research article design and analysis of thinned array

Research ArticleDesign and Analysis of Thinned Array PatternReconfigurable Antenna to Enlarge the Scanning Range

Zhangjing Wang, Xing Fan, Haijuan Cui, and Shaoqiu Xiao

School of Electronic Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China

Correspondence should be addressed to Zhangjing Wang; [email protected]

Received 24 December 2015; Revised 13 February 2016; Accepted 18 February 2016

Academic Editor: Ahmed A. Kishk

Copyright © 2016 Zhangjing Wang et al. 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 is properlycited.

A novel thinned array with symmetric distribution along the array center is proposed in this paper. The proposed symmetricthinned array is based on the theory of unequally spaced array and the amplitude of each element in the array can be changed byintroducing the weighted function. The pattern of the proposed array can be properly adjusted by changing the weighted functionand the amplitude of the weighted factor, which obviously releases new degrees of freedom in array design. It has advantages suchas low side lobe level (SLL) in the visible region, no grating lobes, and low nearby side lobe level (NSL), which has good potentialfor wide-angle scanning. Both simulation and experiment have been done; the experiment results show that, by applying this novelsymmetric thinned array with pattern reconfigurable quasi-Yagi antenna, the scanning range of the array is −70∘∼70∘ in 𝐻-planewith SLL almost −10 dB below the maximum of the main beam.The 3 dB beam-width coverage is −86∘∼86∘, which means that theproposed array can realize the entire upper-space beam coverage and restrain the SLL at the same time.

1. Introduction

Phased array has received abundant applications in wirelesscommunication and radar system in recent years due to itsadvantages such as high reliability, rapid speed, and highaccuracy of beam scanning. Particularly, microstrip antennasare good candidates for phased array application becauseof their low cost, ease of fabrication, and integration withmicrowave integrated circuits (MICs) [1]. According to theantenna theory, a microstrip phased array can scan its mainbeam from −50∘ to 50∘ with the array gain reduction of4-5 dB down from its maximum because of the limitationof radiation pattern of array element and mutual couplingbetween elements, which will have huge influence on theradiation pattern when the scanning angle is large [2, 3]. Itobviously restrains the further development and applicationof the phased array. Therefore, the improvement of scanningrange of phased array and suppression of mutual couplingbetween elements in the array are desired.

Generally, there are two main aspects to promote thewide-angle scanning performance of phased array.Oneway is

focused on the antenna element. A lot of research and effortshave been made to enlarge the radiation pattern of antennaelement [4–7]. In [4], composite dielectric substrate is usedto expand the 3 dB beam width of antenna element. A stablewide beam width in both 𝐸 and 𝐻 planes can be realizedby using gaps and stubs-loaded patch in microstrip antenna[5]. The 3 dB beam width of this novel antenna in both mainplanes is from −60∘ to 60∘. In [6, 7], the cavity architecture isused to reduce the mutual coupling of element in the array.The array can realize the wide-angle scanning up to 60∘ at theoperating frequency band. However, it is difficult to expandthe scanning angle further just by enlarging the radiationpattern of antenna element. Andwide-beam antenna elementalso leads to large grating lobes and side lobes when thescanning angle is large and the array is equally spacedwith distance between elements greater than 0.5𝜆 (𝜆 is thewavelength in free space).

In recent years, the existence of pattern reconfigurableantenna provides a new way to widen the radiation pattern ofelement. Pattern reconfigurable antenna can reconfigurate itsradiation pattern by changing the state of switches integrated

Hindawi Publishing CorporationInternational Journal of Antennas and PropagationVolume 2016, Article ID 7487020, 7 pageshttp://dx.doi.org/10.1155/2016/7487020

2 International Journal of Antennas and Propagation

on the antenna element or feeding network, and the radiationpattern can jointly cover a wide range, which makes it apromising solution to overcome the obstacle in wide-anglescanning of the phased array [8, 9].

The other way is focused on the array factor. For example,a lot of optimization algorithms have been proposed, whichcan be used to optimize the amplitude, phase, and distancebetween elements of the array [10, 11]. However, it is time con-suming and sometimes cannot be used in reality because thedistance between elements is too small. Some conformalarrays have been proposed to extend the scanning angle [12,13], but the application of conformal array is often subject tothe conditions of application environments. In [14, 15], thetheory of unequally spaced array has been proposed, whichhas no grating lobes in the visible region when the distancebetween elements is greater than 𝜆/2. The mutual couplingbetween elements is small because the distance between adja-cent elements is large, typically greater than 𝜆/2. The distri-bution of array elements can be easily calculated by formula.

