L Slot Circularly Polarized Broadband AntennaMeenakshi Saini', Nitin Kathuria', Y.K. Pandey'

1M.Tech. Student, Dept. of Electronics & Communication, NIET, Greater Noida).JDept. of Electronics & Communication, AIMT, Greater Noida

meenakshisaini07@gmail.com

Abstract-A single-fed circularly polarized (CP) patchantenna is designed and built using L-slot loaded patchtechnique. The antenna is designed on a high dielectricconstant (s, = 10.02) substrate which achieves a reasonablebandwidth and axial ratio bandwidth with respect to a U slotantenna. At the operating frequency of 1.575 GHz with thesize of the patch is 25mm X 25mm, while ground plane of60mm X 60mm and the thickness ofthe substrate is 9.12mm.Bandwidth is enhanced to 18.42% and Axial RatioBandwidth by 4% by this design. The other Parameters ofantenna like return loss and radiation pattern are alsoanalyzed using HFSS software.

Key Words- Circularly polarized (CP), patch antenna,L-slot

1. INTRODUCTION

Microstrip Patch Antenna (MSA) has severaladvantages such as simple structure, low profile and lowcost, it is often used in various applications. One of thedisadvantages of the traditional MSA is its poorimpedance-bandwidth. The bandwidth enhancementtechniques for the MSA, the MSAs with parasiticelements, and the L-shaped probe-fed MSA are wellknown [1]. With the rapid development of the satellitecommunication and positioning system, more and moreconsideration has been paid to circularly polarized (CP)antennas. The Global Positioning Satellite (GPS)system operates at 1575 and/or 1227 MHz with RHCPsignals [2]. Antennas which operate on both thefrequencies are preferred to address additional anddemanding applications requirements. Circularlypolarized antenna is well-known for its feature ofrelative insensitivity to transmitter and receiverorientations. CP radiation is generated when twodegenerate orthogonal linearly polarized modes, ofequal amplitude and 90° phase difference, areindependently excited. Patch antenna is one attractivecandidate for producing circular polarization owning toits characteristics of wide bandwidth, high gain, lowprofile and low cost. For a single feed patch antenna,truncating a pair of comers and cutting a diagonal slotare two conventional ways to generate CP radiation.However, narrow axial ratio bandwidths ofless than 1%are normally obtained. To enhance the CP bandwidth,some techniques, such as a probe-fed comer truncated

patch with L-shaped slot with ground plane, ameandering probe truncated comers stacked patchantenna, and L-shaped probe-fed patch antenna with across slot were proposed respectively[3]. If the patchshape is like the square or the circle, the bandwidth is thesame and proportional to its size. The deviations startwhen the shape changes drastically and becomes anarrow or wide rectangle. If the radiation edge becomesnarrow, decreases the radiation loss and increases theantenna Q, reducing the bandwidth. For a patch with alarge radiating edge, the reverse is true [4]. In general,the advantages and drawbacks of patch antennas withhigh permittivity substrate are a controversial problemand some interesting results. In this paper we haveperformed an exploration on patch antennas built on ahigh permittivity substrate [5]. To obtain the highbandwidth a fork-like L-probe is used. The dimension ofthe patch as well as the position of the probe feed isoptimized leading to a wideband circular polarizedbehavior [6].

If'a· • .~• 0

a L <L.. c .•.top~e~L~ ~

L slot patch cp patchground plane ±

side view I ~~ _SMA connector

Parameter a b c d e h G L W Er

Unit(mm) 6 10 10 7 2 9.12 60 25 25 10.02

Fig. 1 Geometry of the antenna

II. ANTENNA GEOMETRY AND DESIG

The antenna geometry is shown in Fig. 1.This antennais designed to operate at around 1.575 GHz. The truncatedsquare patch of length and width is printed on amicrowave substrate (with dielectric constant 10.02) forexciting two orthogonal modes for CP radiation. A L-shaped slot (with I-mm width) is cut in the truncated

NIET Journal of Engineering & Technology, Vol. 5, 2014 37

patch. The function of the L-slot is to introduce acapacitance that can suppress the inductance due to thevertical feeding probe so as to enhance the impedancebandwidth. The feeding probe is connected to an SMAlauncher that is mounted underneath the ground plane. Asdiscussed, L-slot enables the use of thicker substrates toobtain larger impedance bandwidth. The total height ofthe dielectric is 9.12 mm, and the dielectric is made up ofsix layers ofthin substrates. Designing and simulation isperformed by using high frequency simulation software(HFSS).

Ill. RESULTS

0

-10

3 -20 -dB(S(l,l))tr: [with L

-30 slot]

-40

1.4 1.5 1.6 1.7 1.8 1.9Frequency(GHz)

Fig. 2 Simulated return loss

~. 30~oo

/

1 ·10.00

\~o

·20.00

·30.00

J

s~ ----

1~0

·'800

·'80

Fig.3 LHCP Radiation pattern at 1.575 GHz (",=90',0')

Fig. 4 RHCP Radiation pattern at 1.575 GHz (8=90', 0')

The measured return loss is shown in Fig.2. Theimpedance bandwidth is 18.5% with 10 dB between1.52-1.80 GHz.

