Fractal Patch Research Articles

Mandelbrot fractal microstrip antennas

This article proposes the use of complex plane fractal Mandelbrot set geometries, which are of the escape-time fractal type, in the development of microstrip patch antennas fed by a coaxial cable. These antennas are developed for near millimeter-wave applications. Basically, the Mandelbrot fractal geometry is designed from a circular geometry enabling intrinsically a patch element size reduction. In addition, this work is aimed to investigate the effect of using Mandelbrot fractal patch geometry with different iterations. Thereafter, Mandelbrot microstrip patch antennas are designed and simulated using Ansoft HFSS software package. Prototypes are fabricated and tested to validate the design procedure. Good agreement is obtained between simulation and experimental results. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:83–86, 2016

Novel star-shaped fractal antenna for multiband applications

Fractals have unique properties such as self-similarity and space-filling. The use of fractal geometry in antenna design provides a good method for achieving the desired miniaturization, multi-band, and wideband properties. In this communication, novel fractal geometry is proposed based on which a multiband antenna is designed. The proposed antenna has fractal patches which are shaped as different iterations of an eight-pointed star. The multiband behavior is in the frequency range from 4.50 to 17.00 GHz. The proposed antenna is designed on a dielectric substrate Roggers RO4003 lossy with a dielectric constant of εr = 3.55. The antenna has applications in commercial and military communication system.

Circularly polarized frequency reconfigurable Koch antenna for GSM/Wi‐Fi applications

ABSTRACTA novel circularly polarized frequency reconfigurable Koch fractal boundary antenna is proposed. Initially, a Koch slot is etched on the Koch fractal boundary patch of larger dimension (48 × 48 mm2). Within the etched slot, an asymmetrical Koch fractal patch of smaller dimension (36 × 36 mm2) is embedded and switches are introduced along x and y‐directions to connect these inner and outer patch structures. By making ON/OFF switching of the diodes frequency reconfiguration is achieved. Measured results are in close agreement with the simulation results which demonstrates that the proposed antenna is well suited for GSM/Wi‐Fi wireless applications. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2895–2898, 2015

A stacked sierpinski gasket fractal antenna with a defected ground structure for UWB/WLAN/RADIO astronomy/STM Link applications

ABSTRACTAn aperture coupled stacked Sierpinski gasket fractal antenna with a defected ground structure is proposed in the current article for ultra wide band (UWB) and wireless local area network (WLAN) applications. The radiating structure is formed of two Sierpinski gasket fractal patch antenna layers on two layers of FR4 substrate stacked one over the other. This stacked structure is fed by a third (bottom) layer also of FR4 substrate, with ground layer at its top and the feed line with a stub, at the bottom. The top ground layer has a ‘†’ shaped slot cut in it to provide a wideband behavior to the antenna, and the feed line is designed with a stub to provide circular polarization to the EM fields radiated by the proposed antenna. The antenna is designed using CST Microwave Studio version 2010 assuming perfect boundary conditions. The proposed antenna shows a dual band wideband behavior with an impedance bandwidth of 630 MHz (4.75–5.38 GHz) and 400 MHz (6.8–7.2 GHz) with a gain of 5.85 dB and 9.5 dB at the center frequencies of the two bands, respectively. The antenna is capable of covering two UWB bands from (4.75–5.28) GHz and (6.8–7.2) GHz, a radio astronomy band from (5.01–5.03) GHz and IEEE 802.11a band from (5.15–5.35) GHz. The prototype of the proposed antenna is tested using a VNA and an anechoic chamber to validate against the simulated results. The proposed antenna has volumetric dimensions of 6 × 6 × 0.483 cm3 which makes it a suitable choice for RF front end circuits. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2786–2792, 2015

