a triband patch antenna with monopole-like and patch-like...

Research ArticleA Triband Patch Antenna with Monopole-like and Patch-likeRadiation Patterns for Multifunctional Wireless Systems

Hai-Na Song ,1 Zhao-Hui Chen,2 and Jian-Feng Li3

1School of Electronic and Information Engineering, South China University of Technology, Guangzhou,Guangdong 510640, China2Guangzhou HaiGe Communications Group Incorporated Company, Guangzhou, Guangdong 510663, China3School of Physics & Optoelectronic Engineering, Guangdong University of Technology, Guangzhou, Guangdong 510600, China

Correspondence should be addressed to Hai-Na Song; [email protected]

Received 15 January 2020; Revised 17 April 2020; Accepted 8 May 2020; Published 11 June 2020

Academic Editor: Hervé Aubert

Copyright © 2020 Hai-Na Song et al. -is is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work isproperly cited.

A triband patch antenna with monopole-like and patch-like radiation patterns for multifunctional wireless systems is proposed.-e antenna consists of a single square radiation patch with an annular slot, a ground plane, and a top-loadedmetal sheet.-e top-loaded metal sheet is shorted to the ground plane for producing a zeroth-order resonant (ZOR) mode, which has an omni-directional radiation pattern at the lowest operation band, and its performance is robust to the location of the probe feed.With theannular slot and the off-center probe feed, a dual-resonant TM01 mode is excited, yielding unidirectional radiation patterns for thetwo upper operation bands.-e ZOR and the dual-resonant TM01 modes can be independently controlled, and a triband antennaprototype with a square patch of 24mm is fabricated and tested. -e first bandwidth is 2.5–2.7GHz with omnidirectionalradiation pattern, the second and the third bandwidths with unidirectional radiation are 3.3–3.9GHz and 4.8–6.1GHz, and therealized gains over the three bands are about 2.6, 6.5, and 7.5 dBi, respectively.

1. Introduction

With merits of 360° full coverage, low profile, low cost, andeasy fabrication, monopolar patch antennas are widely usedin portable devices, such as the mobile phone, laptop, andGPS. Center-fed circular patch antennas can excite TM0mmodes with omnidirectional radiation patterns in the azi-muth plane [1], but suffering narrow bandwidth. Manytechniques have been proposed to solve the problem, in-cluding disk-loaded [2] and loaded annular ring [3], but thefirst nonzero mode of these antenna is TM02 (1.0 λ) ratherthan the eigenmode TM01 mode (0.5 λ), resulting in largeantenna sizes. Great efforts have been devoted to the study ofTM01 mode, the most commonmethod is center-fed circularpatch shorted with via holes [4, 5], and monopolar patchantennas with TM01 mode were presented [6]. By utilizingshorting vias, annular ring, and stacked patch, monopolar

radiation patterns were obtained over a broadband [7] ortwo operation bands [8].

Moreover, antennas with monopole-like and patch-likeradiation patterns over different bands are desired bymultifunctional wireless systems, such as vehicular com-munications. WMAN (Wireless Metropolitan Area Net-work) requires omnidirectional signal coverage for vehicularcommunication system accessing to Internet, and car-to-carcommunication needs unidirectional signal coverage for safedriving control in vehicular communication systems. Torealize the dual-sense radiation patterns, artificial magneticconductor and shorted vias were employed [9], and a smallpatch was stacked on a larger patch with vias [10].

Most of dual-sense radiation pattern antennas are cir-cular shaped and center-fed. But triangular, rectangular, andsquare antennas are also needed in practical applications.Monopolar patch antennas in equilateral triangular shape

HindawiInternational Journal of Antennas and PropagationVolume 2020, Article ID 3268729, 12 pageshttps://doi.org/10.1155/2020/3268729

mailto:[email protected]://orcid.org/0000-0002-9686-9952https://creativecommons.org/licenses/by/4.0/https://creativecommons.org/licenses/by/4.0/https://creativecommons.org/licenses/by/4.0/https://creativecommons.org/licenses/by/4.0/https://doi.org/10.1155/2020/3268729

[11] and in square-ring shape [12] were presented, while aconical-pattern antenna consisting of four symmetricalsquare radiating slots and artificial magnetic conductors wasstudied [13]. Four monopoles shorted to the ground and onesquare patch loaded with a slot were utilized by the antennato obtain dual-band and dual-sense radiation patterns [14].However, the reported antennas suffer from complicatedstructure and large size.

