Annular Ring Slot Research Articles

A Low-Profile Wideband Circularly Polarized Metasurface Antenna Based on Characteristic Mode Theory

A novel low-profile wideband circularly polarized metasurface (MTS) antenna is proposed. The characteristic mode analysis is used to investigate the operating mechanism of the MTS antenna. Then, the desired modes are chosen and excited by the annular ring slot combined with an L-shaped microstrip line. Simulation studies revealed that this type of feeding structure effectively excites the desired modes to accomplish wideband circular polarization and high-gain radiation. Experimental results show that the antenna has both the wide impedance bandwidth (IBW) and axial ratio bandwidth (ARBW), with a maximum radiation gain of 9.3 dBi and a −10 dB relative IBW and 3 dB relative ARBW of 39.8% and 30%, respectively.

Pentaband Dual-Polarized Antenna for Multiservice Wireless Applications

This paper presents a novel design for and an experimental study of a dual-polarized quad-port MIMO antenna. The design achieves resonance at five distinct frequency bands with reduced mutual coupling. The design includes a single annular ring slot, four truncated rectangular corners, and a truncated aperture to improve resonance behavior. The design is then extended to a four-port MIMO antenna by including a ground-plane slit to enhance isolation between antenna elements at the center resonance band. The antenna achieves resonances at 5 distinct bands, ranging from 1.5 to 8.4 GHz, with significant mutual coupling reductions. The resonances of the quad-port pentaband MIMO antenna are achieved at 1.55 GHz (1.5–1.65 GHz), 2.5 GHz (2.4–2.7 GHz), 5.2 GHz (5–5.85), 7.3 GHz (7.1–7.4), and 8.15 GHz (7.9–8.4), with respective mutual coupling reductions of 27 dB, 37 dB, 21 dB, 29 dB, and 21 dB. Additionally, the 3 dB axial ratio bandwidth (ARBW) is observed at 6.5% (1.5–1.6 GHz) and 15% (2.4–2.7 GHz) in 2 distinct bands, and the envelope correlation coefficient and diversity gain are calculated within the specified band range. Experimental measurements of the prototype for the quad-port antenna are conducted, with excellent agreement found between the results and the simulations.

A Polarization and Frequency Reconfigurable Microstrip Antenna for Vehicular Communication System Application

To face a complex wireless communication scenario, a flexible and tunable multi-functional antenna system should be employed to guarantee system quality. This paper presents a polarization and frequency reconfigurable microstrip patch antenna with a wide 3-dB axial ratio beam-width for vehicle communication systems. By controlling the p-i-n diodes, the proposed design can achieve four operating states: linear polarization (LP) in lower frequency bands between 1.45 and 1.47 GHz, and LP, left-hand circular polarization (LHCP), and right-hand circular polarization (RHCP) in higher frequency bands between 1.50 and 1.53 GHz. The proposed antenna has an exceptionally low profile (0.02 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda _{0}$</tex-math></inline-formula> at 1.5 GHz) and a simple structure, consisting of a single-layer square patch with two annular ring slots and four switches placed at appropriate locations in the slots. P-i-n diodes, as the switchs, change the current distribution on the radiating patch to achieve the antenna's polarization and frequency reconfigurability. The proposed antenna was fabricated and tested, and the observed results are identical to those predicted by the simulation. The antenna has outstanding reconfigurable capabilities independent of frequency or polarization in the operational frequency range. Therefore, it can be well used for vehicular communication systems because of its multi-reconfigurability and stable mechanical property.

Wideband mm-Wave Hemispherical Dielectric Resonator Antenna with Simple Alignment and Assembly Procedures

A wideband hemispherical dielectric resonator antenna (DRA) with enhanced gain is proposed for a frequency band of 20 to 28 GHz. The precise alignment and assembly of the DRA represent key challenges at such frequencies that were addressed using three approaches: the first was based on outlining the DRA position on the ground plane, the second involved creating a groove in the compound ground plane in which the DRA is placed, and the third was based on the 3D-printing of the DRA on a perforated substrate. In all cases, the same DRA was utilized and excited in a higher-order mode using an annular ring slot. The high gain was achieved by exciting a higher-order mode, and the wideband was obtained by merging the bandwidths of the two excited modes. The alignment methods used expedite the DRA prototyping by saving substantial time that is usually spent in adjusting the DRA position with respect to the feeding slot. The proposed configurations were measured, with an impedance bandwidth of 33.33% and a maximum gain of 10 dBi observed. Close agreement was achieved between the measured and simulated results.

