research article design of symmetrical beam triple...

Research ArticleDesign of Symmetrical Beam Triple-Aperture WaveguideAntenna for Primary Feed of Reflector

Kanawat Nuangwongsa and Chuwong Phongcharoenpanich

Faculty of Engineering, King Mongkut’s Institute of Technology Ladkrabang, Bangkok 10520, Thailand

Correspondence should be addressed to Chuwong Phongcharoenpanich; [email protected]

Received 20 January 2016; Accepted 10 April 2016

Academic Editor: Shih Yuan Chen

Copyright © 2016 K. Nuangwongsa and C. Phongcharoenpanich. This is an open access article distributed under the CreativeCommons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided theoriginal work is properly cited.

This research presents a triple-aperture waveguide antenna as the primary feed of parabolic reflectors. The proposed antenna isable to rectify the asymmetry and also achieve a symmetrical unidirectional beam through the application of two parasitic couplingapertures. The design of the antenna is that of a rectangular waveguide (radiating aperture) vertically jointed to the two couplingapertures of the samemeasurement widthwise (i.e., one stacked on top and the other underneath) to achieve the symmetrical beam.The rectangular waveguide is 97.60mm and 46.80mm in width (𝑎) and height (𝑏), respectively, to propagate theWLAN frequencyband of 2.412–2.484GHz. Simulations were carried out to determine the optimal antenna parameters and an antenna prototype wassubsequently fabricated and tested. The simulated beamwidths in the 𝐸- and𝐻-planes at −3 dB were equally 67∘ (i.e., 67∘ for boththe 𝐸- and𝐻-planes) and at −10 dB also equally 137∘, while the measured results at −3 dB were equally 65∘ and at −10 dB equally135∘.The simulation andmeasured results are thus in good agreement.The simulated andmeasured antenna gains are, respectively,8.25 dBi and 9.17 dBi. The findings validate the applicability of the antenna as the prime feed for rotationally symmetric parabolicreflectors.

1. Introduction

In recent decades, the point-to-point communications sys-tems have rapidly advanced and become one of the brightestareas of the communications business [1]. Specifically, thepoint-to-point links between hosts and clients are requiredin several wireless systems for communication over longdistances, such as the microwave radio relay link, long lengthWi-Fi, wireless WAN/LAN link, satellite communication,and home satellite television [2].

Horn antennas, which are a principal component of thepoint-to-point communication systems, were first developednearly a century ago for military and scientific purposes butwere not widely adopted until World War II. Typical hornantennas are of either rectangular or conical structures. Therectangular structure can further be divided into the𝐻-plane,𝐸-plane, and pyramidal horn structures [3, 4].

To enhance the performance of the point-to-point com-munication requires a narrow-beam antenna with high gain[5], and one possible method to achieve the narrow beam

is through a parabolic metal reflector antenna. In addition,the feeding point of the parabolic reflector should be locatedat the reflector focus to generate the narrow beam (i.e.,pencil beam). In [6], the authors reviewed publications onthe point-to-point communication and documented that thegeneration of the pencil beam requires an antenna withsymmetrical beam as the primary feed.

The radiation pattern of a parabolic reflector (secondaryantenna) typically corresponds to that of the primary feedantenna. In other words, the asymmetric radiation patternfrom the primary feed contributes to the asymmetricalincidence of the secondary antenna and vice versa [7]. In fact,it is difficult to obtain the symmetrical radiation pattern at theprimary feed due to the beamwidth asymmetry between the𝐸- and𝐻-planes [8].

To address the asymmetry issue, several antenna struc-tures have been proposed. In [9], a pyramidal horn antennawas utilized to obtain the symmetric radiation patterns inthe 𝐸- and 𝐻-planes; nevertheless, the antenna structurewas large with the width, height, and length of 2.80𝜆, 2.03𝜆,

Hindawi Publishing CorporationInternational Journal of Antennas and PropagationVolume 2016, Article ID 5830527, 14 pageshttp://dx.doi.org/10.1155/2016/5830527

2 International Journal of Antennas and Propagation

l

b1 b1

b1

l2

l2

l1l1

xz

y

xz

ya b b

L

Figure 1: Geometry of the proposed antenna.

and 4.35𝜆. In [10], the author experimented with a diagonalhorn antenna with very low cross-polarization and axiallysymmetrical field distribution at the horn aperture; however,the antenna has a large aperture size of 5.00𝜆 and 5.00𝜆 inwidth and height.