So the combination of pattern reconfigurable antenna andthinned array will have much potential in the ability of wide-angle scanning of antenna array. In [16], applying weightedthinned array with pattern reconfigurable antenna has beendone; the proposed array can scan its main beam in the rangeof −60∘∼60∘ in𝐻-plane.

In this paper, a novel antenna thinned array with sym-metric distribution along the array center is proposed. Thepattern of the proposed array can be properly adjusted bychanging the weighted function and the amplitude of theweighted factor, which releases more degrees of freedom inarray design. By properly adjusting theweighted function andweighted factor, the SLL can be suppressed. By applying thisnovel symmetric thinned array with pattern reconfigurablequasi-Yagi antenna, the scanning range of the array is −70∘∼70∘ in𝐻-plane with SLL almost −10 dB below the maximumof the main beam. The 3 dB beam-width coverage is −86∘∼86∘. The simulation results agree well with the experimentresults, which shows the validation of the proposed methodin wide-angle scanning array design.

2. Thinned Array Design

Traditionally, the distribution of elements in phased array isequally spaced and the distance between elements is smallerthan 𝜆/2 to avoid grating lobes in wide-angle scanning.However, small distance will cause strong mutual couplingbetween elements, which has huge influence on the radiationpattern and reflection coefficient of elements, and sometimesit might cause the scanning blindness. Besides, the size ofsome antenna elements is equal to or bigger than𝜆/2, so somesolutions should be figured out to use these elements in thearray. Applying weighted thinned array is a good choice toovercome this difficulty [16]. Not only can the distance andamplitude of antenna elements be adjusted, but the gratinglobes can be eliminated at the same time.

The radiation pattern of 𝑁 isotropic elements can beexpressed as

𝐸 (𝜃) =

𝑁

∑

𝑛=1

𝐼

𝑛𝑒

𝑗𝑘𝑠𝑛sin 𝜃

, (1)

Normalized radiation pattern

Equally spaced arrayThinned array

−50

−45

−40

−35

−30

−25

−20

−15

−10

−5

0

Am

plitu

de (d

B)

10.50 1.5 2−1−1.5 −0.5−2

u

Figure 1: Radiation pattern of equally spaced and thinned array.

where 𝐼𝑛stands for the current of 𝑛th element, 𝑘 = 2𝜋/𝜆 is

the wave number, 𝑠𝑛stands for the distance of 𝑛th element to

the reference point, and 𝜃 is the angle of the radiation pattern.The formula can be further simplified as

𝐸 (𝜇) =

𝑁

∑

𝑛=1

𝑤

𝑛𝑒

𝑗𝑘𝑠𝑛𝜇

, (2)

where 𝑤𝑛is the current amplitude of 𝑛th element and 𝜇 =

sin 𝜃 − sin 𝜃0. This formula can be rewritten as a summation

of series of grating lobes and one main lobe [14]:

𝐸 (𝜇) =

∞

∑

𝑚=−∞

(−1)

𝑚(𝑁−1)

𝐸

𝑚(𝜇)

𝐸

𝑚(𝜇)

=

1

2

∫

1

−1

𝑤 (𝑥)

𝑑𝑦

𝑑𝑥

𝑒

−𝑗𝜓(𝑥)+𝑗𝑚𝜋𝑁(𝑦−𝑥)

𝑒

𝑗(𝜇+𝑚𝜋𝑁)𝑥

𝑑𝑥.

(3)

In (3), 𝐸𝑚(𝜇) stands for the𝑚th grating lobes of the array.

The grating lobes can be effectively avoided by exponentiallyspacing the elements of the array [15]. Figure 1 shows theradiation pattern of 50 isotropic elements which are equallyspaced and exponentially spaced. The length of the array is50𝜆. It can be seen clearly from the picture that the gratinglobes have been inhibited by using exponentially thinnedarray in the visible region.

The radiation pattern of exponentially thinned array canbe adjusted by changing the ratio of the maximum distanceto minimum distance. And the amplitude of current of arrayelement can also be adjusted by introducing a new weightedfunction [17]. In [17], Zhang proposed a general raised cosinefunction to weight the exponentially thinned array. The sidelobe level near the main beam (NSL) can be reduced further.

International Journal of Antennas and Propagation 3

However, the peak side lobe lever (PSL) is still high whenthe number of elements of the array is small. So it might notbe the good choice for the phased array to realize the wide-angle scanning, especially for the array with small number ofelements, which might not achieve the optimal solution. Andthemutual coupling should also be consideredwhile selectingthe weighted function and weighted factor.