Axial ratio tuned disk‐shapedS‐bandtriple notch circularly polarized slot antenna

Microstrip-line fed annular ring circularly polarized antenna is proposed in this work. The antenna is fabricated on a disk-shaped FR-4 substrate with annular ring slots etched in the ground. The overall space requirement of the antenna is 25 × 25 × 1.6 mm3. The antenna is modeled for triple notch wide band circular polarization operation in the frequency range from 2–4 GHz. A wide impedance band operation is be obtained by the introduction of slots and stubs. An impedance band- width of 1.8 GHz is accomplished with three notches at 2.4, 2.8, and 3.3 GHz.

A Low-Profile Broadband Circularly Polarized Metasurface Antenna Aperture Coupled by Shorted Annular-Ring Slot

A low-profile (LP) metasurface antenna is proposed for broadband circularly polarized (CP) operations. The metasurface radiator, formed by a 5 × 5 array of square patches, has a microstrip line fed at its bottom through a shorted annular-ring slot centered on the ground plane. First, the characteristic mode analysis (CMA) methodology is employed to examine the intrinsic modes of the metasurface. Subsequently, a pair of mutually orthogonal modes is selected and excited by the feeding structure with a 90° phase difference to produce CP radiation. For the purpose of verification, a prototype antenna is developed, and the obtained data reveal that the antenna exhibits an impedance bandwidth of 43.9% ranging from 4.8 to 7.5 GHz (S11&lt;−10 dB). The 3-dB axial ratio bandwidth is 22.2% in the range of 5.6–7 GHz, among which a satisfactory left-handed CP radiation is achieved, and the maximum gain in the broadside direction reaches 9.3 dBic at 6.9 GHz.

Single-Layer, Dual-Port, and Dual-Mode Antenna With High Isolation for WBAN Communications

In this letter, a single-layer, dual-port, and dual-mode antenna with high isolation between the ports is suggested. This antenna consists of a short-circuited ring patch antenna that surrounds a substrate integrated waveguide (SIW)-based circular cavity in the center. An annular-ring slot is etched on the upper surface of the circular cavity and constitutes a cavity-backed annular ring slot antenna. Dimensions of the antenna are chosen in a way that TM₂₁ mode and TM₁₁ mode are placed at the frequency of 5.8 GHz for the short-circuited ring patch antenna and SIW cavity-backed antenna, respectively; the former has an omnidirectional radiation pattern and the latter has a broadside radiation pattern. Due to having two rows of vias, one for the short-circuited ring patch antenna and the other for SIW cavity-backed antenna, the isolation between the two ports is excellent owing to reduced surface waves. The measurement results of a fabricated prototype are properly consistent with the simulation results. This antenna is an appropriate option to be used in wireless body area networks for having simple structure, dual-mode, single-frequency, and high isolation.

Design of compact microstrip-fed triple-band slot antenna with defected ground structure for wireless communications

This article presents the design of a compact microstrip-fed triple-band slot antenna for WLAN/WiMAX/C-band downlink satellite communications. The newly designed proposed simple structure has a considerably high-center frequency ratio and can significantly suppress cross-polarization levels. This antenna consists of a double annular-ring slot (DARS), two L- and one I-shaped slot on the radiator, and an ellipse-shaped-slit (ESS) based defective ground structure (DGS) is imposed. Furthermore, to achieve a better impedance bandwidth and impedance matching, an insert-fed has been implemented on the proposed structure. The proposed antenna has the advantages of the easy tuned of individual resonant frequency and relatively simple antenna structure. The fabricated prototype resonates at 11.13% (2.257–2.523 GHz), 5.63% (3.455–3.655 GHz) and 6.05% (4.012–4.262 GHz) and gives a gain of 4.05, 2.52 and 2.15 dBi, respectively, and cross-polarization nearly −38.85 dB. The transmission line model of the proposed antenna is presented, and it shows the antenna behavior based on the effect of each element. It is observed that the characteristics of the RLC circuit model result is close to the simulated results using the CST simulator.

