two vertical slots, are placed in between the two radiating patches for reduction of mutual coupling and enhancing the gain. The proposed compact structure with vertical slots and EBG bestows the isolation and gain up to − 34.76 dB and 7.81 dB, respectively. The antenna exhibits wide angle coverage in the E plane, and beam steering capabilities in the H plane as the phase variation between the antenna elements are applied. [ABSTRACT FROM AUTHOR]

This article presents a dual-band circularly polarized hybrid ring CDRA (Cylindrical dielectric resonator antenna) for wireless applications in C and X-band. A circular ring inclusive of a slotted cross-shaped microstrip feed line is used to excite the ring CDRA and generation of HEM11δ and TEM01δ modes. Multiple inverted Z-shaped apertures and circular ring along with a slotted cross-shaped microstrip feed line are responsible for the generated circular polarization wave between 3.92 and 4.08 GHz in lower band and 8.85 to 9.61 GHz in upper band with 4% (160 MHz) and 8.23% (760 MHz) axial ratio bandwidth (ARBW) respectively. The proposed antenna also offers impedance bandwidth of 20.58% (780 MHz) between 3.40 and 4.18 GHz in lower band while 29.31% (2490 MHz) between 7.25 and 9.74 GHz in upper band resonating at 3.73 and 7.79 GHz with − 26.4 and − 35.61 dB return loss respectively. The proposed ring CDRA shows stable gain of peak value 5.8 dB (simulated) and 5.8 dB (measured) in lower band while 7.7 dB (simulated) and 8.2 dB (measured) in upper band. [ABSTRACT FROM AUTHOR]

Near-Field Meta-Steering (NFMS) is a constantly evolving and progressively emerging novel antenna beam-steering technology that involves an elegant assembly of a base antenna and a pair of Phase-Gradient Metasurfaces (PGMs) placed in the near-field region of the antenna aperture. The upper PGM in an NFMS system receives an oblique incidence from the lower PGM at all times, a fact that is ignored in the traditional design process of upper metasurfaces. This work proposes an accurate optimization method for metasurfaces in NFMS systems to reduce signal leakage by suppressing the grating lobes and side lobes that are innate artifacts of beam-steering. We detail the design and optimization approach for both upper and lower metasurface. Compared to the conventionally optimized compact 2D steering system, the proposed system exhibits higher directivity and lower side-lobe and grating lobe levels within the entire scanning range. The broadside directivity is 1.4 dB higher, and the side-lobe level is 4 dB lower in comparison. The beam-steering patterns for the proposed 2D compact design are experimentally validated, and the measured and predicted results are in excellent concurrence. The versatile compatibility of truncated PGMs with a low gain antenna makes it a compelling technology for wireless backhaul mesh networks and future antenna hardware. [ABSTRACT FROM AUTHOR]

Hollowed aperture pentagon model graphene patch antenna is meant with and without a cylindrical tube by shorting the bottom and feed line which are oscillated correspondingly at 3.96 and 5.275 THz frequency. The designed antenna is formed of graphene as a patch material and polydimethylsiloxane (PDMS) as a substrate material with low dielectric permittivity. The radiation characteristics of the antenna with and without cylindrical tubes are evaluated and are shown to possess a high gain of 8 dB, 4 dB, and directivity of 10.8 dBi, 7.19dBi at 5.275, 3.96 THz respectively. These antennas are compared with existing antennas and that they have enhanced directivity, high gain, wider bandwidth, and better radiation efficiency. The frequency multiband is achieved when the position and variation of the cylindrical tube's inner and outer radius within the built antenna is changed. The planned antennas are designed and simulated by CST studio 2016. This recommended antenna is required for the detection of cancer in biomedical, future 5G technology, and transferring data between satellites in space. [ABSTRACT FROM AUTHOR]

A combined antenna optimized for excitation by the bipolar pulse having the duration of 3 ns is numerically investigated. Three approaches are used. It is shown that the partial phase center of the antenna is situated in the antenna middle in the H plane and closer to the plane of the antenna aperture in the E plane at the central spectral frequency of 350 MHz. The radiation center is between the partial phase centers at a distance from the aperture plane. This distance is approximately equal to 1/4 of the antenna length. [ABSTRACT FROM AUTHOR]

