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Advances in Fractal Antennas: Design, Modeling and Applications

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A special issue of Fractal and Fractional (ISSN 2504-3110). This special issue belongs to the section "Engineering".

Deadline for manuscript submissions: closed (31 July 2024) | Viewed by 15563

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Special Issue Editors

Dr. Mihai-Virgil Nichita

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Guest Editor

Faculty of Applied Sciences, University “POLITEHNICA” of Bucharest, 060042 Bucharest, Romania
Interests: fractals; antenna design; telecommunications; signal processing

Prof. Dr. Viorel-Puiu Paun

*

Guest Editor

1. Department of Physics, University Politehnica of Bucharest, 060042 Bucharest, Romania
2. Academy of Romanian Scientists, 050094 Bucharest, Romania
Interests: gels; mathematical physics; biophysical modelling; complex systems; nonlinear dynamics; chaos theory; fractal analysis; image processing
* We dedicate the memory of the editor Prof. Dr. Viorel-Puiu Paun who passed away during this special issue period.
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Special Issue Information

Dear Colleagues,

Fractal antennas are designed using self-similar shapes to maximize the length or increase the perimeter of a material that can receive or transmit electromagnetic radiation within a given total surface area or volume. Fractal antennas are usually printed structures mounted on a dielectric substrate.

The main advantage of fractal antennas is defined by a reduced space requirement because of their compact size. In addition, they offer higher input resistance because of an increase in the length or perimeter.

Focusing on their attractive features, these antennas seem to be suitable in systems where there is a need to integrate several types of communication techniques in equipment with well-defined constraints for geometric dimensions, parameters and deployment.

The focus of this Special Issue is to continue to advance research on topics relating to the theory, design, implementation and application of fractal antennas. Topics that are invited for submission include (but are not limited to):

Antennas for new-generation mobile devices;
Fractal antennas for satellite communication;
New ways of deploying antennas and antenna systems;
Antennas for testing and measurement;
Embedded antennas for IoT devices;
Wideband communications based on fractal antennas;
Multiband communications based on fractal antennas;
New materials used for fractal antenna enhancements;
Designing and modeling new fractal shapes for antennas.

Dr. Mihai-Virgil Nichita
Prof. Dr. Viorel-Puiu Paun
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Fractal and Fractional is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

fractal shaped antennas
antenna design
antenna enhancement techniques
integrated communication systems
multifrequency antennas

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Published Papers (7 papers)

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Research

15 pages, 9635 KiB

Open AccessArticle

Screen-Printed Metamaterial Absorber Using Fractal Metal Mesh for Optical Transparency and Flexibility

by Jinwoo Choi, Daecheon Lim and Sungjoon Lim

Fractal Fract. 2024, 8(5), 284; https://doi.org/10.3390/fractalfract8050284 - 9 May 2024

Viewed by 1234

Abstract

In stealth applications, there is a growing emphasis on the development of radar-absorbing structures that are efficient, flexible, and optically transparent. This study proposes a screen-printed metamaterial absorber (MMA) on polyethylene terephthalate (PET) substrates using indium tin oxide (ITO) as the grounding layer, which achieves both optical transparency and flexibility. These materials and methods enhance the overall flexibility and transparency of MMA. To address the limited transparency caused by the silver nanoparticle ink for the top pattern, a metal mesh was incorporated to reduce the area ratio of the printed patterns, thereby enhancing transparency. By incrementing the fractal order of the structure, we optimized the operating frequency to target the X-band, which is most commonly used in radar detection. The proposed MMA demonstrates remarkable performance, with a measured absorption of 91.99% at 8.85 GHz and an average optical transmittance of 46.70% across the visible light spectrum (450 to 700 nm), indicating its potential for applications in transparent windows or drone stealth. Full article

(This article belongs to the Special Issue Advances in Fractal Antennas: Design, Modeling and Applications)

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18 pages, 6626 KiB

Open AccessArticle

Optically Transparent Dual-Band Metamaterial Absorber Using Ag Nanowire Screen-Printed Second-Order Cross-Fractal Structures

by Sumin Bark, Junghyeon Kim, Minjae Lee and Sungjoon Lim

Fractal Fract. 2024, 8(3), 153; https://doi.org/10.3390/fractalfract8030153 - 8 Mar 2024

