![Antipodal Linearly Tapered Slot Antenna System
Using Substrate Parallel Plate Waveguide
Feeding Structure
Fan Fan He#*1
, Ke Wu *2
, Wei Hong# 3
#
Poly-Grames Research Center, École Polytechnique de Montreal
Montreal, Quebec, H3C 3A7, Canada
1
fanfan.he@polymtl.ca
2
ke.wu@polymtl.ca
*
State Key Laboratory of Millimeter Waves, Southeast University
Nanjing, 210096, P.R. China
3
weihong@emfield.org
Abstract— An antipodal linearly tapered slot antenna (LTSA)
structure fed by substrate parallel-plate waveguide is presented
in this paper. First, propagation constant of the substrate
parallel plate waveguide is analyzed by full-wave software CST.
The simulated results show that this waveguide support TEM
mode. Second, an LTSA element fed by our proposed parallel
plate waveguide is designed, fabricated and measured. A very
wide bandwidth is shown on the basis of the simulated and
measured results.
I. INTRODUCTION
The linearly tapered slot antenna (LTSA) has attracted
much interest in many practical applications due to its
attractive features such as narrow beam width, high element
gain, wide bandwidth and small transverse spacing between
elements in arrays [1]-[3]. To design an LTSA, the most
important part is how to develop the feeding structure which
determines the performances of this antenna. So far, many
feeding structures such as fin line, inverted microstrip line,
coplanar waveguide, microstrip to slot line transition,
balanced microstrip line and substrate integrated waveguide
(SIW) have been proposed and designed [4]-[6].
Generally speaking, some of the above-mentioned feeding
structures such as SIW and microstrip line transition have the
limitation for wide bandwidth LTSA. As is well known, the
parallel plate waveguide as a TEM mode transmission line has
many applications in wide-band components [7]-[8].
Therefore, a wide-band LTSA excited by parallel plate
waveguide is proposed in this work. The parallel plate
waveguide is fabricated on substrate while it has a small size
feature with finite ground planes. The propagation
characteristics of the substrate parallel plate waveguide are
relatively easy to analyze. This structure is found to be a good
candiddate for microwave and millimeter-wave applications.
Details of the LTSA with substrate parallel plate waveguide
feeding mechanism including the prototype, simulated and
measured results are presented in this paper.
(a)
(b)
Fig. 1. (a) 3D schematic of the substrate parallel plate waveguide. (b) Electric
fields over the cross section.
II. SUBSTRATE PARALLEL PLATE WAVEGUIDE
An The substrate parallel plate waveguide is inspired and
developed from the concept of substrate integrated waveguide
with four additional air gaps, as shown in Fig. 1(a). Four air
gaps allow isolating central flat plates from side metallic walls.
Metallic walls can suppress any potential radiation of the
signal on the fringes of the two central flat plates. Moreover,
metallic walls can reduce the size of the central plates. Fig.
2(b) shows the electric fields over the cross section related to
the working mode. Through 2D simulations, the propagation
constant of this structure can be obtained, as shown in Fig. 3.
The results show that this substrate parallel plate waveguide
can support TEM mode.
978-2-87487-013-2 © 2009 EuMA 28-29 September 2009, Rome, Italy
Proceedings of the 2nd European Wireless Technology Conference
88](https://image.slidesharecdn.com/f2eb01f1-e626-49f0-9b7c-744c86d0e3c6-150814062849-lva1-app6891/85/Antipodal-linearly-tapered-slot-antenna-system-using-substrate-parallel-plate-waveguide-feeding-structure-1-320.jpg)
![Fig. 2. Qualitative dispersion behavior of substrate parallel plate waveguide
mode.
III. DESIGN OF THE PROPOSED LATA
A. Operating Principle of the Proposed LTSA
Fig. 3 depicts the physical 3D configuration of an LTSA
with substrate parallel plate waveguide feeding structure and
microstrip-to-parallel plate waveguide transition, where the
dielectric constant and substrate thickness are denoted by İr
and t, respectively. The transparent and yellow areas identify
the substrate area and metal covers of the substrate. The
parallel plate waveguide-microstrip transition is used for
connecting 50ȍ measurement system, W50 and Wstrip are the
widths at the both ends of the microstrip taper for matching
the antenna impedance to 50ȍ, and Ltaper is the length of the
taper. The parallel plate waveguide section simply transforms
the unbalanced microstrip to the balanced parallel plate
waveguide feeding system for the ALTSA, where D and S are
the diameter and period of the metallic vias used as equivalent
metal wall like SIW, Wh is the distance between tow rows of
metallic vias, Wgap is the air gap width and Lp is the length
of parallel plate waveguide section and. ALTSA has a flare
angle of 2Į and a length of Lant.
Fig. 3. Physical 3D configuration and parameters of the proposed LTSA.
Fig. 4. Photograph of the proposed LTSA.
