1536-1225 (c) 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.

This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/LAWP.2018.2844293, IEEEAntennas and Wireless Propagation Letters

> REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) <

1

Abstract— A broadband symmetrical dual-loop antenna with

enhanced gain is proposed in this letter. It is comprised of a

symmetrical dual-loop radiator, a pair of magneto-electric feeding

structures, two metal shorting pins, and a metal ground plane. To

simultaneously broaden its impedance bandwidth and improve its

radiation patterns, a symmetrical dual-loop radiator excited by a

pair of magneto-electric feeding structures is introduced. By

loading shorting pins between the radiator and the ground plane,

the peak gain can be significantly enhanced over the band of

operation. Measured results demonstrated that the proposed

antenna has a wide impedance bandwidth of 48.2% ranging from

1.68 to 2.76 GHz for VSWR<1.5 and a stable gain of 10.0±0.85 dBi.

Moreover, stable radiation patterns and low cross-polarization

are obtained in the desired frequency band. Due to these

performances above, the proposed antenna is very suitable for

base station applications.

Index Terms— Wideband, gain enhancement, shorting pin, low

cross-polarization, directional antenna.

I. INTRODUCTION

ITH the rapid development of wireless communication

systems, such as GSM1800/GSM1900, the third

generation (3G) system and long term evolution (LTE) system,

antennas with good features of broad impedance bandwidth,

low profile, high gain and stable radiation patterns are more

attractive. In recent years, a lot of open literatures about

broadband antennas with unidirectional radiation patterns have

been published [1]-[4]. In [1], by combining of shorted bowtie

patch antenna and an electric dipole, the proposed antenna

achieves a wide impedance bandwidth from 2.16 to 4.13 GHz

for VSWR< 2. A wideband MIMO antenna is proposed for

WLAN/WiMAX applications [2]. By adopting an integrated

balun, the antenna has a wide bandwidth of 60.6% covering the

band of 2.30-4.30 GHz for return loss >10 dB. Recently, a

parasitic element has been added to each tilted dipole for

bandwidth enhancement [3]. It is found that an impedance

bandwidth of 45% for return loss >10 dB from 1.62 to 2.55

GHz can be achieved by using a parasitic element close to the

dipole. In [4], a stepped transformer and shifted microstrip are

used to feed the parasitic patches stacked above the driven

patch; an enhanced operating bandwidth of 35% from 4.9 to

The authors are with the National Key Laboratory of Antennas and

Microwave Technology, Xidian University, Xi’an, Shaanxi, 710071, China.

(e-mail:liujinhai568@126.com;zhaoyangt@126.com; wangziyang1@126.com;

huiyuezai@163.com;yzyin@mail.xidian.edu.cn)

7.05 GHz is achieved.

As mentioned above, many works have been carried out to

broaden its impedance bandwidth. However, in the case of

communication systems, high gain antennas are highly

demanded for lengthening the communication distance or

compensating the large propagation losses. Therefore, much

attention is paid to the antenna element with gain enhancement.

In recent years, numerous methods for enhancing the gain of

the antennas [5]-[10] have been proposed. In [5], several

directors and a truncated ground plane acting as a reflector have

been added to the antenna so as to maximize the antenna gain.

It is pointed out in [6] that the gain of the antenna could be

enhanced by the virtue of four parasitic rectangular patches. In

[7], the gain of the bow-tie antenna is significantly enhanced by

loading a 2×5 array of end-coupled split-ring cells. A

remarkable increase in the gain of the primary radiator such as

dielectric resonator antenna [8] has been achieved by

introducing the uniaxial anisotropic material. In [9], the gain of

the antenna is greatly improved with a peak enhancement of 2.5

dBi by centrally positioning the antenna above a double layered

EBG structures. In previous work, they have made the desired

results in increasing the antenna’s gain. However, gain

enhancement of these antennas is achieved at the cost of

enlarged equivalent caliber. In [10], a rectangular patch antenna

with slot-loaded technique is developed to reduce the sidelobe

level and enhance the gains. Additionally, another technique

for improving the antenna’s directivity is to load shorting pins

without increasing the occupied volume in [11]. However,

antennas of this type generally have high Q value, resulting in a

narrow band of operation.

In the paper, a broadband symmetrical dual-loop antenna

loaded with shorting pins will be discussed. By introducing a

pair of magneto-electric feeding structures, a wide impedance

bandwidth is realized. Meanwhile, a symmetrical dual-loop

radiator is designed to suppress the cross-polarized field

component. Furthermore, a set of shorting pins is loaded

beneath the radiator patch to strength the peak gain.

