A Compact Metamaterial-Based Horizontally Polarized Omnidirectional Antenna Array

Xianming Qing and Zhi Ning Chen RF, Antenna and Optical Department

Institute for Infocomm Research, Singapore qingxm@i2r.a-star.edu.sg, chenzn@i2r.a-star.edu.sg

Abstract— A metamaterial-based horizontally polarized omnidirectional antenna array using zero phase-shift-line loop element is proposed. The antenna with an overall size of 40 mm × 40 mm × 230 mm shows desirable performance over the frequency range of 2.352.55 GHz with return loss larger than 10 dB, gain greater than 6 dBi, and omnidirectivity less than ± 2.3 dB.

I. INTRODUCTION

Wireless mesh networks can easily and effectively connect entire cities using existing technology. Traditional networks rely on a small number of wired access points or wireless hotspots to connect users. In a wireless mesh network, the network connection is spread out among dozens or even hundreds of wireless mesh nodes that "talk" to each other to share the network connection across a large area. The conventional WiFi wireless 802.11 a/b/g access points utilize vertically polarized omnidirectional antennas for transmissions, which limits the access point to a single spatial stream. The wireless mesh networks, however, using both vertically polarized and horizontally omnidirectional antennas, is able to offer a robust, reliable outdoor transmission.

Vertically polarized omnidirectional antennas have been studies for years, wherein the antenna generates omnidirectional radiation in the H-plane [1-4]. The horizontally polarized omnidirectional antenna is required to radiate equally in the plane aligning the E-field (E-plane), which is more challenging. Some horizontally omnidirectional antenna designs have been reported. Besides the traditional configurations such as folded dipole/monopole structure, multiple dipoles, printed magnetic dipole, dielectric resonator and waveguide slot array [5-7], metamaterial-based horizontally omni-directional antenna have been reported recently[8-10].

In this paper, a compact metamaterial-based omnidirectional antenna array is investigated at 2.4 GHz band to generate desired horizontally polarized omnidirectional radiation with higher gain.

(a)

Segmented loop

Feed point

RO4003

FR4

R18mm

1mm

(b)

(c)

Fig. 1. Configuration of the proposed antenna: (a) three-dimensional

view, (b) radiation element, (c) photo of the antenna prototype.

1792978-1-4673-5317-5/13/$31.00 ©2013 IEEE AP-S 2013

II. ANTENNA CONFIGURATION

The configuration of the proposed antenna is shown in Fig. 1. The antenna is composed of four radiators and a feeding network. The radiator is a segmented loop comprising multiple zero phase-shift-line sections which provide a very small phase delay between the adjacent sections. Therefore, the current flowing along the segmented loop is kept in a single direction without phase reversion and thus generates horizontally polarized omnidirectional radiation. The segmented loops are printed onto an FR4 substrate with thickness of 0.5mm (r = 4.4, tan = 0.02). The four segmented loop elements are connected to the outputs of the parallel line feeding network, respectively. The parallel line feeding network is etched on the opposite sides of a 0.8mm thick RO4003 substrate (r = 3.38, tan = 0.0023) and positioned inside the radiators, which makes the antenna array compact.

III. RESUTLS AND DISCUSSION

The antenna was prototyped and measured in an anechoic chamber. Fig. 2 exhibits the measured |S11| of the antenna prototype; a reflection coefficient of -10 dB is achieved from 2.35 GHz to 2.55 GHz. The measured gain of the antenna is shown in Fig. 3, it is greater than 6 dBi over 2.35 GHz 2.55 GHz. The measured E- and H- plane radiation patterns at 2.45 GHz are illustrated in Fig. 4. Good omnidirectional radiation in E-plane is achieved with an omnidirectivity of ± 2.3 dB.

2.30 2.35 2.40 2.45 2.50 2.55 2.60

-20

-15

-10

-5

0

|S11

|, dB

Frequency, GHz Fig. 2. Measured |S11| of the antenna.

2.30 2.35 2.40 2.45 2.50 2.55 2.600

2

4

6

8

Gai

n, d

Bi

Frequency, GHz

Fig. 3. Measured gain of the antenna.

IV. CONCLUTION

Design an antenna with horizontally polarized omnidirectional radiation is a big challenge. The proposed metamaterial-based horizontally polarized omnidirectional

antenna array has demonstrated desired performance at 2.4 GHz band, which is useful for wireless mesh networks.

-50

-40

-30

-20

-10

0

-50

-40

-30

-20

-10

0

()0o

2.45 GHzE-plane

325o

270o

(dB)0o

45o

90o

135o

180o

225o

-50

-40

-30

-20

-10

0

-50

-40

-30

-20

-10

0

()0o

2.45 GHzH-plane

-45o

-90o

(dB)0o

45o

90o

135o

180o

-135o

Fig. 4. Measured radiation patterns of the antenna at 2.45 GHz.

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[7] C. C. Lin, L. C. Kuo, and H. R. Chuang, “A horizontally polarized omnidirectional printed antenna for WLAN applications,” IEEE Trans. Antennas Propagat., vol. 54, no. 11, pp. 3551–3556, Nov. 2006.

[8] K. Wei, Z. Zhang, and Z. Feng, “Design of a wideband horizontally polarized omnidirectional printed loop antenna,” IEEE Antennas and Wireless Propagation Letter, vol. 11, pp. 49–52, 2012.

[9] X. Qing and Z. N. Chen, “Horizontally polarized omnidirectional segmented loop antenna,” 6th European Conference on Antennas and Propagation (EUCAP), 2012, pp. 2904–2907.

[10] H. Nakano, R. Satake, and J. Yamauchi, “Realization of a horizontally polarized, low-profile, omnidirectional antenna with an EBG reflector,” 4th European Conference on Antennas and Propagation (EUCAP), 2010, pp. 495–498.

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