Resonant frequency of zeroth-order resonant (ZOR)antenna depends on the antenna reactance instead ofphysical size [15], and that is useful to reduce antenna size.Taking advantage of the mushroom structure, omnidirec-tional ZOR antennas were proposed [16, 17], and amushroom patch was inserted in a rectangular patch togenerate the ZOR and TM010 modes at the same frequency[18]. Utilizing a top-loaded small metal strip, a dual-bandcircular patch antenna with omnidirectional ZOR mode forthe lower band and unidirectional TM01 mode for the upperband was studied in [19].

In this paper, a compact triband square patch antennawith monopole-like and patch-like patterns is presented.Compared with the circular patch antenna [19], the pro-posed square patch antenna has a more compact size andbetter impedance matching bands to covering more com-munication bandwidth, so the proposed square patch an-tenna is more suitable to apply in multifunctional wirelesssystems. For the proposed square patch antenna, the methodfor the square radiation patch to excite monopole-like ZORmode is introducing a rectangular metal sheet, and itsperformance is robust to the probe feed position. By etchinga small annular slot into the square radiation patch, itsoriginal TM01 mode is split into two TM01 modes withcontrollable resonant frequencies, and they work at the twoupper operation bands with unidirectional radiation pattern.Based on the equivalent circuit as well as the distributions ofelectric field and current, the principles of the antenna arediscussed. -ese concepts are then verified by a tribandantenna prototype; it exhibits omnidirectional radiation in2.5–2.7GHz and unidirectional radiations in both3.3–3.9GHz and 4.8–6.1GHz. -e radiation efficiencies arelarger than 77%, 84%, and 86% for the three operationbands, respectively.

2. Antenna Design

Figure 1 illustrates the configuration of the proposed an-tenna; the antenna consists of a square patch with a smallannular slot, a ground plane, and a rectangular metal sheet.With an air gap of sizeH between them, FR4 substrates 1 and2 have relative permittivity of 4.4, a dielectric loss tangent of0.002, and a thickness of Hs � 1.6mm. -e square groundplane with side length of Lg is printed on the bottom layer ofFR4 substrate 1. -e square radiation patch with side lengthof Lp is printed on the bottom layer of FR4 substrate 2 and isfed by an off-center coaxial probe. Fy is the offset distance ofthe probe feed from the center of the square radiation patchalong the y-axis. Taking the probe feed as center, a smallannular slot with an outer radius r1 and an inner radius r2 is

etched in the square radiation patch for producing a dual-resonant TM01 mode with unidirectional radiation pattern.

A rectangular metal sheet printed on the top layer of FR4substrate 2 is shorted to the ground plane through twoconductive vias to excite a monopole-like ZOR modeworking at the lowest operation band. -e dimension of therectangular metal sheet is Ml × Mw, and the two conductivevias are arranged symmetrically with a distance of Vd. -ereare two clearance circles etched on the radiation patch andare placed around the two conductive vias, respectively, andthe radiation patch and the conductive vias are separated.

3. Analysis of Working Mechanism

In our design, numerical analysis of the antenna is con-ducted in the commercial electromagnetic software HFSS inVersion 2018, which solves the electric field and magneticfield by using finite element method (FEM). HFSS adoptsadaptive mesh generation technology; the solution type andthe convergence error are chosen as Driven Modal and 0.01,respectively, in the simulation of the proposed design.

