Research ArticleInvestigation on SIW Slot Antenna Array with BeamScanning Ability

Yanfei Li 1,2 and Yang Li1

1State Key Laboratory of Millimeter Waves, Southeast University, Nanjing 210096, China2Information Engineering School, Communication University of China, Beijing 100024, China

Correspondence should be addressed to Yanfei Li; liyanfei@cuc.edu.cn

Received 22 July 2018; Revised 10 September 2018; Accepted 3 October 2018; Published 6 January 2019

Academic Editor: Yu Jian Cheng

Copyright © 2019 Yanfei Li and Yang Li. This 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 sparse substrate integrated waveguide (SIW) slot antenna array and its application on phase scanning are studied in this paper.The genetic algorithm is used to optimize the best arrangement for 8-element and 7-element sparse arrays over an aperture of4 5λ0. Antenna arrays with feeding networks, for steering the main beam pointing to 0° and −15°, are demonstrated with theSIW technology. The comparison between the sparse array and the conventional uniformly spaced array with the sameaperture are presented, which suggest that the same beam width can be obtained with the gain decreased by 0.5 or 1 dBi andthe number of element reduced by 2 or 3, respectively. The sparse antenna array with beam scanning ability presented in thispaper shows that, while the beam scanning in the range of ±15°, the gain fluctuation is less than 0.3 dBi and the side lobe levelis lower than −10 dB.

1. Introduction

Phased array antenna has been widely used in modern wire-less communication systems for the high gain and agile beamscan [1]. The active phased array has transmitting/receiving(T/R) module with each element, which can improve the per-formance but will increase the cost of the whole array.Besides, in order to obtain a narrow main beam, a large radi-ation aperture is needed; the element number of the tradi-tional uniformly distributed phased array will increase. Thecost introduced by control components, T/R modules, andpower dividers will limit the use of phased arrays. In someapplications with the requirement of narrow beam widthand high gain, the phased array with reduced number of cellsattracts more attention.

Sparse array was studied with fewer elements arrangedover the same aperture compared to conventional full feed-ing uniformly spaced array since the 1960s [2]. Theoretically,the low side lobe level (SLL) can be obtained by optimizingthe feeding current and position of each element. Some

algorithms are employed to large scale sparse array opti-mizations, such as genetic algorithm (GA) [3], particleswarm optimization [4], and Harmony Search Algorithm[5]. Among the optimization methods, genetic algorithm isone of the most popular optimization techniques used forside lobe level reduction [6–9], since GAs [10] are well suitedfor sparse and thinning array optimization. GA is a globaland random search algorithm that simulates natural selec-tion and evolution. It searches through the total solutionspace and can find the optimal global solution in a domain.Although GA was applied for optimizing sparse array widely,few sparse arrays with phased scanning have been reportedwith demonstration and measurement results.

In this paper, the genetic algorithm is applied foroptimizing the position of each element in an equal ampli-tude feeding sparse array with an aperture of 4 5λ0, whereλ0 is the free space wavelength at the center frequency14GHz. The sparse arrays with antenna element numberof 7 and 8 are investigated separately, which SLLs arelower than −10 dB at both broadside and −15° direction.

HindawiInternational Journal of Antennas and PropagationVolume 2019, Article ID 8293624, 7 pageshttps://doi.org/10.1155/2019/8293624

Each sparse array consists of antenna elements, phasedshifters, and power dividers based on substrate integratedwaveguide (SIW).

The paper is organized as follows. The design processof the sparse phased array is presented in Section 2. Measure-ment results and analysis are given in Section 3, and theconclusion is drawn in Section 4.