In order to enlarge the scanning angle and suppressthe SLL at the same time, a compromise should be madebetween PSL and NSL of the array factor. In addition, theweighted function and factor should be carefully selected andoptimized. Much simulation has been done in order to findthe desiredweighted function to reduce the SLL inwide-anglescanning. The weighted function can be expressed as

𝑤 (V) = 𝑎 + (1 − 𝑎) [1 − sin 𝜋 (V − 1)

2 (𝑁 − 1)

] , (4)

where𝑁 stands for the total number of elements in the arrayand a is the weighted factor from 0 to 0.5. By placing the arraysymmetrically, the SLL can be further reduced. The positionof each element can be calculated by the following:

𝑋V =𝐿

2 ∫

(𝑁+1)/2

1

𝑟

ℎ(𝑖)

𝑑𝑖

∫

V

1

𝑟

ℎ(𝑖)

𝑑𝑖 (5)

ℎ (V) =∫

V1

|𝑤 (𝑖)|

2

𝑑𝑖

∫

(𝑁+1)/2

1

|𝑤 (𝑖)|

2

𝑑𝑖

. (6)

𝑋V is the distance of Vth elements to the reference point0 and r can be properly adjusted in the range of 1.5 to2.5, which represents the ratio of maximum distance tominimum distance between elements. Once the length of thearray is determined,wide-angle scanning performance can berealized by optimizing the parameters such as r, array factor,and the number of the elements.

3. Pattern Reconfigurable Quasi-Yagi Antenna

The pattern reconfigurable antenna element used in thispaper is quasi-Yagi pattern reconfigurable antenna [16]. Thegeometry of the antenna mentioned above is shown inFigure 2.The antenna is printed on the Rogers 5880 substratewith permittivity of 2.2, height of 8mm, and operatingfrequency of 5.8 GHz. It consists of three parallel metal stripsused as radiators and a DC bias circuit. The driven stripis in the middle of two parasitic strips. The length of theexcitation strip is about 0.5𝜆

𝑔(𝜆𝑔is the guided wavelength

in operating frequency), which is a little shorter than twoparasitic strips. The distance between strips is about 0.25𝜆.The antenna is fed by a SMA connector with its innerconductor soldered to the driven strip and outer conductorsoldered to the ground plane. Six inductances, that is, L

1∼L6,

are inserted in two parasitic strips to block theRF signal to theDC circuit. High impedance lines connected with shortingpins are used to form the DC circuit and reduce the impacton radiation pattern by DC circuit. The parameters for thepattern reconfigurable antenna are given in Table 1.

Table 1: Parameter for pattern reconfigurable antenna.

Parameters Value (mm)𝐿

𝑔

70𝑤

𝑔

60𝑤 1.5𝑔 6𝐿

𝑚

20𝐿

𝑟

22𝑑

𝑙

3.5𝑠 10

g

w

s

Shorting pins

High impedance line

x

y

SMA

H

Top viewx

z

Side view

Lr

L2dl

V1

k1

k2

L1

L5 Lm

V2

k3

k4L4

L6

L3

𝜀r

Figure 2: Geometry of the pattern reconfigurable antenna.

Four PIN diodes integrated on the two parasitic stripsare used as switches to change the radiation pattern of theantenna just by transforming the state of the switches tobe “ON” or “OFF.” The proposed antenna can operate inthree modes, that is, L-mode, B-mode, and R-mode. L-mode stands for the radiation pattern of the pattern recon-figurable antenna tilting to the left side. B-mode stands forthe radiation pattern of the pattern reconfigurable antennatilting to the broad side, and R-mode stands for the radiationpattern of the pattern reconfigurable antenna tilting to theright side.

When the voltage of −5V is applied in the point V1and

5V is applied in the point V2, the PIN diodes in the left

parasitic strip are in “OFF” state while the PIN diodes inthe right parasitic strip are in “ON” state, and the antennaoperates in L-mode. When both points apply the voltage of−5V, the antenna is in B-mode. When the voltage of 5V isapplied in the point V

1and −5V is applied in the point V

2,

the antenna is in R-mode.ThePINdiode used in simulation isMA4GP907with equivalent resistance of 4Ω and capacitance


R-modeB-modeL-mode

0

30

60

90

120

150

180

210

240

270

330

300

10

0

−10

−20

−30

−40

−30

−20

−10

0

10

Gai

n (d

Bi)

5.0 5.2 5.4 5.6 5.8 6.0 6.2 6.4 6.64.8

Frequency (GHz)

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

VSW

R

R-modeB-modeL-mode

Figure 3: Radiation pattern and VSWR of the proposed antenna.

of 0.025 pf. The simulation results can be found in Figure 3.The 3 dB beam width of the antenna can jointly cover anangle in the range of −75∘∼75∘; all of the three modes sharea common 2 : 1 VSWR bandwidth from 5.68GHz to 6GHz.