Space Efficient Meta-Grid Lines for Mutual Coupling Reduction in Two-Port Planar Monopole and DRA Array

Traditionally used mutual coupling (MC) reduction techniques such as electromagnetic bandgap structures, isolators and neutralization lines require extra space between radiators. Besides, metamaterial-based techniques require multi-layer arrangements. However, the proposed meta-grid lines overcomes the above demerits by integrating meta-grid lines in the ground plane itself. As a proof-of-concept, two-port CPW-fed monopole antenna array (TPCFMAA) and two-port DRA array (TPDRAA) are designed, fabricated and tested. It has been observed that the TPCFMAA has mutual coupling below −20 dB for frequency between 2.6 to 4.4 GHz. The envelope correlation coefficient reduces from 0.072 to 0.026 by integrating meta-grid lines in the ground plane of the TPCFMAA. At 3.5 GHz, the inter-element distance between the antennas is noted to be <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${0.015}\lambda _{\mathrm {h}}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{\mathrm {h}}\,\,=$ </tex-math></inline-formula> highest operating wavelength). The TPDRAA’s operating frequency can be tuned by changing the parameters of the annular ring slot in the excitation patch. The bandwidth of TPDRAA can be further increased by merging the two resonances of the two annular ring slots in the excitation patch. For TPDRAA, the measured −10 dB impedance bandwidth is from 5.65 to 6.55 GHz. The mutual coupling between the antenna elements is seen to be below −16 dB for an inter-element spacing of 4.8 mm, which is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.090\lambda _{\mathrm {h}}$ </tex-math></inline-formula> . The measured gain of TPDRAA within the bandwidth is from 4.17 dBi to 5.2 dBi. The TPCFMAA can be used in 3.5 GHz Internet of Vehicles (IoV) multi-user MIMO service, whereas the TPDRAA can be used for satellite communication in the 5.925 to 6.425 GHz frequency band, WiMAX in the 5.7 to 5.85 GHz band, ISM in the 5.725 to 5.85 GHz band, and WLAN in the 5.8 GHz band.

Orthogonally polarized meandered fed multiple input multiple output antenna array for C‐band sub‐6GHz 5G and unlicensed Wi‐Fi smart‐phone applications

An eight-element meandered fed concentric annular ring slot resonator MIMO (multiple input multiple output) antenna array with dual-band operation is presented for sub-6 GHz 5G and unlicensed C-band Wi-Fi applications. The annular slot radiators are fed by meandered elements designed for operation at 3.15–3.9 and 6.27–6.6 GHz frequency bandwidth with enhanced isolation of more than 20 and 15 dB in the respective bands. The resonator rings are placed on the four corners of the smart-phone PCB with orthogonal meandered elements. The double-band operation is because of two rings and the isolation has been improved by meandered feed elements. The performances of the proposed MIMO antenna was analyzed and validated experimentally. The design offers sufficient gain of more than 5 dBi and efficiencies of upto 75% with better radiation coverages. The measured results of the MIMO antenna are found to be in good agreement with the simulated results. Further, the antenna has been studied for SAR effects as well as radiation coverages in the proximity of users head and hand-head. The antenna housed on 130 × 70 mm 2 1.47 λ 0 × 0.79 λ 0 common ground plane has provided good characteristics making it a potential candidate for sub-6 GHz C-Band 5G and unlicensed Wi-Fi smart-phone applications.

Design of Planar Microstrip Ultrawideband Circularly Polarized Antenna Loaded by Annular-Ring Slot

A miniaturized planar microstrip circularly polarized ultrawideband (UWB) antenna loaded by annular-ring slot is proposed and implemented in the paper. With the annular-ring slot loaded in the radiating patch of the antenna, the side of the radiating patch is connected by the asymmetric inverted L-shaped microstrip. At the same time, a quarter of a circle is cut off from the radiating patch. The above designed structure shows improvements on the operating frequency band and realization of the circular polarization radiation. A tapered microstrip is placed between the feed line and the radiating patch to achieve the slow-changing impedance transformation. The results of simulation and measurement demonstrate that the 3 dB axial ratio (AR) fractional bandwidth of the antenna structure achieves 21.25%. The peak gain within the 3 dB axial ratio bandwidth fluctuates between 3.74 and 4.59 dBi. The antenna shows good impedance matching in the ultrawideband range. With the compact structure of the UWB antenna, it has potential application in various wireless communication devices.