2. Design of the Sparse Array

2.1. Genetic Algorithm (GA). A linear sparse array is studiedin this section. The array factor with equal feeding amplitudecan be given in [11] by

AF =〠ejkdn cos θ, n = 1, 2,N , 1

where dn is the distance between the element n and the ele-ment 1. N is the number of the elements of the array. Theprogram in MATLAB GA toolbox is used to optimize thebest arrangement of the linear sparse array. The GA flow-chart is shown in Figure 1. dn is set as optimization variable,and SLL is chosen as fitness function, which is expressed as

f itness d =max AF uAFmax

, 2

where AFmax is the peak main lobe level.For the 8-element case, the position of the first element is

0 and the 8th element is 4 5λ0. The 8-number vector is codedinto a population with 400 randomly generated individuals.In order to avoid the dead loop, as well as considering thespeed of the optimization convergence, after 500 iterations,

Start

Initialize population

i > 500?

Select

Preprocess

Crossover

Mutate

Reprocess

Calculate fitness function

Output bestindividual

End

Yes

No

Figure 1: GA flow chart.

Table 1: The arrangement of two sparse arrays.

Element 1 2 3 4 5 6 7 8

Position (λ0) 0 0.55 1.23 1.85 2.51 3.11 3.66 4.5

Position (λ0) 0 1.45 2.06 2.71 3.34 3.85 4.5 —

Radiationslots

Phase shifters 1-to-8 parallel powerdivider

50ohm-GCPW-to-SIWtransition

(a)

Radiationslots Phase shifters 1-to-7 parallel power

divider

50ohm-GCPW-to-SIWtransition

(b)

dx

dy

lslotwslot

pl

ds

p2

(c)

Figure 2: The structure of (a) 8-element and (b) 7-element sparsearrays and (c) detail of SIW radiation slots.

2 International Journal of Antennas and Propagation

a set of element arrangement will be generated. When thenumber of element is 7, the situation is the same as the8-element case except the population is coded by 7-numbervectors. The optimized arrangements for both cases areshown in Table 1.

2.2. SIW Slot Antenna. By using the optimized position of thesparse arrays, we construct the 8-element and 7-elementsparse antenna arrays which are shown in Figure 2. Theyare both composed of SIW radiation slots, phase shifters,parallel power dividers, and 50-ohm grounded coplanar

waveguide- (GCPW-) to-SIW transitions. The SIW metallicpins are with the radius of 0.25mm and the distance of 1mm.

The two radiation slots in each SIW path are antennaarrays, that is, the substrate integrated waveguide slotantenna unit; the detail of the slot array antenna unit isshown in Figure 2(c); the substrate of the SIW is with thethickness of 1.524mm and with the relative permittivity of3.5. All the dimensions of the slot antenna array unit arelisted in Table 2. The S11 and radiation of the slot arrayantenna unit are shown in Figure 3. The −10dB impedancebandwidth is from 13.4 to 15.2GHz (relative bandwidth is12%), with a gain of 7.86 dB at 14GHz. The beam width is140° in the E-plane, which indicates that it can be used as aunit antenna for a wide-angle coverage phased array.

2.3. Feeding Network. The feeding networks with phaseshifters are designed to steer main beam pointing to 0° and−15° for each sparse array. The structure of Y-type-equalSIW power divider is shown in Figure 4. The distancebetween the two output ports of each power divider dai is dif-ferent from each other. A metallic pin is placed in the centerline to equally deliver the input power to two ports. The dis-tances dyi and dxi can be optimized to reduce the reflectionfrom the SIW branches and bends [12]. And the width ofSIW a is 7.3mm to support the TE10 mode in the wholeoperating frequency band.

The phase of each output port of the parallel powerdivider is different because of the ununiformly distributedsparse array. In the cases of the main beam steering to 0°,the phase shifters are required for in-phase feeding. Forthe cases of beam steering to −15°, the phase shifts of theSIW phase shifters are shown in Table 3. The required

Table 2: Parameters of the slot antenna array unit (mm).

p1 p2 lslot wslot dx dy ds

1 0.9 7.6 1 0.4 8.4 2.5

|S11

| (dB

)

Frequency (GHz)13.4 13.6 13.8 14.0 14.2 14.4 14.6 14.8 15.0 15.2

0

−5

−10

−15

−20

−25

(a) S11

−40

−30

−20

−10

0

100

30

60

90

120

150180

210

240

270

300

330

−30

−20

−10

0

10

Gai

n (d

B)

H-planeE-plane

(b) Radiation pattern at 14 GHz

Figure 3: Simulation results of substrate integrated waveguide slotantenna unit.

dyi

dxi

dxi

a

a

a

dai

Figure 4: Y-type-equal power divider.

