Dipole Elements Research Articles

Compact circularly polarized cross dipole antenna for RFID handheld readers/IoT applications

The radio frequency identification (RFID) and global positioning system (GPS) are employed for indoor and outdoor tracking scenarios. This paper presents an amalgamated identification mechanism for sensing and tracking in an Internet of things (IoT) network. A low-profile, compact, multi-functional antenna configuration is proposed for the amalgamation application. The antenna operates in the 915 MHz (UHF), 2.45 GHz, and 5.8 GHz RFID bands, along with the 1.575 GHz GPS L1 band. The presented antenna is a cross dipole configuration consisting of three pairs of dipole elements printed on both sides of the dielectric substrate. The first and third dipole pairs are larger and smaller metal strips with half-arrow shaped ends that excite the 915 MHz and 5.8 GHz bands, respectively. The second dipole pair is an asymmetric triangular-shaped radiator that excites the 1.575 GHz and 2.45 GHz bands. Using quarter wavelength ring delay lines, circular polarization is obtained in each band. The GPS band, in combination with the RFID bands, improves the efficiency and accuracy of the reader tracking device. The proposed multiband antenna prototype is fabricated on the 45° rotated substrate material, resulting in a compact size of 0.21λ0 × 0.21λ0 × 0.004λ0. The antenna simulation and measurement results are in close agreement.

Investigation of a Miniaturized Four-Element Antenna Integrated with Dipole Elements and Meta-Couplers for 5G Applications.

A miniaturized four-element antenna of 20 mm × 20 mm with edge-to-edge distance of 4.9 mm between the array antennas operating from 4.6–8.6 GHz is investigated in this article. The antenna consists of 4 × integrated dipole driven elements, and complementary split ring resonator (CSRR) metacells are loaded on the both sides of each dipole arms. The loaded meta-couplers magnetically couple to dipole drivers, and the induced resonance effect improves the 10-dB impedance bandwidth (IBW) to 60.6%. To improvise the isolation between antenna elements, metallic vias are implemented that trap electromagnetic (EM)-surface waves to condense into the ground. So, the meta-couplers induce electromagnetic (EM)-propagation as surface wave trapments for radiation and decouple near-field condensed currents, acting as couplers/decouplers. The maximum isolation achieved is >−22.5 dB without any external decoupling network. The diversity parameters indicate good attributes in isotropic, indoor, and outdoor channel environments with an envelope correlation coefficient (ECC) < 0.165 and realized gain of 5.5 dBi with average radiation efficiency of 80–90% in the desired operating bands. An equivalent circuit model using lumped components is designed for the proposed four-element antenna. For validation, a prototype antenna is fabricated and measured to be implemented in 5G applications, which shows good correlation with the full-wave simulated results.

Design of compact multiple‐input and multiple‐output antenna based on slow‐wave corrugated strips

A method of designing two-element compact multiple-input and multiple-output (MIMO) antennas with good isolation based on slow-wave corrugated strips (CSs) is presented in this paper. Using the slow-wave characteristic, a pair of CSs is applied as arms of each dipole antenna element to realise the compact design. A metal plane is placed between the two dielectric boards serving as the reflector so that the antenna can achieve good forward radiation. There are two coupling paths between the closely placed antennas: the coupling between the adjacent antenna arms and the coupling with the reflector. By adjusting the phase constants of the two coupling paths, good isolation is achieved in the operating frequency band without any additional de-coupling structures. A sample of a two-element MIMO antenna is fabricated at the centre frequency of 5.1 GHz with a bandwidth of 330 MHz. Measured results show good performance to support the design method. As each arm is about 1/8λ0 (λ0 is wavelength in free space), the edge-to-edge distance is 0.04λ0, and the isolation in the operating frequency is 15 dB.