DESIGN OF T-SHAPED FRACTAL PATCH ANTENNA FOR WIRELESS APPLICATIONS

Since the evolution of the patch antennas, there is rapid growth observed in the applications of the patch antenna. There are number of advantages such as small size, ease of fabrication and installment, and a stable performance, so there are huge number of designs has been developed and presented by the researchers time to time. Taking an example of the mobile phone antennas, the antenna must have a small size and must be capable to resonate at multiple frequency bands. Reviewing about the various requirements of the antenna design for the wireless applications a novel multiple band fractal patch antenna has been designed. In this paper, a T-shaped patch antenna has been designed and discussed and fractal geometry has been applied to it in order to obtain self-similar characteristics. The dimensions of the Square Patch has been taken as 36 x 36 mm. Dimension of ground has been taken as been taken as 50 x 50 mm. The substrate material used for antenna design is FR-4 having dielectric constant 4.4. Antenna resonates at four operating bands 3.5 GHz, 4.48 GHz, 6.1 GHz and 8.17 GHz. This antenna has return loss of -16.76 dB, -16 dB, -28.63 dB and -15.03dB with bandwidth of 432 MHz, 332 MHz, 295 MHz and 364 MHz at resonant frequencies. Further this antenna has impressive gain of 3.55 dBi, 5.7 dBi and 3.16 dBi and 3.27 dBi at corresponding frequencies. This antenna can be useful for Wi-Max, 4G network, WLAN, Satellite & RADAR communication applications.

Poly Fractal Boundary Circularly Polarised Microstrip Antenna for WLAN/Wi-MAX Wireless Applications

<p class="MsoNormal" style="text-align: justify;">The design of circularly polarised multiband poly fractal boundary microstrip antenna is proposed and experimentally studied. Initially the two orthogonal sides of the square patch are replaced with different fractal curves for circular polarisation (CP) radiation. Along the x and y axes, Minkowski and Koch fractal curves are employed. A 45° rotated poly fractal slot is embedded at the center of the fractal patch for triband CP operation. The indentation depths and indentation angles of the Minkowski and Koch fractal curves are optimised for better CP emission. The inserted fractal slot redistributes the current elements on the patch for tri band CP radiation. The measured 3-dB axial ratio bandwidths of the proposed antenna at 2.4 GHz, 3.4 GHz, and 5.8 GHz are 1.53 per cent, 0.81 per cent, and 1.62 per cent respectively, making it an able candidate for WLAN and Wi-MAX wireless applications.</p>

A CSRR-Fed SIW Cavity-Backed Fractal Patch Antenna for Wireless Energy Harvesting and Communication.

This paper presents a novel compact dual-band and dual-polarized complementary split-ring resonator (CSRR)-fed substrate-integrated waveguide (SIW) cavity-backed fractal patch antenna for wireless energy harvesting and communication. The proposed antenna is composed of a Giuseppe Peano fractal radiation patch with a backed SIW cavity. To enhance the bandwidth and minimize the dimensions, the CSRR structure is designed to feed the Giuseppe Peano fractal patch orthogonally. A prototype of the proposed antenna is simulated, fabricated and measured. The proposed antenna exhibits good directionality and high cross-polarization level with especially compact size.

Microstrip line‐fed fractal antenna with a high fidelity factor for UWB imaging applications

ABSTRACTA printed microstrip line‐fed fractal antenna is presented with a high fidelity factor for UWB applications. The antenna structure of electrical dimension 0.24 λ × 0.33 λ at lower frequency 3.1 GHz is made of a fractal patch, a slotted partial ground plane, and a microstrip feed, which is fabricated on FR4 material of low cost and dielectric. Measured results demonstrates that the fractal antenna achieves fractional bandwidth of 117.88% covering the frequency range from 3.1 GHz to more than 12 GHz with a maximum gain 3.54 dBi at 6.25 GHz. An acceptable analogy is observed between measured and simulation results. The high fidelity factor, sharply surface current distribution, time domain performances, acceptable gain, and nearly omnidirectional radiation characteristic have validated the appropriateness of this proposed fractal antenna for UWB and microwave imaging applications. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2580–2585, 2015

Design Tri-Band Fractal Antenna with Minkowski Island Split Ring Resonator Structures

The paper investigates the effect of Minkowski Island split ring resonator (MI-SRR) on the microstrip fractal patch antenna. Firstly, a basic Minkowski Island had been simulated in the CST Microwave Studio. Then, the addition of several sizes of the Minkowski Island split ring resonator on the substrate had been generated tri-band resonant frequencies. The optimal result of this tri-band antenna 2.394 GHz, 3.528 GHz and 5.257 GHz with a gain of 0.874 dB, 1.41 dB and 2.94 dB and the reflection coefficient magnitudes of - 21.945 dB, - 17.154 dB and – 16.536 dB. The reflection coefficient magnitudes of the simulation and fabricated antenna also had been compared. The target application for this antenna is for WLAN and WiMAX.