II. ANTENNA DESIGN AND ANALYSIS

A. Symmetrical Dual-Loop Antenna Design

The evolution of the broadband symmetrical dual-loop

antenna is shown in Fig.1 (a). First, an ideal dipole antenna

referred to as antenna I with narrow bandwidth is presented. To

improve an impedance bandwidth, a magnetic dipole combined

Gain Enhancement of Broadband Symmetrical

Dual-Loop Antenna Using Shorting pins

Jinhai Liu, Student Member, IEEE, Zhaoyang Tang, Student Member, IEEE, Ziyang Wang, Student

Member, IEEE, Hui Li, and Yingzeng Yin, Member, IEEE

W

1536-1225 (c) 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.

This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/LAWP.2018.2844293, IEEEAntennas and Wireless Propagation Letters

> REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) <

2

Fig.1 (a) Evolution of the proposed antenna;

(b) Comparison of simulated VSWR.

with the electric dipole is introduced which is marked as

antenna II. However, the radiation patterns are degraded due to

the asymmetrical structure, especially the cross-polarization.

As shown in Fig.1 (a), to alleviate this problem, a symmetrical

dual-loop antenna III is designed to improve radiation patterns.

Herein, the resultant antenna has two symmetrical feeding

structures which should be commonly fed. Further, a set of

shorting pins is introduced in the centerline of the antenna IV to

strengthen the peak gain. The corresponding VSWR in

evolution is shown in Fig.1 (b). Note that, antenna II has more

resonances with better impedance matching by combing the

resonance of the magneto-electric feeding structure and the

ordinary loop antenna. Furthermore, antenna IV has an

impedance matching with bandwidth of 46.8% for VSWR < 1.5,

corresponding to the antenna with magneto-electric feeding

structures and symmetrical dual-loop radiator, whereas an

impedance bandwidth of 14.0% (VSWR < 2.5) is presented by

the ordinary loop antenna (antenna I). As desired, the operating

bandwidth performance of antenna IV is greatly improved.

The broadband symmetrical dual-loop antenna loaded with

shorting pins is optimized using the high-frequency structure

simulator software. A Wilkinson power divider is located under

the ground plane to excite the proposed antenna, and it is

fabricated on an F4B substrate with the thickness of 1.5mm and

Fig. 2 Vector surface current at 2.2GHz.

Fig.3 Comparison of simulated radiation patterns between

antenna II and antenna III at 2.2GHz.

relative permittivity of 2.2. Meanwhile, the patch radiator and

magneto-electric feeding structures are fabricated using a

copper with the thickness of 0.7mm. In addition, the optimized

parameters of the antenna shown in Fig.1 (a) are listed as

follows (units: mm)：W=55, wf1=4, wf2=14, L=95, H=34,

L=95, D=17, wa=19, wf=19.5.

As shown in Fig.1 (a), when the ports are excited, the signal

is injected to the hook-shaped probes and then coupled to the

radiator. The surface current distribution of the antenna at 2.2

GHz is illustrated in Fig. 2. It can be seen that the current

intensely flows along ±x axis on the radiator, especially near the

coupling slot. In other words, the yoz-plane can be regarded as

the E-plane while the xoz-plane denotes the H-plane.

Additionally, there is a small amount of instantaneous current

on the horizontal patch and the currents almost in the ±x- axes

directions, which however contribute to the antenna’s

cross-polarization. To effectively suppress the spurious

radiation caused by the current flowing in ±x-axes direction, a

symmetrical configure with respect to antenna II is designed.

As shown in Fig.2 (antenna III), two symmetrical ports can be

excited to produce out-of-phase currents at other horizontal

portions due to the introduction of the symmetrical structure

and commonly feeding technique. Thereby, A and C can be

considered as the joint points connecting radiator with y-axis

component of surface current flowing in the same direction,

thus A-C plane functioning as a perfect magnetic wall. B and D

are joint points connecting radiator with x-axis component of

surface current flowing out of phase, thus B-D plane work as an

electric wall. Theoretically, the spurious radiations can be

cancelled in far field due to the currents’ component along

x-axis with equal amplitude but out of phase. This operating

mechanism introduces the perfect magnetic wall and electric

wall model by physical connection of the surface currents,

1536-1225 (c) 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.