It is worth mentioning that the tilting angle of the singlequasi-Yagi reconfigurable antenna in R-mode and L-modemight have much difference in the array because of themutual coupling between elements. Figure 4 shows the radia-tion pattern of different distance between elements of antennaelement number 1 in R-mode in the existence of anotherelement number 2 that is connected with the matched loadof 50Ω. It can be found that the radiation pattern of number1 nearly directs to broad side when the distance between twoelements is small and gradually tilts to the right side when

0

30

60

90

120

150

180

210

240

270

330

300

25mm30mm

35mm40mm

Number 1 Number 2

s

10

5

0

−5

−10

−15

−20

−25

−20

−15

−10

−5

0

5

10

Gai

n (d

Bi)

Figure 4: Parameter study of the distance between two elements.

the distance becomes large, because the mutual coupling ofthe two elements becomes small when the distance is largeand strong when the distance is small. It indicates the use-fulness of thinned array in wide-angle scanning performancebecause the distance between elements is generally largerthan 0.5𝜆 and the grating lobes can be eliminated at the sametime.

4. Analysis of the Experimental Results

In order to testify the ability of the symmetric weightedthinned array proposed in Section 2 in wide-angle scanning,a 7-element symmetric thinned array has been designed andfabricated. The photograph of the proposed array can befound in Figure 5. The total length of the array is 5𝜆, r = 2,and the weighted factor is chosen to be 0.5. The distributionof elements can be calculated by (5), and the amplitudeof elements can be figured out by (4). The position andamplitude of elements are shown in Table 2.The element usedin the array is the quasi-Yagi reconfigurable antenna. Andonly L-mode and R-mode are used. When the array scans itsmain beam to the right side, all the elements operate in R-mode. When the array scans its main beam to the left side,all the elements operate in L-mode. When the array scans itsmain beam to the broad side, both L-mode and R-mode canbe used.

The scattering matrix 𝑠

𝑚𝑛(𝑚, 𝑛 = 1, 2, 3, . . . , 7) of the

prototype array is measured using an Agilent E8361A VectorNetwork Analyzer. During the measurement of 𝑆-parameter


Table 2: Position and amplitude of the elements.

Number 1 Number 2 Number 3 Number 4𝑤 1 0.75 0.567 0.5𝑋 (mm) 0 30.27 69.94 116.38

Number 5 Number 6 Number 7𝑤 0.75 0.567 0.5𝑋 (mm) −30.27 −69.94 −116.38

(a)

x

y

z

Num

ber 1

Num

ber 2

Num

ber 3

Num

ber 4

Num

ber 5

Num

ber 6

Num

ber 7

(b)

Figure 5: Configuration and distribution of the symmetricweightedthinned array. (a) Prototype of the array. (b) Distribution.

of each element in the array, all the remaining elements areconnected with the matched load. The measured scatteringmatrix is used to compute the active reflection coefficients by(7) [18], where 𝜃 is the scanning angle of the array and 𝑑

𝑚is

the distance from𝑚th element to the reference plane:

Γ

𝑚(𝜃) = 𝑒

𝑗𝑘𝑑𝑚sin(𝜃)7

∑

𝑛=1

𝑠

𝑚𝑛𝑒

−𝑗𝑘𝑑𝑛sin(𝜃)

. (7)

The measured active reflection coefficients at the oper-ating frequency are depicted in Figure 6. As can be seenfromFigure 6, good impedancematching is achieved over thewhole beam scanning range.

Because of the symmetry of the array, only R-mode ismeasured in the experiment to scan from broadside to theright side, and the performance of array scanning in the leftside will be the same.The results of the scanning performancein both simulation and experiment are shown in Figure 7;the simulation result agrees well with the experiment result,which validates the effectiveness of the proposed symmetricweighted thinned array in the performances of wide-anglescanning and SLL reduction. The measurement results showthat the 3 dB beam-width coverage is −9∘∼86∘ when allelements are operating in R-mode. So the beam width of theproposed array can jointly cover the entire upper space.

