Fractal Antenna Array Research Articles

UWB aperture coupled circular fractal MIMO antenna with a complementary rectangular spiral defected ground structure (DGS) for 4G/WLAN/radar/satellite/international space station (ISS) communication systems

In this article, a dual-port aperture-coupled circular fractal antenna array is designed, developed and tested for its usage in 4G, WLAN, radar, satellite and ISS communication systems, covering C-band, X-band and Ku-band of frequencies. The proposed array is designed on two FR-4 substrates (with overall dimensions of 34 × 68.7 × 3.245 mm3) where the upper and lower substrate consists of circular fractal radiators (2nd order of iteration) and a feed network respectively. The aperture slots in the ground are transformed into complementary rectangular spiral slots with a tree-shaped DGS, to achieve the desired operational band (4.6–16.8 GHz) with improved matching performance. It provides a maximum gain of 4.57 dB (at 6.6 GHz) and high port-to-port isolation (S21 ≤ −19 dB) performance. The implementation of the proposed array in MIMO systems is validated by various diversity parameters like low ECC, high DG, high MEG, low CCL and stable TARC attributes. An acceptable agreement is achieved between the simulated and experimental results.

Fractal antennas and arrays: a review and recent developments

AbstractIn mathematical definition, a fractal is a self-similar subset of Euclidean space whose fractal dimension strictly exceeds its topological dimension which in turn involves a recursive generating methodology that results in contours with infinitely intricate fine structures. Fractal geometry has been used to model complex natural objects such as clouds coastlines, etc., that has space-filling properties. In the past years, several groups of scientists around the globe tried to implement the structure of fractal geometry for applications in the field of electromagnetism, which led to the development of new innovative antenna configurations called “fractal antennas” which is primarily focused in fractal antenna elements, and fractal antenna arrays. It has been demonstrated that by exploiting the recursive nature of fractals, several marvellous kinds of properties can be observed in antennas and arrays. The primary focus of this article is to provide a compressed overview of the developments in fractal-shaped antennas as well as arrays over the last few decades where the most prominent contributions mostly from IEEE journals have been highlighted. The open intention of this review work is to show an encouraging path to antenna researchers for its advancement using fractal geometries.

A Wideband Rectenna Using High Gain Fractal Planar Monopole Antenna Array for RF Energy Scavenging

This paper introduces a wideband rectenna that can scavenge ambient wireless power to a range of frequency band from 0.91 GHz to 2.55 GHz efficiently. The proposed rectenna is based on a wideband 2 × 2 fractal monopole antenna array with omnidirectional radiation patterns and high gains of 5 to 8.3 dBi at the desired bands. An improved two-branch impedance matching technique is presented which is designed to enhance the rectifier circuit performance with a relatively low input power ranging from −25 dBm to 10 dBm. Also, a full-wave wideband rectifier that can suitably improve the RF-to-DC power conversion efficiency is designed for the rectenna. A peak efficiency of 76%, 71%, 61%, and 62% is obtained at 950, 1850, 2100, and 2450 MHz, respectively. Measurement results show that a conversion efficiency of 68% has been achieved over an optimal 4.7 kΩ resistor when the simultaneous four-band input power level is −10 dBm. Moreover, an output DC voltage of around 243 mV with voltage varying within 160–250 mV can be achieved by gathering the low ambient wireless power inside laboratory. This study proves that the proposed rectenna can be applied to a range of many low-power electronic applications.

A complementary Sierpinski gasket fractal antenna array integrated with a complementary Archimedean defected ground structure for portable 4G/5G UWB MIMO communication devices