Emerging technologies such as 5G communication systems, autonomous vehicles and satellite Internet have led to a renewed interest in 2D antennas that are capable of generating fixed/scannable pencil beams. Although traditional active phased arrays are technologically suitable for these applications, there are cases where other alternatives are more attractive, especially if they are simpler and less costly to design and fabricate. Recently, the concept of the Peripherally-Excited (PEX) antenna array has been proposed, promising a sizable reduction in the active-element count, especially when compared with traditional phased arrays. Albeit at the price of exhibiting some constraints on the possible beam-pointing directions. Here, we demonstrate the first practical implementation of the PEX antenna concept, and the proposed design is capable of generating single or multiple independently scannable pencil beams at broadside and tilted radiation directions, from a shared radiating aperture. The proposed structure is also easily scalable to higher millimeter-wave frequencies, and can be particularly useful in MIMO and duplex antenna applications, commonly encountered in automotive radars, among others. Two-dimensional antennas that can create and steer narrow beams are of interest for modern communication systems. Here, the authors demonstrate a scalable antenna array design that performs these functions with fewer elements than standard approaches and excited only with peripheral sources. [ABSTRACT FROM AUTHOR]

The gain of some aperture antennas can be significantly increased by making the antenna near-field phase distribution more uniform, using a phase-transformation structure. A novel dielectric-free phase transforming structure (DF-PTS) is presented in this paper for this purpose, and its ability to correct the aperture phase distribution of a resonant cavity antenna (RCA) over a much wider bandwidth is demonstrated. As opposed to printed multilayered metasurfaces, all the cells in crucial locations of the DF-PTS have a phase response that tracks the phase error of the RCA over a large bandwidth, and in addition have wideband transmission characteristics, resulting in a wideband antenna system. The new DF-PTS, made of three thin metal sheets each containing modified-eight-arm-asterisk-shaped slots, is significantly stronger than the previous DF-PTS, which requires thin and long metal interconnects between metal patches. The third advantage of the new DF-PTS is, all phase transformation cells in it are highly transparent, each with a transmission magnitude greater than − 1 dB at the design frequency, ensuring excellent phase correction with minimal effect on aperture amplitude distribution. With the DF-PTS, RCA gain increases to 20.1 dBi, which is significantly greater than its 10.7 dBi gain without the DF-PTS. The measured 10-dB return loss bandwidth and the 3-dB gain bandwidth of the RCA with DF-PTS are 46% and 12%, respectively. [ABSTRACT FROM AUTHOR]

Recently, with the faster pace of development on the sophisticated detection and stealth technology, extensive attention is being paid to the reduction of Radar Cross Section (RCS) as it emerges in security and commercial applications. The Vivaldi antennas are one of the best choices for wide impedance bandwidth, planar configuration, and low profile as well. However, RCS reduction affects the antenna gain due to the complexity of radiation property. This paper intends to design an optimized vivaldi antenna to enhance gain performance. More particularly, the antenna is designed with the fine-tuning of antenna parameters like taper length l t , aperture width w ap , opening rate, slot line width w s , cavity diameter d , cavity to taper spacing s , ground plane length l and ground plane width w , respectively. More particularly, optimization algorithms play a vital role in fine-tuning of the parameter, and hence this paper intends to propose a new Improved Grey Wolf Optimization Algorithm with Fitness based Update evaluation (IGWO-FU), which is the enhanced version of traditional GWO. Finally, the performance of the proposed IGWO-FU model is compared over other traditional algorithms with respect to gain, VSWR, directivity, charge and current distribution, return loss as well. [ABSTRACT FROM AUTHOR]

