Planar Leaky-Wave AntennasBased on Microstrip Line and

Substrate Integrated Waveguide (SIW)

Dr. Juhua Liu liujh33@mail.sysu.edu.cn

Forum for Electromagnetic Research Methods and Application Technologies (FERMAT)

Copyright

2

© The use of this work is restricted solely for academic purposes. The authorof this work owns the copyright and no reproduction in any form is permittedwithout written permission by the authors.

Abstract

3

Abstract: Recent advances of our researches on planar leaky-wave antennasare summarized. The planar leaky-wave antennas are fabricated onmicrostrip line and substrate integrated waveguide (SIW), which are lowprofile, low cost and easy to manufacture. They can inherently generate anarrow beam that scans with frequency. Researches were performed withspecial emphasis on the theoretical calculation and the excitation of the firsthigher mode in the microstrip leaky-wave antennas, and the endfireradiation and the circular polarization with the SIW leaky-wave antennas.

Key words: Leaky-wave antennas, microstrip antennas, SIW antennas,wavenumber.

Biography

4

Juhua Liu was born in Heyuan, Guangdong, China, in September,1981. He received the B.S. and Ph.D. degrees from the Sun Yat-senUniversity, China, in 2004 and 2011, respectively.

From 2008 to 2009, he was a Visiting Scholar in the Department of Electrical and Computer Engineering, University of Houston, Houston, TX, USA.

From September 2011 to September 2012, he was a Senior Research Associate with the State Key Laboratory of Millimeter Waves, City University of Hong Kong, Hong Kong, China.

From 2012-2015, he was a Lecture in the Department of Electronics andCommunication Engineering, Sun Yat-sen University, Guangzhou, China. Since 2015 hehas been an Associate Professor in the same department.

His present research interests include leaky-wave antennas, microstrip antennas,substrate integrated waveguide antennas, antenna theory, and computationalelectromagnetics.

Outline

1. Introduction

2. Microstrip leaky-wave antennas

3. SIW leaky-wave antennas

4. Conclusion

5

History● In 1940, (Hansen) waveguide

leaky-wave antenna

● 1981, (Menzel) microstrip leaky-wave antenna

● This century, SIW leaky-wave antenna

y

xz

y

xz

h

via d s

w z

x y

ε

1. Introduction

6

Advantages● Narrow beamwidth, high gain

● Beam scanning

● Simple structure

● Easy feeding

1. Introduction

7

0o

30o

60o

90o

120o

150o

180o

0 dB

-10 dB

-20 dB

-30 dB

1. Introduction

Applications● Collision-avoidance radar (e.g., vehicle), radar

sensor ● Wireless location● Military（target tracking in high-speed flight）● Wireless communications

8

1. Introduction

Key parameter: propagation wavenumber kz = β − jα

● Phase constant β → θ0

● Attenuation constant α → ∆θ

● Region |kz | ≤ k0

0 0cos kθ β=

0

0

2sin

kαθθ

∆ =

kz = β − jα θ09

Microstrip leaky-wave antenna● Simple structure● Usually working in the first higher mode● Difficulty: kz = β − jα

2. Microstrip leaky-waveantenna

10

2.1. Propagation wavenumber

• Target: kz = β − jα• Method:

– Transverse resonant method• Difficulties: Yt = Yt11 + Yt12

– Self-admittance Yt11

– Mutual admittance Yt12

• Methods– Wiener-Hopf method: Yt11

– Spectral domain method: Yt12

Ground plane

Substrate ,r rε µ h

y

W Top plane

x

2W

0 1, xY k tY

11

2.1. Propagation wavenumber

• Numerical results (low permittivity)

5 6 7 8 9 10 11 120

0.2

0.4

0.6

0.8

1

1.2

1.4

Frequency (GHz)

β / k

0

Our accurateOur approximateOlinerMoMHFSS

hW

εr , µr

W = 15 mmh = 0.794 mmεr = 2.32, µr = 1

5 5.5 6 6.5 7 7.5 8 8.5 90

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

Frequency (GHz)

α / k

0

Our accurateOur approximateOlinerMoMHFSS

hW

εr , µr

W = 15 mmh = 0.794 mmεr = 2.32, µr = 1

Phase constant Attenuation constant

12

• Numerical results (high permittivity)

