Circularly Polarized Broadband Antenna Deploying Fractal Slot Geometry

Circularly Polarized Broadband Antenna Deploying Fractal Slot Geometry

Jayaram Kizhekke Pakkathillam and Malathi Kanagasabai,Member,IEEE

Abstract—This letter introduces a new method of achieving broad VSWR bandwidth and axial ratio bandwidth(ARBW) deploying fractal geometry in a single feed compact annular slot antenna loaded with diagonal slots.Various studies have been carried out for different iteration order(IO)and iteration factor (IF)on antenna performance.A measured VSWR bandwidth (2:1)of400MHz(1.37GHz to1.77GHz)and measured ARBW of360MHz(1.47GHz to1.83GHz)is achieved.A measured peak gain of6.6dB is reported at1.775GHz.This antenna can be ap-plied to handheld devices applications and WSN node positioning requiring GPS Data.

Index Terms—Broadband antenna,circular polarization(CP), fractals,GNSS.

I.I NTRODUCTION

F RACTAL is a mathematical set,which exhibits a repeating

pattern that displays at every iteration.If the replication is exactly same for every iteration,that is called as a self-similar pattern[1].Fractal geometriesfind applications in antenna en-gineering.They can be employed to achieve broadband/multi-band miniaturized antennas[2]–[5].For navigation and commu-nication in handheld devices and positioning of sensor nodes in temperature mapping applications,circularly polarized an-tennas are highly desired because it offers better mobility,higher weather penetration and very less polarization loss.Also the signal traversing through the space experiences Faraday rota-tion.Hence,the circularly polarized receiver offers high degree of signal reception[6].

Conventional circularly polarized receivers such as helical and spiral antennas are undesirable due to their high form factor. Conventional diagonal slot design[7]provides narrow VSWR and axial ratio bandwidth(ARBW)(0.94%).Hence,they are not sufficient considering the band excursion due to errors in reception[6]as well as the leeway to include various naviga-tion and communication applications.The fractal slots can be employed to achieve wide VSWR bandwidth in microstrip fed antennas[8].But to achieve wide ARBW,we need to go for multiple feed antenna systems[9].The crossed dipole structure

Manuscript received November27,2014;revised January08,2015;accepted February07,2015.Date of publication February10,2015;date of current ver-sion June02,2015.This work was supported by the Anna centenary research fellowship(ACRF)program of Anna University,Chennai,India.

The authors are with the Electronics and Communication Department,CEG, Anna University,Chennai600025,India(e-mail:jayaramkarivellur@gmail. com;mala@).

Color versions of one or more of thefigures in this letter are available online at .

Digital Object Identifier10.1109/LAWP.2015.2402286with complex feed also is a good choice,but it increases the size and system level complexity[10].

In this letter,a single straight line microstrip fed printed an-nular slot antenna with diagonal slots is described.The pro-posed antenna achieves broadband circularly polarized radia-tion without any parasitic structure.Deployment of fractal struc-ture brings compactness()for the proposed an-tenna.The proposed antenna shows improved ARBW compared to[7],[11],and[12].Also the simple profile reduces the com-plexity in integrating the antenna with handheld devices and sensor nodes.The main design essentials dealing with a fractal structure are iteration order(IO)and iteration factor(IF).In fractal geometry,IO represents the number of iterations car-ried out for the particular fractal structure.IF deals with the factor by which geometry is scaled in each iteration[8].Lit-erature[5],[12]employ constant IF and vary IO for the per-formance evaluation.In the proposed work,IF is also varied to study the performance of the antenna.The novel aspect of the work is linking the IF with ARBW for the design of a broadband antenna,in order to prove that IF is also an influential param-eter in fractal CP antenna design.The method used here is a hybridization of fractal structure and diagonal slots.A broad-band response is achieved compared to conventional diagonal slot design.

II.F RACTAL A NTENNA D ESIGN

Circular polarization can be achieved if the orthogonal modes are excited which result in afield with equally strong planar field components and quadrature phase.The various methods includes patch antennas with truncated edges[13],Exciting or-thogonal modes by using dual/multiple feed technique[9]and Stubs from ground as in[12]with a fractal CPW fed geometry having two arms separated by.This antenna uses the fractal geometry for impedance matching.The ARBW is obtained by using a stub from the ground part.The main drawback of using of stubs is the reduced ARBW.In order to obtain broad VSWR and ARBW using fractal geometry,it requires a study unrav-eling the effect of different parameters of the particular fractal geometry on the antenna bandwidth response.

Fig.1shows the fractal antenna schematic.The antenna is designed in such a way that the resulting geometry will have a set of fractal slots arranged along a skewed line to the x-axis.These perturbations will help in exciting the orthogonal degenerate modes[14].Here,mode degeneracy can be removed by equating the amplitudes of thefields at the two modes and providing the phase quadrature,through a study,leading tofix the parameters of the fractal structure.

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