The article proposes a direct algorithm for reconstructing the electromagnetic field at the antenna aperture, which can be used to solve problems of diagnostics and spatial filtering. The algorithm is based on the solution of Maxwell's equations in the form of advanced potentials of the electromagnetic field. It is shown that advanced electromagnetic waves, which are a solution to Maxwell's equations, are equivalent to retarded electromagnetic waves when the parameters of the medium are stationary and linear. The direct algorithm is formulated as the multiplication of the transformation operator matrix by the known vector of the electromagnetic field on a closed surface. In this case, the transformation outward (to the far field) or inward (to the aperture) of the surface is described by the same operator and differs only in the signs of the input quantities. Unlike the known algorithms, the direct one does not require scanning the electromagnetic field on canonical surfaces or solving a large system of integral equations. It makes the new algorithm optimal for use in new near-field antenna measurement systems based on industrial robots, unmanned aerial vehicles, etc. Verification of the developed algorithm using experimental data has shown the possibility of reconstructing the normalized distribution of the electric field strength at the antenna aperture with an error less than 2 dB. [ABSTRACT FROM AUTHOR]

Reliability of multielement antenna devices and the problems of distortions under conditions for unrepeatability, construction of algorithms for remote control, and correction of antenna characteristics of multielement antennas are considered. A new approach is proposed for the development of an algorithm for reconstruction of original (specified) radiation patterns within planar apertures. Reconstruction of the radiation pattern is provided in the absence of a priori data on the deformation of the emitting surface and disturbed phase distribution along the aperture and without application of additional measurement equipment in the vicinity of the phased array antenna (PAA). Examples of reconstruction of the radiation patterns of deformed PAAs are presented. [ABSTRACT FROM AUTHOR]

Metamaterial loaded star-shaped dielectric resonator antenna (SDRA) fed by aperture-coupled mechanism is used for the enhancement of bandwidth and gain. The star-shaped structure is made-up using biodegradable poly-lactic acid having a dielectric constant (εr) of 3.45 and loss tangent (tan δ) of 0.05, which adopt the cost-effective manufacturing i.e. additive manufacturing technique. The alteration in rectangular dielectric resonator antenna to make SDRA is the foundation for broad bandwidth while hybrid exciting-modes are due to feeding of two apertures (slots) of unequal length. Correspondingly, metamaterial i.e. an arrangement of the split-ring resonators have been used for gain enhancement of antenna. The enhanced peak gain of the metamaterial loaded SDRA is more than 12 dBi and the average radiating efficiency is ~ 81%. The proposed antenna attained a broad bandwidth of 41.1% ranging from 4.15 to 6.3 GHz which is suitable for the IEEE 802.11 WLAN standards and C-band wireless communications. The proposed antenna has also offer circularly polarized characteristics at 6 GHz. Thus such an antenna with a trait of circular polarization can be promising for other wireless applications. [ABSTRACT FROM AUTHOR]

In microwave antenna applications, continuum structures usually support attached functional surfaces to realize some specific electromagnetic performance. Topology optimization of continuum supporting structures with functional surfaces is a challenge for microwave antenna applications. By introducing the concept of aperture field distribution into the design domain, a weighting approach for the topology optimization of continuum supporting structures with functional surfaces is presented based on the SIMP model. With the weighting aperture field distribution, the objective function of compliance in the previous SIMP method is changed to a weighted compliance. By selecting an optimized control factor, a different truss topology structure with several components from the previous method is clearly obtained. The effectiveness of the proposed method is validated through three typical applications: array antennas, reflector antennas, and conformal antennas with planar and curved functional surfaces. [ABSTRACT FROM AUTHOR]

It is shown that for microwave radiometric systems for remote sensing of natural environments, the issue of unambiguous determination of the correspondence of the output signal to the value of the radio brightness temperature of the probed region, from which the physical parameters are estimated, is important. Microwave radiometric systems operate under external noise and background noise. This article explores the effect of background noise on the external calibration of a microwave radiometric system using an external "deterministic" noise signal source. The conditions for performing calibration in a system with compensation for the influence of background noise are analyzed. The analysis of the output signal of the microwave radiometric system showed a significant effect of background noise on the parameter that determines the reference origin of the receiver scale. The possibility of reducing the interference effect of background noise on the measurement results in a microwave radiometric system with a two-channel antenna operating on two modes of a circular waveguide is considered. It is shown that an additional compensation signal is formed at the antenna output. An analytical assessment of the degree of compensation of the influence of background noise on the output difference signal of the system is carried out. We perform a numerical analysis of the error of external calibration of a three-band microwave radiometric system with compensation of background noise when receiving thermal radiation to a common aperture of the antenna. [ABSTRACT FROM AUTHOR]