Compact dual‐band quasi‐Yagi antenna with pattern diversification for WI‐FI 6E applications

AbstractA dual‐band quasi‐Yagi antenna with diverse radiation patterns at different frequency bands is presented for the Wi‐Fi 6E applications. It has multiple working bands that cover the two existing bands of traditional Wi‐Fi 6, that is, from 2.4–2.4835 to 5.17−5.835 GHz, as well as the upcoming extended Wi‐Fi 6E band that covers the 5.925−7.125 GHz band. The proposed antenna consists of a microstrip (MS) line, a coplanar strip‐line (CPS), a bow‐tie driven dipole element, a slotted ground plane and a parasitic director element. By jointly employing these structures, multiple resonances can be generated, where the resonance with largest current path results in low‐frequency working band, while the others are merged to form a relatively wide high‐frequency band. In the low‐frequency band, the antenna has an omnidirectional radiation pattern with wide beam‐coverage, while in the high‐frequency band, the antenna can achieve directional radiation pattern with high gain value. An antenna prototype is then fabricated and measured for validation. Good agreement between the simulated and measured results is observed. The measured −10 dB impedance fractional bandwidth are 4.3% (2.38−2.484 GHz) and 60.6% (4.47−8.36 GHz) in the low‐ and high‐frequency bands, respectively, associated with peak gain values 0.64 and 6.22 dBi. The antenna's overall size is 0.22 λL × 0.20 λL × 0.006 λL. The proposed antenna is a good candidate for multiple kinds of Wi‐Fi applications.

A portable non-invasive microwave based head imaging system using compact metamaterial loaded 3D unidirectional antenna for stroke detection

A metamaterial (MTM) loaded compact three-dimensional antenna is presented for the portable, low-cost, non-invasive microwave head imaging system. The antenna has two slotted dipole elements with finite arrays of MTM unit cell and a folded parasitic patch that attains directional radiation patterns with 80% of fractional bandwidth. The operating frequency of the antenna is 1.95–4.5 GHz. The optimization of MTM unit cell is performed to increase the operational bandwidth, realized gain, and efficiency of the antenna within the frequency regime. It is also explored to improve radiation efficiency and gain when placed to head proximity. One-dimensional mathematical modelling is analyzed to precisely estimate the power distribution that validates the performance of the proposed antenna. To verify the imaging capability of the proposed system, an array of 9 antennas and a realistic three-dimensional tissue-emulating experimental semi-solid head phantom are fabricated and measured. The backscattered signal is collected from different antenna positions and processed by the updated Iterative Correction of Coherence Factor Delay-Multiply-and-Sum beamforming algorithm to reconstruct the hemorrhage images. The reconstructed images in simulation and experimental environment demonstrate the feasibility of the proposed system as a portable platform to successfully detect and locate the hemorrhages inside the brain.

Design of a high-efficiency thin-type metasurface hologram

To improve the imaging efficiency and reduce profile, a high efficiency, thin-type metasurface hologram based on induced magnetism is proposed. Both types of units consist of two asymmetric electric dipole elements printed on a thin-type dielectric substrate with only 1.3 mm thickness (λ 0/6.4 at 36 GHz). By tuning the magnetic and electric responses, the transmitting phase of the units can be changed. Both types of units are designed to cover the quantized 2π phase range with the transmittance above 90%. Based on holographic theory, the target image field distribution and the incident plane wave can be regarded as object wave and reference wave respectively. A holographic metasurface is designed to record phase information of the target image. The simulation and experiment show that the designed metasurface can reproduce a clear image with a 65.86% imaging efficiency, which provides a new way to realize high-efficiency holographic imaging.

A Broadband Dual-Polarized Magneto-Electric Dipole Antenna Element for Low-Frequency Astronomical Arrays

This paper presents simulation-based design and analysis of a broadband dual-polarized magneto-electric dipole antenna element that can be used to construct VHF astronomical antenna arrays. The antenna consists of two pairs of radiating structures, each fed by a Γ-shaped feeding section. The feeding section and radiating parts are physically disconnected from each other. The antenna is evaluated by simulation, and its −10 dB impedance matching bandwidth ranges from 115 to 340 MHz. The maximum gain of the antenna is about 8 dB over the operating range. Isolation of about 20 dB is observed between the two input ports.