Generally, the corrugated horn consisting of parallelslots or grooves can create a hybrid-mode pattern in theaperture which straightens out the electric field and reducesdiffractions from the edge [11, 12]. In [13–18], the conicalcorrugated horn antennas were utilized to generate thesymmetrical beam with high gain and low side lobe level.The antennas structures are however complicated. On thecontrary, for the typical rectangular corrugated horn antennastructure, the slots or grooves are located inside both verticaland horizontal planes around the rectangular aperture area.The rectangular corrugated horn [19] was experimented andit was reported that this antenna type failed to generate thesymmetrical beam despite its relatively large size. In [20], theauthors proposed a flared rectangular horn corrugated alongthe 𝐸-plane flaring walls to achieve the symmetry in the 𝐸-and𝐻-planes; nevertheless, the antenna construction is verycomplicated and the antenna aperture is considerably large.For the rectangular waveguide aperture perpendicular to the𝑧 direction, the diffracted wave is almost in 𝑦𝑧-plane andit is minimal in 𝑥𝑧-plane. The parasitic coupling aperturesare proposed to locate in 𝑦𝑧-plane (vertical plane) outsidethe radiating aperture. One aperture is stacked on top (topsection) and the other is stacked underneath (bottom section)the radiating rectangular waveguide (middle section). Thismakes the proposed triple-aperture waveguide antenna lesscomplicated and easy fabricated compared to the typicalcorrugated horn antenna.

This research has thus proposed a triple-aperture waveg-uide antenna as the primary feed of a parabolic reflector.The antenna can achieve a symmetrical unidirectional beamthrough the use of two parasitic coupling apertures. In fact,an independent use of an open-ended rectangular waveguideas the primary feed of a parabolic reflector is rare dueto the asymmetry and low directivity [21]. The proposedantenna design consists of a rectangular radiating waveguidejointed to the two coupling apertures, one stacked on topand the other underneath. In this research, the rectangular

waveguide is 97.60mmand 46.80mm inwidth (𝑎) and height(𝑏), respectively, to propagate the WLAN frequency bandof 2.412–2.484GHz. The proposed antenna is for point-to-point communication and thus requires a front feed parabolicreflector [5, 22, 23] and is appropriate forWLANapplicationsalong IEEE 802.11b/g/n. Moreover, the technique of couplingapertures can be applied to other frequency ranges byadjusting the antenna electrical size.

The organization of the research is as follows: Section 1is the introduction. Section 2 describes the design of theproposed triple-aperture waveguide antenna, while Section 3discusses the parametric study and the simulation resultsof the antenna. Section 4 deals with the antenna prototypeand the experimental results. The concluding remarks areprovided in Section 5.

2. The Antenna Design

The structure of the triple-aperture waveguide antenna, as thename implies, is made up of one radiating section and twocoupling sections.The configuration of the proposed antennais illustrated in Figure 1, in which the radiating aperture isthe middle section with the width and height of 𝑎 and 𝑏,while the two coupling apertures refer to those on top andunderneath the radiating aperture, with the width, height,and length of 𝑎, 𝑏

1, and 𝑙

2. The width (𝑎 = 97.60mm) and

height (𝑏 = 46.80mm) of the rectangular waveguide (themiddle section) are fixed, where the relationship between itswidth (𝑎) and length (𝑏) is that of 𝑎 = 2𝑏, to achieve the centerfrequency of 2.45GHz in the dominantmode (TE

10) [24–28].

Inside the middle section (the radiating section) ismounted a linear electric probe at a distance of 0.25𝜆 fromits closed end (𝑙

1) along the 𝑦 direction with the axial 𝑧-

axis propagation. The height of linear electric probe (𝑙) is0.25𝜆. The inclusion of both parasitic coupling apertures onthe vertical plane at the open end is to reduce the diffractionfield and achieve symmetry.

In this research, the initial length of the radiating section(𝐿) is 0.75𝜆

𝑔because the standing wave pattern is repeated

every 0.50𝜆𝑔. Therefore, the distance between the maximum

and minimum electric field distributions is 0.25𝜆𝑔and the

entire length of the radiating section (𝐿) is approximately

International Journal of Antennas and Propagation 3

Table 1: Parameters of the antenna without the parasitic couplingapertures.

Parameters Physical size (mm) Electrical size𝑎 97.60 0.797𝜆

𝑏 46.80 0.382𝜆

𝐿 152.40 1.244𝜆

𝑙 30.00 0.244𝜆

𝑙1

52.40 0.427𝜆

L

zx

y

02.829.1020.340.275.6139251

1043

E (V

/m)

Figure 2: The simulated electric field distribution of the radiatingsection of the proposed antenna.