AbstractThis article presents the design, development, and experimental validation of an aperture coupled complementary Sierpinski gasket equilateral triangular fractal antenna array for portable 4G/5G UWB communication devices. The proposed antenna array is printed on two FR‐4 substrate layers (ε r = 4.4, height = 1.57 mm, and tan δ = 0.024) with two fractal triangular patches on the top layer (separated by a distance of 3λ/2) and feed network on the bottom layer of FR‐4. The fractal patches (optimized up to second order of iteration) are fed using an aperture‐coupled feeding mechanism, where the aperture slots in the ground layer are modified to complementary Archimedean spiral slots which are interconnected by a modified “X” shaped slot to improve the impedance matching at the operational bands. The proposed array has overall volumetric dimensions of 41 × 99.4 × 3.245 mm3 and provides a size reduction of 46% for the metallic area using the fractal geometry. The proposed array shows a simulated UWB response from 4.3 to 11.6 GHz (fractional bandwidth of 91.8% at 7.95 GHz) with a simulated peak gain of 4.7 dB (at 9.2 GHz) and port‐to‐port isolation of ≤−15.8 dB for the entire band. For validation of simulated responses, the proposed array is fabricated and tested for S‐parameters (S11, S22, S12, and S21). A measured impedance bandwidth of 6.3 GHz is observed for a frequency band from 5.7 to 12 GHz. Two additional frequency bands are also exhibited by the array from 4.1 to 4.25 GHz and 4.7 to 5.3 GHz. The array diversity parameters such as envelope correlation coefficient (≤0.007 [simulated], ≤0.0057 [measured]), diversity gain (≥9.999 [simulated], ≥9.971 [measured]), mean effective gain (≥−3.9 dB [simulated], ≥−5.1 dB [measured]), and channel capacity loss, (≤0.37 bits/s/Hz [simulated], ≤0.4 bits/s/Hz [measured]) which are calculated using the simulated and measured S‐parameters of the array are also observed. These parameters allow the proposed fractal array to be implemented in a diversity combining technique to improve the overall SNR and hence support a high data rate for 4G/5G multimedia services.

Design and Simulation of Two Elements Fractal Tree Antenna Arrays

Fractal reception apparatuses have been appeared to exhibit monotonous multi-band or log-intermittent conduct that has been ascribed to the self-comparable scale factor of the recieving wire's geometry. This geometry, which has been utilized to display complex articles found in nature, for example, mists and coastlines, has space filling properties that can be used to scale down reception apparatuses. These exceptional properties of fractals have been abused to build up another class of recieving wire component plans to have a few profoundly attractive properties, including multiband execution, low side flap levels, and its capacity to create quick shaft framing calculations dependent on the recursive idea of fractals. There are a few focal points of these fractal gadgets including decrease of full frequencies, littler size and broadband width. In this paper, another structure of fractal tree recieving wire Arrays dependent on ternary fractal tree geometry for meet the addition or radiation design prerequisites is proposed.Farctal tree radio wire exhibits are plan with two for gain improvement and radiation pattern.Fractal tree reception apparatus clusters upgrade the increase upto 10 dB.

Formation of Fractal Antenna Array for Multiband Applications

Antennas play a vital role in wireless communication; a thirst of excellence in this area is unending. Proposed work describes a concept of fractal multiband antenna designed in the hexagon shape. Basically fractal is the concept used in Microstrip antenna for giving better results than conventional Microstrip antenna. By using hexagonal fractal antenna we can possibly achieve the radiation pattern with high gain. The coaxial feeding is used and multiple hexagons are interconnected in array for maintaining conductivity and to preserve electrical self similarity. Hexagonal antenna is used for different wireless applications. The proposed antenna frequency band covers a large number of wireless communication applications including GPS (1.6GHz), Bluetooth (2.4 GHz) & WLAN (3.6GHz). Antenna design has been designed and simulated by using the software Ansoft’s HFSS and parameters like bandwidth return loss, directivity, VSWR are analyzed. Fabrication of the antenna is done by using wet-etching method, on FR-4 dielectric substrate material. Experimental results are taken on Vector Network Analyzer (VNA) and those obtained results were compared with simulated results. The hexagonal fractal antenna array is found to possess predictable multiband characteristics.

Design and development of virtual instrument for fault diagnosis in fractal antenna array

This paper deals with the development of a virtual instrument for fault diagnosis in fractal antenna array using Lab-VIEW software. Faults in antenna array are considered on the basis of the radiation pattern. In this study, theta and gain values of radiation patterns for each fault are used in Lab-VIEW for curve fitting. An artificial neural network (ANN) has been developed for fitted data points using the Leavenberg Marquard algorithm in MATLAB software and mean square error (MSE) is minimized. The designed ANN model has been embedded in the virtual instrument. The proposed virtual instrument system gets test patterns as input and generates output for several faults present in antenna array. Simulated and measured results of the fractal antenna array are validated experimentally. This virtual instrument model has not been developed for fractal antenna array so far.

