Effect of Complementary Triangular Split Ring ...

Effect of Complementary Triangular Split Ring Resonator on Microstrip Patch Antenna Sunanda Roy, M. Abdus Samad

Swadesh Podder

Electrical and Electronic Engineering Khulna University of Engineering & Technology Khulna, Bangladesh [email protected],[email protected]

Electronics and Communication Engineering Khulna University Khulna, Bangladesh [email protected]

Keywords—Complementary triangular split ring resonator (CTSRR); gain; directivity; microstrip patch antenna (MPA); wireless local area network (WLAN)

Now a day’s split ring resonator (SRR) is used to produce the desired magnetic response which influences the applied EM field. Several theoretical and experimental works have been studied by researchers on SRR and their potential applications [4],[5].There are many types of split ring resonator design such as edge coupled SRR (EC-SRR) [6],broadside-couple SRR (BC-SRR) [7], nonbianisotropic SRR (NB-SRR) [8] and etc. However, there is a very few work on resonator based patch antenna with conventional substrates. Therefore, proper background understanding of resonator and possible impacts on conventional MPA are indispensable. In this work, a complementary triangular split ring resonator (CTSRR) has been proposed on conventional inset feed patch antenna and effect of the CTSRR on regular MPA has been analyzed from various viewing platform.

I. INTRODUCTION

II. GEOMETRIC VIEW OF CTSRR

During modern centuries, there is immense evolution in wireless local area network (WLAN) applications. Providing of a quality service for the recently increased demand in WLAN is a core level concern as usually for antenna and communication devices. The WLAN is used in our everyday life applications such as notebooks, mobile phones, routers etc. To meet the daily increasing needs, antennas used in WLAN applications are noteworthy factor. With respect to performance, a low cost feed network with miniaturization in size is also very important to carry out in terms of antenna design. Therefore, microstrip patch antenna (MPA) with compactness, low cost and ease of fabrication is effective for WLAN applications and these are widely presented in books and papers in the last decade [1]-[3].

The geometric view of the single unit of complementary triangular split ring resonator is shown in Fig. 1. The outer and inner length of the CTSRR structure is Lout = 4.25mm and Lin = 3.25mm respectively. The dimension of the resonator gap Ws =0.98mm and the thickness of the triangle Tr =1mm. The distance between two TSRR is 0.66 mm and each dimension is similar to the single unit of CTSRR structure.

Abstract—In this paper, a new complementary triangular split ring resonator (CTSRR) is proposed and the impact of CTSRR on conventional patch antenna is investigated at 2.44 GHz for WLAN applications. The electromagnetic behavior of CTSRR, as well as their equivalent circuit is developed and explained. The demonstrated theoretical approaches result in a meaningful improvement than in comparison to conventional patch antenna. The parametric studies are completed in this work with the different orientation pattern of CTSRR structure. This is exposed that with the increment of CTSRR on patch, antenna performances improve, but resonance frequency shifts toward lower frequency region.

The standard microstrip patch antenna has a very low gain, low efficiency, low power handling capacity, narrow bandwidth, simple, and inexpensive to manufacture using modern printed–circuit technology [1]. Many researchers have amended the parameters and modified geometry to produce better performance of the patch antenna considering required applications. These improvements cover several shapes of antennas, addition of special structures, and attachment of RF components or integrated circuits into the patch antenna [2].

For a given resonance frequency (fr), dielectric constant (εr), the design equations for calculating patch width (W) and length (L) of our conventional inset feed rectangular microstrip patch antenna (RMPA) are [9] W=

1 2f r μ 0 ε 0

2

=

c

ε r +1 2f r

2 ε r +1

(1)

Where, C = free space velocity of light, ߝ௥ =Dielectric constant of substrate, fr = Resonance Frequency. This width, W makes equal to about half a wavelength. It leads to good radiation efficiencies and acceptable dimensions. In order to account for the fringing and the wave propagation in the line [10] an effective dielectric constant (εreff) must be obtained.

III.

ws

ws

Tr

Lin Fig. 1. Top view of CTSRR structure.

L eff =

c 2f r ε reff

(2)

L eff > L .Thus, the resonance condition is

π 2

β(n) Leff = n. , n = 1, 2,....... which depends on Leff , not L.