0.75𝜆𝑔so as to realize the maximum electric field density

at the aperture, as shown in Figure 2. The length of therectangular radiating waveguide (𝐿) is thus 152.40mm [29].

3. Parametric Study and Simulation Results

3.1.TheAntennawithout Parasitic Coupling Apertures. Underthis scenario, simulations were carried out on a waveg-uide without the parasitic coupling apertures using CSTMicrowave Studio. The waveguide is of rectangular shape,where the relationship between its width (𝑎) and length (𝑏)is that of 𝑎 = 2𝑏. In addition, the waveguide is of aluminummaterial and 2mm in thickness. Inside the waveguide is anelectric probe that is connected to a 50Ω N-type connector.Thewidth (𝑎) and length (𝑏) of the rectangular waveguide arecapable of achieving the resonant frequency (𝑓

𝑟) at the center

frequency of 2.45GHz. Table 1 tabulates the physical andelectrical sizes of the rectangular waveguide (i.e., the antennawithout the coupling apertures).

Figure 3 illustrates the simulated electric field distributionat the center of the width (𝑎) side of the antenna withoutthe parasitic coupling apertures at the 2.45GHz frequency. Itis found that the distribution travels in the 𝑧 direction andthat the diffraction grows stronger around the edges of thewaveguide (the 𝑦𝑧-plane). On the other hand, the diffractionon the 𝑥𝑧-plane is minimal. The 𝑦𝑧-plane phenomenoncontributes to the asymmetry between the 𝐸- and 𝐻-planeradiations.

Figures 4 and 5, respectively, depict the simulated |𝑆11|

and gain as well as the input impedance of the antennawithout the parasitic coupling apertures. As illustrated in thefigures, in the absence of the coupling apertures, the antennagain (6.70 dBi) is relatively low despite the fairly satisfactory

y

z02.829.1020.340.275.6139251

1043

E (V

/m)

Figure 3: The simulated electric field distributions at the centerof the width (𝑎) side of the antenna without parasitic couplingapertures at 2.45GHz (side view).

|S11|

(dB)

−30

−25

−20

−15

−10

−5

0

0

2

4

6

8

10

12

Gai

n (d

Bi)

2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.92.0 3.0

Frequency (GHz)

Figure 4: Simulated |𝑆11

| and gains relative to frequency of theantenna without parasitic coupling apertures.

ResistanceReactance

2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.92.0 3.0

Frequency (GHz)

−100−80−60−40−20

020406080

100

Inpu

t im

peda

nce (

Ω)

Figure 5: Input impedance of the antenna without parasitic cou-pling apertures.

input impedance (𝑍0= 48.75 + 𝑗4.44Ω) and |𝑆

11| < −10

dB.In Figure 6, the simulated beamwidths at −3 dB and−10 dB in the 𝐸-plane, respectively, are 106∘ and 270∘ and inthe 𝐻-plane are 65∘ and 110∘. Since the principle applicationof the proposed triple-aperture waveguide antenna is theprimary feed of a parabolic reflector, this research has thustaken into account the beamwidth at −10 dB. As illustrated


−30dB

−20dB

−10dB

0 dB𝜃 𝜃0∘

30∘30∘

60∘60∘

90∘90∘

120∘120∘

150∘150∘

180∘

𝜙 = 90∘

(a)

−30dB

−20dB

−10dB

0 dB𝜃 𝜃0∘

30∘30∘

60∘60∘

90∘90∘

120∘120∘

150∘150∘

180∘

𝜙 = 0∘

(b)

Figure 6: The simulated radiation patterns of the antenna without parasitic coupling apertures at 2.45GHz: (a) 𝐸-plane and (b)𝐻-plane.

Table 2: Parameters of the antenna with the parasitic couplingapertures.

Parameters Physical size (mm) Electrical size𝑎 97.60 0.797𝜆

𝑏 46.80 0.382𝜆

𝐿 152.40 1.244𝜆

𝑙 30.00 0.244𝜆

𝑙1

52.40 0.427𝜆

𝑏1

28.98 0.236𝜆

𝑙2

50.80 0.414𝜆

in Figure 6, the radiation patterns of the antenna withoutthe parasitic coupling apertures in the 𝐸- and 𝐻-planes areasymmetrical.

3.2.TheAntennawith Parasitic CouplingApertures. To rectifythe asymmetry, two parasitic coupling apertures are incorpo-rated with the rectangular waveguide whereby one apertureis stacked on top (top section) and the other underneath(bottom section) the radiating waveguide (middle section).To achieve the resonant frequency at the center frequencyof 2.45GHz, this research has utilized the TE

101mode to

determine the length (𝑙2) and height (𝑏

1) of the parasitic

coupling apertures [28, 29] while its width (𝑎) is identicalto that of the radiating rectangular waveguide (97.60mm).Simulations were then carried out using CST MicrowaveStudio and the optimal simulation results for the waveguideantenna with the parasitic coupling apertures are tabulatedin Table 2. The realization of the target resonant frequency islargely subject to 𝑎 and 𝑏

1.