Table 3: Simulated scanning characteristics of the prototype.

𝜃 Gain (dBi) 3 dB beam-width coverage SLL (dB)0∘ 10.66 −7

∘

∼9

∘ 11.110∘ 12.19 4

∘

∼16

∘ 11.420∘ 12.23 14

∘

∼27

∘ 11.930∘ 11.99 23

∘

∼36

∘ 12.040∘ 11.43 34

∘

∼47

∘ 10.750∘ 10.04 42

∘

∼57

∘ 9.060∘ 8.49 50

∘

∼71

∘ 8.970∘ 9.01 59

∘

∼86

∘ 10.575∘ 9.05 64

∘

∼96

∘ 10.7

−40

−35

−30

−25

−20

−15

−10

−5

Activ

e refl

ectio

n co

effici

ent (

dB)

0 8020 40 60 100

Number 1Number 2Number 3Number 4

Number 5Number 6Number 7

∘)𝜃 (

Figure 6: Measured active reflection coefficients of the seven-element phased array.

The maximum gain and SLL of the proposed array whenscanning from broad side to the end-fire direction are shownin Figure 8. More details can be found in Tables 3 and 4.As can be seen, the thinned array can scan its main beamin the range of 0∘∼70∘ with the SLL almost −10 dB belowthe maximum of the main beam except for the scanningangles 60∘ (−8.2 dB) and 70∘ (−7.3 dB). The gain fluctuationis almost less than 3 dB except for the scanning angles 60∘(4 dB) and 70∘ (3.27 dB). In general, the simulation resultsagree well with the experiment results, which indicates thevalidation of the novel symmetric weighted thinned array inthe performance of wide-angle scanning with low SLL.

5. Conclusion

A novel symmetric weighted thinned array with patternreconfigurable antenna as elements has been proposed. Anda prototype has been fabricated. Both the simulation andmeasurement results show that this novel array can scan itsmain beam from −70∘ to 70∘ in 𝐻-plane with SLL almost


0

30

60

90

120

150

180

210

240

270

330

300

20

10

0

−10

−20

−30

−50

−40

−40

−30

−20

−10

0

10

20

Gai

n (d

Bi)

0∘

10∘

20∘

30∘

40∘

50∘

60∘

70∘

75∘

(a)

0

30

60

90

120

150

180

210

240

270

330

300

0∘

10∘

20∘

30∘

40∘

50∘

60∘

70∘

20

10

0

−10

−20

−30

−50

−40

−40

−30

−20

−10

0

10

20

Gai

n (d

Bi)

(b)

Figure 7: Scanning performance of the symmetric weightedthinned array. (a) Simulated results. (b) Measured results.

−10 dB below the maximum of the main beam. The 3 dBbeam-width coverage is −86∘∼86∘, which means that thisnovel symmetric thinned antenna array can realize the entireupper-space beam coverage and restrain the SLL at the sametime.

Table 4: Measured scanning characteristics of the prototype.

𝜃 Gain (dBi) 3 dB beam-width coverage SLL (dB)0∘ 10.78 −8

∘

∼8

∘ 14.2910∘ 12.02 5

∘

∼17

∘ 10.3820∘ 11.85 14

∘

∼27

∘ 11.4630∘ 11.80 24

∘

∼37

∘ 10.0840∘ 11.52 33

∘

∼46

∘ 10.150∘ 9.95 41

∘

∼56

∘ 10.0360∘ 8.02 49

∘

∼72

∘ 8.2170∘ 8.75 60

∘

∼86

∘ 7.36

−4

−2

0

2

4

6

8

10

12

Gai

n (d

Bi)

0 10 20 8040 50 60 7030−10

Scanning angle (deg)

−4

−2

0

2

4

6

8

10

12

SLL

(dB)

SimulatedMeasured

SimulatedMeasured

Figure 8: Maximum gain and SLL when the array scans its mainbeam from 0∘ to 70∘.

Competing Interests

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

Acknowledgments

This work has been supported by the Advanced ResearchFoundation under Grant nos. 9140A07030514DZ02101 and9140A07010715DZ02001.

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Volume 2014

The Scientific World JournalHindawi Publishing Corporation http://www.hindawi.com Volume 2014

SensorsJournal of


Modelling & Simulation in EngineeringHindawi Publishing Corporation http://www.hindawi.com Volume 2014


Chemical EngineeringInternational Journal of Antennas and

Propagation




Navigation and Observation



DistributedSensor Networks


research article design and analysis of thinned array

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