On the Design of 2×2 MIMO Fractal Antenna Array for C band applications

A 2×2 MIMO planar fractal antenna array using Sierpinski gasket along with microstrip feed line has been investigated. Different configurations of antenna array has been studied. The optimized unit element used in array is further modified geometrically by corner rounding and cut in feed to improve its performance including gain. Proposed fractal array antenna resonates at 4.19 GHz and 7.86 GHz lies in C band and simulated using High frequency structure simulator. Such an attempt has been rarely reported in the literature. Simulated reflection coefficient shows that Proposed antenna works in C band frequency range for various applications and results are quite promising

On the Design of Fractal Antenna Array for Multiband Applications

This paper presents the design of fractal antenna array with eight elements for multiband applications, such as WiMax (3.3–3.7 GHz), WLAN (4.82–5.95 GHz), X-band for satellite communication (7.1–7.76 GHz) and point-to-point (5.92–8.5 GHz) for high-speed wireless communication. Each element of array is separated by λ/2 distance. FR4 glass epoxy substrate with dielectric constant 4.4 and thickness of 1.6 mm is used for the designing of the proposed antenna array. ANSYS/ANSOFT HFSS V13 software is used for designing and simulating the proposed antenna. Different parameters like gain, radiation pattern and reflection coefficient are obtained at all frequencies in the range of 3 to 10 GHz. It is observed that the proposed antenna array works on eight different frequencies, whereas conventional antenna array works at seven frequencies. The three iterations of the proposed antenna array are fabricated and tested using VNA (vector network analyzer). The experimental and simulated results are compared, and both are in good agreement with each other. Measured results of the proposed antenna array are also compared with the results of antenna array present in the literature, and it is found that the proposed antenna array operates on eight frequency bands, whereas the antenna array in the literature operates on at most three frequency bands.

DESIGN AND DEVELOPMENT OF IMPROVED FRACTAL MIMO ANTENNA

The design and development of a 23 triangular patch fractal multiple input multiple output (MIMO) antenna with the improved gain and bandwidth is presented in this paper. The MIMO structure is framed by integrating the elements such as coplanar waveguide feed and triangular patch fractal antenna array. The combined element is designed and fabricated. The proposed antenna is designed using HFSS software and the antenna parameters are validated using Vector network analyzer (E5071C ENA). The comparison is made between the simulated and fabricated results. The results show that the proposed antenna can be able to yield minimum return loss, larger bandwidth and improved gain at the designed resonant frequency.

A complementary Sierpinski gasket fractal antenna array for wireless MIMO portable devices

AbstractThis research work reports the design and development of a novel complementary Sierpinski gasket fractal microstrip antenna array to achieve a good impedance bandwidth and hence support high data rates for 4G/5G MIMO applications. The proposed array is a compact structure (136 mm × 136 mm) designed with complimentary Sierpinski gasket fractal up to two iterations and has a defected ground to improve the antenna's performance. The antenna performance reports an 8.2% bandwidth at the center frequency of 4.94 GHz (4.7434‐5.1514 GHz), a simulated diversity gain of 9.99 allows the proposed array to be well suitable for proposed applications and a directivity of around 5.8 dBi suits good range characteristics. The array designing and optimization is carried out with 3D EM tool CST MWS V'14 using perfect boundary approximations. A simulated low value of envelope correlation coefficient (0.04) indicates that the two antennas in the array provide least interference to each other while radiating. The measured S11 results on a VNA E 5071C show a close match with the simulated results. Thus a compact array size with good bandwidth, radiation characteristics, low ECC and a high diversity gain allow the antenna array to be well suitable for portable MIMO 4G/5G wireless applications specifically for C band and military applications.