Miniaturized stacked implant antenna design at ISM band with biocompatible characteristics

Purpose – A vertically stacked, three layer hybrid Hilbert fractal geometry and serpentine radiator-based patch antenna is proposed and characterized for medical implant applications at the Industrial, Scientific and Medical band (2.4-2.48 GHz). Antenna parameters are optimised to achieve miniaturized, biocompatible and stable transmission characteristics. The paper aims to discuss these issues. Design/methodology/approach – Human tissue effects on the antenna electrical characteristics were simulated with a three-layer (skin, fat and muscle) human tissue model with the dimensions of 180×70×60 mm3 (width×height×thickness mm3). Different stacked substrates are utilized for the satisfactory characteristics. Two identical radiating patches are printed on Roger 3,010 (ε r=10.2) and Alumina (ε r=9.4) substrate materials, respectively. In addition, various superstrate materials are considered and simulated to prevent short circuit the antenna while having a direct contact with the metallization, and achieve biocompatibility. Finally, superstrate material of Zirconia (ε r=29) is used to achieve biocompatibility and long-life. A finite element method is used to simulate the proposed hybrid model with commercially available Ansoft HFSS software. Findings – The antenna is miniaturized, having dimensions of 10×8.4×2 mm3 (width×height×thickness mm3). The resonance frequency of the antenna is 2.4 GHz with a bandwidth of 100 MHz at return loss (S11) of better than −10 dB characteristics. Overall, the proposed antenna have 50 Ω impedance matching, −21 dB far field antenna gain, single-plane omni-directional radiation pattern properties and incident power of 5.3 mW to adhere Specific Absorption Rate regulation limit. Originality/value – Vertically stacked three layer hybrid design have miniaturized characteristics, wide bandwidth, biocompatible, and stable characteristics in three layer human tissue model make this antenna suitable for implant biomedical monitor systems. The advanced simulation analysis of the proposed design constitutes the main contribution of the paper.

A novel extended edge-based compact PIFA antenna for mobile devices

In this paper, an optimized ultra-compact planar inverted F antenna (PIFA) is proposed. Planar inverted F antenna (PIFA) is most commonly used antenna in modern day Mobile devices. While electronics industry is starving for compactness in their design, the concept used in the proposed design further reduces size of antenna. The overall dimensions of proposed antenna are 14.94×16mm for 3G/4G standards. In proposed design 21.61% size reduction is reported in comparison to conventional rectangular patch PIFA designs. The concept can be further utilized in designing antenna for different standards by optimizing size for specific frequency. A fractal shape Patch shorted at one end is used in the proposed design. The fractal patch is extended 6.59mm above the ground plane. The comparison is performed between measurement of fabricated and simulated S11 for proposed antenna. The novelty of design is inherited in extension of edges of patch towards ground which enable further reduction in size of antenna. Parametric optimization of antenna is performed for calculation of extended edge dimensions. Return loss for fabricated antenna is measured using vector network analyzer. The results of fabricated antenna show good agreement with simulated results and calculations.

Design and Synthesis of Multilayer Frequency Selective Surface Based on Antenna-Filter-Antenna Using Minkowski Fractal Structures

A multilayer frequency selective surface (FSS) with subwavelength fractal elements based on the antenna-filter- antenna (AFA) concept is proposed in this paper. The upper fractal patches are inductive and non-resonant, and the fractal slots on the ground provide a capacitance. The thin substrate is equivalent to a transformer and some resonant modes are produced. Multiple transmission poles are obtained by cascading multilayer two-dimensional periodic structure array of the fractal patches and slots on the ground. The cell periods along x and y directions are the same and the total height is 8 mm, and the fractional bandwidth reaches 30% at normal incidence. To analyze and understand the operating mechanism of the FSS, the equivalent circuit model (ECM) is proposed to analyze the transmission and reflection characteristics. The results of the synthesis from ECM agree well with the results of full-wave simulation. The multilayer AFA-FSS has been manufactured and measured to verify the effectiveness and correctness of the design and synthesis. The simulated results are in good agreement with the tested ones.

