Fractal Electromagnetic Bandgap Research Articles

Fractal Localized EBG Structure Intelligently Optimized by K-GRNN and GA Method for Signal and Power Integrity

In this article, a miniaturized fractal localized electromagnetic bandgap (EBG) structure for signal and power integrities is intelligently modeled and optimized with a K-means generalized regression neural network (GRNN) and genetic algorithm (GA). The proposed EBG structure is realized with a combination of L-shaped bridge and slit patch, which is inserted by a Koch fractal resonator with a smaller electric length. To minimize the influence of the period EBG structure on the signal integrity, the fractal structure is only designed on the noise source and sensitive area with localized topology. In comparison with the traditional GRNN method, the modeling precision for discontinuous points such as resonance and antiresonance peaks of the scattering parameter curve can be improved with K-means-GRNN. Finally, a power distribution network sample with the proposed localized fractal EBG structure is designed with a steep suppression level of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 50 dB from 0.36 to 20 GHz.

Mutual coupling reduction with a novel fractal electromagnetic bandgap structure

This work shows the effect of a novel fractal-based electromagnetic bandgap (FEBG) structure between dual planar inverted-F antenna (PIFA) elements. The FEBG structure without any shorting pins builds on a well-known fractal structure called Sierpinski carpet, where two iterations have been applied as a uniplanar EBG between dual PIFAs elements to increase the isolation. The proposed antenna can operate at ~2.65GHz for wireless long-term evolution application with compact design dimensions. The simulations are carried out with Ansoft HFSS ver. 17.0. The second iterative order FEBG band-gap characteristic is verified using more computationally efficient analysis. An investigation on coupling reduction showed more than 27 and 40dB in E -plane and H -plane, respectively, between the dual antenna elements is achieved for an antenna spacing less than half wavelength. The proposed antennas with and without second iterative order FEBG are fabricated and measured. The measurement results are in good agreement with the simulated results. Moreover, the envelope correlation of antenna elements with the proposed FEBG is quite smaller than that of antenna elements without FEBG, which gives the proposed system an excellent diverse performance and suitable for the use in low-frequency narrow-band multiple-input, multiple-output applications.

Study on isolation improvement between closely‐packed patch antenna arrays based on fractal metamaterial electromagnetic bandgap structures

A decoupling metamaterial (MTM) configuration based on fractal electromagnetic-bandgap (EMBG) structure is shown to significantly enhance isolation between transmitting and receiving antenna elements in a closely-packed patch antenna array. The MTM-EMBG structure is cross-shaped assembly with fractal-shaped slots etched in each arm of the cross. The fractals are composed of four interconnected-`Y-shaped' slots that are separated with an inverted-`T-shaped' slot. The MTM-EMBG structure is placed between the individual patch antennas in a 2 × 2 antenna array. Measured results show the average inter-element isolation improvement in the frequency band of interest is 17, 37 and 17 dB between radiation elements #1 & #2, #1 & #3, and #1 & #4, respectively. With the proposed method there is no need for using metallic-via-holes. The proposed array covers the frequency range of 8-9.25 GHz for X-band applications, which corresponds to a fractional-bandwidth of 14.5%. With the proposed method the edge-to-edge gap between adjacent antenna elements can be reduced to 0.5λ 0 with no degradation in the antenna array's radiation gain pattern. Across the array's operating band, the measured gain varies between 4 and 7 dBi, and the radiation efficiency varies from 74.22 and 88.71%. The proposed method is applicable in the implementation of closely-packed patch antenna arrays used in SAR and MIMO systems.