The effective patch length W (εerff + 0.3)( + 0.264) ΔL h = 0.412 W h (εerff − 0.258)( + 0.8) h

(3)

Equation (3) shows that the extension of the length ∆L is a W and εerff . function of the ratio h To calculate the effective length, it has been added the length L to the extension of the length ∆L. Leff = L + 2ΔL as

(4)

The length and width of ground plane ‫ܮ‬௚ and ܹ௚ are given L g = 6h + L

(5)

Wg = 6h + L

(6)

In Fig. 2(a), the geometrical view of a CTSRR and other dimensions are indicated. The modified structure of CTSRR is newly designed with strip width c and spacing g1 and g2 between the divided parts of triangle. The equivalent circuit model of the TSRR is presented in Fig. 2(b), which behaves as a resonant cavity modeled by an LC circuit. The inductance is due to the gap between the two halves of CTSRR and the capacitance is due to the gaps in the rings itself. The divided pure copper part of triangle contributes a total inductance L and Cg1, Cg2 are the gap capacitances due to the triangular splits within the upper and the bottom part respectively. Here, magnetic field H, perpendicular to the plane, allows the creation of gaps capacitance at the opening of the ring. The electromagnetic properties of CTSRRs have been already analyzed in [11] and [12]. This analysis shows that CTSRRs behave as an LC resonator that can be excited by an external magnetic flux and exhibits a strong diamagnetism above their first resonance. CTSRRs also exhibit crosspolarization effects (magneto electric coupling) [12] so that excitation by a properly polarized time-varying external electric field is also possible. This resonant behavior is due to capacitive elements such as gaps and splits, and in turn results in very high positive and negative values of permeability close to f0 .Therefore, the orientation of the TSRR structure with respect to an electric field may affect the strength of the resonance. CTSRR can be mainly considered as a resonant magnetic dipole that can be excited by an axial magnetic field [11]. In a more rigorous analysis, the cross-polarization effects in the SRR [11], thus, this element will also exhibit a resonant magnetic polarizability along its y-axis (see Fig. 2 (a)) and, therefore, its main resonance can also be excited by an external magnetic field applied along this direction [13].These features do not affect the intrinsic circuit model of the elements, although they may affect its excitation model. Y

X

Where h = substrate height

d

Substrate height h is chosen considering surface wave & spurious radiation minimization for a given dielectric constant such that h≤

c 4 fr εr − 1

g1

Lout

EQUIVALENT CIRCUIT MODEL: CTSRR GEOMETRY

(7)

After calculating all the data, optimized values (εr =2.2, substrate height h =1.5 mm) for patch width and length are W = 49.4 mm and L =40 mm. For impedance matching, edge impedance of 50 ohm has been used for all cases and simulation has been done by CST microwave studio. Along the width of the patch, the voltage is supreme and current is minimum due to the open ends. The fields at the edges can be resolved into normal and tangential components with respect to the ground plane [1].

(a) Fig. 2.

g2

c

(b)

(a) Geometric view of CTSRR, (b) Equivalent circuit of CTSRR.

IV. ANTENNA DESIGN WITH COMPLEMENTARY TRIANGULAR SRR DESIGN This design is simulated in CST Microwave Studio using a commercially available Roger RT/Duroid 5880 material as substrate with dielectric constant εr =2.2 and dielectric loss tangent δ=0.0002. The dimension of the substrate is 50 mm width x 51 mm length. The ground plane is printed in the back side of the substrate with same dimension. A 50Ω port is used to feed power into the radiator.

Wf

ws

(b)

Lf

(a)

Fi Lout

LP

Lin ws

(c)

(d)

Fi

Tr

Wf

Wf

Wp Gpf

Fi Lp

Lp

Wp Gpf

Wp Gpf

Fig. 3. Schematic diagram of (a) Conventional patch antenna, (b) Top view of CTSRR, (c) Antenna with CTSRR, and (d) Antenna with dual CTSRR. TABLE I.

DIMENSION OF ANTENNA AND PROPOSED CTSRR

Geometric Name

Symbol

Dimension (mm)

Resonator outer width

Lout

4.25

Resonator inner width

Lin

3.25

Thickness of TCR

Tr

1.00

Resonator gap

Ws

0.98

Patch length

Lp

40

Patch wide

Wp

49.4

Substrate length

Ls

52.7

Substrate wide

Wsb

50

Lf

25.5

Feed length Feed wide

Wf

4.85

Slot or Gap of Feed line

Gpf

3.5

Substrate height

H

1.5

A 50Ω port is used to feed power into the radiator. The length of the inset feed (Lf) and the width of the feed line (Wf) for all antennas have been adjusted considering impedance matching. Fig. 3 shows the geometrical top view of inset feed patch with different structures. The dimension parameters are shown in following Table I.