Cited by 1 | Viewed by 1588

Abstract

In this paper, we propose an optically transparent dual-band metamaterial absorber (MMA) that uses Ag nanowire screen-printed fractal structures. The proposed MMA exhibits near-perfect absorption in the C- and K-bands. This dual-band absorption property is achieved through two inductive–capacitive (L-C) resonances located at 6.45 and 21.14 GHz, which are generated by the second-order fractal structures. We analyzed the microwave absorbing mechanisms through the distributions of the surface current and electromagnetic field on the top and bottom layers. The MMA demonstrates an optical transmittance of 63.1% at a wavelength of 550 nm. This high optical transmittance is attained by screen printing transparent Ag nanowire ink onto a transparent PET substrate. Since screen printing is a simple and low-cost fabrication method, the proposed MMA offers the advantages of being low cost while having the properties of optical transparency and effective dual-band absorption. Consequently, it holds great potential for the radar stealth application of C- and K-bands in that it can be attached to the windows of stealth aircraft due to its optical transparency and dual-band near-perfect absorption property. Full article

(This article belongs to the Special Issue Advances in Fractal Antennas: Design, Modeling and Applications)

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27 pages, 20554 KiB

Open AccessArticle

Novel Meta-Fractal Wearable Sensors and Antennas for Medical, Communication, 5G, and IoT Applications

by Albert Sabban

Fractal Fract. 2024, 8(2), 100; https://doi.org/10.3390/fractalfract8020100 - 6 Feb 2024

Cited by 5 | Viewed by 2189

Abstract

Future communication, 5G, medical, and IoT systems need compact, green, efficient wideband sensors, and antennas. Novel linear and dual-polarized antennas for 5G, 6G, medical devices, Internet of Things (IoT) systems, and healthcare monitoring sensors are presented in this paper. One of the major goals in the evaluation of medical, 5G, and smart wireless communication devices is the development of efficient, compact, low-cost antennas and sensors. Moreover, passive and active sensors may be self-powered by connecting an energy-harvesting unit to the antenna to collect electromagnetic radiation and charge the wearable sensor battery. Wearable sensors and antennas can be employed in smart grid applications that provide communication between neighbors, localized management, bidirectional power transfer, and effective demand response. A low-cost wearable antenna may be developed by etching the printed feed and matching the network on the same substrate in the printed antenna. Active modules may be placed on the same dielectric board. The antenna design parameters and a comparison between the computation and measured electrical performance of the antennas are presented in this paper. The electrical characteristics of the new compact antennas in the vicinity of the patient’s body were simulated by using electromagnetic simulation techniques. Fractal and metamaterial efficient antennas and sensors were evaluated to maximize the electrical characteristics of smart communication and medical devices. The dual- and circularly polarized antennas developed in this paper are crucial to the evaluation of wideband and multiband compact 5G, 6G, and IoT advanced systems. The new efficient sensors and antennas maximize the system’s dynamic range and electrical characteristics. The new efficient wearable antennas and sensors are compact, wideband, and low-cost. The operating resonant frequency of the metamaterial antennas with circular split-ring resonators (CSRRs) may be 5% to 9% lower than the resonant frequency of the sensor without CSRRs. The directivity and gain of the metamaterial fractal antennas with CSRRs may be up to 3 dB higher than the antennas without CSRRs. The directivity and gain of the metamaterial fractal passive sensors with CSRRs may be up to 8.5 dBi. This study presents new wideband active meta-fractal antennas and sensors. The bandwidth of the new sensors is around 9% to 20%. At 2.83 GHz, the receiving active sensor gain is 13.5 dB and drops to 8 dB at 3.2 GHz. The receiving module noise figure with TAV541 LNA is around 1dB. Full article

(This article belongs to the Special Issue Advances in Fractal Antennas: Design, Modeling and Applications)