Figure 7 illustrates the simulated electric field distribu-tion of the waveguide antenna with the parasitic couplingapertures at the center of the width (𝑎) side. It is found

y

z

0

2.82

9.10

20.3

40.2

75.6

139

251

1043

E (V

/m)

Figure 7: The simulated electric field distributions at the center ofthe width (𝑎) side of the antenna with parasitic coupling aperturesat 2.45GHz (side view).

that the wave diffraction is reduced with the use of thecoupling apertures (the top and bottom shorter sections)in conjunction with the radiating waveguide (the middlesection).

3.2.1. Impedance Bandwidth for Various Antenna Parameters.Figure 8 depicts the simulated |𝑆

11| < −10 dB for various

rectangular waveguide lengths (𝐿) and at 𝐿 = 1.244𝜆 thesimulated |𝑆

11| resonates at the center frequency of 2.45GHz.

Figure 9 illustrates the simulated |𝑆11| < −10 dB for various

electric probe heights (𝑙) and the results indicate the optimalheight of the probe (𝑙) of 0.245𝜆. In Figure 10, the simulated|𝑆11| for various distances between the probe and the closed

end of the radiating waveguide (𝑙1) reveal that the optimal

distance that achieves the resonance at the target centerfrequency is 0.414𝜆.

International Journal of Antennas and Propagation 5|S11|

(dB)

−30−25

−40−35

−50−45

−20−15−10−5

0

2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.92.0 3.0

Frequency (GHz)

L = 1.228𝜆

L = 1.236𝜆

L = 1.244𝜆L = 1.252𝜆

L = 1.261𝜆


| for various waveguide lengths (𝐿).

2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.92.0 3.0

Frequency (GHz)

|S11|

(dB)

−30−25

−40−35

−50−45

−20−15−10−5

0

l = 0.229𝜆l = 0.237𝜆

l = 0.245𝜆

l = 0.253𝜆

l = 0.261𝜆


| for various electric probe heights (𝑙).

2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.92.0 3.0

Frequency (GHz)

|S11|

(dB)

−30

−25

−40

−35

−45

−20

−15

−10

−5

0

l1 = 0.398𝜆

l1 = 0.406𝜆

l1 = 0.414𝜆

l1 = 0.423𝜆l1 = 0.431𝜆


| for various distances between the probeand the closed end of the waveguide (𝑙

1

).

2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.92.0 3.0

Frequency (GHz)

|S11|

(dB)

−30−25

−40−35

−50−45

−20−15−10−5

0

b1 = 0.057𝜆

b1 = 0.155𝜆

b1 = 0.236𝜆

b1 = 0.351𝜆

b1 = 0.449𝜆


| for various heights of the parasiticcoupling apertures (𝑏

1

).

|S11|

(dB)

−30−25

−40−35

−50−45

−20−15−10−5

0

2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.92.0 3.0

Frequency (GHz)l2 = 0.329𝜆

l2 = 0.378𝜆

l2 = 0.427𝜆

l2 = 0.476𝜆

l2 = 0.525𝜆


| for various lengths of the parasiticcoupling apertures (𝑙

2

).

Figure 11 illustrates the simulated |𝑆11| of the proposed

waveguide antenna for various heights (𝑏1) of the coupling

aperture, which were varied between 0.057𝜆 and 0.449𝜆. Theresults indicate that 𝑏

1exerts little influence over |𝑆

11| and

the optimal coupling aperture height (𝑏1) is 0.236𝜆, at which

the beamwidths at −3 dB and −10 dB in both the 𝐸- and𝐻-planes are symmetrical. This confirms that the utilizationof the coupling apertures contributes to the reduction ofthe diffraction field at the edges of the radiating waveguide.Figure 12 depicts the simulated |𝑆

11| for various lengths of

the coupling aperture (𝑙2) and the results show that |𝑆

11| vary

considerably with the variation in 𝑙2. The resonant frequency

is however achieved at 𝑙2of 0.427𝜆.