30.835 dB is obtained for conventional patch antenna and 28.64 dB and -33.39 dB is achieved at fr of 2.422 GHz and 2.440 GHz for CTSRR and DCTSRR respectively. The RL of patch antennas with various structures are described in Fig. 4. The fr has been shifted because of fringing effect on MPA due to inclusion of CTSRR. Intersecting point of return loss at - 10 dB line of this design has been evaluated for bandwidth (BW) calculation and for all three antennas obtained BW is almost equal. For WLAN antenna design the gain and directivity are some other important features need to consider achieving good signal strength for end point user. For conventional antenna gain and directivity of 7.72 dB and 8.09 dBi has been obtained, respectively. Here, proposed resonator structure contains split gaps in opposite ends which store charges and influences radiation pattern on Z direction. For 1 CTSRR, gain, and directivity of 7.85 dB, and 8.15 dBi and for 2 TSRR, 7.75 dB and 8.11 dBi has been obtained, individually. The radiation pattern is a graphical representation of the relative field strength transmitted from or received by the Antenna, Simply it can be said that the power radiated or received by the Antenna is the function of angular position and radial distribution from the Antenna. In Fig. 5 radiation pattern of the proposed Antenna is revealed. The directivity has been improved by 0.02dBi and radiation efficiency of antenna increase from 91.76% to 94.49%. From above analysis, we found better RL, optimized gain and directivity for dual CTSRR. So orientation of CTSRR and increment of CTSRR unit cell on conventional patch antenna may have some influence. TABLE II.

SIMULATED PERFORMANCE OF THE CONVENTIONAL PATCH AND THE OPTIMIZATION DIMENSION OF PATCH ANTENNA

Normal

Resonance Frequency (fr) (GHz) 2.400

- 30.835

7.72

8.09

1 TSRR

2.422

- 28.864

7.85

8.15

2 TSRR

2.440

- 33.392

7.75

8.11

Antenna

Return Loss(dB)

Gain (dB)

Directivity (dBi)

V. RESULT AND DISCUSSION In this comparative study it has been studied on the analysis of CTSRR structure on patch antenna design, increment of the number of CTSRR on patch and various orientations of CTSRR structures. The key performance analysis results have been investigated. The return loss (RL) is a ratio between reflected and transmitted waves at the input of an antenna. In the impedance matching network, better RL is desirable for lower insertion loss, surface wave loss, and spurious radiation loss. From Table II, we find that at resonance frequency (fr), 2.400 GHz, RL of -

Fig. 4.

Return loss of normal patch antenna, TSRR & proposed DTSRR.

Fig. 5.

Farfield directivity of Normal and CTSRR Antenna. A

Fig. 7. The return loss of patch anntenna A to pattern E and pattern F to pattern J.

Fig. 6.

Orientation of dual TSRR Pattern A, B, C, D, D E, F, G, H, I and J.

TABLE III.

THE RETURN LOSS OF PATCH ANTEN NNA FOR DIFFERENT DETSRR PATTERN A TO PATTERN NE

TSRR Orientation

Resonant frequency, fr (GHz)

Return loss (dB)

A

2.443

- 33.391

7.775

8.11

B

2.443

- 28.245

7.773

8.10

C

2.443

- 28.175

7.773

8.21

D

2.428

- 23.968

7.339

8.29

E

2.428

-24.727

7.440

8.16

TABLE IV.

Gain B) (dB

Directivity(dBi)

THE RETURN LOSS OF PATCH ANTEN NNA FOR DIFFERENT DETSRR PATTERN F TO PATTERN NJ

TSRR Orientation

Resonant frequency, fr (GHz)

Return loss (dB)

F

2.428

G

Gain B) (dB

Directivity(dBi)