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16 pages, 3542 KiB

Open AccessArticle

O-Shape Fractal Antenna Optimized Design with Broad Bandwidth and High Gain for 6G Mobile Communication Devices

by Shobhit K. Patel and Abdullah Baz

Fractal Fract. 2024, 8(1), 17; https://doi.org/10.3390/fractalfract8010017 - 24 Dec 2023

Cited by 4 | Viewed by 2677

Abstract

Optimization of antenna parameters is important for achieving the best design that has higher results for gain and bandwidth while also having a smaller size. One such antenna design is numerically investigated and presented in this research. The antenna is optimized to an O-shape fractal design from a square patch design. The antenna is created by etching a slot of a square patch and making an O-shape fractal metamaterial patch antenna that operates on the THz band. The THz patch antenna is also investigated for its metamaterial properties. The optimization of the THz patch antenna is carried out for substrate height, slot length, and slot width. The optimized design has a size of 65 × 65 µm². The highest bandwidth of 31.4 THz (138%) and the highest gain of 11.1 dBi is achieved. The optimized design is then investigated for multiple elements. The two-element MIMO antenna design using an O-shape patch is investigated to observe its performance and compare it with an O-shape single-element design. The two-element MIMO antenna design gives two bands with a bandwidth of 18 THz (113%) and 21 THz (56%). The gain of this design is 5.18 dBi and the size is 130 × 65 µm². A comparison between the O-shape single-element fractal design, two-element fractal MIMO design, and other published designs is carried out. The compact, broadband, and high gain design presented can be used for 6G high-speed mobile communication devices. Full article

(This article belongs to the Special Issue Advances in Fractal Antennas: Design, Modeling and Applications)

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12 pages, 8621 KiB

Open AccessArticle

Miniaturization and Bandwidth Enhancement of Fractal-Structured Two-Arm Sinuous Antenna Using Gap Loading with Meandering

by Junghyeon Kim, Jongho Keun, Taehoon Yoo and Sungjoon Lim

Fractal Fract. 2023, 7(12), 841; https://doi.org/10.3390/fractalfract7120841 - 27 Nov 2023

Cited by 2 | Viewed by 1814

Abstract

A sinuous antenna is a frequency-independent antenna known for its wide bandwidth and consistent gain, which makes it valuable in broadband applications such as ultrawideband (UWB) radar and ground-penetrating radar (GPR). However, sinuous antennas tend to be rather large. Consequently, numerous studies have explored miniaturization methods, with the gap-loading method emerging as a prominent approach. Unfortunately, it is still difficult to achieve broad bandwidths for conventional miniaturized sinuous antennas. In this paper, we use a novel approach incorporating a meander shape into the sinuous curve and employing gap loading with meandering. This innovative technique results in the development of a fractal-structured two-arm sinuous antenna characterized by an ultra-compact size and significantly expanded bandwidth. Adding a meander line in the outermost part maximizes the capacitance, thereby enhancing the gap-loading effect and minimizing the overall size of the sinuous antenna. In addition, the introduction of an inner meander line increases the inductance, contributing to a further expansion of the antenna’s bandwidth. For example, the electrical length of the antenna without the meander line is 0.552 × 0.552 × 0.052

λ_{g}^{3}

, while the electrical length of the antenna with the meander line is only 0.445 × 0.445 × 0.036

λ_{g}^{3}

, i.e., 19.4% smaller. The antenna lacking the outermost meander line exhibits a 10 dB impedance bandwidth, spanning from 0.74 to 10.53 GHz. In contrast, the antenna featuring the outermost meander line has a 10 dB impedance bandwidth, extending from 0.51 to 10.72 GHz, which results in a remarkable enhancement in the fractional bandwidth (by 8.1%). Hence, the proposed antenna design is a good candidate for broadband applications that require miniaturization. Full article

(This article belongs to the Special Issue Advances in Fractal Antennas: Design, Modeling and Applications)

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22 pages, 10429 KiB

Open AccessArticle

Design of a Modified MIMO Antenna Based on Tweaked Spherical Fractal Geometry for 5G New Radio (NR) Band N258 (24.25–27.25 GHz) Applications

by Nitasha Bisht, Praveen Kumar Malik, Sudipta Das, Tanvir Islam, Sivaji Asha and Moath Alathbah

