Dipole Arms Research Articles

Polarization-Independent Reconfigurable Graphene Gas Sensor Using Crescent Plasmonic Antenna

A polarization-independent gas sensor based on crescent plasmonic dipole antenna loaded with graphene monolayer is introduced in this paper for environment monitoring applications. Single, dual, and four arms crescent dipoles are designed, analyzed and investigated. The proposed gas sensor has reconfigurable absorption characteristics in the wavelength range from 900 to 1600 nm which covers the different gases responses. A parametric study on the effect of the sensor dimensions and polarization of the illuminated waves on the total absorption of different gases is investigated. A graphene monolayer is used to enhance the gas molecule absorption in its unbiased state. An enhancement of the total absorption cross section (ACS) values for n = 1.4 is 1.028 × 105 nm2 for the unloaded sensor case and is 1.77 × 105 for the graphene loaded sensor case. The unloaded graphene sensor sensitivity is 630 nm/RIU, and for the graphene loaded case is 677.5 nm/RIU. Dual-polarized crescent dipole consists of two orthogonal arms is designed to maintain the same sensitivity for x- and y-polarized E-field illumination. A polarization independent gas sensor consists of four crescents dipole arms rotated with 45° is explained. An enhancement of gas absorption is achieved by using a sensor array of four-arm dipole sensor. Different array sizes loaded with graphene monolayer are investigated. The total ACS peak value is 7.84 × 106 nm2 for 6 × 6 dipole array is obtained.

Compact printed log-periodic dipole antenna (LPDA) with T-shaped arm for wide band applications

Compactness of printed log-periodic dipole antenna (LPDA) is an essential requirement in developing low-weight communication system. With this aim, in the present work, we utilized two-step approach to reduce size of this kind of antenna. First, to achieve compactness, a maximum apex angle was taken for the desired gain of 6 dBi, which reduces the boom length to minimum possible value. Secondly, after fully optimizing the width and length of each dipole, a T-shaped arm is introduced in place of straight dipole arms. For comparison, initially printed LPDA is designed with full arm structure of gain 6.5 dBi in 1.5 to 3.5 GHz band using CST Microwave Studio. In T-shaped arm LPDA, the antenna size eventually reduces by 82% compared to full arm structure, which offers a bore sight gain level varies from 2 to 4.5 dBi in the frequency band of 1.8 to 3.5 GHz. Simulation analysis are discussed in detail along-with a size comparison of various printed LPDAs. The measured results of the fabricated LPDA with T-shaped arm are found to closely match with the simulation results.

Compact Folded Crossed-Dipole for On-Metal Polarization Diversity UHF Tag

For the first time, the folded crossed-dipole structure is explored for designing a compact metal tag (40 mm $\times $ 40 mm $\times $ 1.6 mm) that can be read in all boresight directions. The tag structure consists of a pair of folded crossed-dipoles which are orthogonally displaced for achieving polarization diversity, where the angular reading range has been extended by removing the null points. In the design, a parasitic metal ring is loaded beneath the radiator for tuning down the tag resonant frequency effectively. Good impedance matching with high power transmission is achievable by employing additional tuning mechanisms such as slotting the radiating dipole arms and adding rectangular patches beneath the slots. Design schemes for optimizing the impedance matching between the antenna and the chip have also been thoroughly discussed. Conjugate impedance match is found to be easily achievable by tuning the design parameters. To understand the impedance characteristics, an equivalent circuit has been derived for the proposed tag antenna. When tested using a linearly polarized reader antenna with a transmitting power of 4 W EIRP, the tag antenna is detectable from 5.6 m to 7.7 m in the boresight and it can be read in all directions.

