Gain Improvement of A Metasurface for U-slot Microstrip Patch Antenna Array at 5.8 GHz

DucDung Nguyen1 and Chulhun Seo1

1Department of Information and Communication, Material Convergence Soongsil University, Seoul, Korea E-mail: dungnd@vinhuni.edu.vn

Abstract – This paper concentrate on improvement of gain

for microstrip planar array antenna. The structure in this project is 2 by 1 microstrip line fed U-slot rectangular antenna array using metasurface, in which the metasurface acts as a superstrate at a small distance. The metasurface is a Mu-near-zero (MNZ) type, an array of 7x7 double-square-closed ring resonators printed on a thin dielectric slab to obtain the maximum gain high at frequency 5.8 GHz array antenna. Frequency 5.8 GHz can be applied to unlicensed WiMAX. The proposed antenna shows improved gain, return loss, and radiation pattern.

Index Terms — Metasurface, Microstrip Antennas, MNZ, WiMAX, U-Slot.

1. Introduction

Antenna is an important component that has been an attractive choice in compact and various application in communication systems. Because they may have a lot of advantages such as small size, simple, low manufacturing costs, circular polarization, and frequency agility. However, at the same time they have some serious drawbacks like small bandwith, poor directionality, low efficiency, etc.

Improving the gain of antenna has been the goal of many researchers in recent years. To overcome this issue, several methods have been suggested such as reflectors, using thick substrate, defected ground structure, parasitic elements, slot or array techniques, etc. The array methods provide considerable enhancement in the gain of antennas [1], but they have difficult task in designing of power dividers and the dip in the radiation any feed network suffer from the poor matching. In[2] has been presented of coaxially fed U-slot using rectangular.

In recent years, MNZ metamaterials have been widely successfully used to improve the performance of antennas, as a result, the performance comparison of the antenna with MNZ metamaterials has a good potential than the one without MNZ metamaterials [3]. Many researchs have engineed MNZ materials for differents applicatios. The Mu-near-zero (MNZ) is used as a grounded substrates for directivity enhancement, but the gaind bandwith and matching impedance are not addressed [4]. In this paper presents a simultaneous improvement on gain of the U-slot antenna by using a metasurface of MNZ type. The MNZ metasurface consists of unit-cells of two-square-loops, which is a near-zero refractive index at 5.8 GHz, a very high gain can be obtained.

2. Metasurface and antenna design

The proposed antenna configuration with its design parameters is illustrated in Fig.1. The overall size of this low-cost metasurface antnenna is 60 mm x 60 mm x 9.145 mm.

Fig. 1. Geometry of the proposed antenna (a) U-slots array antenna; (b) unit-cell and 7x7 cells (c) slide view of

metasurface antenna.

TABLE I Dimensions of proposed antenna

Parameters Dimensions

(mm) Parameters

Dimensions (mm)

a 30.8 g3 0.5 b 14.4 h 1.555 c 20.3 h1 1.52 c1 6.7 l 1.1 e 5 L1 8.62 f 10 m1 7.62

g1 0.5 m2 5.62 g2 0.7 P 60

As it is observed in Fig1. (a) the geometrical structure of U-slot antenna, the antenna is designed to be operated at 5.8GHz. Fig 1(b) depicts detailed of a unit cell MNZ-metasurface, which has a periodic structure compose 7x7 double-closed-squared ring resonators. The unit cell has a square periodic of L1 = 8.62 mm, the length outer and iner of square loop have side m1 = 7.62 mm, m2 = 5.62 mm, respectively.

2018 International Symposium on Antennas and Propagation (ISAP 2018)October 23~26, 2018 / Paradise Hotel Busan, Busan, Korea

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Fig.2. Effective permeability for a single unit-cell

And the widths and gaps separation between the double-closed-squared ring represented by g3 = 0.5 mm. Slide view of the proposed antenna is illustrated in Fig.1 (c). Both, U-slot antenna array and metasurface, are printed on Taconic TLY-5 substrate of thickness h = 1.52 mm, dielectric constant ɛr =2.2 and loss tangent = 0.0009. Various dimensions of the proposed antenna are presented in Table 1.

3. Result and discussion

Based on the effective permeability for a single unit-cell operating at the desired frequency of 5.8GHz, as play in Fig.2, the unit-cell exhibits a near-zero-index of nʹ = 0.58.

Fig.3. Simulated S-parameter compared to the patch only

The return loss characteristics of the only U-slot antenna array and the proposed MNZ metasurface U-slot antenna array showns in Fig.3. It is observed that, at the same resonator frequency, attributed to the effect of the cover reflected electromagnetic, the operating frequency of the U-slot antenna array covered with MNZ metasurface slightly shifts to 5.8 GHz. It indicates that the antenna with designed metasurface placed on the top has a good matching condition, itself return loss cover the bandwidth 5.725 - 5.875 GHz. Whereas the return loss of the only U-slot array antenna is plotted in Fig.3 for comparison, thus corresponding to the bandwidth enhancement of 50%. It can be seen that the strong resonance of MNZ metasurface improves the matching and the resonant, it implies that the enhancement gain and bandwidth of WiMAX band can be achieved.

Fig.4 shows the plane radiation patterns characteristic of only patch U-slot array antenna with designed metasurface. Fig.5 and Fig 6 show the elevation plane pattern Gain of the only U-slot array antenna and the U-slot array antenna with metasurface, respectively. The Fig.5 and Fig.6 depicts that for MNZ metasurface palace on the top of U-slot array antenna the gain produce is 11.4 dBi while for the case only U-slot array antenna the gain is 7.46 dBi. The 3.84 dBi enhancement is obtained, it implies that the designed metasurface could improve gain characteristic as well.

Fig.4. Radiation pattern characteristic for two different alignments

Fig.5. Elevation Pattern Gain display of only U-slot

antenna

Fig.6. Elevation Pattern Gain display of U-slot antenna covered by MNZ metasurface

4. Conclusion

This article presents a high-gain low-cost U-slot array antenna for 5.8 GHz WiMAX application. The proposed antenna improved gain is achieved by utilizing the MNZ metasurface which is designed by a single layer with array double-square-close ring. At the resonance frequency 5.8 GHz, the improvement of gain is 3.84 dB increased, that result in a 11.3 dB peak gain at this frequency. The different performance between two design implies that metarsurface is capable enough to enhance the performance of antenna.

References [1] C. Arora, S. S. Pattnaik, “Metamaterials superstrate for performance

enhance of microstrip patch antenna array,” in Proc. International Conference on Signal Processing and Integrated Networks, 2016, pp.775-779

[2] T. Huynh and K. F. Lee, “Single-layer single-patch wideband microstripantenna,” Electron Lett., vol. 31, ,pp. 1310–1312, 1995.

[3] M. H. Ullah, M. S. Islam, “A near-zero-refractive index meta-surface for antenna performance improvement,” Metarials., vol. 6, pp. 5058-50668, 2013.

[4] K. Lovat, P. B, “Combinna-tion of low/high permittivity and/or permeability substrate for highly directive planar MMs antenna,” IET Proc Microwave Antennas Propag., vol. 1, pp. 177-183, 2007.

2018 International Symposium on Antennas and Propagation (ISAP 2018)October 23~26, 2018 / Paradise Hotel Busan, Busan, Korea

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