A COMPACT FRACTAL ANTENNA FOR 5G MODERN VEHICULAR APPLICATION
Abstract:
This study presents and integrates a new fractal iterative structure of a progressive defect patch with a triangular array structure. To achieve broadband operations, the antenna patchis designed using fractal geometry and a rectangular slot for feed. The antenna archives return losses of less than –10dB. Theproposed antenna achieved a total gain in the operating band with a highly directive and efficient range of operation. Results from simulations and measurements are contrasted and found to be accord.
Keywords: Fractal Geometry, Recessed Ground, 5G, millimeter communication, Vehicular Communication Applications.
1. Introduction:
In the present generation, there is a huge demandfor connected vehicles and the features evolved using high-frequency communication. The automotive industry has had a significant impact from vehicular communication thanks to its top-notch safety and
security capabilities. The communication is mostly referredtoasVehicletoEverything(V2X)communication which involves many standards such as pedestrian, infrastructure, cloud, fog, driver, and other nearby vehicles. [1] An ultra-wideband antenna is constantly in greatdemand to provide all these qualities. Throughout thedecades, designers have developed a wide range of antenna designs to meet current demands for 4G communication frequencies. Future connected vehicles willbeconstrainedbythecurrent4Gcellularsystemsand the Dedicated Short- Range Communications (DSRC) spectrum allotted for vehicular communications. Most designsmakeuseoftheavailablefrequencyspectrumup to 6GHz. connected vehicleswill be constrained by the current 4G cellular systems and Dedicated Short-Range Communications (DSRC) spectrum allotted for vehicular communications. Most designs make use of the available frequency spectrum up to 6GHz. connected vehicleswill be constrained by the current 4G cellular systems and Dedicated Short-Range Communications (DSRC) spectrum allotted for vehicular communications. Most designsmakeuseoftheavailablefrequencyspectrumup
to 6GHz. A lot of interference is observed when these frequenciesareusedforcommunication.[5]Anewset of frequencies needed to be established to communicate without interference. The most appropriate method is toshift the gearfrom 4G to 5G which is designed for enabling instantaneous connectivity to billions of devices across the human earth which leads to a truly connected universe with speeds that are ten times better than that of the previous generation. Low latency and stable connectivity will enable a new generation of applicationsinalmostalldomains.Evenfantasieshave bounds,but5Gwillhavenosuchrestrictionsinterms ofservicesandeconomicpotential.[1]
1.1 Similar works:
The most recent research initiatives in the areas of fractal antennas, 5G communications, and vehicular communicationsare presented in this section. [14] The focus is on the properties of the antenna and its behavioratfuturefrequencies.Theauthorssuggested a hexagonal-shaped ultra- wide bandwidth Fractal dipoleantennawithafrequencyrangeof0.5–12GHz. [5] The simulation was done with a focus on the antenna's gain, which for various penetration angles averaged 6.9 dBi. The previously presented fractal module is incredibly compact and can be used for vehiclecommunications. With aminimum reflection coefficient of29.18dB,theVSWRwasintherangeof 3.4 dB. In the analysis that followed, the author proposedatriangular-shapedfractalgeometryantenna for usage in UWB applications. The self-
complementing idea is applied to the first iteration of theplannertriangularmonopoleantennaenhancement. It is observed that this strategy reduces the reflection coefficient tobelow10dBforthefrequencyrangeof410GHz.Whencomparedtosingleandmultiplepatches, the triangle patch's performance level was up to 30% better. [7] We developsingle-layer patch antennas as well as multi-layer antennas intending to analyze this antenna. The antenna's ability to be employed in a variety of applications is one of its primary qualities. For extremely wide-band applications, the author proposed a hexagonal wide slot antenna based on fractals. At frequencies between 3 and 30 GHz, the suggested antenna achieves a ratio impedance bandwidthof15:19foraVSWRof1.Whencomparedto thebandwidthneededforSWBfunctioning,therealized bandwidthistwiceaslarge.[2]
Theauthorsuggestedahexagonaltuningstubloadedat themicrostripfeedlineforbandwidthincrease,evenat lowerfrequencies,whichisagreatconceptforthesmall antennasthatcanbemountedonavehicle.Theantenna must nowbe wearable and conformal so that itmay be positionedonaperson'sbodyanddeliverthenecessary data [13]. For improved antenna performance and SAR reduction, the author suggested a wearable Fractal monopole antenna incorporated with a reflector. At an operating frequency of 2.36–2.50 GHz, the suggested antenna exhibits enhanced bandwidth of 130 MHz in free space and 128 MHz when placed on a at homogenous phantom. The most crucial component of any antenna, according to 484 A. RAHIM ET AL.,is its bandwidth [21]. For UWB applications, the author
proposedafractalantennawithamodifiedhexagonal form with multi-band notch characteristics. FR4 Epoxywasusedtomanufacturetheantenna,resulting inabandwidthof2.36GHzinthefrequencyrangeof 9.6GHz–15GHzandanS11oflessthan10dBacross the full UWB range. The author noted that these enhanced qualities have several uses in the telecommunications and vehicular communicationsindustries.