Microstrip antenna miniaturization with fractal EBG and SRR loads for linear and circular polarizations

In this paper, combination of electromagnetic band gap (EBG) and split-ring resonator (SRR) loads with fractal formation for miniaturization of microstrip antenna is noticed. Here two different shapes of antenna have been studied with two well-known metamaterial structures as parasitic elements. A conventional microstrip antenna, which is surrounded by four EBG unit cells, is chosen as the first antenna. It has an effective resonance at 2.5. The Minkowski fractal method is applied to EBG unit cells in this stage. The Minkowski fractal structure is implemented for accession of effective capacitance in EBG unit cells. The second antenna frequencies are 2.5 and 5.9 GHz. It contains a slot structure with four SRRs, used for making parasitic elements and for achieving multi-band characteristic. The fractal method is used to improve the inductance of SRR structure by increasing the effective length of microstrip line. At this stage, the applied fractal structure has been modified, so that the frequency of wireless application could be achieved. In the last step, by some changes in feed line of the slot antenna, circular polarization (CP) is obtained for the second antenna, which shows that SRR load can be helpful for making the CP.

Optimisation of chirped and tapered microstrip Koch fractal electromagnetic bandgap structures for improved low‐pass filter design

This study presents electromagnetic bandgap (EBG) structures in microstrip technology based on one-dimensional Koch fractal patterns (Koch fractal EBG (KFEBG)). This fractal geometry allows to adjust the radius r and distance a between patterns so that a low-pass filter response is obtained when the ratio r/a is higher than 0.5. However, in such case undesired strong ripples appear in the low bandpass region. We demonstrate that the performance in the passband of this filter can be improved by applying a tapering function to the Koch fractal dimensions and to the width of the microstrip line, while simultaneously chirping (modulating) the Koch fractal periodic pattern distance (a) so as to maintain a constant r/a ratio. Several tapering functions scaled by a factor K are presented, and the results of their application to the KFEBG microstrip structure are compared by means of relevant characteristic parameters. Optimal performance has been obtained for the Kaiser and Cauchy distributions applied to the Koch fractal pattern, combined with a rectangular and Cauchy distribution applied to the microstrip width, respectively.

Gain enhancement of microstrip patch antenna using Sierpinski fractal-shaped EBG

This is the first report on novel mushroom-type electromagnetic band gap (EBG) structures, consisting of fractal periodic elements, used for enhancing the gain of microstrip patch antennas. Using CST Microwave studio the performance of rectangular patch antenna has been examined on proposed fractal EBG substrates. It is found that fractal EBGs are more effective in suppressing surface wave thus resulting in higher gain. The gain of rectangular patch has been improved from 6.88 to 10.67 dBi. The proposed fractal EBG will open new avenues for the design and development of variety of high-frequency components and devices with enhanced performance.

Substrate Integrated Waveguide (SIW) With Koch Fractal Electromagnetic Bandgap Structures (KFEBG) for Bandpass Filter Design

High-performance bandpass filters (BPFs) based on substrate integrated waveguide (SIW) and half mode SIW (HMSIW) with Koch fractal electromagnetic bandgap (KFEBG) patterns etched on the waveguide surface are proposed. These BPFs are designed using a new methodology. The BPF responses are improved by applying a chirped and tapered technique to the KFEBG patterns which exhibit a radius-to-period ratio r/a ≥ 0.5. Simulation results and experimental verification are presented. Good values for insertion losses and stopband rejection are achieved.

Study of different shape Electromagnetic Band Gap (EBG) structures for single and dual band applications

In this paper, single and dual band EBG structures for wider bandwidth are proposed. In each of the discussed EBGs, a metallic patch of regular geometry is chosen for the unit element. The patch is further modified by cutting slots to get extra inductance and capacitance which results into lower cut-off frequency and larger bandwidth. The proposed EBG structures are compared with the standard mushroom type EBG with respect to surface wave attenuation. The -20 dB cut-off frequencies and bandwidths of the various EBGs are compared. The effect of unit element size, gap between unit elements and via diameter on the transmission response is presented. Among the discussed EBGs, the swastika type structure is compact, single band and has wider bandwidth. The square patch with a single disconnected loop type slot EBG and the Fractal EBG are dual band. While square patch is more compact, the fractal EBG has wider bandwidth. All the EBGs can be useful in the design of antenna and other microwave circuits.