This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/LAWP.2018.2844293, IEEEAntennas and Wireless Propagation Letters

> REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) <

3

Fig.4 Current distributions on the radiator at 2.7GHz

(I1 & I3 represent the source currents).

Fig.5 Pattern comparisons of the proposed antenna at 2.7GHz.

TABLE I

RADIATION PARAMETERS OF ANTENNA III AND ANTENNA IV

Antennas Antenna IV Antenna III

E-plane HBPW (º) 57 70.1

H-plane HBPW (º) 46.5 51.0

Gain (dBi) 10.95 9.70

which achieves an improved phase canceling effect and

suppresses the cross-polarized radiation.

To further illustrate the improvement of the

cross-polarization, a comparison between the simulated

radiation patterns of antenna II and antenna III is presented in

Fig.3. It is observed that the polarization purity of the antenna

III can be greatly improved compared to that of the antenna II,

especially in the E-plane.

B. Gain Enhanced with Shorting pins

In order to illustrate the operating principle of gain

enhancement of the proposed antenna, surface current

distributions of the antennas with and without shorting pins are

compared and shown in Fig. 4. As shown, the surface current

intensity on the radiator (antenna IV) is more uniform in the

middle area and a much larger area is strengthened because of

the presence of the shorting pins. Meanwhile, it is obvious (as

shown in Fig.2 (antenna III)) that the vector current on the

central line of the radiator flows with the same direction as that

of the source currents on both sides of the radiator.

Consequently, currents on the vertical portions of the

symmetrical radiator flow in same directions and their radiation

can be superposed in the far field. As such, the electrical size of

Fig.6 Comparison of simulated gains between antenna III and

antenna IV.

Fig .7 VSWR and gain against frequency.

the proposed antenna is effectively enlarged and the radiation

gain is hence enhanced.

Furthermore, the simulated radiation patterns of the

proposed antenna with and without shorting pins are plotted in

Fig.5. Herein, it can be seen that the half-power beamwidth

(HPBW) of the antenna with shorting pins is narrowed in both

E- and H-planes. Meanwhile, the HPBWs and the gains are

numerically investigated, as tabulated in Table I. As shown in

Fig.5, the pin-loaded antenna has notably narrowed HPBW

compared with those of the antenna without pins. To be specific,

the HPBWs of the antenna with shorting pins are, respectively,

57 º and 46.1 º at E- and H-plane, while they are 70.1 º and 51 º

for the antenna without shorting pins loaded. The gain of the

proposed antenna has been enhanced to as high as 10.95 dBi,

with an increase of 1.25 dB.

To further illustrate the function of the shorting pins, the

comparison of simulated gains between antenna III and antenna

IV is shown in Fig.6. Compared with the antenna without

shorting pins, the peak gain of antenna IV is greatly increased

within the operating frequency band, and its gain without a

significant decline at high frequencies scope.

1536-1225 (c) 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.

This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/LAWP.2018.2844293, IEEEAntennas and Wireless Propagation Letters

> REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) <

4

Fig.8 Simulated and measured radiation patterns of the

proposed antenna in the E- and H-plane.

III. EXPERIMENTAL RESULTS

To validate the antenna design, a broadband symmetrical

dual-loop antenna with a set of shorting pins is designed and

fabricated. The fabricated antenna is shown in Fig.7. Herein,

the VSWR versus frequency is also illustrated in Fig.7. There is

a reasonable agreement between the simulated and measured

results and a wide measured impedance bandwidth of 48.2% is

obtained, ranging from 1.68 to 2.76 GHz. Fig.8 depicts the

simulated and measured radiation patterns at frequencies of 1.7,

2.2 and 2.7 GHz, respectively. It is observed that the proposed

antenna achieves unidirectional radiation patterns with stable

radiation directivity and low cross-polarization within the

operating band. The measured cross-polarization radiation

level is less than -21 dB in the operating frequency band. It

should be pointed out that the simulated cross-polarization at

some frequencies is lower than −40 dB, which cannot be

appeared in the figures. Finally, the gain of the proposed

antenna was measured in an anechoic chamber with the Satimo

system, as shown in Fig.7. It can be seen that the measured gain

varying within 10.0 ±0.85 dBi is obtained across the whole

operating frequency band.