Table 3: Phase shifts of phase shifters for two sparse arrays to steermain beam pointing to −15°.

Phase shifter 1 2 3 4 5 6 7 8

Phase shift 1 (°) 0 52.9 118.6 177.5 240.5 299.1 351.7 72

Phase shift 2 (°) 0 139.5 198.6 260.3 321.0 9.2 72 —

3International Journal of Antennas and Propagation

phase shifts are realized by adjusting the widths and lengthsof the phase shifters, which changes the propagation con-stant and characteristic impedance of the SIW [13]. In thecase of phase shift larger than 180°, the radiation slots canbe mirrored along the center line of the SIW to provide180° phase shift in addition. The scanning performance ofthe array is studied by feeding each element with equalamplitude and gradual phase shifts.

The structure of 50-ohm GCPW-to-SIW transition isshown in Figure 5(a). It is used to transform low impedanceSIW to 50 ohm for testing purpose. The metallic pins nearGCPW are with the radius of 0.15mm and distance of0.6mm. The 50-ohm GCPW has a width of w and a gap ofg. The simulated S parameters are shown in Figure 5(b),which indicate a low reflection coefficient among operationfrequency band.

After combining the antenna array and feeding networktogether, four SIW antennas including 8-element and7-element sparse arrays pointing to 0° and −15° are simulatedand fabricated. The measurement results of S11 of the wholesparse array with feeding networks are shown in Figure 6.

3. Measurement and Analysis

Four sparse array antennas with feeding networks are dem-onstrated by low-cost single-layer printed circuit board

(PCB) process, which are shown in Figure 7, each sparsearray is composed of top layer and bottom layer. Thesubstrate is with a dielectric permittivity of 3.5, dielectricloss tangent of 0.0018, which thickness is 1.524mm with

wc b g

(a)

0

13.4 13.6 13.8 14.0 14.2 14.4 14.6 14.8 15.0 15.2

S11S12

S21S22

−5

−10

−15

−20

−25

−30

−35

Freq (GHz)

(b)

Figure 5: (a) GCPW-to-SIW transition and (b) the simulated Sparameter: w = 2 25 mm; g = 0 4 mm; b = 6 2 mm; c = 5 85 mm.

13.6 13.8 14.0 14.2 14.4 14.6 14.8 15.0 15.2 15.4 15.6 15.8 16.0−65−60−55−50−45−40−35−30−25−20−15−10−5

0

S11

(dB)

Frequency (dB)8-element arraypointing to 0 degree8-element arraypointing to 15 degree

7-element arraypointing to 0 degree7-element arraypointing to 15 degree

Figure 6: S11 measurement results of the sparse antenna arrayswith SIW feed network.

(a) 8-element sparse array

(b) 7-element sparse array

Figure 7: Photography of the fabricated sparse arrays, for (a) and(b), left: top layer, right: bottom layer, top: pointing to 0°, under:pointing to 15°.

4 International Journal of Antennas and Propagation

a dimension of 12.4× 14.7 cm2. The simulated and mea-sured radiation patterns of the sparse array antennas areshown in Figure 8. The measured results agree well withthe simulated ones, and the SLLs lower than −10 dB and crosspolarization lower than −20dB for all arrays pointing todifferent angles.