2.1. Propagation wavenumber

Phase constant Attenuation constant

12 12.5 13 13.5 140

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Frequency (GHz)

α / k

0

Our accurateOur approximateOlinerMoMHFSS

hW

εr , µr

W = 3 mmh = 0.635 mmεr = 10.2, µr = 1

12 12.5 13 13.5 140.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

Frequency (GHz)

β / k

0

Our accurateOur approximateOlinerMoMHFSS

hW

εr , µr

W = 3 mmh = 0.635 mmεr = 10.2, µr = 1

Juhua Liu*, D. R. Jackson, Yunliang Long, “Propagation wavenumbers for half- and full-width microstrip lines in the EH1 mode,” IEEE Trans. Microw. Theory Tech., vol. 59, no. 12, pp. 3005–3012, Dec. 2011. 13

2.2. Suppression of EH0 mode

• Operating leaky mode: EH1 mode• Unwanted mode: EH0 mode

– Decreases the excitation efficiency of EH1mode

– Needs to be suppressed

substrate εr h

x

ground planey

z

W

substrate εr h

x

ground planey

z

W

substrate εr , µr

x

ground planey

z

W

14

2.2. Suppression of EH0 mode

• Technique: periodic shorting vias• Operation principles

– Stop band generated by periodic shorting vias– EH0 mode decays in the stop band, but not

the EH1 mode– EH0 is effectively suppressed in the stop band

h

W p d

z

x y

εr

p1 d

p

x

z

15

2.2. Suppression of EH0 mode

• EH0 stop band vs. EH1 leaky region

EH0 mode EH1 mode

5 6 7 8 9 100

0.10.2

0.30.4

0.5

0.60.70.8

0.9

11.1

1.2

β /k

05 6 7 8 9 10

0

0.10.2

0.30.4

0.5

0.60.70.8

0.9

11.1

1.2

Frequency (GHz)

α /k

0

No via (TRM)No via (HFSS)1 via (HFSS)4 vias (HFSS)

5 6 7 8 9 100

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

α /k

0

5 6 7 8 9 100.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

Frequency (GHz)

β / k

0

1 via2 vias3 vias4 vias5 vias

16

2.2. Suppression of EH0 mode

6 6.5 7 7.5 8 8.5 9-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

Frequency (GHz)

|S11

| (d

B)

No via, HFSS1 via, HFSS4 vias, HFSS4 vias, measure

6 6.5 7 7.5 8 8.5 9-4

-2

0

2

4

6

8

10

12

14

16

18

Frequency (GHz)

Gai

n (d

Bi)

No via, HFSS4 vias, HFSS4 vias, measure

• Wider bandwidth• Lower reflection coefficient• More stable and higher gain

17

2.2. Suppression of EH0 mode

0o

30o

60o90o

120o

150o

180o

210o

240o

270o300o

330o

f = 6.3 GHz

0 dB-10 dB

-20 dB-30 dB

0o

30o

60o90o

120o

150o

180o

210o

240o

270o300o

330o

f = 6.9 GHz

0 dB-10 dB

-20 dB-30 dB

0o

30o

60o90o

120o

150o

180o

210o

240o

270o300o

330o

f = 7.5 GHz

0 dB-10 dB

-20 dB-30 dB

0o

30o

60o90o

120o

150o

180o

210o

240o

270o300o

330o

f = 8.1 GHz

0 dB-10 dB

-20 dB-30 dB

Eφ , HFSS Eθ , HFSS Eφ , measure Eθ , measure

• Beam scanning with frequency

Juhua Liu*, Yuanxin Li, Yunliang Long, “Design of periodic shorting-vias for suppressingthe fundamental mode in microstrip leaky-wave antennas,” IEEE Transactions onAntennas and Propagation, vol. 63, no. 10, pp. 4297-4304 October 2015.