- 25.449

7.339

8.16

2.428

- 24.790

7.441

8.25

H

2.434

- 32.747

7.556

8.27

I

2.437

- 31.636

7.557

8.29

2.434

-34.127

7.556

8.28

J

In this phase of optimizatioon process, antenna performance has been measured with respecct to unit cell orientation keeping internal distance equal for all case studies. Fig. 6 shows the various orientation of resonant cut triangle of proposed antenna which has been denoted from A to J. All oriented dual CTSRR pattern perform on nearly saame resonant frequency. The comparison of return loss among a various orientations is represented in Table III, IV andd RL in Fig. 7, 8. After extensive analysis of data and simulateed results among ten oriented patterns from A to J, optimum performance has been obtained by pattern A with 7.75 dB gainn and -33.391 dB of return loss while others are inferior than A. A These intensive analyses prove that antenna performance also varies with orientation of recommended CTSRR. The directivity is alternative noticeable feature need to consider on WLAN antenna design. The directivity is the capability of an antenna to concentrate energy in a particular direction when transmitting orr receiving energy in a specific course. The gain can be linkedd with directivity using a factor named antenna efficiency. Theerefore, the design of MPA with high-directivity is not only essential but also a puzzling assignment. In Fig. 9, (a) and (bb) represent the Far field gain in polar form and (c) and (d) denotes d the Far field directivity pattern from A to J. In this phase of researchh our goal is to analysis the performance measurement of WLAN W antenna with respect to the increment of CTSRR unitt cell. The number of CTSRR addition has been aligned varioous ways on the patch antenna. Table V describes the various antenna a parameters with respect to the number of triangular ressonators. The variation of return loss in patch antenna with resspect to increment of TSRR is expressed in Fig. 10. This may be due to addition of capacitive charge concentration across wiidth of MPA. So, incorporation of CTSRR on MPA can be utiliized as frequency shifter.

Fig. 8.

The return loss of patch antenna pattern F to pattern J.

Fig. 10.

Return loss of patch antenna with respect to increment of TSRR.

(b)

(c)

(d)

Fig. 11. Fairfield gain and directivity of patch antenna with respect to increment of TSRR. TABLE VI.

Fig. 9. (a) Far field gain from orientation A to pattern E(b) Far field gain from orientation F to pattern J (c) Far field directivity from orientation A to pattern E (d) Far field directivity from orientation F to pattern J. TABLE V.

RETURN LOSS OF PATCH ANTENNA WITH INCREMENT NUMBER OF TSRR ROW WISE ALIGNMENT

Antenna

Resonant frequency, fr (GHz)

Return loss (dB)

One CTSRR

2.446

- 28.864

7.85

8.29

Two CTSRR

2.443

- 33.391

7.75

8.25

Three CTSRR

2.437

- 36.114

7.31

8.21

Four CTSRR

2.434

- 41.765

7.34

8.30

Five CTSRR

2.434

-35.824

7.33

8.31

Six CTSRR

2.434

-45.386

7.29

8.24

Gain (dB)

Directivi ty (dBi)

From Table V, and Fig. 11, we observe that highest gain is achieved on antenna with one CTSRR and most directivity is achieved on antenna with five CTSRR. But on the other hand, return loss improves with respect to increment of CTSRR on patch and interestingly this shift to lower frequency region.

Other study Huda, 2008[14] Rahim, 2009[15] Jiun-Peng, 2011[16] Xiaoyu, 2011[17]

Norikman 2013[18]

COMPARISON OF DIFFERENT ANTENNA PARAMETERS WITH RECENT RELATED WORKS SRR structure Square edge-couple SRR with 2 ring gap Square edge-couple SRR with 2 ring gap Edgecoupled SRR S Complemen tary rectangular edge couple SRR Rombic Split Ring Resonator

Applicatio n SRR Microstrip antenna Microstrip antenna

Size (mm )

Freq. (GHz )

RL (dB)

Gain (dBi)

9.1 x 9.1

2.4

- 18

7.47

49 x 17

2.7

>10

11.08

2.49

>25 4

4.71

Slot dipole antenna

6x6

Folded patch antenna

15 x 7.3

2.36

18.4

0.1

3.9x 3.9

2.40

24.0 29

6.37

Microstrip antenna

This may be due to concentration of electron and its impact on electromagnetic field distribution. Therefore, this finding can be indispensable for frequency tunable solution.

VI. CONCLUSION The impact of CTSRR on the performance of microstrip patch antenna is theoretically investigated. For various orientation of CTSRR and increment of CTSRR unit cell, the antenna resonates between 2.43 to 2.45 GHz bands. The antenna shows a directional radiation pattern and capacitive charge develops in gap-cut position improves gain and directivity. Numerical study of the effect and physical parameters of CTSRR on antenna has been carried out. Resonance frequency shifts toward the lower frequency region with the increment of CTSRR unit cell. So, proposed design may be helpful for frequency tunable solution. Expected improvement in bandwidth, and impact of gain and directivity with respect to addition of CTSRR on Patch has not been observed flawlessly due to patch antenna feeding technique or perfect impedance matching. Future modified feeding network or designs can be effective to overcome this problem. REFERENCES [1] [2]