An optimal far field radiation pattern synthesis of mutually coupled antenna arrays

This article presents a precise approach for far-field radiation pattern (FFRP) correction of mutually coupled discrete dipole element (DDE) array of monopole antennas and concentric circular antenna array (CCAA) of dipole elements by employing the parametric assimilation technique (PAT). The effect of mutual coupling is a crucial part of any practical antenna array design issue. Various techniques have been suggested to calculate, compensate and reduce the mutual coupling effect during the last few decades. This article shows an exact method for mutual coupling inclusive corrected radiation pattern synthesis using PAT. The parameters of mutual impedance are calculated and assimilated with the values of the desired radiation pattern. The employed technique is cost-effective, less complex and easy to implement while achieving better performance for mutually coupled DDE array and CCAA synthesis. Grey wolf optimisation (GWO) is a state-of-the-art stochastic algorithm applied here to find the optimal values of the current amplitude excitation weights and the inter-element spacing between each element of the array in the DDE array and three-rings structure CCAA for the desired, uncorrected and corrected FFRP synthesis. Some well-established evolutionary optimisation techniques like particle swarm optimisation (PSO), differential evolution (DE) and social spider algorithm (SSA) are also employed in this article for the sake of comparison with the results achieved by using the GWO algorithm. Finally, the supremacy of GWO algorithm based design is demonstrated and validated by employing the 16-elements DDE array of monopole antennas and the three-ring CCAA of dipole elements.

Design Analysis of Array of Dipole Transmitters for Wireless Power Transfer

Considered in this work are the radiation aspects of a radio-frequency wireless power transfer system. Using the halfwave dipole as a candidate of choice, the current distribution on the antenna is first evaluated and presented using the versatile electromagnetic numerical Method of Moment technique (MoM). Using the current distribution obtained from the kernel of integration, the radiation fields for the single dipole element was obtained. Also, the analysis is extended to uniformly space linear antenna arrays using broadside and ordinary endfire arrays as candidates of interest. The simulation results for the broadside and endfire arrays were presented for 5, 6, 7, 10, 20 and 30 array elements at 0.3, 0.4 and 0.5 inter-element spacing. The peak directivity of broadside array occurs at 30 elements, 0.5λ spacing, and exceeds endfire array peak directivity by 11.27%. In addition to the advantage of an improved directivity achieved by the 7-element broadside array, an improved peak sidelobe level (PSLL) with the lowest PSLL for 7, 20, and 30 elements broadside array occurring at -12.0534 dB, -12.4298 dB, -12.6642 dB, -13.2246 dB, and -13.2747 dB respectively.

Dual-Polarized Filtering Magneto-Electric Dipole Antenna Arrays With High Radiation-Suppression Index for 5G New Radio n258 Operations

In this communication, a dual-polarized filtering magneto-electric dipole (FMED) antenna and arrays are proposed for 5G n258 (24.25–27.5 GHz) operations. The FMED antenna was devised to incorporate filtering mechanisms using a built-in substrate integrated waveguide (SIW)-based filter plus slot-and-notch etching on the dipole element. As such, lower and upper radiation cutoffs and nulls were produced and tuned, independently. To overcome the problem of “high selectivity” of a filtering antenna that has not been correctly quantified and thus has no comparison, a new skirt measure metric named as radiation suppression index is initiated here. Design steps of the FMED element and novel feeding techniques are elaborated, where the SIW-based series-parallel slot-coupled feeders and the slot-coupled differential power divider were conceived for large-size array, to combat with the insertion losses. A prototype of 4 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 4 FMED array was implemented and tested for experimental verification. A high gain of 16.8 dBi ± 1.4 dBi with a 3 dB gain bandwidth of 24–27.7 GHz and a radiation efficiency of 78% were accomplished.

A novel antisymmetric 16-element transceiver dipole antenna array for parallel transmit cardiac MRI in pigs at 7 T.