3.1. Generation of the Dual-Resonant TM01 Mode. To revealthe operating mechanism of the proposed antenna, a squarepatch antenna named Design 1 is first investigated. Design 1has the same dimensions of the proposed antenna shown inFigure 1 but without the metal sheet and the two conductivevias. -e resonant frequency f0 of TM01 mode is decided by[20, 21]

f0 �c

2Lp��εeq

√ , εeq �εre H + Hs( Hεre + Hs

, (1)

where c is the velocity of electromagnetic waves in the freespace, εeq denotes the equivalent permittivity of the substratewith an air gap, εre � 4.4 is relative permittivity of thesubstrate, and Hs � 1.6mm and H� 4mm represent thethickness of the substrate and the air between the twosubstrates. Based on (1), the value of f0 is 4.8GHz when thesquare radiation patch side length Lp � 24mm, and that isagreed well with the simulated result for the case ofFy � 0mm, as shown in Figure 2. Coupling existing in theannular slot can split the original TM01 mode (at about4.8GHz) into two TM01 modes. But at the central area of thesquare radiation patch, the input impedance of the antennais high due to the strong electric field and the weak magneticfield. -erefore, the impedance matching is poor whenFy � 0mm, and only one TM01 mode appears.

A larger Fy means a larger distance between the probefeed and the center of the square patch. With the probe feedmoving away from the center, the balance between theelectric and magnetic fields can be enhanced to improve theimpedance matching gradually, and TM01 mode at aboutf0 � 4.8GHz is splitted into two TM01 modes. -erefore, adual-resonant TM01 mode with controllable resonant fre-quencies of f1 and f2 is produced, due to the capacitanceexisting in the annular slot. When the annular slot is close tothe central part of the square patch, where antenna inputimpedance is high, the effect of the annular slot on the

2 International Journal of Antennas and Propagation

resonant modes will become weak. In other words, with alarger Fy, the annular slot has a stronger capacity of splittingthe original TM01 mode into two TM01 modes, so the ratio off1/f2 becomes larger, as shown in Figure 2.

Keeping r2 � 2.0mm, a smaller r1 represents a smallerannular slot width (r1 − r2), leading to a stronger coupling ofthe annular slot, thereby both f1 and f2 shift towards thelower frequencies, as shown in Figure 3. Observing fromFigures 2 and 3, we can find that the trends of f1 and f2 are thesame with varying r1 but are opposite when Fy is changed, sof1 and f2 can be effectively controlled by tuning r1 and Fy, and

r1 and Fy are chosen as 3.0 and 8.0mm for the desiredoperation bands in the paper.

-e current distributions and the simulated 3D radiationpatterns of Design 1 at f2 � 3.75GHz and f1 � 5.35GHz areshown in Figures 4 and 5, respectively. -e off-centered feedcan modify the current distribution of the square patch, sothe currents have the same direction in general and only onemaximum, as shown in Figure 4. -at suggests that the tworesonant modes of Design 1 at 3.75 and 5.35GHz are TM01mode, based on the cavity model of patch antenna [22]. Forthe two TM01 modes, the only one theoretical maximum of

Rectangular metal sheet

Annular slot

Square patch

FR4 substrate 2

FR4 substrate 1

Top layer ofFR4 substrate 2

Bottom layer ofFR4 substrate 2

Bottom layer ofFR4 substrate 1

Clearance circle

Ground plane

(a)

Ground plane

Square patch

Lp

LgMl

MwVd

r2

r1

Fy

Feed point

AirH

y

xz

SAM connector

Conductive via

Rectangularmetal sheet

FR4 substrate 2

FR4 substrate 1

Annular slot

(b)

Figure 1: Configuration of the proposed antenna: (a) exploded view; (b) top view and size view. Lg � 80mm, LP � 24mm, Fy � 8mm,Ml � 24mm, Mw � 7.2mm, Vd � 15mm, H� 4mm, r1 � 2.5mm, and r2 � 2mm.

International Journal of Antennas and Propagation 3

radiation at the broadside direction is obtained in somedegree, as shown in Figure 5. -e original TM01 mode of thesquare patch is at about f0 � 4.8GHz and (f0 − f2)> (f1 − f0).

As a result, the uniformity of current distribution at f2 isworse than that of at f1, as shown in Figure 4; the direction ofthe radiation pattern at f2 deviates from the broadside

|S11

| (dB

) VSWR 2:1

–25

–20

–15

–10

–5

0

2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.02.0Frequency (GHz)

Fy = 4.0mmFy = 9.5mm

Fy = 0mmFy = 2.0mmFy = 8.0mm

Figure 2: Variation of |S11| for Design 1 with respect to Fy.