3.2.2. Radiation Patterns for Various Heights of the ParasiticCoupling Apertures (𝑏

1). Figures 13–15, respectively, illustrate


−30dB

−20dB

−10dB

0 dB

𝜃 𝜃0∘

30∘30∘

60∘60∘

90∘90∘

120∘120∘

150∘150∘

180∘

𝜙 = 90∘

b1 = 0.057𝜆 b1 = 0.155𝜆

b1 = 0.236𝜆

b1 = 0.351𝜆 b1 = 0.449𝜆

(a)

−30dB

−20dB

−10dB

0 dB

𝜃 𝜃0∘

30∘30∘

60∘60∘

90∘90∘

120∘120∘

150∘150∘

180∘

𝜙 = 0∘

b1 = 0.057𝜆 b1 = 0.155𝜆

b1 = 0.236𝜆

b1 = 0.351𝜆 b1 = 0.449𝜆

(b)

Figure 13: Simulated radiation patterns for various parasitic coupling aperture heights (𝑏1

) at the lower frequency of 2.412GHz in (a) the𝐸-plane and (b) the𝐻-plane.

−30dB

−20dB

−10dB

0 dB

𝜃 𝜃0∘

30∘30∘

60∘60∘

90∘90∘

120∘120∘

150∘150∘

180∘

𝜙 = 90∘

b1 = 0.057𝜆 b1 = 0.155𝜆

b1 = 0.236𝜆b1 = 0.351𝜆 b1 = 0.449𝜆

(a)

−30dB

−20dB

−10dB

0 dB

𝜃 𝜃0∘

30∘30∘

60∘60∘

90∘90∘

120∘120∘

150∘150∘

180∘

𝜙 = 0∘

b1 = 0.057𝜆 b1 = 0.155𝜆

b1 = 0.236𝜆

b1 = 0.351𝜆 b1 = 0.449𝜆

(b)


) at the center frequency of 2.45GHz in (a) the𝐸-plane and (b) the𝐻-plane.


−30dB

−20dB

−10dB

0 dB

𝜃 𝜃0∘

30∘30∘

60∘60∘

90∘90∘

120∘120∘

150∘150∘

180∘

𝜙 = 90∘

b1 = 0.057𝜆 b1 = 0.155𝜆

b1 = 0.236𝜆

b1 = 0.351𝜆 b1 = 0.449𝜆

(a)

−30dB

−20dB

−10dB

0 dB

𝜃 𝜃0∘

30∘30∘

60∘60∘

90∘90∘

120∘120∘

150∘150∘

180∘

𝜙 = 0∘

b1 = 0.057𝜆 b1 = 0.155𝜆

b1 = 0.236𝜆

b1 = 0.351𝜆 b1 = 0.449𝜆

(b)


) at the upper frequency of 2.484GHz in (a) the𝐸-plane and (b) the𝐻-plane.

the simulated radiation patterns for various heights of theparasitic coupling apertures (𝑏

1) in the 𝐸- and 𝐻-planes

at the lower, center, and upper frequencies of 2.412, 2.45,and 2.484GHz, where 𝑏

1was varied between 0.057𝜆 and

0.449𝜆. Interestingly, in the 𝐻-plane, the beamwidths at−3 dB (HPBW) and −10 dB for the three frequencies exhibitslight differences. On the other hand, those in the 𝐸-planefor the aperture heights (𝑏

1) between 0.057𝜆 and 0.155𝜆 are

noticeably wider than the corresponding beamwidths for thethree frequencies in the𝐻-plane. For 𝑏

1of 0.236𝜆 and 0.351𝜆,

the beamwidths at both −3 dB and −10 dB in both planesat the three frequencies are symmetrical. Thus, the couplingaperture height of 0.236𝜆 is selected due to the smallest cross-sectional area with the symmetrical radiation pattern. Table 3tabulates the beamwidths at −3 dB (HPBW) and −10 dB forthe three frequencies in the 𝐸- and 𝐻-planes for the variousheights of the parasitic coupling apertures (𝑏

1).

3.2.3. Radiation Patterns for Various Lengths of the ParasiticCoupling Apertures (𝑙

2). Figures 16–18, respectively, illustrate

the simulated radiation patterns for various lengths of theparasitic coupling apertures (𝑙

2) in the 𝐸- and 𝐻-planes at

the lower, center, and upper frequencies of 2.412, 2.45, and2.484GHz, where 𝑙

2was varied between 0.329𝜆 and 0.525𝜆.

It is found that at 𝑙2of 0.427𝜆 the symmetry in both planes

for the beamwidths at −3 dB and −10 dB is achieved. Table 4tabulates the beamwidths at −3 dB (HPBW) and −10 dB forthe three frequencies in the 𝐸- and 𝐻-planes for the variouslengths of the parasitic coupling apertures (𝑙

2).