To improve parallel transmit (pTx) and receive performance for cardiac MRI (cMRI) in pigs at 7 T, a dedicated transmit/receive (Tx/Rx), 16-element antisymmetric dipole antenna array, which combines L-shaped and straight dipoles, was designed, implemented, and evaluated in both cadavers and animals in vivo. Electromagnetic-field simulations were performed with the new 16-element dipole antenna array loaded with a pig thorax-shaped phantom and compared with an eight-element array of straight dipoles. The new dipole array was interfaced to a 7 T scanner in pTx mode (8Tx/16Rx). Imaging performance of the novel array was validated through MRI measurements in a pig phantom, an 85 kg pig cadaver, and two pigs in vivo (74 and 81 kg). Due to the improved decoupling between interleaved L-shaped and straight dipole elements, the 16-element dipole array fits within the same outer dimensions as an eight-element array of straight dipoles. This provides improvement of both transmit and receive characteristics and additional degrees of freedom for shimming. The antisymmetric dipole array demonstrated efficient suppression of destructive interferences in the field, with up to 25% improvement in the homogeneity achieved using static pTx-RFPA shimming in comparison with the hardware-adjusted state, which was optimized for single transmit. High-resolution (0.5 × 0.5 × 4 mm3 ) anatomical images of the heart after cardiac arrest proved good transmit and receive characteristics of the novel array design. Parallel imaging with an acceleration factor up to R= 6 was possible while maintaining a mean g factor of 1.55 within the pig heart. CINE images acquired in vivo in two pigs demonstrated SNR and parallel imaging capabilities similar to those of a reference 8Tx/16Rx dedicated loop array for cMRI in pigs.

Dual‐wideband dual‐polarized rhombic antenna array for base‐station applications

AbstractA compact dual‐wideband dual‐polarized antenna array with a narrow beam and low side‐lobe level for indoor base‐station applications is presented. Four higher‐band dipole elements are inserted inside four lower‐band rhombic‐arranged dipole elements. Dipole elements for each band are excited by two 1‐to‐4 power dividers with equal magnitude and phase. By using this scheme, stable narrow radiation patterns with low side‐lobe levels both in the horizontal and vertical planes are obtained over the dual‐frequency bands. For verification, a dual‐wideband rhombic antenna array with bandwidths of 49.3% (0.64–1.06 GHz) and 52.3% (1.61–2.75 GHz) for VSWR &lt; 1.5 is designed. It has a stable radiation pattern with 3‐dB beamwidths of around 33° and low side‐lobe levels of less than −22 dB both in the horizontal and vertical planes.

Application of a BEM model with dipole elements

A potential flow code is extended to include dipole elements to handle potential flow problems for offshore structures consist of thin shell geometry with both sides exposed to ocean waves. The solution on dipole elements can be represented by the drop of fluid potential across the thin shell surface. By adjusting the porous effect parameter, such a dipole element model can be applied for the solid impervious thin shell structures, porous surfaces and even the imaginary sheets attached to the sharp edges where the local flow dissipation occurs. Special attention is paid on different approaches to evaluate the drift forces on floating bodies with porous surface, including the traditional far field and pressure integration methods as well as the control surface integration approach. The solutions from the BEM model on excitation forces, off-body kinematics and drift forces are verified against the analytical solutions for a concentric porous cylinder system fixed at the seabed. The numerical performance of a two-layer source/sink model with very small gaps is investigated, taking the results from the corresponding dipole element model as the baseline. It is suggested that the mesh size requirement from DNV-RP-C205 is too strict for the two-layer panel model in the case that the exact fluid velocity on both sides of the wall is not needed. The proposed model is demonstrated in two case studies which involve the internal fluid dynamics inside tanks with interior web frame structures of a floating barge for one case and the damping effects from the sharp edge of a box barge model for the other case.

Cylindrical conformal wideband antenna with enhancement of gain using integrated parasitic triangular shaped elements for WiMAX application