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0–30

–25

–20

–15

–10

–5

0

f2 f1|S11

| (dB

) VSWR 2:1

Frequency (GHz)

r1 = 2.2mmr1 = 2.4mm

r1 = 2.7mmr1 = 3.0mm

Figure 3: Variation of |S11| for Design 1 with respect to r1.

2.0E + 1

1.6E + 1

1.2E + 1

8.0E + 0

4.0E + 0

0.0E + 0

Jsurf (A/m)

(a)

1.5E + 1

1.2E + 1

9.0E + 1

6.0E + 0

3.0E + 0

0.0E + 0

Jsurf (A/m)

(b)

Figure 4: Current distributions on the radiation square patch of Design 1: (a) f2 � 3.75GHz and (b) f1 � 5.35GHz.


direction in some degree, but the TM01 mode at f1 still has amaximum of radiation in the broadside direction, as shownin Figure 5.

3.2. Generation of Monopole-like Mode. By utilizing a rect-angular metal sheet, which is shorted to the ground plane bytwo conductive vias, a monopole-like ZOR mode for thesquare radiation patch is achieved, and that is the mostoutstanding contribution of the proposed design. Experi-mental results show that the performance of the ZOR modeis robust to the location change of the probe feed, and that isdifferent from the reported omnidirectional antennas[16, 17], of which probe feeds must be fixed at the center ofthe circular radiation patch. In our design, there are the twoclearance circles around the two conductive vias, whichisolates the top-loaded rectangular metal sheet and the ra-diation square patch, so the probe feed can be located off-center without affecting the monopole-like radiationpattern.

For illustrating the excitation principle of the ZOR, anequivalent circuit of the proposed triband square patchantenna is derived and is shown in Figure 6. Lf models theinductance of the feed probe, LP describes the inductiveeffect associated to the radial currents flowing on the squareradiation patch, and CR is the capacitance of the annular slot.-e capacitive coupling between the square patch part insidethe annular slot and the ground plane is expressed by CP1;CP2 is the capacitive coupling between the part of the squarepatch outer the annular slot and the ground, while CM is thecapacitive coupling between the rectangular metal sheet andthe square radiation patch. -e inductances of the con-ductive vias and the rectangular metal sheet are modeled byLv and LM, respectively, while RP represents the antennaradiation resistance. By applying the rectangular metal sheetand the two conductive vias, two parallel branches bothhaving Lv and LM/2 are introduced and can be replaced byone branch with an inductance of (Lv + LM/2)/2. -e branchhaving CM and (Lv + LM/2)/2 is parallel to the branch with

Cp2, ZORmode is only related to the shunt components [18],and thus the proposed square patch antenna can support aZOR mode at around 2.6GHz.

-e effects of the square patch side length Lp andrectangular metal sheet width Mw on the input impedanceand |S11| of the proposed antenna are studied in Figures 7(a)and 7(b), respectively. For the lowest resonant mode at about2.6GHz, the resistance tends to the maximum value of about50Ω when the reactance of the input impedance goes tozero, which proves that the lowest resonant mode is aparallel resonant mode. In Figure 7(a), we also can see thatthe two TM01 modes both are series resonant modes. -eparallel resonant mode at about 2.6 GHz is also a ZORmode,which is related to the shunt components; its resonantfrequency is not affected by the varying Lp in theory, since itsresonant frequency depends on antenna reactance ratherthan antenna physical dimensions. However, a smaller Lpbrings to a smaller effective area of capacitor plate betweenthe square patch and the ground plane and gives rise to asmaller capacitance Cp2. -en the resonant frequency of theZORmode moves to the higher frequency, but this tendencycan be held up by increasing the value of CM and that can bededuced from Figure 6. A larger Mw results in a larger CM.When LP is decreased from 26 to 23mm, Mw is increasedfrom 4.8 to 8.8mm correspondingly; resonant frequency of

Max: 8

Min: –18

10

5

0

–5

–10

–15

–20

(a)

Max: 8

Min: –18

10

5

0

–5

–10

–15

–20

(b)

Figure 5: 3D radiation square patch of Design 1: (a) f2 � 3.75GHz and (b) f1 � 5.35GHz.