Compact SIW Fed Dual-Port Single Element Annular Slot MIMO Antenna for 5G mmWave Applications

In this article, a compact dual-port single element MIMO antenna is presented for millimeter wave (mmWave) 5G wireless applications. The presented antenna design consists of an annular ring slot that is fed by a Substrate Integrated Waveguide (SIW) at the two opposite sides of the substrate. The antenna resonates at 28GHz and its 10dB impedance bandwidth is 400MHz. The isolation between the ports is reduced by introducing additional annular slot that acts as a cavity which results in an isolation better than 20dB at 28GHz. The measured gain of both ports are 6.9 dBi which is the highest gain per unit element at 28GHz in the literature. The measured diversity gain and envelope correlation coefficient are 9.98dB and 0.065, respectively, at the band of interest. The measured and simulated results are in good agreement.

Extending a birdcage coil for magnetic resonance imaging of a human head with an artificial magnetic shield

In magnetic resonance imaging, a birdcage coil is the most commonly used volumetric resonator creating a highly homogeneous radiofrequency magnetic field in a conductive sample. An artificial magnetic radiofrequency shield was recently shown to improve the magnetic field amplitude per unit power (transmit efficiency) of a preclinical birdcage coil by reducing the intrinsic losses in the coil and increasing power absorbed by the sample. In this paper, we propose a new application of an artificial shield in clinical MRI. Thanks to the proposed artificial shield a birdcage coil for human brain imaging operating at 300 MHz (Larmor frequency of protons at static fields of 7 T) can be expanded to increase free space. As a result, the coil becomes more comfortable for the patient and keeping comparable transmit efficiency. The same extended coil with a conventional copper shield would have at least 10% lower efficiency. The proposed artificial shield is implemented as an annular-ring cavity-backed slot in a copper cylinder that tightly surrounds the birdcage. To demonstrate the effect, radiofrequency magnetic field and specific absorption rate distributions were compared numerically and experimentally for the initial and extended coils with different shields.

Design and Simulation of Triple Band Circular Patch Microstrip Antenna Based on Shape of Ring and Rectangular Slots

In this work, new structures of circular microstrip antenna based on slots are designed and simulated to operate with triple band applications. These slots are annular ring and rectangular shapes in different sizes. The annular ring slot is etched inside the circular patch while the other two rectangular slots are etched on the circular patch edge. The suggested antennas are simulated using version 13 of Ansoft High Frequency Structure Simulator (HFSS). The various parameters such as input impedance, reflection coefficient, gain, radiation patterns and surface currents were investigated. The present results observed that the optimum antenna designed is resonating at three frequencies 2.695, 5.799 and 8.323 GHz. Also, the bandwidths of simulated reflection coefficients at -10 dB are 106, 204 and 371 MHz which are identical with the S-, C- and X-bands frequencies, respectively. Therefore, the optimum antenna designed can be used in the space saving applications in addition to its important role in variety applications at these three frequency bands.

Dual-Band Circularly Polarized Annular Slot Antenna With a Lumped Inductor for GPS Application

A dual-band circularly polarized antenna with a lumped element for global positioning system (GPS) applications is proposed and analyzed in this communication. The proposed antenna mainly consists of a square patch with an annular-ring slot, an inductor, and a metallic reflector. The square patch with the annular-ring slot is excited by a T-shaped microstrip line. This produces the left-handed circular polarization (LHCP) in the GPS L1 (1.563–1.587 GHz) and L2 (1.215–1.240 GHz) bands with the help of the inductor and the metallic reflector. In addition, the antenna with the reflector exhibits a unidirectional radiation in both operating bands. A prototype of the antenna is fabricated and measured to verify the simulation results. The measured results show a wide −10 dB reflection coefficient bandwidth of 40.57% (1.12–1.69 GHz) and 3 dB axial ratio bandwidths of 6.56% (1.18–1.26 GHz) and 7.74% (1.49–1.61 GHz) in the lower and higher bands, respectively. LHCP gains of 7.72 and 8.11 dBic are also observed at 1.227 and 1.575 GHz, respectively.

Polarization reconfigurable annular ring slot antenna design

This paper proposes a simple polarization reconfigurable annular ring slot antenna (ARSA). The proposed ARSA is able to switch among three polarizations, i.e. left-handed circular polarization (LHCP), right-handed circular polarization (RHCP), and linear polarization (LP). The circular polarization (CP) property can be attained by introducing an appropriate inductance at a particular angle across the annular slot. In the design, two PIN diodes are incorporated to provide the required inductance, and at the same time the antenna polarization can be switched by controlling the state of the diodes. The simple design employs the parasitic inductance of the active elements, and hence eliminates the necessity of additional CP perturbation structures. The measured results show that all three polarizations exhibit good impedance matching. Excellent CP performance has been obtained for both circular polarizations with a 3-dB axial ratio (AR) bandwidth (BW) of roughly 6.0%.