Our knowledge of how to construct the suggested work has significantly improved as a result of the research indicated above, making it more applicable to multi-band applications in vehicular communications in 5G scenarios. To obtain broadband and multi-band characteristics with wide impedance,slotshavebeenaddedtothedesign.
2. Introduction to fractal structure of gradual defect patch:
The term "fractal," which is used to deny a class of geometric structures with self-similar features, was initially put out by French mathematician Mandelbrot in 1983 [24]. The fractal theory is now being used more and more in antenna design. The fractal structure's self-similarity causes the current distribution inside the antenna to be relatively uniform, its working bandwidth to be higher, and its intricate foldingstructure to enable the antenna to be made smaller. The progressive defect patch fractal structureanditsfractaliterationprocessarebothnew structures. A triangle that has been further divided serves as the basic building block of the progressive defect patch's fractal structure. The array element
antenna in the design of the antenna structure is the gradual defect patch fractal antenna. The progressive defectpatchfractalisself-similarinbothitsentiretyand itsparts.Withinthefractalstructure,theradiofrequency currentcanbedispersedveryequally[8].Theantennais quite good.When the radiating antenna patch is designed using the fractal structure of the gradual defect patch, broadband working performance is achieved. The progressive defect patch fractal includes numerous defects with various side lengths that act as "digging holes," creating numerous radiation slits of various lengths that operate in various frequency bands, and their radiation superposition can create a wider operatingbandwidth[9].
2.1 Design methodology:
The following flow diagram symbolizes the workflow indesigningconventionalpatchantennasinHFSS.
The antenna was initially designed using Ansys EM (HFSS) software. It is fed by a slot line, on which an SMAconnectorissoldered formeasurements [17].The
design is indicated and inspired by the need for the antenna to resonate in two different frequencies [14]. The resonator close to C-V2X frequency bands and the extended half circles allow the antenna to operateatthelowercellularfrequencies.
2.2 Proposed Antenna Geometry:
In this section, the designing procedure of the proposed fractal antenna with defected ground has been described in detail along with the substrate materialanditspropertiesaredescribed.
Table2.Parametersofdifferentsubstratesmaterials.
The antenna is designed and simulated using HFSS andobtainedagoodoutputresponse.Itresonatesat frequency ranges of 4.7, 5.9 GHz, which makes it suitablefor5Gapplications[4].
2.3 Antenna Design and Simulation Results:
The antenna's radiation pattern is distorted at the higherfrequency bands. The antenna at 5.9 GHz is not designedtobelinearly polarized due to the SMA (SubMiniatureversionA)connector,thesizeofthefeedline is comparable to the wavelength since the crosspolarization is created due to the transverse currents of the higher order modes [13]. The co- and crosspolarization of the antenna as simulated in Ansys EM (HFSS)andmeasured duringthe various experimental setupsareindicated.Themeasuredmaximumvaluesof the copolarization are higher than the simulated one.
The reflections created by the obstacles in the real environment, the ground, and the vehicle's body modify the antenna's radiation patterns and add more to its maximum radiation pattern values [15]. The smallest value of the cross-polarization at the angle where we have the maximum co-polarization value at 5.9 GHz when the vehicle is present, is measuredtobe 10dBiwhentheantenna isplaced insidethemirror'scover[3].
Fabricated antenna:
The following diagram shows that the fabricated antennaofproposedgeometry.
Theproposedgeometryoftheantennasystemisbetter at maintaining the total conductivity and radiating characteristicsoftheantenna.The antennais59mmin totalandthelengthofthethreesidesare20,23,and16 mm, while the height of the substrate is 1.6 mm, loss tangent, tanδ = 0.019, and dielectric constant εr = 4.4. Fortheseconditeration,thefractalantennahadmadea furthersmalltriangleslotatitscenter.Furthermore,the miniaturization produced seven smaller half-circles inside of a large triangle in the third iteration. The smaller compact half circles within the patch increase the surface radial current distribution and, hence, the overall conductivity of the patch's energy, resulting in strongerradiation.
2.4 Performance Evaluation:
Simulated and measured results of the proposed compact fractal antenna in terms of performance parameters like reflection coefficient, VSWR, gain, current distribution, and radiation pattern are discussed in this section. Also, the effect of different parameters like the height of the substrate, size of the ground plane, substrate material, and feedwidth isstudied.