18

2.3. Half-Mode SIW leaky-wave antenna

• Half-mode substrate integrated waveguide (HMSIW) leaky-wave antenna– Similar to half-width microstrip leaky-wave antenna– No need to suppress any other mode (e.g., EH0 mode)– Fundamental mode: leaky mode, similar to the EH1

mode in the a microstrip line– Gain: not as high as a full-width microstrip leaky-wave

antenna

19

x

z

y

p

w d

h ,r rε µ

2.3. Half-Mode SIW leaky-wave antenna

• Accurate and efficient calculation of the propagation wavenumber

• Analysis method:– Method of auxiliary sources (MAS)– Equivalent transverse network– Simple, accurate, efficient

20

vδ

uδ r′ r

d

sJ tnY 1nY 1nY

w x′+

2.3. Half-Mode SIW leaky-wave antenna

• Propagation wavenumber kz = β − jα

21

Juhua Liu*, Yuanxin Li, Shaoyong Zheng, Yunliang Long, “Method of auxiliary sourcesfor analyzing half-mode substrate integrated waveguide,” IEEE Antennas Wirelessand Propagation Letters, vol. 13, pp. 1043 – 1046, 2014.

2.4. EH0 leaky mode in via-loaded microstrip line

• EH0 mode in non-loaded microstrip line• Fundamental mode• Slow wave, bound mode• Even mode

• EH0 mode in via-loaded microstrip line• Fast wave• Leaky mode• Even mode

22

• Via-loaded microstrip line • Propagation wavenumber• Method of auxiliary sources (MAS)• Transverse equivalent circuit

23

h

W p d

z

x y

εr

AS

CP CP

AS r r′ d sJ tnY cY 1nY

2W x′− x′

x

2.4. EH0 leaky mode in via-loaded microstrip line

• Propagation wavenumber kz = β − jα• EH0 mode: even mode• EH1 mode: odd mode

24

5 6 7 8 9 10 11 120

0.2

0.4

0.6

0.8

1

1.2

1.4

α /k

0

5 6 7 8 9 10 11 120

0.2

0.4

0.6

0.8

1

1.2

1.4

Frequency (GHz)

β /k

0

p = 3 mm, MASp = 6 mm, MASp = 6 mm, HFSSp = 9 mm, MASp = 12 mm, MASp = ∞, TRM

Even

Odd

2.4. EH0 leaky mode in via-loaded microstrip line

• Microstrip EH0-mode leaky-wave antenna

25

z

x

y

Juhua Liu*, Yuanxin Li, Yunliang Long, “Fundamental even leaky mode in microstrip lineloaded with shorting vias,” IET Microwaves Antennas & Propagation, vol. 11, no. 1, pp.129-135, Jan. 2017.

2.4. EH0 leaky mode in via-loaded microstrip line

3. SIW leaky-wave antennas

Substrate integrated waveguide (SIW)• Advantages

– Low cost, light weight– Easy fabrication– Easy integration

• Can be approximated as rectangular waveguide

h

via d s

w z

x y

ε 26

3.1. SIW leaky-wave antennawith transverse slots

h

via d s

p W w

slot L z

x y

rε

SIW with periodic transverse slots• Leaky-wave antennas: usually can not scan to

endfire• This antenna: scan to endfire• Why? Leaky wave + surface wave

– Leaky wave: scan from near broadside to near endfire– Surface wave: endfire

27

3.1. SIW leaky-wave antennawith transverse slots

Theoretical analysis• SIW → rectangular waveguide

– Magnetic field integral equation– Solve: kz = β − jα

b

a

,r rε µ

x

z

y

p

W L

( ) ( )2

2 212 2

1 2 22 21,3,5,... 1

2

cos cot2sinc 2 016

1

ymn rzn n

n m ymn

m Lk bm aak W k j I

a k b L bm La

ππ π µ∞ ∞

=−∞ =

⋅ − + ⋅ ⋅ = −

∑ ∑

Juhua Liu*, D. R. Jackson, Yunliang Long, “Modal analysis of dielectric-filled rectangularwaveguide with transverse slots,” IEEE Transactions on Antennas and Propagation, vol.59, no. 9, pp. 3194-3203, September 2011. 28

8 9 10 11 120

0.2

0.4

0.6

0.8

1

1.2

1.4

Frequency (GHz)

β /k

0

Leaky, TheoryLeaky, HFSSProper, TheoryProper (Surface), HFSSProper (Waveguide), HFSS

3.1. SIW leaky-wave antennawith transverse slots

• Numerical results:– (a) Leaky mode, (b) surface-wave mode,

(c) proper waveguide mode

8 8.2 8.4 8.6 8.8 9 9.2 9.4 9.6 9.8 1010

-4

10-3

10-2

10-1

100

Frequency (GHz)