Table 5 compares the simulated −3 dB and −10 dBbeamwidths of the proposed antenna with and without the

parasitic couplings apertures at the frequencies of 2.412,2.45, and 2.484GHz. Without the coupling apertures, thebeamwidths at −3 dB and −10 dB in the 𝐸-plane and those inthe𝐻-plane for the three frequencies are dissimilar; in otherwords, the incidence of asymmetry is observed. Nevertheless,with the parasitic coupling apertures on top and underneaththe width (𝑎) side of the radiating rectangular waveguide, the−3 dB and −10 dB beamwidths in both planes for the threefrequencies become symmetrical.

Figure 19 depicts the simulated antenna gains for var-ious parasitic coupling aperture heights (𝑏

1). For 𝑏

1=

0.236𝜆 and 0.449𝜆, the antenna gains are relatively similarfor the entire WLAN frequency range. The aperture height(𝑏1) of 0.236𝜆 is thus selected for the smallest cross-sectional

area with symmetrical pattern. Figure 20 illustrates thesimulated input impedance of the proposed antenna with thecoupling apertures. The input impedance (𝑍

0) at the center

frequency of 2.45GHz is 50.12 + 𝑗0.77Ω.When comparing the proposed triple-aperture waveg-

uide antenna with the conventional pyramidal horn antenna,it is obvious that the proposed antenna possesses smallertotal antenna length. The length of the probe-fed waveguidemust be appropriately designed to achieve the acceptableimpedance matching [30]. The total length of the hornantenna is composed of the length of horn aperture andwaveguide feeder. However, the radiating aperture andwaveguide feeder of the proposed antenna are integrated intosingle structure. Therefore, the proposed antenna requiressmaller total length to achieve the acceptable impedancematching. For instance, the total length of the conventionalpyramidal horn antenna is 18.5% larger than that of the


Table 3: Simulated beamwidths at −3 dB and at −10 dB for various heights of the parasitic coupling apertures (𝑏1

) in the 𝐸- and𝐻-planes forthe lower, center, and upper frequencies of WLAN.

Aperture heights (𝑏1

)

2.412GHz 2.45GHz 2.484GHzHPBW Beamwidth HPBW Beamwidth HPBW Beamwidth(−3 dB) −10 dB (−3 dB) −10 dB (−3 dB) −10 dB

𝐸-plane 𝐻-plane 𝐸-plane 𝐻-plane 𝐸-plane 𝐻-plane 𝐸-plane 𝐻-plane 𝐸-plane 𝐻-plane 𝐸-plane 𝐻-plane𝑏1

= 0.057𝜆 104∘ 67∘ 200∘ 124∘ 208∘ 66∘ 202∘ 124∘ 105∘ 64∘ 202∘ 124∘

𝑏1

= 0.155𝜆 78∘ 66∘ 196∘ 130∘ 74∘ 64∘ 196∘ 130∘ 72∘ 63∘ 128∘ 196∘

𝑏1

= 0.236𝜆 67∘ 67∘ 137∘ 137∘ 67∘ 67∘ 137∘ 137∘ 66∘ 66∘ 138∘ 138∘

𝑏1

= 0.351𝜆 69∘ 69∘ 144∘ 142∘ 69∘ 69∘ 142∘ 142∘ 69∘ 69∘ 142∘ 142∘

𝑏1

= 0.449𝜆 70∘ 71∘ 154∘ 148∘ 70∘ 70∘ 154∘ 148∘ 71∘ 70∘ 152∘ 148∘

Table 4: Simulated beamwidths at −3 dB and at −10 dB for various lengths of the parasitic coupling apertures (𝑙2

) in the 𝐸- and𝐻-planes forthe lower, center, and upper frequencies of WLAN.

Rectangularaperture lengths(𝑙2

)

2.412GHz 2.45GHz 2.484GHzHPBW Beamwidth HPBW Beamwidth HPBW Beamwidth(−3 dB) −10 dB (−3 dB) −10 dB (−3 dB) −10 dB

𝐸-plane 𝐻-plane 𝐸-plane 𝐻-plane 𝐸-plane 𝐻-plane 𝐸-plane 𝐻-plane 𝐸-plane 𝐻-plane 𝐸-plane 𝐻-plane𝑙2