Analysis and design of circular fractal antenna array for multiband applications

In this paper eight element circular fractal antenna array is designed. The elements of this antenna array are separated by a distance λ/2. FR4 glass epoxy with 4.4 relative permittivity and 1.6 mm thickness is used as substrate material for the design of proposed antenna array. The resonant frequency of the proposed antenna array is taken as 4 GHz. Three iterations of the proposed fractal antenna array are designed and fabricated. It is found that as the iteration number increases, the gain of this array at resonant frequency increases and the beam-width decreases. The effects of various parameters on the performance of antenna array is analyzed using 3D electromagnetic simulator (HFSS) based on FEM method. Proposed fractal antenna array resonates at ten frequencies in the frequency range from 1 to 10 GHz. The values of reflection coefficient and the gain at all the resonant frequencies have acceptable values. The resonant frequency of fractal antenna array is also shifted towards the lower frequency from 3.91 to 3.80 GHz which reduces the size of fractal antenna array by 6% than the conventional antenna array. Proposed fractal antenna array covers the different wireless standards such as Wi-Max (3.5–3.8 GHz), C-band applications (3.8–4.4 GHz and 4.8–5.4 GHz), WLAN (5.15–5.85 GHz), X-band for satellite communication (7.1–7.76 GHz). The simulated and experimental results are found in good agreement with each other.

Design of thinned fractal antenna arrays for adaptive beam forming and sidelobe reduction

This study introduces, for the first time, a new design methodology that combines the unique multi-band features of thinned fractal antenna arrays with the adaptive beamforming requirements. The major challenges of fractal array design are the high sidelobe level (SLL), the huge number of elements at higher-growth stages, and the radiation pattern synthesis. In this study, the ant colony optimisation algorithm is utilised for thinning fractal arrays by estimating the optimum combination of ‘on’ and ‘off’ elements corresponding to lowest possible SLL, while the least mean square algorithm is investigated as an adaptive beamforming method in the proposed design. The capability of the proposed design is demonstrated by investigating hexagonal and pentagonal fractal antenna arrays under various parameter regimes. The results show that the proposed design is much superior in terms of multi-band frequency operation, array element reduction, and beamforming accuracy. This reveals the effectiveness of the proposed technique as a promising design in smart antenna technology.

Thinning of Sierpinski fractal array antennas using bounded binary fractal-tapering techniques for space and advanced wireless applications

Abstract Fractal arrays are repetitive-geometry-based smart arrays having impressive array factor properties. However, the performance of these arrays degrades owing to their large number of antenna elements at higher expansion levels. This research work presents the thinning of Sierpinski fractal arrays while keeping an applicable balance between all array factor properties by using two types of bounded binary-fractal-tapering techniques known as Sierpinski and Haferman carpet anti-diagonal tapering techniques. Approximately 22% to 50% of antenna elements are thinned in each successive iteration of the Sierpinski fractal array with the proposed tapering techniques.

Fractal antenna arrays for MIMO radar applications

In this contribution, fractal antenna arrays are analyzed for their applicability in multiple-input multiple-output (MIMO) radars. Array geometries based on the Fudgeflake fractal and the Gosper island fractal are investigated. In addition, a concept for the combination of both fractals is shown in order to increase the flexibility concerning the number of transmitting and receiving antennas. The presented fractal MIMO concepts can be utilized in order to improve the angular resolution and to reduce the sidelobe level for a given number of transmitting and receiving antennas. It is shown that a fractal MIMO concept with 21 transmitting antennas and 21 receiving antennas improves the angular resolution to 4.6 degrees and reduces side lobe level by 3.1 dB compared to a MIMO configuration based on two linear arrays with the same number of antenna elements. In addition, the results are experimentally validated by broadband radar measurements.

Mutual coupling reduction in wideband tree shaped fractal dielectric resonator antenna array using defected ground structure for MIMO applications

AbstractIn this letter, a novel fractal tree shaped two‐element dielectric resonator antenna (DRA) design for wideband multiple input multiple output (MIMO) applications is proposed. Fractal tree shaped geometry is proposed to achieve wideband characteristics while a C‐shaped periodic defected ground plane structure (PDGS) is used to achieve reduction in mutual coupling between two closely spaced antenna elements. Extensive parametric study is carried out to obtain desired mutual coupling reduction without much affecting the bandwidth of the DRA array. The proposed antenna was fabricated and its performance was tested. Measured impedance bandwidth of around 89.9% (–10 dB as reference) is achieved over a frequency band of 3.95–10.4 GHz. Measured mutual coupling less than −15 dB is obtained over the entire band of interest. Both the measured results are quite in accordance to the simulated results. The antenna design parameters, its associated results and parametric study of antenna parameters are discussed in the paper.