PurposeThis paper aims to propose a cylindrical conformal wideband antenna with increased directive behaviour using integrated parasitic triangular-shaped elements for WiMAX application.Design/methodology/approachThe proposed antenna is a wideband directional cylindrical conformal antenna consisting of three fork-shaped dipole elements incorporated with parasitic triangular-shaped reflecting components increases the gain of reference conformal antenna. The novel parasitic elements with triangular shapes are designed on the radiating patch as well as the ground plane side. The parasitic triangular elements enable the antenna to enhance the gain along the end-fire direction.FindingsThe proposed antenna has a 20.2% impedance bandwidth ranging from 3.1 to 3.8 GHz. The half power beam-width (HPBW) of the reference antenna in the H-plane is 122.9° and falls to 99.1° after integrating with parasitic elements at 3.3 GHz, whereas it falls from 56.7° to 54.7° in the E-plane. However, at 3.5 GHz, the reference antenna’s HPBW is at 116.8°, which decreases to 92.4° in the H-plane, whereas it reduces from 57.9 to 53.4° in the E-plane. The proposed antenna has a lower HPBW than reference antennas and achieved a gain enhancement of 1.2 dBi, indicating that the pattern becomes more directed.Originality/valueIn the proposed work, the directive behaviour of cylindrical conformal antenna structure with a 30 mm radius of curvature is improved using parasitic reflective elements. The fabricated antennas’ experimental findings are an excellent contender for wireless point-to-point WiMAX applications because it features a wideband, directional properties, and strong gain over the whole operational frequency range of 3.1–3.8 GHz.

Undulators Consisting of Magnetized Helices

A ferromagnetic helix magnetized axially or radially is apparently the simplest helical undulator. Four helices with alternating magnetization can provide a stronger helical field than a pair of conventional planar Halbach arrays. Such undulators and microundulators seem promising for various powerful high frequency sources. The fields of infinite helices uniformly magnetized in the longitudinal and radial directions are found analytically by integration of contributions from elementary dipoles. The analytical values of the field magnitudes are close to the numerically calculated ones for a helix with a relatively small number of periods five–ten. According to simulation, a magnitude of about 1 T can be obtained on the axis of a system of helices with small inner radii.

Wideband Monostatic Co-Horizontally Polarized Simultaneous Transmit and Receive Antenna Subsystem With Integrated Beamforming Network

A wideband monostatic simultaneous transmit and receive (STAR) antenna subsystem with high isolation and Co-horizontally polarized (Co-HP) omnidirectional radiation is presented. The antenna subsystem consists of a STAR antenna and a beamforming network (BFN). The STAR antenna consists of a planar circular array having four printed dipole elements surrounded by two groups of parasitic strips. The parasitic strips are used to improve the impedance bandwidth (IMBW) and reduce the gain variation in transmit (TX) and receive (RX) modes. To achieve high isolation, the four ports of the STAR antenna are excited with two orthogonal phase modes for TX and RX using the BFN. The BFN is a six-port network consisting of two 180&#x00B0; hybrid couplers, one 90&#x00B0; hybrid coupler, and a Wilkinson power divider. The 180&#x00B0; hybrid coupler is elaborately designed with low imbalances since it is most key to achieve high TX/RX isolation. Measured results show that the proposed STAR subsystem achieves a TX/RX overlapping IMBW of 4.71&#x2013;6.2 GHz, and a 40 dB TX/RX isolation bandwidth of 4.81&#x2013;5.88 GHz, while maintaining horizontally polarized omnidirectional radiation patterns for TX and RX over the entire operating frequency band.

DOA Estimation of Linear Dipole Array With Known Mutual Coupling Based on ESPRIT and MUSIC

AbstractIn this paper, multiple signal classification and estimation of signal parameters via rotational invariance technique (ESPRIT) algorithms are proposed to estimate the direction of arrival (DOA) of multiple incident signals under known mutual coupling among elements of the antenna array. These algorithms use the same subspace based techniques to achieve the separation of the eigenvectors into two subspaces: the signal space and the noise space. However, ESPRIT only uses the signal space. The performance of subspace based DOA estimation algorithm is evaluated using uniform linear arrays of dipole elements. The simulation results show the exact number of samples and elements, signal‐to‐noise ratio and spacing between the antennas elements used are the most important parameters in the algorithms, to sustain the accuracy of the DOA of the incident signals. The problem of calculating mutual coupling coefficient of the array elements is formed into a matrix has been considered. It is shown from the simulation results that the performance of the DOA estimation techniques considering the mutual coupling effect can be improved by the proposed compensation method. The different results obtained are in good agreement with those of the literature.