Fig. 3 and Fig. 4 show the measured radiationpatterns at 1.575 GHz. The 3-dB beam widths are 92° and90° in 8=90° and ~=Oo planes respectively. It can beobserved that in the plane, the cross polarization is 25 dBbelow the copolarization above the ground plane. In theplane, it is 25 dB below the copolarization. Referring tothe operating frequency of 1.575 GHz, the patchdimensions are about 25X25 square patches and thesubstrate thickness is about 9.12mm. For realapplication of GPS, the receiving antenna should bedesigned as a right-hand circularly polarized (RHCP)antenna. In this design, it is easy to adjust the antennawith RHCP operation by changing the truncated comerofthe patch to another diagonal axis[7].

IV. SIMULATION

This simulation is carried out by using anelectromagnetic (EM) commercial software tool, HFSS.For small antenna design, the size of the ground plane isa very important parameter to be considered. In thissection, a study for an impedance bandwidth responsewith different ground plane sizes is carried out. (For this

38 NIET Journal of Engineering & Technology, Vol. 5, 2014

simulation, the size of the ground plane is equal to thesubstrate size). The square-shaped ground plane with alength varied from 40 to 60 mm is investigated.

0~

-10 I

~,.-...CO -20 \~ G=50~ -30 f=

I IC/) V

G=40-40

--G=60-50

1.4 1.5 1.6 1.7 1.8 1.9

Freq (GHz)

Fig. 5 Measured return loss with different size of ground plane with L slot

Fig. 5 depicts the return loss responses for the L-slot CP antenna with different ground plane sizes.The result indicates that when the size of the groundplane is too small, the impedance bandwidth of thisantenna would significantly reduce. When Groundplane is 60 mm the impedance bandwidth is 18.5%whereas, the bandwidth decreases for 40 mm Groundplane.

Fig. 6 illustrates responses of the AR withdifferent ground plane sizes. When G=60 mm, theminimum value of the axial ratio for the antenna ismaximum. However, if the ground plane size isreduced, the value of AR is deteriorated. For theantenna gain, a smaller ground plane size would alsocause the decrease in gain. Since L-slot loadedtechnique is employed for improving the bandwidthperformance for a small CP antenna, a study ofchanging the values of L-slot parameters are carriedout to show the effect of the L-slot in the CP antenna.Two parameters band c are investigated.

Fig.7 shows the impedance bandwidth responsewith different and fixed b= I0 mm. For this antenna,when the value ofb is selected between 8-12 mm, theantenna has good and wide bandwidth characteristic.However, as b is increased (b> 12) mm, the overallimpedance bandwidth is deteriorated as considerablemismatch occurred.

Fig.8 shows the impedance bandwidth responsewith different c and fixed b= 10 mm. The value of c isvaried from 9 to 12 mm. It is observed that it cannotbe either too small or large; otherwise the antennawould have a narrow impedance bandwidth.

Finally, a comparison for a CP antenna with-Llwith U-slot is given in Table 1 and shown in Fig.9.The simulated return loss and axial ratio for CPantenna is measured and reported.

15 "14 "131211

CO 10 \'9U 8

7 if ------.... G=50c:::: 16-< 54 G=40321 --G=600

1.4 1,5 1.6 1.7 1.8Freq (GHz)

Fig.6 Axial ratio with different size of ground plane

0

oS .:,....,~ I -:!O

'-'- . I-(I)V

sH

a

so

ss,

Freq (GHz)

Fig. 7 Simulated Return loss with different size ofb

It is observed that the presence of L-slot gave asignificant bandwidth enhancement in the impedancebandwidth but only less improvement in the axialratio bandwidth. However, since a thick substrate isemployed in the proposed CP antenna, the absence ofthe L-slot would generate very high inductance fromthe feeding probe and would causes the impedancebandwidth and axial ratio bandwidth not to overlap.For a CP antenna, the usable bandwidth is the rangeoffrequencies for s 11 :510 dB. Therefore, if the patchantenna is designed using thick substrate material,the use of the L-slot loaded technique can providebandwidth enhancement, but also ensure both axialratio and impedance bandwidth to overlap.