[3] [4]

[5]

[6]

[7]

C. A. Balanis, Antenna Theory: Analysis & Design, John Willey & Sons, Inc., 1997. Y. Qin, S. Gao, A. Sambell, E. Korolkiewicz, and M. Elsdon, “Broadband patch antenna with ring slot coupling,” Electronics Letters, Vol. 40, no., 1, pp. 4-6, January 2004. J.R. James, P.S Hall, and C. Wood, Microstrip Antenna Theory and Design, 1981. R. W. Ziolkowski, and E. Heyman,“Wave propagation in mediahaving negative permittivity and permeability,“Physical Review,” vol. 64, no., pp. 56625.1-056625.15, Oct. 2001. T. F. Gundogdu, M. Gokkavvas, K. Guven, M. Kafesaki, C. M. Soukoulis, and E. Ozbay, “Simulation and micro-fabrication of optically switchable split ring resonators,” Photonics and Nanostructures Fundamental and Applications, vol. 5, pp. 106-112, October 2007. H. A. Majid, M. K. A. Rahim, and T. Masri, “Left handed metamaterial design for microstrip antenna application,” in RF and Microwave Conference, 2008. RFM 2008. IEEE International , vol., no., pp. 218221, 2-4 Dec. 2008. E. Ekmekci, and G. T. Sayan, “Metamaterial sensor applications based on broadside-coupled SRR and V-Shaped resonator structures,” in Antennas and Propagation (APSURSI), 2011 IEEE International Symposium on , vol., no., pp. 1170-1172, 3-8 July 2011.

[8]

[9] [10] [11]

[12]

[13]

[14] [15]

[16]

[17]

[18]

M. Marques, R., R. Medina and E. I. Raffi, “Role of Bi-anistropy in negative permeability and left-handed metamaterials,” Physical Review B, vol. 65(1), pp. 1-6, April 2002. C. A. Balanis, Antenna Theory and Design, John Wiley & Sons, Inc., 1997. J. R James, and P.S. Hall, Handbook of Microstrip Antennas, vol. 2, Peter Peregrinus Ltd., London, 1989. R. Marqués, F. Mesa, J. Martel, and F. Medina, “Comparative analysis of edge- and broadside coupled split ring resonators for metamaterial design Theory and experiment,” IEEE Trans. Antennas Propag., vol. 51, no. 10, pp. 2572–2581, Oct. 2003. R. Marqués, F. Medina, and R. Rafii-El-Idrissi,“Role of bianisotropy in negative permeability and left handed metamaterials,” Phys. Rev. B, Condens.Matter, vol. 65, pp. 144441(1)–144441(6), April 2002. F. Falcone, T. Lopetegi, M. A. G. Laso, J. D. Baena, J. Bonache, M.Beruete, R. Marqués, F. Martín, and M. Sorolla, “Babinet principle applied to metasurface and metamaterial design,” Phys. Rev. Lett., vol. 93, pp. 197 401(1)–197 401(4), Nov. 2004. M. Gil, J. Bonache, F. Martin, “Metamaterial Filters: A Review”, Metamaterial, vol. 2, pp. 186-197, 2008. M. K. A Rahim, H. A. Majid, and T. Masri, , “Microstrip antenna incorporated with left-handed metamaterial at 2.7 GHz,” in Antenna Technology, 2009. iWAT 2009. IEEE International Workshop on , vol., no., pp. 1-4, 2-4 March 2009. J. P. Chen, and P. Hsu, “A miniaturized slot dipole antenna capacitively fed by a CPW with split-ring resonators,” in Antennas and Propagation (APSURSI), 2011 IEEE International Symposium on , vol., no., pp. 779781, 3-8 July 2011. X. Cheng; J. Shi; C. Kim, and D. E. Senior, and Y. K. Yoon, “A compact self-packaged patch antenna with non-planar complimentary split ring resonator loading,” in Antennas and Propagation (APSURSI), 2011 IEEE International Symposium on , vol., no., pp. 1036-1039, 3-8 July 2011. H. Nornikman, B. H. Ahmad, A. Aziz, and A. R. Othman, “Effect of single complimentary split ring resonator structure on microstrip patch antenna design,” in Wireless Technology and Applications (ISWTA), 2012 IEEE Symposium on , vol., no., pp. 239-244, 23-26 Sept. 2012.