Furthermore, the comparison between the sparse arrayand conventional half-wavelength spaced array with 10 ele-ments as well as the phase scanning performance of thesparse array is shown in Figures 9 and 10, respectively. Boththe sparse array and the uniform 10-element array are withthe same radiation slot array antenna unit. It suggests thatthe sparse array can generate the same beam width as thefully arranged array while the gain decreased by 0.5 or 1 dBiwhen the element number reduced by 2 or 3, respectively.Both sparse arrays show a good performance during the fullscanning range of ±15° with the gain fluctuation less than0.3 dBi and SLL lower than −10 dB.

0

−5

−10

−15

−20

−25

−30

−35

−40

−45

−18

0

−15

0

−12

0

−90

−60

−30 0

Angle (deg)Co-pol measured

Co-pol simulatedX-pol measured

Radi

atio

n pa

ttern

(dB)

30 60 90 120

150

180

(a)

0

−5

−10

−15

−20

−25

−30

−35

−40

−45

−18

0

−15

0

−12

0

−90

−60

−30

Angle (deg)Co-pol measured

Co-pol simulatedX-pol measured

Radi

atio

n pa

ttern

(dB)

300 60 90 120

150

180

(b)

0

−5

−10

−15

−20

−25

−30

−35

−40

−45

−18

0

−15

0

−12

0

−90

−60

−30

Angle (deg)Co-pol measured

Co-pol simulatedX-pol measured

Radi

atio

n pa

ttern

(dB)

300 60 90 120

150

180

(c)

0

−5

−10

−15

−20

−25

−30

−35

−40

−45

−18

0

−15

0

−12

0

−90

−60

−30

Angle (deg)Co-pol measured

Co-pol simulatedX-pol measured

Radi

atio

n pa

ttern

(dB)

300 60 90 120

150

180

(d)

Figure 8: Radiation patterns (simulation results are at 14GHz, measured at 13.9GHz). (a) 8-element array pointing to 0°; (b) 8-element arraypointing to −15°; (c) 7-element array pointing to 0°; (d) 7-element array pointing to −15°.

18.0

17.5

17.0

16.5

16.0

15.5

15.013.6

7-element8-elementconventional

14.0 14.4Freq (GHz)

Gai

n (d

B)

14.8 15.2

Figure 9: The broadside gain of the sparse and conventional arrays.

5International Journal of Antennas and Propagation

4. Conclusion

In this paper, the sparse SIW slot antenna arrays with beamscanning ability are studied. GA is used to optimize the loca-tions of the elements to make SLL lower than −10dB. The8-element and 7-element sparse arrays are designed by usingthe optimized arrangement, and SIW technology is used inthe feeding network. In order to verify the beam scanningability of the sparse arrays, the arrays pointing to −15° arerealized by using the designed feeding network. Althoughthe broadside gain of sparse arrays is decayed, the same beamwidth can be obtained with a reduced element number. Afterbeing fed with the equal amplitude and gradual phase shift,

the phase scanning performance of two sparse arrays is stud-ied. The designs are demonstrated and tested, which indi-cates a good sparse array which also has the beam scanningproperty when the proper phase is given.

Data Availability

The data used to support the findings of this study areincluded within the article.

Conflicts of Interest

The authors declare that there is no conflict of interestsregarding the publication of this paper.

Acknowledgments

This work was supported in part by the National KeyTechnology Support Program (2015BAK05B01 and2015BAK05B01-01).

Supplementary Materials

The simulation and measurement data used to support thefindings of this study are included within the supplementaryinformation file. (Supplementary Materials)

References

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20

10

0

−10

−20

−30

−40

−18

0

−1515−10

−12

0

−15

0

−60

−30

−90

Angle (GHz)

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−1515−10

−12

0

−15

0

−60

−30

−90

Angle (GHz)

0 30 60 90 120

150

180

10

−550

(b)

Figure 10: Phase scanning performance for (a) 8-element and (b)7-element sparse arrays.

6 International Journal of Antennas and Propagation

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7International Journal of Antennas and Propagation

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