A linear waveguide slot antenna with a frequency scanning sector of 180° is proposed and studied. The antenna represents a rectangular metal waveguide filled with a two-layer dielectric with periodic steps of thickness in one layer and periodic triple transverse slots in the wide wall of the waveguide. A scanning sector of 180° is reached with the aid of two scanning regimes that employ the fundamental (zero) and minus first spatial harmonics. Such a waveguide slot antenna is characterized by a high antenna aperture efficiency in almost entire frequency scanning sector. [ABSTRACT FROM AUTHOR]

In this work, we investigate the performance comparison of different modulation schemes viz. non return-to-zero (NRZ), alternate mark inversion (AMI), return-to-zero differential phase shift keying (RZ-DPSK), and non return-to-zero differential phase shift keying (NRZ-DPSK) in a 2 × 40 Gbps–40 GHz Radio over free space optics (RoFSO) transmission link incorporating mode division multiplexing (MDM) of two distinct Hermite Gaussian (HG) modes (HG00 and HG01) under the influence of different atmospheric turbulence conditions. Further, the effect of increasing receiver antenna aperture diameter on the link performance is investigated and compared for all four modulation schemes under different turbulence conditions. It is observed that as the strength of the atmospheric turbulence increases, the performance of the link degrades whereas the Bit error rate and the Quality Factor (Q Factor) of the received signal are significantly improved by increasing the receiver aperture diameter. Among the four modulation schemes, link with NRZ-DPSK modulation scheme gives the best performance under the influence of atmospheric turbulence followed by RZ-DPSK, AMI, and NRZ scheme. Also, the proposed NRZ-DPSK scheme based MDM-RoFSO link is investigated under different weather conditions and the results are compared with the previously reported works in the literature. [ABSTRACT FROM AUTHOR]

Microstrip patch antennas are designed and investigated in L/S bands simultaneously using the sharing of aperture. The antenna is designed on commercially available dielectric material FR4 with εr = 4.3. In the present communication two cases of design (horizontal and vertical layout) are analyzed and tested. In both configurations, the resonant frequencies lie in L and S band. The antenna characteristics measured and simulated are in agreement. Orientation of antenna layout from horizontal to vertical also enhances co/cross-polarization. The present work is important for cost effective applications. [ABSTRACT FROM AUTHOR]

We analyze the construction of a system for processing space-time signals in a radio system that takes into account technical limitations in the measurement of the bearing. A desired efficiency can be achieved by using simplified processing procedures with stochastic controlled bearing interpolation. For implementation, we use processing based on truncated (low-element) managed apertures of antenna arrays and coarse ("binary") robust signal statistics. We propose an alternative approach that involves applying the Monte Carlo method with feedback in the process of digital processing: we implement randomization and incremental stochastic control for the phase center position by sequentially activating a small number of elements during the accumulation and averaging of rough samples of the input signal. We also present quantitative results of reducing instrumental errors in bearing measurement. [ABSTRACT FROM AUTHOR]

This article presents the design and development of a compact broadband "+" shaped aperture coupled carpet fractal antenna with a defected ground structure (I shaped slot in the ground) for broadband/ultra wideband (UWB) and a multiband characteristics. The antenna has overall dimensions of 8.4 cm × 5.5 cm × 3.2 mm and is fed using aperture coupled feeding mechanism. It shows an impedance bandwidth (< 10 dB) of 4460 MHz from 6.93 to 11.39 GHz with fractional bandwidth of 0.48 at the center resonant frequency of 9.16 GHz. A multiband behavior is also exhibited by this antenna from 3.9–4.08 GHz, 4.8–5.06 GHz and 6.1–6.4 GHz with impedance bandwidths of 180 MHz, 260 MHz and 300 MHz respectively. It therefore supports the wireless applications of Wi-MAX (3.8–4.1 GHz), Wi-BAN/long distance radio telecommunication (4.8–5.06 GHz), wireless sensor networks (6.1–6.4 GHz), satellite (7.4–7.8 GHz) and UWB (6.9–11.03 GHz). The antenna is designed as a '+' shaped patch with fractal rectangular slots cut out from it up to iterations of second order that allow the antenna to support multiband characteristics. The bandwidth at these bands is improved by using I shaped defected ground structure (DGS) and a parasitic feeding method i.e. aperture coupled feeding (Karur et al., in: ICMARS (IEEE), Jodhpur, India, pp. 266–270, 2014).The antenna has a compact structure with two layers of FR4 substrate, the '+' shaped carpet fractal printed on the upper substrate layer and the lower substrate has a ground layer printed on its top and feed line on its bottom layer respectively. It shows a simulated peak gain of 4 dB at an operation frequency of 7.95 GHz. The antenna design and simulations are done using CST MWS V14. The Simulation results in terms of impedance bandwidth, smith chart, gain are presented in this article. To validate the impedance bandwidth results, the proposed carpet fractal antenna is experimentally tested using a vector network analyzer and the measured results are found to be closely matching with the simulated ones, allowing the antenna to be practically suitable for the afore mentioned wireless applications. [ABSTRACT FROM AUTHOR]