Design of circular antenna arrays of circular subarrays exploiting rotational symmetry

This paper presents a design of fractal antenna arrays based on circular arrays of circular subarrays for scannable pattern using rotational symmetry properties of the complex feeding excitations for a maximum performance in terms of side lobe level (SLL) and directivity (DIR). This fractal array design considers the optimization of the amplitude and phase excitations exploiting the fractal characteristics of the geometry (rotational symmetry) in order to generate a scannable pattern. The synthesis process is carried out by the method of Differential Evolution (DE). The main advantages of using rotational symmetry are that the optimal excitations for a particular beam steering angle could be applied to other beam steering angles remaining in the same array factor characteristics (SLL and directivity) for every beam steering angle. This design of fractal antenna arrays provides a complete scanning of the azimuth plane with optimal characteristics of the radiation pattern using just one optimal design vector of amplitude and phase excitations. Furthermore, the performance of the fractal antenna array optimized with DE is compared with respect to the cases of Genetic Algorithms (GA), Particle Swarm Optimization (PSO), and the conventional progressive phase for the same array geometry.

Designing of a Fractal Annular Array Antenna with use of Power Divider

Objective: The prime objective of the proposed work is to design a single antenna on low cost FR4 substrate that will work for multiband frequencies with improved gain. It provides acceptable return loss at 2GHz, 2.76GHz, 3.47GHz, 4.57GHz and 5.35GHz.Method/Analysis-A power-divider is used to form an array of two elements. In this paper, a T-junction power divider is used. For making a power-divider the three-port network is used for power division. In this design one input line is later divided into two parallel lines. Antenna is attached at the output of both the ends. For simulation HFSS(High Frequency Structure Simulator)version 13 is used. HFSS is very accurate and easy software for antenna designing. Findings-In this design, initially a simple sierpinski structure is modified. In place of a triangular patch, annular ring is designed and etched out from the structure. This process is continued upto 2nd iteration. Two such antennas are attached through equal-split power divider. The simple triangular patch with modifications (annular shape) is firstly simulated and later with use of power divider (T-shaped power divider). With use of power divider same antenna works for multiband frequencies and providing good gain. Microstrip feed has been used for feeding the antennas. Novelty-This unique antenna will work for RFID, W-Lan, Wi-Fi applications. Single antenna work for multiband frequency.

Design of two by three element fractal tree antenna array for WLAN and WiFi applications

For more antenna miniaturization, novel fractal tree geometry designed for 5 iterations using rectangular and triangular patches that allow decrease in the resonance frequency without occupying more space. Impedance Matching can be improved without changing the main beam direction or current distribution to five iterations with branching half angle of 60 degrees. The antenna fed by a Coaxial or probe feed to improve the narrow bandwidth of Fractal Antenna. The proposed antenna achieves a bandwidth of 31.5% for 10 dB return loss, covering the frequency range 2.4–3.6 GHz for WLAN and WiFi applications. The antenna gain of the fractal element is about 3 dBi. Array is designed to increase the gain and radiation energy. Arrays are configured at operating frequency of 2.4 GHz by using six elements to enhance the gain up to 11 dBi. The obtained gain and frequency are suitable for WLAN and WiFi applications.

Planar array of right-angled isosceles triangular microstrip antenna using Koch and meander lines for the Internet of things

An ultrawideband antenna array using a right-angled isosceles triangular microstrip antenna as a basic element is presented using inset feed for applications in the Internet of things. A Koch fractal antenna array with defected ground plane is used to generate multiband applications. Further, meander lines are added to increase the equivalent inductance that reduces the size of the antenna and increases the bandwidth and gain. Antenna arrays have been constructed and experimentally studied. The measured results show good agreement with the numerical prediction and wideband operation.