Fractal Fract. 2023, 7(10), 718; https://doi.org/10.3390/fractalfract7100718 - 29 Sep 2023

Cited by 9 | Viewed by 1850

Abstract

This article describes a fractal-based MIMO antenna for 5G mm-wave mobile applications with micro-strip feeding. The proposed structure is a fractal-based spherical configuration that incorporates spherical slots of different iterations on the patch, as well as rectangular slots on the ground plane. These additions are meant to reduce patch isolation. The two-element MIMO antenna has closely spaced antenna elements that resonate at multiple frequencies, 9.5 GHz, 11.1 GHz, 13.4 GHz, 15.8 GHz, 21.1 GHz, and 26.6 GHz, in the frequency range of 8 to 28 GHz. The antenna’s broadest operational frequency range spans from 17.7 GHz to 28 GHz, encompassing a bandwidth of 10,300 MHz. Consequently, it is well-suited for utilization within the millimeter wave (mm wave) application, specifically for the 5G new radio frequency band n258, and partially covers some other bands X (8.9–9.9 GHz, 10.4–11.4 GHz), and Ku (13.1–13.7 GHz, 15.4–16.2 GHz). All the resonating bands have isolation levels below the acceptable range of (|S12| > −16 dB). The proposed antenna utilizes a FR4 material with dimension of 28.22 mm

\times

44 mm. An investigation is conducted to analyze the effectiveness of parameters of the antenna, including radiation pattern, surface current distributions and S parameters. Furthermore, an examination and assessment are conducted on the efficacy of the diversity system inside the multiple input multiple output (MIMO) framework. This evaluation encompasses the analysis of key performance metrics such as the envelope correlation coefficient (ECC), diversity gain (DG), and mean effective gain (MEG). All antenna characteristics are determined to be within a suitable range for this suggested MIMO arrangement. The antenna design underwent experimental validation and the simulated outcomes were subsequently verified. Full article

(This article belongs to the Special Issue Advances in Fractal Antennas: Design, Modeling and Applications)

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16 pages, 5093 KiB

Open AccessArticle

Design and Modelling of a Compact Triband Passband Filter for GPS, WiMAX, and Satellite Applications with Multiple Transmission Zero’s

by Abdul Basit, Amil Daraz, Muhammad Irshad Khan, Farid Zubir, Salman A. AlQahtani and Guoqiang Zhang

Fractal Fract. 2023, 7(7), 511; https://doi.org/10.3390/fractalfract7070511 - 28 Jun 2023

Cited by 4 | Viewed by 1627

Abstract

Designing microwave filters with high selectivity and sharp roll-off between the stop and pass bands can be challenging due to the complex nature of the R.F. signals and the requirements for achieving high performance in a limited physical space. To achieve a high selectivity and sharp roll-off rate, this paper presents a compact filter with a triple passband response. The two different passbands at 1.57 GHz and 3.5 GHz are achieved using a step impedance resonator (SIR) with metallic slots perturbation added to the lower corner of the high impedance section of the SIRs, which helps to enhance the filter’s selectivity and size reduction greatly. The embedded L-shaped structure originates a third passband at 4.23 GHz, resulting in a triband response with eight transmission zeros below and above the passbands at 1.22/1.42/1.98/3.18/3.82/3.98/4.38/4.53 GHz, respectively. The prototype has low signal attenuation of <1.2 dB and high signal reflection of >25 dB for the three passbands. The fractional bandwidths achieved are 2.54%, 4.2%, and 1.65% at 1.57/3.57/4.23 GHz, respectively, with rejection levels in the stopband greater than 15 dB. Lastly, the structure is fabricated on RO-4350B PCB and observed good matching between experimental and measured results. This demonstrates that the prototype can be successfully implemented in real-world applications such as GPS, WiMAX, and Satellite systems. The area occupied by the filter on a substrate or in a circuit is 0.31 λ_g × 0.24 λ_g, where λ_g is the guided wavelength of the material calculated at the lowest frequency. Full article

(This article belongs to the Special Issue Advances in Fractal Antennas: Design, Modeling and Applications)

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