Rrad

Lf Lp

(LV + LM/2)/2

CM

Feeding

CR

CP1 CP2

Figure 6: Equivalent circuit of the proposed triband patch antenna.


the ZOR mode is preserved at around 2.6GHz, as shown inFigures 7(a) and 7(b). However, despite the fact that a largerMw is chosen, the resonant frequencies of the two TM01modes move towards the higher frequencies with the de-creasing of LP, as shown in Figure 7.

Moreover, the increase of the rectangular metal sheetlength ML also leads to an increase of CM; the ZOR moderesonant frequency shifts to the lower frequency, as shown inFigure 8, but the two TM01 modes are almost not affected byML. LM is decreased with the decrease in the distance Vdbetween the two conductive vias, leading to a smaller antennareactance, as shown in Figure 9(a). -e resonant frequency ofthe ZOR mode, which mainly depends on the antenna reac-tance, moves to the lower frequencies, as shown in Figure 9(b).However, the effect of the varying Vd on the resonant fre-quencies of the two TM01 modes is slight. Observing fromFigures 7–9, we can draw a conclusion that the resonant modeat about 2.6GHz is ZOR mode and can be controlled by thedimensions of the top-load rectangular metal sheet, but it hasignorable effect on the dual-resonant TM01 mode.

Figure 10 shows the variation of |S11| of the proposedantenna with respect to different Fy; its effects on the twoTM01 modes are the same as that shown in Figure 2, but forthe ZOR mode, the effect can be neglected. In Figure 11, the3D electric fields and the equivalent magnetic currents of theproposed triband square antenna are sketched for the casesof Fy � 0mm and Fy � 8.0mm.-e electric field distributionsfor both the two cases are similar. Omitting the slightdisturbances of the two conductive vias and the probe feed,the electric fields under the square patch and the rectangularmetal sheet vary in phase and are uniformly vertical to thesquare patch for the two cases. Based on the cavity model ofthe patch antenna, the equivalent magnetic loop currentsalong square patch peripheries can be produced and give riseto perfect monopole-like radiation patterns, as presented inFigures 12(a) and 12(b). -is is further proved that theperformance of the ZOR mode is robust to the locationchange of the probe feed. -e radiation patterns from the

two TM01 modes at 3.6 and 5.3GHz are shown inFigures 12(b) and 12(c), and their performances are similaras that in Figures 5(a) and 5(b), respectively, showing onceagain that the effect of the rectangular metal sheet on the twoTM01 modes is very slight.

4. Results and Discussion

-e proposed triband patch antenna with a profile of about0.06λ0 at 2.5GHz and dual-sense radiation patterns isfabricated, and its photographs are shown in Figure 13. -esimulated and measured |S11| shown in Figure 14 are in agood agreement and both are less than −10 dB in2.5–2.7GHz, 3.3–3.9GHz, and 4.8–6.1GHz.

It is clear from Figure 15(a) that both the measured andsimulated radiation patterns in xy and xz planes at 2.6GHzshow a monopole-like radiation pattern. -e radiationpatterns in yz and xz planes at 3.6 and 5.3GHz are shown inFigures 15(b) and 15(c), respectively. It is observed that theantenna has the maximum radiation at the direction ofPhi� 90o and-eta� −30o for 3.6GHz, while the maximumradiation is in the broadside direction at 5.3GHz, and that isbecause the uniformity of current distribution at f2 is worsethan that of at f1, as shown in Figure 4.-e simulated Co-polpattern agrees well with the measured one, and the dis-crepancy for simulated and measured Cross-pol levels is dueto the limit of the anechoic chamber. -e results show thatthe proposed antenna has different radiation patterns for thethree operation bands of 2.5–2.7GHz, 3.3–3.9GHz, and4.8–6.1GHz. Figure 16 shows the simulated and measuredgains for the three operation bands are 2.0–3.2 dBi, 5.5–7.0dBi, and 6.2–8.1GHz, respectively. -e measured efficiencyis also given in Figure 16, and the efficiencies are higher than77%, 84%, and 86% for the lower, middle, and highestoperation bands, respectively.