Dislocation dipole in graphene at finite temperatures

In the present work, the evolution of defect structure of graphene with dislocation dipole of three types in thermal equilibrium is studied by molecular dynamics simulations. The presence of defects can considerably reduce the temperature at which graphene remains stable in thermal equilibrium. It is found, that at elevated temperatures, there is a movement of dislocations in a dipole with arm equal to 7 Å, so that a new dipole with the arm 3 Åis formed with the further transformation to the Stone-Wales defect. This reveals that dipole arm is less than annihilation distance for dislocation dipole. Again, the Stone–Wales defect at elevated temperatures disappears as a result of the rotation of the C–C bond. The obtained results will allow describing the dynamics of defects in graphene in thermal equilibrium, which can be helpful to analytically describe dislocation dynamics in graphene.

Common-Aperture Sub-6 GHz and Millimeter-Wave 5G Antenna System

The realization of a common-aperture (or shared-aperture) 5G antenna system is proposed for compact and integrated wireless devices. As a combination of a dipole and tapered slots, an integrated antenna design, which operates at multi-bands, i.e. sub-6 GHz at 3.6 GHz and mm-wave at 28 GHz, is validated. The antenna design procedure starts with a dipole operating at 3.6 GHz, which is fed by a modified balun consisting of a tapered slot and a microstrip line. Here, the tapered slot has a dual feature, i.e., it is used to excite the dipole at 3.6 GHz and works as a tapered slot antenna at 28 GHz. Only a single feeder is optimized and used for both structures making the design unique and provides an extremely large frequency ratio. Moreover, the dipole's arms are utilized as an antenna footprint for two tapered slot mm-wave arrays, making the dipole dual-functional. The tapered slot antenna and the mm-wave arrays are optimized in a way that the main beams point at different directions. By this configuration, the design is able to cover an angle of 120° of space in θ-direction. As a proof of concept, a prototype is fabricated on Rogers RO-5880 with an overall size of 75 × 25 × 0.254 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . The simulated and measured results confirm the validity of the proposed concept.

Broadband printed MIMO dipole antenna for 2.4 GHz WLAN applications

Broadband printed dipole antenna with elliptical-arms and integrated balun for multiple-input-multiple-output (MIMO) antennas at 2.4 GHz frequency is designed and presented. The MIMO structure is composed of four symmetrical dipole elements and a circular ground plane. To enhance the isolation between contiguous elements, they are placed in a perpendicular direction. Isolation of parallel dipoles with identical polarization is guaranteed by a suitable distance. Outstanding impedance matching, good isolation, high-gain, and stable directional radiation pattern are advantages of this design. Structural simplicity is achieved by printing dipole arms, balun structure, and the ground plane on FR4 substrates. The proposed MIMO antenna is manufactured and tested in the anechoic chamber. The empirical results have a proper discrepancy with the simulation outcomes.

Dual-Polarized Multi-Resonance Antennas With Broad Bandwidths and Compact Sizes for Base Station Applications

In this paper, a novel design method for dual-polarized multi-resonance antennas is presented for base station applications. The radiator of the antenna is configured as cross-dipoles with four thin metal strips connected to the adjacent dipole arms. The attached strips create multiple current paths and introduce additional resonant points. As a result, the bandwidth of the antennas is broadened while maintaining a very compact size. Based on this working mechanism, two multi-resonance antennas are designed, fabricated, and tested. The antennas achieve bandwidths of 46.7% and 66.7% respectively, with excellent matching capabilities. The antennas also exhibit high port isolation levels and stable radiation performances. The promising wideband performances with compact physical sizes make the antennas highly suitable for the base station applications.

Broadband Filtering Magnetoelectronic Dipole Antenna With Quasi-Elliptic Gain Response

A filtering magnetoelectronic dipole antenna (MEDA) with quasi-elliptic gain response and wide operating band is investigated. Different from the conventional MEDA, the antenna studied here is fed by fork-shaped microstrip line aperture-coupled excitation. The intrinsic radiation null of the MEDA at the lower passband edge is utilized, and a mathematical model is first put forward to demonstrate its working mechanism. Four driven stubs connected to the shorted walls of MEDA are used to excite the planar dipole arms. The parasitic inductor and the coupling capacitor introduced by driven stubs form an equivalent low-pass filter network, leading to a radiation null at higher frequency. Furthermore, a third radiation null is generated by introducing two quarter-wavelength U-shaped shorted stubs to improve the out-of-band suppression. Besides, due to the introduction of multiple coupling structure, including the fork-shaped microstrip line coupling slot and driven stubs, a wide operating band can be realized while maintaining a low profile of 0.15 wavelength. The experimental results show that an impedance bandwidth of 53.5% (2.95-5.1 GHz) is achieved and an out-of-band suppression level higher than 17.9 dB is obtained. What is more, an average gain of 8 dBi and good radiation patterns are realized over the whole operating band.