= 0.329𝜆 65∘ 69∘ 210∘ 142∘ 65∘ 68∘ 206∘ 142∘ 65∘ 68∘ 202∘ 140∘

𝑙2

= 0.378𝜆 66∘ 68∘ 158∘ 138∘ 65∘ 67∘ 148∘ 138∘ 65∘ 67∘ 146∘ 136∘

𝑙2

= 0.427𝜆 67∘ 67∘ 137∘ 137∘ 67∘ 67∘ 137∘ 137∘ 66∘ 66∘ 138∘ 138∘

𝑙2

= 0.476𝜆 71∘ 68∘ 138∘ 136∘ 70∘ 67∘ 138∘ 134∘ 70∘ 66∘ 138∘ 132∘

𝑙2

= 0.525𝜆 75∘ 68∘ 138∘ 134∘ 74∘ 67∘ 140∘ 134∘ 73∘ 67∘ 140∘ 132∘

−30dB

−20dB

−10dB

0 dB

𝜃 𝜃0∘

30∘30∘

60∘60∘

90∘90∘

120∘120∘

150∘150∘

180∘

𝜙 = 90∘

l2 = 0.329𝜆 l2 = 0.378𝜆

l2 = 0.427𝜆

l2 = 0.476𝜆 l2 = 0.525𝜆

(a)

−30dB

−20dB

−10dB

0 dB

𝜃 𝜃0∘

30∘30∘

60∘60∘

90∘90∘

120∘120∘

150∘150∘

180∘

𝜙 = 0∘

l2 = 0.329𝜆 l2 = 0.378𝜆

l2 = 0.427𝜆

l2 = 0.476𝜆 l2 = 0.525𝜆

(b)

Figure 16: Simulated radiation patterns for various parasitic coupling aperture lengths (𝑙2



−30dB

−20dB

−10dB

0 dB

𝜃 𝜃0∘

30∘30∘

60∘60∘

90∘90∘

120∘120∘

150∘150∘

180∘

𝜙 = 90∘

l2 = 0.329𝜆 l2 = 0.378𝜆

l2 = 0.427𝜆

l2 = 0.476𝜆 l2 = 0.525𝜆

(a)

−30dB

−20dB

−10dB

0 dB

𝜃 𝜃0∘

30∘30∘

60∘60∘

90∘90∘

120∘120∘

150∘150∘

180∘

𝜙 = 0∘

l2 = 0.329𝜆 l2 = 0.378𝜆

l2 = 0.427𝜆

l2 = 0.476𝜆 l2 = 0.525𝜆

(b)



−30dB

−20dB

−10dB

0 dB

𝜃 𝜃0∘

30∘30∘

60∘60∘

90∘90∘

120∘120∘

150∘150∘

180∘

𝜙 = 90∘

l2 = 0.329𝜆 l2 = 0.378𝜆

l2 = 0.427𝜆

l2 = 0.476𝜆 l2 = 0.525𝜆

(a)

−30dB

−20dB

−10dB

0 dB

𝜃 𝜃0∘

30∘30∘

60∘60∘

90∘90∘

120∘120∘

150∘150∘

180∘

𝜙 = 0∘

l2 = 0.329𝜆 l2 = 0.378𝜆

l2 = 0.427𝜆

l2 = 0.476𝜆 l2 = 0.525𝜆

(b)




Table5:Simulated

beam

widthsa

t−3d

Bandat−10dB

ofthep

ropo

sedantenn

awith

andwith

outthe

parasiticcoup

lingaperturesa

tthe

lower,center,andup

perfrequ

encies

ofWLA

N.

Frequency(G

Hz)

HPB

W(−3d

Bbeam

width)

−10dB

beam

width

With

outp

arasiticc

ouplingapertures

With

parasiticcoup

lingapertures

With

outp

arasiticc

ouplingapertures

With

parasiticcoup

lingapertures

𝐸-plane

𝐻-plane

𝐸-plane

𝐻-plane

𝐸-plane

𝐻-plane

𝐸-plane

𝐻-plane

2.412

105∘

65∘

67∘

67∘

275∘

116∘

137∘

137∘

2.450

106∘

64∘

67∘

67∘

275∘

116∘

137∘

137∘

2.484

108∘

63∘

66∘

66∘

276∘

116∘

138∘

138∘


0123456789

10

Gai

n (d

Bi)

b1 = 0.057𝜆b1 = 0.155𝜆

b1 = 0.236𝜆

b1 = 0.351𝜆

b1 = 0.449𝜆

2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.92.0 3.0

Frequency (GHz)

Figure 19: Simulated antenna gains for various heights of the parasitic coupling apertures (𝑏1

).

ResistanceReactance

−150

−100

−50

0

50

100

Inpu

t im

peda

nce (Ω

)

2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.92.0 3.0

Frequency (GHz)

Figure 20: Simulated input impedance of the proposed antenna with the parasitic coupling apertures.

proposed antenna structure with the same radiating apertureand antenna gain. In addition, the proposed triple-aperturewaveguide antenna has 11-dB lower cross-polarization levelthan the conventional pyramidal horn antenna with the sameantenna size. The reason is that the larger width of thepyramidal horn causes the higher horizontal electric fieldcomponent.

