ATMS INDIA

2015

The 8th Annual International Conference ATMS -2015, Bangalore

© ATMS (INDIA)

Dualband Monopole antenna for LTE Femtocell Base Station

Idayachandran G Dept. of Electronics Engineering

School of Engineering and Technology Pondicherry University

Puducherry - 605014, India idayachandrang@gmail.com

Nakkeeran R Dept. of Electronics Engineering

School of Engineering and Technology Pondicherry University

Puducherry - 605014, India nakkeeranpu@gmail.com

Abstract In this paper, a dualband monopole antenna for LTE femtocell base station is proposed. The proposed antenna consists of rectangular loop ground and a stepped monopole radiator. By varying the geometry of loop ground and stepped monopole radiator, a dual broadband characteristic is observed. The dual broad band is achieved without employing any complex antenna geometry or DGS as reported in the recent literature. The antenna is printed on FR4 substrate and has an overall dimension of (63 × 50 × 1.6) mm3. The simulated -10 dB impedance bandwidth of the proposed antenna for the band 1 is 63.55 % (1.61

3.11 GHz). Similarly, the impedance bandwidth for the band 2 is 32.58 % (3.185

4.425 GHz). The proposed antenna covers most of the LTE bands in the frequency range from 1.7 to 2.7 GHz and LTE-A bands in the range from 3.4 GHz to 3.8 GHz. Also, the antenna exhibits stable radiation pattern and has gain varying from 1.8 dBi to 4.8dBi.

Keywords Base station antenna; dualband; femtocell; LTE;monopole.

I. INTRODUCTION

Due to rapid evolution of mobile communication from 2G to LTE, there is a great demand for broadband antenna to cover wide band of frequencies. Different types of broadband antennas were reported in recent years [1- 3]. Most of these antennas cover only single broadband of frequencies, say 1.7GHz to 2.7GHz. Recently, new LTE bands like band 22 (3410

3590 MHz), band 42 (3400

3600 MHz) and band 43 (3600

3800 MHz) were released by Third generation partnership program (3GPP) [4]. Hence there is a great demand for dual broadband antenna to cover more than one band, say 1.7 - 2.7 GHz (band 1) and 3.4

3.8 GHz (band 2).

Very few dual broadband antennas were reported in the literature [5, 6]. In [5], using a trapezoidal patch excited by

shaped feed, a impedance bandwidth of 49.5%measured at RL < -10 dB was obtained for higher band (1.58-2.62 GHz) . Similarly, at the lower band (0.78-1.1 GHz); an impedance bandwidth of 34% was obtained by using triangular patches. The dual wideband double layer antenna was proposed in [6]. The antenna consists of lower folded dipoles and upper inclined rectangular patches. At SWR < 2, the measured impedance bandwidths are24.4 % (0.79-1.01 GHz) and 67.3 % (1.38-2.78 GHz). In both of these designs, complex geometry

structure wasemployed to achieve dual broadbandand none of them covers higher frequency band, namely 3.4

3.8 GHz.

In this paper, dual broadband monopole antenna covering band1(1.7

2.7 GHz) and band2 (3.4

3.8 GHz) is proposed. The antenna consists of stepped monopole radiator and rectangular loop ground. Only by varying the three segments of the monopole radiator, dual broadband is achieved without using defected ground structure (DGS) or complex geometry structure[7-10].

II. ANTENNA DESIGN

The geometry of the proposed dualband monopole antenna is shown in Fig. 1. The antenna consists of stepped monopole radiator and rectangular loop ground. The stepped radiator is etched on the top side of the substrate and the rectangular loop ground is printed on the back side of the substrate. The size of the FR4 substrate is (SL × SW) mm2. The thickness of the substrate is 1.6 mm. The width of the loop ground is LW mm. The stepped radiator consists of three segments. The length and width of the first segment is (W1 × L1) mm2. Similarly, the length and width of second and third segments are (W2 × L2) mm2 and (W3 × L3) mm2, respectively.

Fig. 1. Proposed antenna geometry

ATMS INDIA

2015

The 8th Annual International Conference ATMS -2015, Bangalore

© ATMS (INDIA)

The two stage evolution of the proposed antenna is illustrated in Fig.2. In the first stage, antenna with straight monopole radiator and loop ground is designed. In the next stage, straight monopole radiator is replaced with stepped three segment structure. By varying the length and width of the three segments of the monopole, a dual band characteristic is achieved without using DGS or complex antenna geometry. Fig. 3 shows the return loss response of straight and stepped monopole antenna. Table I shows final antenna s structural parameter values. The overall dimension of the antenna is(63 × 50 × 1.6) mm3.

Fig. 2. Evolution of proposed antenna (a) Initial design (b) Final design.

Fig. 3. Returm loss response of straight and stepped monopole antenna

TABLE I. STRUCTURAL PARAMETERS OF THE PROPOSED ANTENNA

Parameters SL SW LW L1 W1 L2 W2

Dimensions (mm)

63 50 9.6 1.7 1.7 0.8 10.4

Parameters L3 W3

Dimensions (mm)

0.6 16.7

III. SIMULATED RESULTS

The simulated return loss response of the proposed antenna is shown in the Fig. 4. At -10 dB, the simulated impedance bandwidth of the proposed antenna at band 1 (1.61

3.11

GHz) is 63.55 %. Similarly, at band 2 (3.185

4.425 GHz),

the impedance bandwidth is 32.58 %. Additional resonance at higher frequency that is band 2 is observed due to stepped monopole radiator.

Fig. 4. Simulated returm loss response of proposed antenna

ATMS INDIA

2015

The 8th Annual International Conference ATMS -2015, Bangalore

© ATMS (INDIA)

Fig. 5. Simulated Radiation pattern of proposed antenna (a) 1.74 GHz (b) 2.255 GHz (c) 3.92 GHz

Fig. 5 shows radiation pattern of the proposed antenna at different frequencies in the = 0 and = 90 plane. The simulated gain of the proposed antenna is shown in the Fig.6. The antenna gain varies from 1.8 dBi to 4.4 dBi at band1. At band 2, the gain varies from 3.7 dBi to 4.8 dBi. Table II shows the summary of functional characteristics of the proposed antenna.

Fig. 6. Simulated gain response of proposed antenna.

TABLE II. SUMMARY OF FUNCTIONAL CHARACTERISITCS OF THE PROPOSED ANTENNA

Band Impedance Bandwidth for S11<

-10 dB Gain (dBi)

Band 1 63.55 % (1.61

3.11 GHz) 1.8 to 4.4

Band 2 32.58 % (3.185

4.425 GHz) 3.7 to 4.8

IV. CONCLUSION

In this communication, a dual broadband monopole antenna is presented. Using a simple stepped monopole

radiator backed by loop ground, a dual broadband characteristic is achieved. The observed impedance bandwidth of the proposed antenna through simulation at band 1(1.61

3.11 GHz) and band 2 (3.158

4. 425 GHz) is 63.55 % and

32.58 %, respectively. Stable gain and omnidirectional radiation pattern is observed along the entire band of interest. Thus the proposed antenna would be a better candidate for femtocell base station.

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[9] M.S. Ellis, Z. Zhao, J. Wu, Z. Nie and Q. H. Liu, A Novel Miniature Band-Notched Wing-Shaped Monopole Ultrawideband Antenna, IEEE Antennas Wireless Propag. Lett., vol. 12, pp. 1614 - 1617, Dec. 2013.

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