Ultra‐high‐frequency wideband circularly polarized crossed‐dipole antenna with wide axial‐ratio beamwidths for SATCOM applications

AbstractIn this study, an ultra‐high‐frequency (UHF) wideband circularly polarized (CP) crossed‐dipole antenna with wide axial‐ratio beamwidth (ARBW) is proposed for SATCOM applications. The antenna is composed of two pairs of dipoles with umbrella‐shaped arms, and they are fed by a feeding network to generate CP radiation. Two pairs of parasitic patches are introduced symmetrically between the dipole arms and the ground plane. Due to coupling of the dipoles, currents can be induced on to the metal patches, which can not only decrease the antenna volume by increasing the current path of the dipole arms, but also additional radiation can be provided to enhance the ARBW. A prototype of proposed antenna was fabricated and measured. The measured results indicate that it operates at the UHF band ranging from 280 to 420 MHz, with a –10‐dB impedance bandwidth of 40.5% and a 3‐dB AR bandwidth of 42%. Furthermore, the antenna exhibits a 3‐dB ARBW of more than 190°within a wide operating band of 23.1%.

Ultrawideband circularly polarized antenna with dual band‐notched characteristics

This article presents an ultrawideband (UWB) crossed dipole antenna with circularly polarized (CP) and dual band-notched characteristics. The proposed design is based on two orthogonal tapered dipoles for UWB CP operation and a square-shaped cavity for high broadside gain over the entire operating bandwidth (BW). To generate dual band-notched characteristics, two separated slots are inserted into each dipole's arm. This antenna yields measured impedance BW of 100% (3.2-9.6 GHz) with dual-band rejection centered at 5.2 and 5.8 GHz. Correspondingly, dual rejected bands are also observed in the original UWB CP band, which ranges from 3.2 to 8.2 GHz. Additionally, the proposed antenna exhibits high broadside gains better than 6.2 dBic and radiation efficiency greater than 82%.

FREQUENCY-TUNABLE DUAL-BAND PRINTED ANTENNA EQUIPPED WITH COAXIALSPLIT BALANCING UNIT

In this paper, we present initial design of dual-band dipole antenna which able to perform when shifting high frequency band by inserting of inductive element between high-, and low-frequency dipole arms. Responses of high frequency and bandwidth at –10 dB level on the inductivity are presented in the paper. The maximum value of inductivity to be inserted is about hundreds of nH, hence, it can be implemented by microstrip lines. It is also possible to use lumped elements. Approximations of such responses with polynomials power two and lower are presented in the paper. It is shown, that the bandwidth of the S11 below –10 dB high frequency response has approximately linear behavior, so that can be used when carrying out experimental verifying of the numerical simulations. When simulating radiation characteristics the Russian standard FAF‑4D substrate was used, which can operate at frequencies up to 8–10 GHz.

Reconfigurable graphene-based V-shaped dipole antenna: From quasi-isotropic to directional radiation pattern

In this paper, a compact reconfigurable V-shaped dipole antenna in THz frequency with two parasitic elements on the substrate of SiO2 is presented. The antenna is designed in the center frequency of 0.95 THz. Designs have been improved based on two modes of antenna radiation pattern: quasi-isotropic and directional pattern. For providing a quasi-isotropic radiation pattern, by making V-form of the dipole, the radiation pattern nulls in the lateral of the antenna is reduced as much as possible although two antenna parasitic elements also affect the antenna radiation pattern. In another mode, only by changing of graphene chemical potential, designing of the directive antenna with the same structure is proposed. In the first mode, physical structure and the angle between dipole arms are more determinative, while in the second mode size and positions of parasitic elements, as well as other mentioned parameters, are effective. In the first mode, quasi-isotropic radiation pattern antenna with changing of antenna gain below than 8 dB, and in the second mode a directional antenna with 5.3 dB maximum gain, and 6 dB F/B ratio is proposed.