NIET Journal of Engineering & Technology, Vol. 5, 2014 39

V. CONCLUSION

A miniature circularly polarized patch antennahas been designed which consists of one L-slotsquare patch with truncated corners supported by asubstrate with dielectric constant of 10.02 forachieving small size. The operating frequency,square patch size, ground plane size and thickness ofsubstrate are 1.575 GHz, 25X25, 60X60, 9.12mmsuccessively. Measured results show that this single-feed CP patch antenna attains bandwidth of 18.42%in the frequency range 1.52-1.80 GHz and axial ratiobandwidth is 4%, which is within the impedancebandwidth. This small antenna can be used for anumber of wireless communication applications,including GPS receivers.

o

·lU

·15 (=9

.......•. (=11·20------~1-++------

• -- -- (=12

·15 -------...;+...o.f------- --c-10

·~n

·35

14 15 1916 17 18

Freq (GHz)

Fig.8 Simulated return loss with different size of ground plane

0

-10-CO"0 -20 -- with L slot

rlrl ••••••• With U slotV1 -30

-40

1.4 1.5 1.6 1.7 1.8 1.9Freq(GHz)

Fig.9 Comparison ofretum loss with different UIL slot

TABLE 1. Summary for simulated ImpedanceBandwidth and Axial Ratio Bandwidth for CP antenna

with U slot and L slot

CP Imp.BW AR

Antenna (S11:O:;-10 dB) BW (AR:o:;3 dB)

With U Slot 15.11% 3.16%

1.53GHz to 1.56 GHz

1.78 GHz 1.61 GHz

WithL 18.42% 4%

Slot 1.52 GHz to 1.53 GHz to

1.80 GHz 1.59 GHz

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Shigeru Makino, "Basic Study on Wideband MicrostripPatch Antenna Incorporating Matching-Stubs onto Patch

Conductor"l EEE,PP.885-888,07 12007.

[2] Xiaoye Sun, Zhijun Zhang, Zhenghe feng, "Dual-Band

Circularly Polarized Stacked Annular-Ring Patch Antenna

for GPS Application", IEEE Antennas And Wireless

Propagation 49-52 Letters, VOL. IO,pp 2011

[3] Can-Hui Chen and E. K. N. Yung "A ovel Unidirectional

Dual-Band Circularly-Polarized

[4] Patch Antenna", IEEE Transactions On Antennas AndPropagation, Vol. 59, NO. 8,pp,3052-3057, August 2011

[5] Zarreen Aijaz I& S.C. Shrivastava, "Effect of the Different

Shapes: Aperture Coupled Microstrip Slot Antenna"International Journal of Electronics Engineering, 2( I), pp.

103-105,20 IO.

[6] D. D. Sandu, O. Avadanei, A. Joachim, G. Banciu, P. Gasner,

"Microstrip Patch Antenna With Dielectric Substrate",

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No.5, pp. 1381 - 1387,2003

[7] M. Pirai and H. R. Hassani, "L-Probe fed Circular Polarized

Wideband Planar Patch Antenna On Cylindrical Structure,Progress In Electromagnetics Research C, Vol. 3, 161-167,

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[8] Ka Yan Lam, Kwai-Man Luk, Kai Fong Lee, Hang Wong,

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40 NIET Journal of Engineering & Technology, Vol. 5, 2014

Meenakshi Saini was born in RoorkeeIndia, in 1982. She received Engg.Diploma in Electronics Engineeringfrom GGPS College, Shamli. Shereceived the A.M.I.E degree inelectronics and communication

engineering from the Institution of Engineers Kolkata,India, in 2009, and the M.Tech. Degree inTelecommunication engineering from the Uttar PradeshTechnical University UP, India, in 2014. She has workedas an Electronics Engineer in Research Developmentdepartment at Balaji Telecom Solutions (Roorkee) fromApril 5, 2005 to May 10,2006. She is also having oneyear apprenticeship in maintenance of electronicsapparatus & computer work of BHEL (Haridwar) fromFeb l8th,2004toFeb 17th 2005.

Nitin Kathuria received his B.E.degree In Electronics &Telecommunication from IT.MahajanCollege of Engineering, under NorthMaharashtra University in 2004, theM.E. degree in Communication &

Information from Griffith University, Brisbane,Australia, in 2007. He was joined teaching as a lecturerin the Department of Electronics & Communication,Moradabad in 2009-10. Presently he is an Assistant

Professor in Department of Electronics &Communication at Accurate Institute of Technology &Management Communication, Greater NOIDA, UP,India. His research interests include Antenna Design &Microwave Engineering. At present he is activelyengaged in design and analysis of Ultra WidebandAntennas.

V K Pandey graduated in ElectronicsEngineering from The University ofPoona in 1990. He obtained M.E.(Control & Instrumentation) withhonors from Delhi University in 1997.He received his Ph.D (Electronics

Engineering) degree from I.T. BHU Varanasi in 2006. Atpresent he is working as Professor in Electronics &Communication Engineering Department. He received agrant of Rs. 14.5 lacs under MODROB scheme fromAICTE, New Delhi for establishing Project andResearch laboratory in the Department of Electronicsand Communication.

Prof. Pandey has around 23 years experience, teachingunder graduate and post graduate classes. His field ofresearch is Microwave Engineering. He has publishedaround 25 research papers in Intemational/Nationaljournals and conferences of repute.

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