Multipath phenomenon reduces the performance of elevation angle estimation, intensively. In this study, a precise even symmetry relation and novel iterative array processing method have been presented based on the fixed beam method for estimating the elevation angle of low-altitude targets in specular and diffuse multipath environment. We propose an iterative beamforming process for retaining antenna aperture with precise even symmetry to eliminate multipath. The Kalman filter (KF) prediction have been used to reduce the computational load of the proposed method, and the frequency diversity and KF estimation to smooth sudden fluctuations in angle estimation. The proposed method estimates the elevation angle with very high precision as shown in simulation results in the multipath environment without the need for any advance knowledge. [ABSTRACT FROM AUTHOR]

This paper presents a novel design of antenna using sapphire. An aperture coupled two- layer stacked rectangular dielectric resonator antenna structure design consists of sapphire and TMM13i. Due to sapphire and TMM13i physical attributes such as hardness, resistance to physical change and chemical erosion the designed antenna is best suited for long distance, underground and rugged communication in addition to C band and 5G applications. The Aperture coupled feed has been employed because of its advantage of providing better isolation between antennas and the feed network. The designed antenna provides the gain of 5.2 dB and impedance matching of 50 ohms. The software High-Frequency Structure Simulator has been employed to simulate antenna design. The prototype of the antenna has been designed and tested on Vector Network Analyzer and Anechoic Chamber. The simulated results are in close proximity of tested results. [ABSTRACT FROM AUTHOR]

We consider a solution of the optimal control problem for an adaptive multidirectional mirror antenna. With the Pontryagin maximum principle, we reduce the problem to solving a system of ordinary differential equations. The resulting system can be solved numerically using modern approaches such as the Runge–Kutta methods or hybrid evolutionary algorithms. Estimation of the state vector is performed by the maximum likelihood criterion with solving the generated Fokker–Planck–Kolmogorov stochastic differential equation. In this case, the posterior probability density function is associated with the normalized value of the energy flux density in the aperture of antenna feeders. We determine the ability to suppress interference with an adaptive multidirectional mirror antenna and give an example of solving the control problem. [ABSTRACT FROM AUTHOR]

The main parameters of a small spacecraft (SSC) (Condor-E) and its onboard radar with a synthetic aperture antenna (SAR) are presented in the paper. Two such SSCs were launched in Russia into a 500-km orbit in June 2013 and in December 2014. The structure of the radar with synthetic aperture antenna and the basic parameters of three standard imaging modes: detailed Spotlight (DSL), detailed Stripmap (DSM), and Scan- SAR are also presented. All three modes are accompanied by radar images generated during flight tests. In this paper it is examined whether it is possible to introduce new modes (an interferometric assessment of terrain relief in the case of an "oblique" survey and the selection of moving targets) and the relevant pictures are provided. Condor-E SAR and TerraSAR are compared as typical space radars in their design and experimental modes. We conclude that the SARs perform similarly and give hope for the further augmentation of both SAR capabilities, including new modes without serious hardware modifications. [ABSTRACT FROM AUTHOR]