Design of Dual-Mode Arc-Shaped Dipole Arrays for Indoor Base-Station Applications

In this letter, two novel designs of dual-mode beam-steerable antenna arrays using arc-shaped dipoles are proposed for indoor base-station applications. To obtain the optimal distribution of excitations for each array, its gain and front-to-back ratio are optimized by using the method of maximum power transmission efficiency. The first design operates at 2.45 GHz and consists of a circular ring reflector and four arc-shaped dipoles, with the electrical length of one dipole arm being 1/4 wavelength. It can switch between omnidirectional mode and directional mode, and has 360° beam scanning capability in azimuth when operating in the directional mode. The realized omnidirectional gain of the first design is 1.5 dBi, and its peak gain and front-to-back ratio in the directional mode are 7.4 dBi and 15.5 dB, respectively. The second design also operates at 2.45 GHz, composed of two circular ring reflectors and eight arc-shaped dipoles distributed in two substrates, separated by a foam layer. Compared with the first design, it has a higher omnidirectional gain of 2.9 dBi and more uniform gain distribution in azimuth in the directional mode, with a peak gain of 8.4 dBi and a front-to-back ratio of 12.5 dB.

Energy Harvesting Enhancement of Nanoantenna Coupled to Gemometric Diode Using Terhertz Transmitarray

This paper introduces the use of rhombus shaped dipole nanoantenna coupled to geometric diode in energy harvesting at 19.4 THz. An arc-shaped geometric diode is placed in the gap between the dipole arms. The diode I–V characteristics are investigated using the Monte Carlo simulation. Two approaches for enhancing the received voltage of nanoantenna energy harvesting at 19.4 THz are investigated. In the first approach, a terahertz transparent transmitarray is used to focus the electromagnetic waves on the surface of the nanoantenna coupled to the geometric diode. The received voltage is increased from 16.5 μV for single nanoantenna to 97.6 μV for the transmitarray coupled to the nanoantenna. In the second approach, Yagi nanoantenna arrangements are used to enhance the directivity of the single element and is coupled to the transmitarray.

Enhanced Bandwidth and Directivity of a Dual-Mode Compressed High-Order Mode Stub-Loaded Dipole Using Characteristic Mode Analysis

A dual-mode compressed dipole resonating at high-order modes is proposed to enhance bandwidth and directivity by loading the two dipole arms with two stubs. Characteristic mode analysis shows that with by introducing the loading stubs, the fifth-order mode of the proposed dipole shifts close to its third-order mode for achieving a wideband operation with enhanced gain. A prototype is designed to validate the principle and design approach experimentally. These measurements show that the gain of the proposed compressed dipole is 4 dBi, higher than that of a conventional dipole over the desired operating band of 3.3–3.6 GHz for the coming 5G applications.

A Dipole Sub-Array With Reduced Mutual Coupling for Large Antenna Array Applications

The use of large array antennas in multiple-input multiple-output (MIMO) exploits diversity and reduces the overall transmission power making it a key enabling technology for 5G. Despite all the benefits, mutual coupling (MC) between elements in these array antennas is a concerning issue as it affects the antenna terminal impedance, reflection coefficients, etc. In this paper, a four-element printed dipole sub-array with reduced MC for S-band has been proposed. A balanced transmission line structure has been designed with two dipole arms on the opposite side of the substrate. Simulated and measured results are in good agreement making the design suitable for large array applications such as phased array radars. The proposed array exhibits good impedance matching with a reflection coefficient of -45 dB and resonating at the center frequency of 2.8 GHz. Moreover, isolation of -20 dB has been achieved for each element in a 2×2 planar array structure using out of band, parasitic elements, and planar shift by distributing the separation between the elements.