α /k

0

Leaky, TheoryLeaky, HFSS

(a)

(b)(c)

Phase constant Attenuation constant29

3.1. SIW leaky-wave antennawith transverse slots

12.9 22.5 10.5 4.55

220 30 30 Units: mm

Microstrip line Vias Microstrip line

40

Slots

9.5 10 10.5 11 11.5 12 12.5-40

-35

-30

-25

-20

-15

-10

-5

0

Frequency (GHz)

|S|

(dB

)

S11, HFSS

S21, HFSS

S11, measured

S21, measured

Antenna configuration S11 & S21

30

3.1. SIW leaky-wave antennawith transverse slots

• Capable to scan to endfire

-10 dB 0 dB

30

210

60

240

90

270

120

300

150

330

180 0

f = 11.7 GHz

MeasuredTheoryHFSS (infinite)HFSS (finite)

-10 dB 0 dB

30

210

60

240

90

270

120

300

150

330

180 0

f = 12 GHz

TheoryHFSS (infinite)HFSS (finite)

-10 dB 0 dB

30

210

60

240

90

270

120

300

150

330

180 0

f = 10.2 GHz

MeasuredTheoryHFSS (infinite)HFSS (finite)

Juhua Liu*, D. R. Jackson, Yunliang Long, “Substrate integrated waveguide (SIW) leaky-wave antenna with transverse slots,” IEEE Transactions on Antennas and Propagation,vol. 60, no. 1, pp. 20-29, January 2012.

31

3.2 Endfire radiation

• Consider: a traveling-wave antenna

• Usually, when 𝛽𝛽 < 𝑘𝑘0 , a line source withuniform 𝐴𝐴 𝑧𝑧 distribution has a higher directivitythan a tapered one.

• However, when when 𝛽𝛽 > 𝑘𝑘0, we found that therule is not correct.

𝑀𝑀 𝑧𝑧 = 𝐴𝐴 𝑧𝑧 𝑒𝑒−𝑗𝑗𝛽𝛽𝑧𝑧

32

3.2 Endfire radiation

• Comparison of different amplitude distributions• When 𝛽𝛽 > 𝑘𝑘0, a tapered distribution provides a higher

peak directivity than the uniform one.

Amplitude distribution Directivity 33

3.2 Endfire radiation

SIW travelling-wave antenna withtapered slots

• Geometry

• Top view

• Bottom view34

3.2 Endfire radiation

• The pattern for the tapered antenna with the highest directivity

Juhua Liu*, David R. Jackson, Yuanxin Li, Chaoqun Zhang, and Yunliang Long,“Investigations of SIW leaky-wave antenna for endfire-radiation with narrow beamand sidelobe suppression,” IEEE Transactions on Antennas and Propagation, vol.62 , no. 9, pp. 4489-4497, September 2014. 35

SIW with H-shaped slots• Circular polarization• High and flat leakage constant

3.3. SIW leaky-wave antenna with H-shaped slots

h

via d s

W

w 1L z

x y

rε

slot 2L p

r

36

3.3. SIW leaky-wave antenna with H-shaped slots

37

• Analysis method: magnetic field integral equation

h

via d s

W

w 1L z

x y

rε

slot 2L p

r

x

y

z

a

b

L1

L2 W

r p

εr

Juhua Liu*, Yunliang Long, “A full-wave numerical approach for analyzingrectangular waveguides with periodic slots,” IEEE Transactions onAntennas and Propagation, vol. 60, no. 8, pp. 3754-3762, August 2012.

37

10 10.5 11 11.5 12 12.50

0.2

0.4

0.6

0.8

1

1.2

Frequency (GHz)

β /k

0

Closed waveguideLeaky, MFIELeaky, HFSSProper, MFIEProper (surface-wave), HFSSProper (waveguide), HFSS

(a)

(b) (c)

10 10.5 11 11.50

0.005

0.01

0.015

0.02

0.025

0.03

Frequency (GHz)

α /k

0

Leaky, MFIELeaky, HFSS

• Modes: (a) leaky-wave mode, (b) surface-wave mode, (c) proper waveguide mode

• Leaky constant: flat, high

Phase constant Leakage constant

3.3. SIW leaky-wave antenna with H-shaped slots

38 38

3.3. SIW leaky-wave antennawith H-shaped slots

Antenna configuration S11 & S21

220 30 30 Units: mm

Microstrip line Vias Microstrip line H-shaped slots

22 10.5 12.9 50

9.5 10 10.5 11 11.5 12 12.5-40

-35

-30

-25

-20

-15

-10

-5

0

Frequency (GHz)

|S|

(dB

)

S11, HFSS

S21, HFSS

S11, Measured

S21, Measured

39

3.3. SIW leaky-wave antennawith H-shaped slots

0 10 20 30 40 50 60 70 80 90-20

-10

0

θ (deg.)