IV. CONCLUSION

A wideband and high gain symmetrical dual-loop antenna is

presented. By employing the magneto-electric feeding

structures, an impedance bandwidth of 48.2% ranging from

1.68 to 2.76GHz is obtained for VSWR<1.5. Meanwhile, the

spurious radiations can be effectively suppressed by a

symmetrical dual-loop radiator. Furthermore, since a pair of

shorting pins is symmetrically loaded beneath the radiator,

surface current across the centerline of the antenna can be

remarkably strengthened so as to enhance its radiation

directivity and gain. The proposed antenna exhibits advantages

of wide impedance bandwidth, stable radiation patterns and

high gain. Owing to these properties, the proposed antenna will

be an appropriate replacement for conventional Yagi–Uda

antenna in some point-to-point communications, or as a part of

a broadband high-gain antenna array for base-station

applications.

V. REFERENCE

[1]. Hang Wong, Ka-Ming Mak, and Kwai-Man Luk, “Wideband Shorted Bowtie Patch Antenna With Electric Dipole,” IEEE Trans. Antennas

Propag., vol. 56, No. 7, pp. 2098-2101, 2008.

[2]. HanWang, Longsheng Liu, Zhijun Zhang, Yue Li, and Zhenghe Feng, “A Wideband Compact WLAN/WiMAX MIMO Antenna Based on Dipole

With V-shaped Ground Branch,” IEEE Trans. Antennas Propag., vol. 63,

No. 5, pp. 2290-2295, 2015. [3]. Yi Fan, XuLin Quan, Yan Pan, YueHui Cui, and RongLin Li, “Wideband

Omnidirectional Circularly Polarized Antenna Based on Tilted Dipoles,”

IEEE Trans. Antennas Propag., vol. 63, No. 12, pp. 5961-5966, 2015. [4]. Ankita Katyal, and Ananjan Basu, “Compact and Broadband Stacked

Microstrip Patch Antenna for Target Scanning Applications,” IEEE

Antennas and wireless propagation letters, VOL. 16,pp.381-384, 2017. [5]. Ramadan A. Alhalabi and Gabriel M. Rebeiz, “High-Gain Yagi-Uda

Antennas for Millimeter-Wave Switched-Beam Systems,” IEEE Trans.

Antennas Propag., vol. 57, No.11, pp. 3672-3676, 2009. [6]. Wenwen Yang, Jianyi Zhou, Zhiqiang Yu, and Linsheng Li, “Bandwidth-

and Gain-Enhanced Circularly Polarized Antenna Array Using

Sequential Phase Feed,” IEEE Antennas and wireless propagation letters, VOL. 13, pp1215-1218,2014.

[7]. Z Abdolmehdi Dadgarpour, Behnam Zarghooni, Bal S. Virdee, Tayeb A.

Denidni,“High-gain end-fire bow-tie antenna using artificial dielectric layers,” IET Microwaves, Antennas & Propagation Year: 2015, Volume:

9, Issue: 12 Pages: 1254 - 1259.

[8]. Saeed Fakhte, Homayoon Oraizi, Ladislau Matekovits, and Gianluca Dassano, “Cylindrical Anisotropic Dielectric Resonator Antenna With

Improved Gain,” IEEE Trans. Antennas Propag., vol. 65, No.3, pp.

1404-1409, 2017. [9]. Pui-Yi LAU, Kenneth Kin-On YUNG, Zhi-Ning CHEN, “A Wideband

High Gain Double EBG Reflector Antenna,” 2011 8th International

Conference on Information, Communications & Signal Processing, pp. 1-4.

[10]. Xiao Zhang, Lei Zhu and Qiong-Sen Wu, “Side-lobe-reduced and

gain-enhanced square patch antennas with adjustable beamwidth under

TM03 mode operation”, IEEE Transactions on Antennas and

Propagation, vol. 66, no. 4, Apr. 2018. [11]. Xiao Zhang, and Lei Zhu, “Gain-Enhanced Patch Antennas With

Loading of Shorting Pins,” IEEE Trans. Antennas Propag., vol. 64, No. 8,

pp. 3310-3318, 2016.

本文献由“学霸图书馆-文献云下载”收集自网络，仅供学习交流使用。

学霸图书馆（www.xuebalib.com）是一个“整合众多图书馆数据库资源，

提供一站式文献检索和下载服务”的24 小时在线不限IP

图书馆。

图书馆致力于便利、促进学习与科研，提供最强文献下载服务。

图书馆导航：

图书馆首页 文献云下载 图书馆入口 外文数据库大全 疑难文献辅助工具