Design and optimization of a microstrip patch antenna for increased bandwidth

With the ever-increasing need for wireless communication and the emergence of many systems, it is important to design broadband antennas to cover a wide frequency range. The aim of this paper is to design a broadband patch antenna, employing the three techniques of slotting, adding directly coupled parasitic elements and fractal electromagnetic band gap (EBG) structures.The bandwidth is improved from 9.3 to 23.7%. A wideband ranging from 4.15 to 5.27 GHz is obtained. Also, a comparative analysis of embedding EBG structures at different heights is also done. The composite effect of integrating these techniques in the design provides a simple and efficient method for obtaining low-profile, broadband, and high-gain antenna. By the addition of parasitic elements the bandwidth was increased to 18%. Later on by embedding EBG structures the bandwidth was increased up to 23.7%. The design is suitable for a variety of wireless applications like WLAN and radar applications.

1D Koch fractal electromagnetic bandgap microstrip structures with r /a ratios higher than 0.5

A 1D Koch fractal electromagnetic bandgap (KFEBG) microstrip structure is proposed.It is conceived by replacing the conventional holes etched in the ground plane of a microstrip line by level-1 Koch fractal cell geometries, which have been obtained from a hexagonal shape. In the case of the conventional 1D electromagnetic bandgap (EBG) microstrip structure with periodic hole pattern, the design is limited to r/a ratios lower than 0.45, whereas the proposed pattern allows achieving r/a ratios higher than 0.5. It is shown that the conventional EBG and KFEBG microstrip structures behave as a stopband filter as r/a 0.5 can be useful for the design of low-pass filters. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:646–649, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25763

Low‐profile dual‐frequency GPS patch antenna enhanced with dual‐band EBG structure

AbstractA novel low‐cost low‐profile dual‐frequency circularly polarized patch antenna for GPS applications is presented. By stacking two square patches with truncated corners on a two‐layer fractal electromagnetic bandgap structure substrate, the coverage of the entire GPS bandwidth is achieved. Two bandgaps exist for the proposed fractal EBG structure, from 1.16 to 1.32 GHz and from 1.45 to 2.10 GHz, which include the lower and upper frequency GPS band. The antenna is low‐profile and has improved gain and axial ratio bandwidth, as well as broader impedance bandwidths compared to the same antenna without EBG. Good circularly polarized radiation patterns are realized. Measurements on prototypes are in good agreement with simulation. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2630–2634, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22815

Micromachined tunable filter using fractal electromagnetic bandgap (EBG) structures

A tunable bandstop filter using fractal electromagnetic bandgap (EBG) structure is designed, simulated and fabricated. The uniform fractal EBG (U-FEBG) structure is realized by replacing the etched rectangular holes with a Minkowski loop generator. A new technique of doubly tapered fractal EBG (DT-FEBG) structure is designed by non-uniform Kaiser distribution on the fractal structures. The Kaiser distribution improves the pass band performance and generates two distant bandgaps. The tunable bandstop filter is tuned by micromachined capacitive bridges. The propagation characteristic of the periodic microelectromechanical system (MEMS) bridges is determined by the dispersion behavior. Different types of parametric analysis are applied to investigate the performance of the MEMS bridges. Surface micromachining fabrication process is employed on the high resistivity silicon substrate to fabricate the filter. The measurement results for the DT-FEBG structure show insertion loss of 1.2 dB and the stop-band rejection of 44 dB. The tuning range of the U-FEBG structure is 1.1 GHz with insertion loss of 1.7–2.5 dB.

Fractal Two-Dimensional Electromagnetic Bandgap Structures

Fractal two-dimensional electromagnetic bandgap (EBG) materials are proposed and studied by means of a full-wave method developed for diffraction gratings. Such technique allows us to characterize, In an accurate and rapidly convergent way, the transmission and reflection properties of periodic fractal structures with an arbitrary geometry in the unit cell. Both polarization cases can be treated. A validation of the employed method is performed through a comparison with theoretical results and experimental data taken from the literature; the convergence properties of our method when applied to fractal EBG materials are checked. In particular, three different fractal EBGs are considered here. Numerical results are reported for the transmission efficiency as a function of the frequency and the incidence angle. Typical effects due to the fractal geometry are observed, like multiband behavior and enlargement of stopbands.