Numerical model has been developed in this study based on Huygens and Fermat principles applied to calculate the interference of signals emitted by all elements in an active group of a phased array probe for one focus law. Calculations are presented as ultrasonic field emitted by point source substituting for the active group of the phased array probe, and located in its center. Kirchhoff approximation model is also used to present the field emitted by each rectangular element in the active group, thus accounting for the element length influence on the field emitted by a phased array probe. Findings are shown of ultrasonic field transmitted and received by the same active group of linear phased array probe, after its reflection from infinite plane and disk reflector. Results are illustrated in amplitude-distance type nomographic charts for various reflector diameters (DGS) for one focal law. The theoretical model developed has been validated by experimental results of immersion ultrasonic testings. [ABSTRACT FROM AUTHOR]

Seepage through foundation and abutments of a dam can potentially result in a waste of the water stored in dam reservoir, erosion of foundation materials, and development of uplift pressure in dam foundation which, consequently, threatens the long-term stability of the dam. In this study, the grout volume is estimated based on parameters such as joint aperture, the maximum penetration length of the grout, and calculated grout take in Bazoft dam site. Bazoft Dam is a hydroelectric supply and double-curvature arch dam with a height of 211 m located in Chaharmahal and Bakhtiari Province of Iran. The bedrock of Bazoft dam site consists of Asemari Formation (limy marl and marly lime), in the middle and upper parts of left abutment, and Jahrom Formation (limestone and dolomite) in the right abutment, river bed, and lower part of left abutment. The joint apertures were calculated based on the permeability and the joint spacing. Next, the maximum penetration length of the grout and grout volume were calculated. Using a statistical analysis, the relationship of the joint aperture, maximum penetration length, and the calculated grout volume with real grout take was also investigated. The results show that the grout take can be predicted with appropriate accuracy based on the calculated grout volume. [ABSTRACT FROM AUTHOR]

In this paper, a novel multifunctional metasurface combining linear-to-circular polarization conversion and electromagnetic waves focusing has been proposed and applied to design a high-gain lens antenna working at Ku band. The multifunctional metasurface consists of 15 × 15 unit cells. Each unit cell is composed of four identical metallic layers and three intermediate dielectric layers. Due to well optimization, the multifunctional metasurface can convert the linearly polarized waves generated by the source to circularly polarized waves and focus the waves. By placing a patch antenna operating at 15 GHz at the focal point of the metasurface and setting the focal distance to diameter ratio ( F/ D) to 0.34, we obtain a multifunctional lens antenna. Simulated and measured results coincide well, indicating that the metasurface can convert linearly polarized waves to right-handed circularly polarized waves at 15 GHz with excellent performances in terms of the 3 dB axial ratio bandwidth of 5.3%, realized gain of 16.9 dB and aperture efficiency of 41.2%. Because of the advantages of high gain, competitive efficiency and easy fabrication, the proposed lens antenna has a great potential application in wireless and satellite communication. [ABSTRACT FROM AUTHOR]

Since Metasurfaces are playing important roles in optical devices such as optical polarizers and detectors, in this article, we have proposed a novel shape of nano aperture antenna for mid-infrared applications such as bio-sensing and other potential optical applications based on plasmonic characteristic of the gold layer over the SiN substrate. The transmittance tensor is obtained for vertical and horizontal linear polarization and base on boundary condition of the metasurface, the circular polarizations are extracted which are confirmed by the electric field distributions. We have shown by the parametric studies that the phase difference is altered by the gap and slot width and so with the dimension modification, we are able to achieve circular polarizer in the optical range. The biological materials with a thickness of 80 nm have then been placed over the metasurface layer and the figures of merits have been obtained. We have revealed that when the circular polarization is osculated to the metasurface at a special frequency the linear polarization is obtained in the other side of the metasurface. The nano aperture has been modeled and the finite difference time domain calculations are performed in CST Microwave Studio as a commercial full wave simulation software. [ABSTRACT FROM AUTHOR]