4. Experimental Results

Figure 21 presents photographs of the prototype of theproposed triple-aperture waveguide antenna. The proposedantenna is operable in the 2.30–2.60 frequency range(12.245%), which also covers the WLAN frequency, for|𝑆11| < −10 dB. The antenna prototype was fashioned from

aluminum of 2mm in thickness. The radiation pattern ofthe prototype antenna is symmetrical with unidirectionalpattern, rendering it appropriate for use in the front feedingparabolic reflector in the point-to-point communication.

Table 6: Measured beamwidths at −3 dB and at −10 dB of theproposed antennawith the parasitic coupling apertures in the𝐸- and𝐻-planes at the lower, center, and upper frequencies of WLAN.

Frequency(GHz)

HPBW (−3 dB beamwidth) −10 dB beamwidth𝐸-plane 𝐻-plane 𝐸-plane 𝐻-plane

2.412 65∘ 65∘ 135∘ 135∘

2.450 65∘ 65∘ 135∘ 135∘

2.484 65∘ 65∘ 135∘ 135∘

Figure 22 compares the simulated and measured |𝑆11| of

the waveguide antenna with the parasitic coupling apertures.The simulation and measured results show the operatingrange of the antenna of 2.28–2.80GHz and 2.30–2.60GHz,respectively, indicating their good agreement.

Figure 23 compares the simulated and measuredbeamwidths at 2.45GHz in the 𝐸- and𝐻-planes. Meanwhile,Table 6 tabulates the −3 dB and −10 dB beamwidths in both


(a) (b) (c)

Figure 21: Photographs of the antenna prototype: (a) perspective view, (b) front view, and (c) side view.

SimulatedMeasured

2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.92.0 3.0

Frequency (GHz)

|S11|

(dB)

−30

−25

−40

−35

−45

−20

−15

−10

−5

0

Figure 22: The simulated and measured |𝑆11

| of the waveguide-dependent triple-aperture antenna.

SimulatedMeasured

−30dB

−20dB

−10dB

0 dB

𝜃 𝜃0∘

30∘30∘

60∘60∘

90∘90∘

120∘120∘

150∘150∘

180∘

𝜙 = 90∘

(a)

SimulatedMeasured

−30dB

−20dB

−10dB

0 dB

𝜃 𝜃0∘

30∘30∘

60∘60∘

90∘90∘

120∘120∘

150∘150∘

180∘

𝜙 = 0∘

(b)

Figure 23: The simulated and measured radiation patterns at 2.45GHz: (a) 𝐸-plane and (b)𝐻-plane.


0

3

6

9

12

15G

ain

(dBi

)

SimulatedMeasured

2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.92.0 3.0

Frequency (GHz)

Figure 24: The simulated and measured antenna gains in front ofthe antenna (0∘).

planes for the three frequencies. In Figure 24, the simulationantenna gain in front of the antenna at 0∘ is compared againstthe measured gain. The proposed antenna could achieve themaximum gain of 9.17 dBi at the WLAN center frequency.

5. Conclusion

This research has proposed the triple-aperture waveguideantenna as the primary feed of parabolic reflectors. Theantenna could rectify the asymmetry and achieve the sym-metrical unidirectional beam with the incorporation of twoparasitic coupling apertures. The antenna consists of theradiating rectangular waveguide vertically jointed to the twocoupling apertures to achieve the symmetrical beam. Therectangular waveguide is 97.60mm and 46.80mm in width(𝑎) and height (𝑏), respectively, to propagate the WLANfrequency band of 2.412–2.484GHz. In this research, the CSTMicrowave Studio program was deployed in simulation todetermine the optimal antenna parameters and an antennaprototype was subsequently fashioned and experimented.The simulated beamwidths in the 𝐸- and 𝐻-planes at −3 dBwere equally 67∘ and at −10 dB equally 137∘, while themeasured beamwidths at −3 dB were equally 65∘ and at−10 dB equally 135∘ in the 𝐸- and 𝐻-planes. The simulationand measured results are in good agreement. The simulatedand measured antenna gains are, respectively, 8.25 dBi and9.17 dBi.The findings confirm the applicability of the antennaas the prime feed for rotationally symmetric parabolic reflec-tors. In addition, the proposed antenna is light, inexpensive,and of low profile.

Competing Interests

The authors declare that there are no competing interestsregarding the publication of this paper.

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