Pat

tern

(dB

)

0 20 40 60 800

3

6

9

θ (deg.)

AR

(dB

)

f = 10.6 GHz

Juhua Liu*, Xihui Tang, Yuanxin Li, Yunliang Long, “Substrate integrated waveguideleaky-wave antenna with H-shaped slots,” IEEE Transactions on Antennas andPropagation, vol. 60, no. 8, pp. 3962-3967, August 2012.

• At 10.6 GHz, circular polarization.

40

4. Conclusion

Microstrip leaky-wave antenna• Calculate kz for the EH1 mode accurately• Suppress the unwanted EH0 mode with the stop band generated by

shorting vias• Analyze the half-mode SIW leaky-wave antenna using the method of

auxiliary sources (MAS)• Investigate the EH0 leaky mode in via-loaded microstrip line

SIW leaky-wave antenna• SIW leaky-wave antenna with transverse slots for endfire scanning

capability• A tapered traveling wave antenna provides higher endfire directivity than a

uniform one• SIW leaky-wave antenna with H-shaped slots for circular polarization

41

References

42

[1]. Juhua Liu*, D. R. Jackson, Yunliang Long, “Propagation wavenumbers for half- and full-width microstrip lines in the EH1 mode,” IEEE Transactions on Microwave Theory and Techniques, vol. 59, no. 12, pp. 3005-3012, December 2011.[2]. Juhua Liu*, Yuanxin Li, Yunliang Long, “Design of periodic shorting-vias for suppressing the fundamental mode in microstrip leaky-wave antennas,” IEEE Transactions on Antennas and Propagation, vol. 63, no. 10, pp. 4297-4304 October 2015.[3]. Juhua Liu*, Yuanxin Li, Shaoyong Zheng, Yunliang Long, “Method of auxiliary sources for analyzing half-mode substrate integrated waveguide,” IEEE Antennas Wireless and Propagation Letters, vol. 13, pp. 1043 – 1046, 2014.[4]. Juhua Liu*, Yuanxin Li, Yunliang Long, “Fundamental even leaky mode in microstrip line loaded with shorting vias,” IET Microwaves Antennas & Propagation, vol. 11, no. 1, pp. 129-135, Jan. 2017.[5]. Juhua Liu*, D. R. Jackson, Yunliang Long, “Modal analysis of dielectric-filled rectangular waveguide with transverse slots,” IEEE Transactions on Antennas and Propagation, vol. 59, no. 9, pp. 3194-3203, September 2011.[6]. Juhua Liu*, D. R. Jackson, Yunliang Long, “Substrate integrated waveguide (SIW) leaky-wave antenna with transverse slots,” IEEE Transactions on Antennas and Propagation, vol. 60, no. 1, pp. 20-29, January 2012.[7]. Juhua Liu*, David R. Jackson, Yuanxin Li, Chaoqun Zhang, and Yunliang Long, “Investigations of SIW leaky-wave antenna for endfire-radiation with narrow beam and sidelobe suppression,” IEEE Transactions on Antennas and Propagation, vol. 62, no. 9, pp. 4489-4497, September 2014.[8]. Juhua Liu*, Yunliang Long, “A full-wave numerical approach for analyzing rectangular waveguides with periodic slots,” IEEE Transactions on Antennas and Propagation, vol. 60, no. 8, pp. 3754-3762, August 2012.[9]. Juhua Liu*, Xihui Tang, Yuanxin Li, Yunliang Long, “Substrate integrated waveguide leaky-wave antenna with H-shaped slots,” IEEE Transactions on Antennas and Propagation, vol. 60, no. 8, pp. 3962-3967, August 2012.

43