3-D-Printed Compact Wideband Magnetoelectric Dipoles With Circular Polarization

A three-dimensional (3-D)-printed compact unidirectional wideband antenna, based on two crossed magnetoelectric dipoles, is proposed in this letter. The antenna consists in folding the electrical dipole elements; thus, the surface of the radiation element is reduced to 0.23 λ 0 × 0.23 λ 0, where λ 0 is the wavelength at the lowest operation frequency for a standing-wave ratio (SWR) <2.5, corresponding to a reduction factor of 48%. Despite a complex 3-D structure, each dipole arm is prototyped using 3-D printing technology. The excellent agreement between measured and simulated results (impedance and radiation) demonstrates the quality of such realization process for low-cost prototyping of such antenna structure. In dual-polarization mode, the measured input impedance bandwidth is 57% from 1.67 to 2.94 GHz with an SWR <2.5. Circular-polarization mode is obtained by connecting a 90° hybrid coupler circuit. Axial ratio is lower than 3 dB in measured and simulated results from 1.5 to 3 GHz.

Folded Antipodal Dipole for Metal-Mountable UHF Tag Design

A compact folded dipole antenna that consists of two C-shaped arms, which are placed in the antipodal constellation, is proposed for designing a metal-mountable miniature tag antenna in the UHF band. Here, each of the dipole arms is composed of four unequal line segments for reducing the current crowding effect and for improving the tag’s performance. Two inductive shorting stubs are introduced for tuning the tag’s resonant frequency. The proposed tag antenna is made using a flexible substrate and it is electrically small, having a circuit size of 50 mm $\times30$ mm $\times1.6$ mm ( $0.153\lambda \times 0.092\lambda \times 0.005\lambda$ ). It has been found that conjugate match can be easily obtained by adjusting the dimensions of the C-shaped arms and the inductive shorting stubs. When mounted on metal, the proposed tag antenna is able to achieve a maximum read distance of 9.1 m at the equivalent isotropic radiated power of 4 W. The proposed tag antenna is found to be platform insensitive and it can read beyond 7 m when placed on dielectric objects.

A frequency reconfigurable dipole antenna with solid-state plasma in silicon

A frequency reconfigurable dipole antenna based on a silicon radiator is presented. The silicon radiator is activated with the aid of highly dense solid-state plasma by injecting carriers into the intrinsic region of p-i-n diodes. The fabrication and design guideline of the reconfigurable dipole antenna with this plasma radiator are described. When the plasma radiator is activated or deactivated, the length of the dipole arm changes, which means that the operating frequency of the dipole antenna is reconfigurable. When all the channels in the plasma radiator are activated, the operating frequency is tuned from 6.3 GHz to 4.9 GHz. The measured tunable bandwidth of our fabricated dipole antenna is approximately 31%, which is a practical value in comparison to conventional frequency reconfigurable antennas whose tunable bandwidth is in a range from 20% to 50%. To further support the validity of our results, we provide the well-matched simulation results from an antenna simulation. These results demonstrate that silicon with its commercial technology, which has not attracted attention in comparison to a metal antennas, is a promising tunable material for a frequency reconfigurable antenna. This plasma-based reconfigurable antenna has great potential for use in the dynamic communication environment.

A Wideband Dual-Polarized Dipole Antenna With Folded Metallic Plates

A wideband dual-polarized dipole antenna with fourfolded metallic plates is proposed in this letter. The folded metallic plates are vertically placed on the ground plane, under the dipole arms. Owing to the coupling with the nearby dipoles, an additional resonance beside the original impedance passband of the dipole antenna can be generated by the parasitic plates, leading to a very wide operating bandwidth. A prototype was fabricated and tested to verify the design. The measured results show that the prototype has a −10 dB impedance bandwidth of about 92%, a port isolation of over 20 dB, and an average gain of 6.2 dBi within the operating band.