A compact circularly polarized antenna using CRLH inspired transmission line and coupled ring resonator

This paper discusses the miniaturization process and bandwidth enhancement of circularly polarized (CP) antenna using asymmetric coplanar strip (ACS) feeding. The antenna mainly uses an ACS feeding scheme on which a via-less composite right/left-handed (CRLH) transmission line (TL) inspired unit cell is implemented for antenna miniaturization and a rectangular shaped annular ring slot is introduced in the asymmetric ground plane (AGP) for generating extended CP radiation. Due to this, the intended antenna offers a compact electrical size of 0.22 λ0 × 0.35 λ0 × 0.028 λ0 at 5.5 GHz and a smaller physical dimension of 12 mm × 19.5 mm × 1.52 mm with ka = 1.32. The novelty of the antenna is to generate an improved impedance bandwidth (IBW) of (5.33–5.86 GHz) 9.90%, and enhanced axial ratio bandwidth (ARBW) of (5.33–5.79 GHz) 8.27% with less design complexity. The intended CP antenna provides a measured gain of 2.43 dBic at 5.53 GHz and radiation efficiency better than 87% is obtained by maintaining the antenna compactness without the use of complicated vias. Also, the intended antenna provides a good AR beamwidth of 80° (+40° to -40°) and positive gain values for theta = ±36° and for all phi values (phi = 00–360°) at 5.55 GHz. Moreover, the intended antenna provides 42.85% miniaturization compared to a conventional monopole antenna. Hence, the intended antenna is well suited for the 5.80 GHz WLAN (5.725–5.875 GHz), and 5.5 GHz WiMAX (5.25–5.85 GHz) applications.

Design and Analysis of Figure Eight Shaped Slot Antenna Array for Wideband Applications

An eight shaped annular ring slot antenna array is presented. Feed is designed with T shaped Power divider and quarterwave transformer is used. Antenna element is comprised of two linked annular slots to achieve high band width. Analysis is carried out with HFSS simulation software. Array is configured with corporate feed structure. It has been observed tha gain is increased to 4dB to 5dB and return loss band width increased from 600 MHz to 1.2 GHz around 55%, Cross polarization level also significantly decreased,

Design of a 3D Top-Loaded Low-Profile Sleeve Antenna for UAV Applications

In this article, a 3D top-loaded low profile sleeve antenna for unmanned aerial vehicle (UAV) applications is proposed. By loading a 3D disc cone structure on the top of a sleeve antenna, the overall height of the antenna can be significantly reduced compared with the height of a traditional quarter-wavelength monopole antenna. In addition, adding shorted columns between the top plate of the disc cone and the ground can generate a new resonant point at lower frequency, so that the frequency bandwidth can be effectively extended. Finally, in order to further achieve the miniaturization of the antenna, an annular slot ring structure was etched on the upper surface of the top plate. Under the conditions of $S_{11} , the designed antenna with a total size of $160mm\times 160mm\times 26.6mm\,\,(0.44\lambda \times 0.44\lambda \times 0.07\lambda)$ has a wide band covering from 840MHz to 1.69GHz (67.2%), while the height of the proposed antenna is only $0.07\lambda $ (where $\lambda $ is the wavelength of the lowest frequency point). Moreover, omnidirectional radiation performances through the operating band can be achieved for both the measured and simulated results.

Isolation enhanced MIMO antenna for software defined networking (SDN) adapted ultrawide band (UBW) radio tech applications

In this paper four element, four-port “enhanced bandwidth reduced radius single stub annular ring slot” (EBRRSS-ARS) Multiple Input Multiple Output (MIMO) antenna with isolation enhancement structure is proposed. The prospective antenna with stub in annular slot reduces the mutual coupling has simple and compact structure. The EBRRSS-ARSA resonates at 4.4 GHz with a bandwidth of 0.9 GHz with minimum isolation of 10 dB between its elements. The parametric study for the proposed fabricated antenna agrees well with the measurements.