Table 1 compares the proposed triband patch antennawith the other four reported antennas having omnidirec-tional and unidirectional radiation patterns.-e comparison

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

–50

0

50

100

TM01 mode (f2)TM01 mode (f1)ZOR mode

Inpu

t im

peda

nces

(Ω)

Frequency (GHz)

LP = 23mm: MW = 8.8mm:LP = 24mm: MW = 7.2mm:LP = 25mm: MW = 6.0mm:LP = 26mm: MW = 4.8mm:

Re: ImRe: ImRe: ImRe: Im

(a)

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0–30

–25

–20

–15

–10

–5

0

LP = 23mm:MW = 8.8mmLP = 24mm:MW = 7.2mm

LP = 26mm:MW = 4.8mm

|S11

| (dB

)

VSWR 2:1

Frequency (GHz)

LP = 25mm:MW = 6.0mm

(b)

Figure 7: -e effects of LP and MW on (a) input impedances and (b) |S11| of the proposed patch antenna.


Im, ML = 15mmIm, ML = 18mmIm, ML = 21mmIm, ML = 24mm

TM01 mode (f2) TM01 mode (f1)ZOR mode–50

0

50

100In

put i

mpe

danc

es (Ω

)

2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.02.0Frequency (GHz)

Re, ML = 15mmRe, ML = 18mmRe, ML = 21mmRe, ML = 24mm

(a)

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0Frequency (GHz)

–25

–20

–15

–10

–5

0

|S11

| (dB

) VSWR 2:1

ML = 18mmML = 24mm

ML = 15mmML = 21mm

(b)

Figure 8: -e effect of ML on (a) input impedances and (b)|S11| of the proposed patch antenna.

–100

–50

0

50

100

ZOR mode

Re,Vd = 15mm Im,Vd = 15mmRe,Vd = 12mm Im,Vd = 12mmRe,Vd = 10mm Im,Vd = 10mm

Inpu

t im

peda

nces

(Ω)

Frequency (GHz)

TM01 mode (f2)TM01 mode (f1)

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

(a)

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

0

–5

–10

–15

–20

–25

–30

Frequency (GHz)

|S11

| (dB

)

VSWR 2:1

Vd = 12mmVd = 15mm

Vd = 10mm

(b)

Figure 9: -e effect of Vd on (a) input impedances and (b) |S11| of the proposed patch antenna.

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0–25

–20

–15

–10

–5

0

Fy = 0mm

Fy = 2.0mm Fy = 8.0mm

|S11

| (dB

) VSWR 2:1

Frequency (GHz)

Fy = 9.5mm Fy = 4.0mm

Figure 10: -e effect of Fy on |S11| of the proposed triband patch antenna.


Equivalent magnetic current

E field (V/m)1.0E + 4

8.0E + 3

6.0E + 3

4.0E + 3

2.0E + 3

0.0E + 0

(a)

Equivalent magnetic current

E field (V/m)1.0E + 4

8.0E + 3

6.0E + 3

4.0E + 3

2.0E + 3

0.0E + 0

(b)

Figure 11: Distribution of electric field and equivalent magnetic current at 2.6GHz of the proposed triband patch antenna: (a) Fy � 0mm;(b) Fy � 8.0mm.

Max: 2

Min: –46

10

0

–10

–20

–30

–40

–50

(a)

Max: 3

Min: –31

5

0

–5

–10

–15

–20

–25

–30

–30

(b)

Figure 12: Continued.


(a) (b)

Figure 13: Photograph of the fabricated antenna: (a) top and (b) size view.

Max: 6

Min: –24

10

5

0

–5

–10

–15

–25

–20

(c)

Max: 7

Min: –29

10

5

0

–5

–10

–15

–25

–30

–20

(d)

Figure 12: 3D radiation patterns of the proposed antenna: (a) f� 2.6GHz; Fy � 0mm; (b) f� 2.6GHz; Fy � 8mm; (c) f� 3.6GHz; Fy � 8mm;(d) f� 5.3 GHz; Fy � 8mm.