2.5 S11 Parameter and VSWR:
The S11 parameter denies the extent of backscattering thatoccurredattherequiredfrequency[26].Thereturn loss orreflection coefficient or S11 is the fundamental parameter to observe the radiation efficiency of an antenna. It gives information about the extent of the electromagnetic wave reflected toward the tested antenna.Thereflectioncoefficientversusfrequencyplot
for the 0th, 1st, and 2nd iterations of the proposed antennaareshowninFig.5.The2nditerationshows more bandwidth as compared to the 0th and the 1st iterations.
(Re=1, Im=1), and at these frequencies, the impedanceishighlymatched.Therearetwotypesof lines in the Smith chart horizontal and vertical.The horizontal line indicates the imaginary value of impedance, and the vertical line indicates the real valueofimpedance.Impedanceisperfectlymatched when real and imaginary lines cut each other [22]. Thisgraphshowsthattheproposedantennais
perfectlymatchedatdifferentresonantfrequencies.
ThesimulatedandmeasuredS11versusfrequency plot andVSWR versus frequency plot for CFA are shown in Fig. 5 and6 respectively. The value of VSWR lies between 1 and 2 at all resonant frequencies which are 1.21 and1.34 showing that the proposed antenna source and load terminal are perfectly matched at these frequencies.
2.7 Radiation Pattern:
Itrepresentsthegeographicalareaatwhichthe
antenna can transmit electromagnetic waves surrounding the antenna [8]. There are two major angles azimuth (Eφ) and elevation (Eϕ), which representtheXYplaneandYZplanerespectively[12].
VSWR
2.6 Impedance:
TheimpedanceplotfortheCFAintheSmithchart
isshowninFig.7.Somefrequencieslienear1
Theazimuthangleismeasuredat0°intheredcolorline andtheelevationangleismeasuredat90°inthegreen areobservedatphi0°and90°,andtheta180°and270°at every
line. The radiation patterns at different angles are calculatedfor2Dfar-eldradiationandgainisassigned alongwiththeradiationpattern.Theradiationpatterns resonantfrequency[19].Theradiationpatternsas shown in Fig. 8 represent that the proposed CFA can operateomnidirectionallyaswellasbi-directionally.
Thegainanddirectivityofanantennaiscalculatedata 3Dfarfieldplot atthe resonant frequency asshownin
The electrical magnitudes are strong throughout the antenna and on the patch and ground, which provides excellent stability and radiates the most energy that is takeninattheport.
2.8 Comparing performance parameters:
A comparison of the performance of compact fractal antenna array (CFA) antennas of different iterations withtheotherconventionalGPSnavigationantennasis showninTable3.Oneoftheadvantagesofthisdesign isthattheradiationpatternintheantennawithastrip is of the broadside type throughout the entire matching bandwidth. Table 3 summarizes the measured gain, axial ratio (AR) bandwidth, and impedance bandwidth of the conventional fractal antenna,withandwithoutdefectivegroundstructure, at the mentioned frequencies. The expected improvement in radiation characteristics may be observed clearly, particularly around 3.6 GHz. For correct impedancematching of the fed system with antennaimpedance,theCPW-Fedisaone-stepsystem withfedwidth(f)=1.6mm.
3. Conclusion:
With this structure, there has been some improvement inreturnlossandradiationcharacteristicsatlowerand higher frequencies. By implementing defected ground structure (DGS), the radiating patch achieves better impedance matching. The simulated radiation characteristics, comprisingof return loss, is −25 dB at 2.52GHz,witha1.58%returnlossbandwidthatthefirst iteration, where the radiation pattern isdirective. The transceiver'ssimulatedreturnlosswasfound tobe 29
dBat2.6GHzand 26dBat3.5GHz,witha620MHz bandwidthof−10dB(1.26%).Forthereturnthathas been experimentally confirmed with a return loss of −32 dB at 5.8 GHz, the loss is very promising at 340 MHz bandwidth (1.52%). The findings showed that there was a trade-off between antenna impedance and thickness with bandwidth. In this work, the dimensions of a microstrip patch antenna were reduced using a fractal slot at the ground plane (DGS); gains have been improved substantially by about 4.2 dBi at 2.6GHz, 3.8 dBi at 3.5 GHz, and 3.6 dBi at 5.8 GHz. It is concludedthat in the vertical polarization pattern, the horizontal polarization patternhas thefewestnulls atlowerfrequenciesand more nulls at higher frequencies. Wideband features increase surface current distribution compared to traditionalantennas [23]. With the addition of DGS, thesizeoftheseconditeratedantennawasdecreased by 43.67%; additionally, DGS also results in the suppression of higher harmonics. However, DGS reduces an antenna's gain slightly without affecting its efficiency. The difference in gain can be further enhanced by reducing the thickness and varying fractalstructures.
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