Simple, Compact, and Multiband Frequency Selective Surfaces Using Dissimilar Sierpinski Fractal Elements

This paper presents a design methodology for frequency selective surfaces (FSSs) using metallic patches with dissimilar Sierpinski fractal elements. The transmission properties of the spatial filters are investigated for FSS structures composed of two alternately integrated dissimilar Sierpinski fractal elements, corresponding to fractal levelsk=1, 2, and 3. Two FSS prototypes are fabricated and measured in the range from 2 to 12 GHz to validate the proposed fractal designs. The FSSs with dissimilar Sierpinski fractal patch elements are printed on RT/Duroid 6202 high frequency laminate. The experimental characterization of the FSS prototypes is accomplished through two different measurement setups composed of commercial horns and elliptical monopole microstrip antennas. The obtained results confirm the compactness and multiband performance of the proposed FSS geometries, caused by the integration of dissimilar fractal element. In addition, the proposed FSSs exhibited frequency tuning ability on the multiband frequency responses. Agreement between simulated and measured results is reported.

Full-Wave Analysis of Stable Cross Fractal Frequency Selective Surfaces Using an Iterative Procedure Based on Wave Concept

This work presents a full-wave analysis of stable frequency selective surfaces (FSSs) composed of periodic arrays of cross fractal patch elements. The shapes of these patch elements are defined conforming to a fractal concept, where the generator fractal geometry is successively subdivided into parts which are smaller copies of the previous ones (defined as fractal levels). The main objective of this work is to investigate the performance of FSSs with cross fractal patch element geometries including their frequency response and stability in relation to both the angle of incidence and polarization of the plane wave. The frequency response of FSS structures is obtained using the wave concept iterative procedure (WCIP). This method is based on a wave concept formulation and the boundary conditions for the FSS structure. Prototypes were manufactured and measured to verify the WCIP model accuracy. A good agreement between WCIP and measured results was observed for the proposed cross fractal FSSs. In addition, these FSSs exhibited good angular stability.

Dual Band and Beam-Steering Antennas Using Reconfigurable Feed on Sierpinski Structure

Fractal patch antennas based on the Sierpinski structure are studied in this paper. The antennas operate at dual bands (around 2 and 5 GHz) and are designed to steer the beam directions at around 5 GHz band (the first harmonic). The antennas use reconfigurable triple feeds on the same antenna plane to have three beam directions. The same scale factor defines the geometrical self-similarity of the Sierpinski fractal. The proposed antennas are fabricated through three iterations from 1st order to 3rd order and utilize FR-4 (εr= 4.4) for the microwave substrate. The performances of the antennas, such as reflection coefficients and radiation patterns are verified by simulation and measurement. The results show that the properties of the proposed antennas in three orders are similar.

English

Microstrip antennas find applications in aircraft, satellite and missile applications where important characteristics are size, weight and complexity. Design and simulation has been carried out using IE3D simulation software. Minkowski fractal geometry has been applied on patch of antenna to form self similar H-shaped patch antenna. By applying DGS in horizontal direction and vertical direction, characteristics of antenna are observed. When DGS has been changed in horizontal direction and Fr-4 has been used as substrate then antenna resonated at 2.7 GHz, 4.8 GHz and 6.2 GHz with return loss of -17.66 dB, -13.6 dB and -23.66 dB. This antenna has gain of 6.05 dBi, 5.6 dBi and 3.66 dBi. Results are also obtained for H-shaped fractal patch antenna by applying plus shaped DGS and slot shaped DGS, hence antenna can be used for WLAN applications. When microstrip feed line has been used, proposed antenna can be useful for GPS application

Modeling Earthquakes Using Fractal Circular Patch Models with Lessons from the 2011 Tohoku-Oki Earthquake