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0–25

–20

–15

–10

–5

0

VSWR 2:1

Frequency (GHz)

|S11

| (dB

)

Simulated |S11|Measured |S11|

Figure 14: Simulated and measured |S11| of the proposed patch antenna.


focuses on the number of antenna radiator, operation bands,size of antenna radiators in terms of their wavelengths at thelowest operating frequencies, antenna profiles in terms ofwavelengths at the lowest operating frequencies, and theperformance of radiation patterns. -is comparison showsthat just the proposed antenna, the antenna [14], and theantenna [19] employ a single one radiator to achieve theomnidirectional radiation pattern and the unidirectional

radiation pattern simultaneously. However, the sizes ofradiator for the two antennas [14, 19] are larger than that ofthe proposed antenna. -e antenna [14] has a lower antennaprofile compared with the proposed antenna, but only theproposed antenna has three operation bands. Comparingwith the other antennas, we can say that the proposedantenna with a single square patch, compact size, low-profile, triband, monopole-like, and patch-like radiation

030

60

90

120

150180

210

240

270

300

330

x-z plane

030

60

90

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150180

210

240

270

300

330

–40

–20

0

–40

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0

–40

–20

0

–40

–20

0x-y plane

(a)

030

60

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120

150180

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–30

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0

–20

–10

0y-z plane

030

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150180

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0x-z plane

(b)

030

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0x-z plane

030

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150180

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330

–30

–20

–10

0

–20

–10

0y-z plane

(c)

Figure 15: Simulated and measured radiation patterns of the proposed triband patch antenna at (a) 2.6GHz, (b) 3.6 GHz, and (c) 5.3 GHz.


patterns is more suitable to be applied in the multifunctionalcommunication system with limited space.

5. Conclusions

A compact triband antenna with a single square patch, low-profile, monopole-like, and patch-like radiation patterns hasbeen presented. By using a rectangularmetal sheet shorted to theground plane, a small annular slot etched on the square radiationpatch, and an off-center feed probe, a ZOR mode withmonopole-like radiation pattern at the lowest operation has beenobtained, and a dual-resonant TM01 mode has been excited,yielding unidirectional radiation pattern for the middle and thehighest operation bands. -e triband antenna has been fabri-cated and tested, and themeasured and simulated results are in agood agreement. -e measured realized gain and the radiationefficiency in 2.5–2.7GHz are 2.0–3.2 dBi and 77–80.5%, re-spectively. -e measured realized gain and the radiation effi-ciency in 3.3–3.9GHz are 5.5–6.8 dBi and 84–88%, respectively.-e measured realized gain and the radiation efficiency are,respectively, 6.2–8.1 dBi and 86–88.5% in 4.8–6.1GHz.

Data Availability

-e numerical and experimental data used to support thefindings of this study are included within the article.

Conflicts of Interest

-e authors declare that there are no conflicts of interestregarding the publication of this paper.

Acknowledgments

-is work was supported by the National Science Foun-dation for Young Scientists of China under Grant 61901126.-e authors would like to thank Professor Bin-Jie Hu for hisinvaluable assistance in the preparation of this manuscript.

References

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Measured efficiency

Simulated realized gainMeasured realized gain

75

80

85

90

95

Mea

sure

d effi

cien

cy (%

)

1

2

3

4

5

6

7

8

Real

ized

gai

n (d

Bi)

3.50 3.75 5.00 5.25 5.50 5.75 6.002.50Frequency (GHz)

Figure 16: Realized gain and efficiency of the proposed patch antenna.

Table 1: Comparison with other antennas having omnidirectional and unidirectional radiation patterns.

Antenna RadiatornumberOperation

bandSize of radiator at the lowest

operating frequenciesAntennaprofile

Radiation patternLower band Middle band High band

[9] 2 Dual band 0.026λ20 0.03λ0 Omnidirectional — Unidirectional[10] 2 Dual band 0.694λ20 0.09λ0 Unidirectional — Omnidirectional[14] 1 Dual band 0.0676λ20 0.26λ0 Omnidirectional — Unidirectional[19] 1 Dual band 0.074λ20 0.047λ0 Omnidirectional — Unidirectional-iswork 1 Triband 0.040λ

20 0.06λ0 Omnidirectional Unidirectional Unidirectional


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