A Polarization and Beam Steering Reconfigurable Cavity-Backed Magneto-Electric Dipole Antenna Array Using Reflection-Type Phase Shifter

This article introduces a reconfigurable cavity-backed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\,\,\times4$ </tex-math></inline-formula> magneto-electric (ME) dipole antenna array with agile polarization and steerable beam features for both linear and circular polarizations (CPs). The proposed ME dipole element backed by a cavity can reduce the mutual coupling and enhance the scanning performance of the antenna array. To achieve continuous beam-scanning ability, reflection-type phase shifters are designed with varactor diodes and integrated with the feeding network. The polarization agility is determined by embedding two switchable cross strips into the ME dipole element. By manipulating the states of the two switchable cross strips through dc bias controls, three different polarization states including linear polarization (LP), left-hand CP (LHCP), and right-hand CP (RHCP) can be realized. For verification, a prototype of the antenna array was fabricated and measured. A good agreement between the simulation and the measurement is obtained, thus validating the multiple reconfigurable capability of the antenna array in polarization and radiation pattern. The measured results demonstrate that the beam can be scanned continuously in a range between ±40° for the three polarization states. Meanwhile, the measured overlapped bandwidth for the reflection coefficient ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert \text{S}_{11}\vert \le -10$ </tex-math></inline-formula> dB) and the 3 dB axial ratio (AR) is from 2.0 to 2.4 GHz for all states.

Co- and Cross-Polarization Decoupling Structure With Polarization Rotation Property Between Linearly Polarized Dipole Antennas With Application to Decoupling of Circularly Polarized Antennas

A decoupling structure with polarization rotation (DSPR) property is proposed to reduce the mutual coupling between co- or cross-polarized antennas. The proposed DSPR generates a neutralization wave with two orthogonally polarized components that can be controlled to cancel the original mutual coupling. The DSPR is placed above the arrays with orthogonal and parallel dipole elements. After applying the DSPR, the mutual coupling at the center frequency of 3.5 GHz is reduced to −40 dB for both arrays, and the overall mutual coupling is better than −26 dB within the band of 3.3–3.7 GHz, and the reflection coefficients remain below −12 dB. The antennas maintain stable radiation patterns within the operation bandwidth with a 0.5 dB increase of the realized gain. Since the DSPR can effectively reduce both co- and cross-polarization coupling, the mutual coupling between circularly polarized antennas in a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1 \times 4$ </tex-math></inline-formula> array is reduced to below −35 dB thanks to the DSPR. Finally, a prototype of the antenna array with orthogonal dipole elements loaded with the DSPR is fabricated and measured. The measured results are in excellent agreement with the simulated ones, demonstrating the effectiveness of the proposed DSPR for isolation enhancement between cross-polarized antennas.

Wideband Gain Enhancement of High-Isolation and Quasi-Omnidirectional Metamaterial MIMO Antenna for Vehicular Radar

In this paper, a gain-enhanced wideband multiple-input-multiple-output (MIMO) antenna with high isolation and quasi-omnidirectional radiation is proposed. It is a hexagonal structure and includes six identical end-fire log-periodic dipole antenna (LPDA) elements. These antenna elements are distributed in the same plane and uniformly placed in a rotating arrangement with an angle difference of 60°, and then are suspended over a large metallic plate (LMP). To enhance the wideband gain, different metasurface (MS) lens with high refractive index is deployed around the end-fire log-periodic dipole. The uniform MS lens makes electromagnetic waves deflect toward the array axis of the LPDA, whereas the gradient MS lens could form focused plane electromagnetic waves in the end-fire direction. Furthermore, these antenna elements are isolated with a complementary split ring resonator (CSRR)-based electromagnetic band-gap (EBG) structure owing to its wide bandstop frequency and small-size characteristics. To validate the design concept, the prototype is fabricated and measured. The measured -10-dB impedance bandwidth covers 2.85-10.9 GHz (FBW 117.1%) and the gain varies from 10.37 to 14.82 dBi. Moreover, high isolation of better than 22.4 dB and low envelope correlation coefficient (ECC) of less than -62.3 dB are achieved between antenna elements. The proposed wideband MIMO antenna could be suitable for vehicular radar.