Earthquakes occur in a complex hierarchical fault system, meaning that a realistic mechanically-consistent model is required to describe heterogeneity simply and over a wide scale. We developed a simple conceptual mechanical model using fractal circular patches associated with fracture energy on a fault plane. This model explains the complexity and scaling relation in the dynamic rupture process. We also show that such a fractal patch model is useful in simulating longterm seismicity in a hierarchal fault system by using external loading. In these studies, an earthquake of any magnitude appears as a completely random cascade growing from a small patch to larger patches. This model is thus potentially useful as a benchmarking scenario for evaluating probabilistic gain in probabilistic earthquake forecasts. The model is applied to the real case of the 2011 Tohoku-Oki earthquake based on prior information from a seismicity catalog to reproduce the complex rupture process of this very large earthquake and its resulting ground motion. Provided that a high-quality seismicity catalog is available for other regions, similar approach using this conceptual model may provide scenarios for other potential large earthquakes.

Ground motions characterized by a multi-scale heterogeneous earthquake model

We have carried out numerical simulations of seismic ground motion radiating from a mega-earthquake whose rupture process is governed by a multi-scale heterogeneous distribution of fracture energy. The observed complexity of the Mw 9.0 2011 Tohoku-Oki earthquake can be explained by such heterogeneities with fractal patches (size and number), even without introducing any heterogeneity in the stress state. In our model, scale dependency in fracture energy (i.e., the slip-weakening distance Dc) on patch size is essential. Our results indicate that wave radiation is generally governed by the largest patch at each moment and that the contribution from small patches is minor. We then conducted parametric studies on the frictional parameters of peak (τp) and residual (τr) friction to produce the case where the effect of the small patches is evident during the progress of the main rupture. We found that heterogeneity in τr has a greater influence on the ground motions than does heterogeneity in τp. As such, local heterogeneity in the static stress drop (Δτ) influences the rupture process more than that in the stress excess (Δτexcess). The effect of small patches is particularly evident when these are almost geometrically isolated and not simultaneously involved in the rupture of larger patches. In other cases, the wave radiation from small patches is probably hidden by the major contributions from large patches. Small patches may play a role in strong motion generation areas with low τr (high Δτ), particularly during slow average rupture propagation. This effect can be identified from the differences in the spatial distributions of peak ground velocities for different frequency ranges.

Analysis and design of frequency selective surfaces using teragon patch elements for WLAN applications

This paper describes a fractal design methodology for frequency selective surfaces (FSSs) composed of teragon metallic patches on a single-layer fiberglass dielectric. Shapes presented by teragons are exploited to design compact FSSs acting as dual-band band-stop spatial filters. An FSS parametric analysis is performed in terms of the fractal dimension and unit cell size of fractal patches. The transmission properties of the proposed periodic arrays are initially investigated through simulations performed by Ansoft DesignerTM commercial software. To validate the used methodology, three FSS prototypes are selected for fabrication, and one of them is designed to reject wireless local area network signals in the bands of 2.4–2.5 GHz (IEEE 802.11b) and 5.0–6.0 GHz (IEEE 802.11a). Experimental characterization of the FSS prototypes is accomplished through an alternative setup with elliptical monopole microstrip antennas for low-cost FSS measurements. The obtained results point to interesting features for FSS spatial filters: compactness, with high values of frequency compression factor (up to 80.4%); dual polarization; dual-band frequency responses; and stable resonance frequencies at oblique incidence.

Complementary stacked patch antenna with fractal shape defect for wideband characteristics

A complementary staked microstrip antenna with a modified Minkowski fractal shaped defect is presented which has a wide bandwidth of 1.8–6.4 GHz with a fractional BW of 89.1%. The concept of the complimentary stacked parasitic fractal patch has been incorporated to enhance the impedance bandwidth in comparison to the conventional stacked patch antenna. The antenna has a dimension of 42 × 55 × 4.8 mm3, which is printed on a low cost FR4 substrate of dielectric constant 4 and a height of 1.6 mm. The gain of the antenna varies from 5 to 7 dBi throughout the operating band. Simulated and experimental characteristics of the antenna are in good agreement. The proposed antenna can be a potential candidate for wideband communication systems and also capable to operate satisfactorily in 3.3–3.7 GHz (WiMAX), 3.7–4.2 GHz (C-Band), and 5.15–5.825 GHz (WLAN) frequency bands. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:944–947, 2014