In this paper, we report on the direct positioning of small multi-directional radar reflectors, so-called octahedrons, with the synthetic aperture radar (SAR) satellite TerraSAR-X. Its highest resolution imaging mode termed staring spotlight enables the use of such octahedron reflectors with a dimension of only half a meter, but still providing backscatter equivalent to 1-2 cm observation error. Four octahedrons were deployed at Wettzell geodetic observatory, and observed by TerraSAR-X with 12 acquisitions in three different geometries. By applying our least squares stereo SAR algorithm already tested with common trihedral corner reflectors (CRs), and introducing a novel differential extension using one octahedron as reference point, the coordinates of the remaining octahedrons were directly retrieved in the International Terrestrial Reference Frame (ITRF). Contrary to our standard processing, the differential approach does not require external corrections for the atmospheric path delays and the geodynamic displacements, rendering it particularly useful for joint geodetic networks employing SAR and GNSS. In this paper, we present and discuss both methods based on results when applying them to the aforementioned Wettzell data set of the octahedrons. The comparison with the independently determined reference coordinates confirms the positioning accuracy with 2-5 cm for the standard approach, and 2-3 cm for the differential processing. Moreover, we present statistical uncertainty estimates of the observations and the positioning solutions, which are additionally provided by our parameter estimation algorithms. The results also include our 1.5 m CR available at Wettzell, and the outcomes clearly demonstrate the advantage of the multi-directional octahedrons over conventional CRs for global positioning applications with SAR. [ABSTRACT FROM AUTHOR]

In this paper, a new spatially spread electromagnetic vector sensor (SS-EMVS) is proposed by a two-step design. In addition, a novel DOA estimator with coarse-fine estimate combination is presented for the proposed array. The first step aims to make the configurations of SS-EMVS satisfy the 'vector cross-product' estimator, leading to a coarse estimation of three direction-cosines. The second step focuses on extending the two dimensional (2-D) array apertures of SS-EMVS, resulting in two fine but ambiguous estimations on the direction-cosines by extracting inter-sensor phase-delay. Combination the coarse and fine estimations, the high-accuracy 2-D DOA estimation can be obtained by using the coarse estimation to disambiguate the fine estimation. The three- dipoles and loops of the proposed configuration are located separately, which are found to reduce mutual coupling as compared with collocated EMVS. Moreover, the new configuration is able to extend 2-D array aperture to improve the accuracy of 2-D direction-finding. Numerical Simulations are conducted to demonstrate the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Fiber-coupled semiconductor lasers have been studied when pumped by high-power short electrical pulses of 5 ns width and leading front duration below 1 ns. In this pumping regime, it is possible to ensure significant sharpening of output pulses, the duration of which decreases below 80 ps for a single-mode laser and below 120 ps for a broad aperture multimode laser at an output peak optical power as high as 1.5 and 27 W, respectively. [ABSTRACT FROM AUTHOR]

A method for construction of a 2D radio image of an asteroid from the radar data obtained with the use of a continuous monochromatic signal has been tested. The method is based on the inverse focused synthesis of the antenna aperture due to the rotational motion of the object and reconstructive computeraided tomography. On the basis of the analysis of the echo signals from asteroid Golevka, a 2D distribution of its surface radio brightness has been constructed. Reconstruction of the asteroid silhouette confirmed that Golevka has a not very elongated angular body whose maximum diameter is 620 m and the minimum diameter is 460 m. [ABSTRACT FROM AUTHOR]

The Square Kilometre Array (SKA) will be the biggest radio telescope ever built, with unprecedented sensitivity, angular resolution, and survey speed. Collectively, the SKA's antennas are expected to gather exabytes of data per second and store one petabyte of data every day, requiring exa operations per second for the processing. This paper focuses on the SKA1-Low, the SKA's aperture-array instrument consisting of 131,072 antennas that will be built in the first phase of the deployment of the project. In particular, our work explores the design of a custom architecture for the central signal processor (CSP) of the SKA1-Low. The CSP processes digitized samples sent by antennas receiving extra-terrestrial radio-frequency signals between 50 and 350 MHz. We describe the challenges in building the CSP, and present a quantitative study for the implementation of a custom hardware architecture for executing the main CSP algorithms. By taking advantage of emerging 3D-stacked-memory devices and by exploring the design space for a 14-nm implementation, we estimate a power consumption of 9.62 W for processing all channels of a sub-band and an energy efficiency at application level of up to 312 GFLOPS/W for our architecture. [ABSTRACT FROM AUTHOR]