In Fig. 3, the substrate parallel plate waveguide is designed
to support TEM mode free from cut-off frequency. The TLSA
is designed by gradually flaring the metallic covers on
opposite sides of the substrate by an angle of 2Į. In order to
match the high impedance of LTSA with the low impedance
parallel plate waveguide, the flaring metal covers are
overlapped each other. The metallic covers gradually stretch
out on the opposite side of the substrate by angle 2Į. Linear
tapers from the overlapped metallic covers to tapered slot
antenna can change the vertical field polarization of the
parallel plate waveguide to the horizontal field polarization of
the LTSA. A good impedance matching can be obtained by
adjusting length Lant and angle 2Į. If a good matching
performance cannot be obtained, we may match the LTSA
with air by adjusting width W1, consequently the entire LTSA
matching can be adjusted to its optimal performance. The gain
of an LTSA is mainly determined by length Lant [2].
In this work, the proposed LTSA is designed only for
demonstration purpose. The parameters of the antenna are
listed in Table. I. The antenna is designed and fabricated on
Rogers Duroid 5880 substrate with İr=2.2 and t=0.254mm.
Fig. 4 shows the photograph of the fabricated LTSA sample.
TABLE II
DIMENSIONS OF THE DESIGNED LTSA
D(mm) 0.3 Ltaper (mm) 20
S (mm) 0.6 Lt (mm) 40
Lp (mm) 10 Wh (mm) 4.8
Wp (mm) 4 Į(degree) 19.8
W50(mm) 0.75 W1(mm) 5
Wgap (mm) 0.2 WA (mm) 5
B. Simulated and Measured Results
The LTSA using substrate parallel plate waveguide as
feeding structure is simulated by the full-wave CAD software
(CST in our case).
Simulated and measured return losses are shown in Fig. 4,
which show a very good agreement. Measured return loss S11
is lower than about -10dB from 12 GHz to 50GHz. Actually
simulated return loss is lower than -10dB from 12.5 GHz to 80
GHz. The highest measured frequency is limited by the
89](https://image.slidesharecdn.com/f2eb01f1-e626-49f0-9b7c-744c86d0e3c6-150814062849-lva1-app6891/85/Antipodal-linearly-tapered-slot-antenna-system-using-substrate-parallel-plate-waveguide-feeding-structure-2-320.jpg)
![measurement system. The results show that the proposed
antenna has a very wide bandwidth.
The antenna gain is measured from 10 to 40 GHz because
some measurement equipment above 40 GHz is not available
during this work. Fig. 5 shows simulated and measured
antenna gain versus frequency. Both simulated and measured
results indicate that the antenna gain slowly increases from 6
to 12 dBi as the working frequency is swept from 10 to 40
GHz. This trend with regards to these curves is coincident
with the Zucker’s standard curves for TSA [2].
Fig. 4. Simulated and measured return losses of the proposed LTSA cell.
Fig. 5. Simulated and measured gain versus frequency
Fig. 6 shows the measured radiation patterns of the LTSA
with substrate integrated parallel plate antenna feeding
structure at 18GHz and 30 GHz respectively. The sidelobe is
below than -10 Db at both frequencies. The E-plane radiation
pattern has a 3dB beamwidth of 50 degree and 28 degree at
18GHz and 30 GHz, respectively. The H-plane radiation
pattern has a 3dB beamwidth of 78 degree and 57 degree at
18GHz and 30 GHz, respectively. At these two frequencies,
antenna gain is 8dBi and 9.5dBi shown in Fig. 5.
(a)
(b)
Fig. 6. Measured normalized radiation patterns for the proposed LTSA.(a)
Radiation patterns at 18GHz. (b) Radiation patterns at 30GHz.
IV.CONCLUSIONS
The antipodal linearly tapered slot antenna using the
substrate parallel plate waveguide feeding structure has been
designed, fabricated and tested. The proposed substrate
parallel plate waveguide supporting TEM mode, can be used
in not only wideband antenna but also other wideband
components such as wideband divider, coupler, etc. For the
purpose of demonstration, wideband LTSA using this feeding
structure are measured. The results indicate that the LTSA
using the proposed feeding structure can yield wideband
characteristics.
ACKNOWLEDGMENT
The authors are grateful to Guohua Zai for his help during
the test and to Liang Han and Jing Zhang for revision.
90](https://image.slidesharecdn.com/f2eb01f1-e626-49f0-9b7c-744c86d0e3c6-150814062849-lva1-app6891/85/Antipodal-linearly-tapered-slot-antenna-system-using-substrate-parallel-plate-waveguide-feeding-structure-3-320.jpg)
![REFERENCES
[1] K. S. Yngvesson et al., “Endfire tapered slot antennas on dielectric
substrates,” IEEE Trans. Antennas Propag., vol. 33, pp. 1392-1400,
1985.
[2] K. S. Yngvesson, T. L. Korzeniowski, Young-Sik Kim, E. L. Kollberg,
and J. F. Johansson, “The tapered slot antenna- A new integrated
element for millimeter-wave applications,” IEEE Trans. Microwave
Theory Tech, vol. 37, No.2, pp. 365-374, 1989.
[3] Y.-S. Kim, and K. S. Yngvesson, “Characteristics of tapered slot
antenna feeds and feed array,” IEEE Trans. Microwave Theory Tech.,
vol. 37, pp. 1559-1564, 1990.
[4] Z. C. Hao, W. Hong, J.X. Chen, X. P. Chen, and K. Wu, “A novel
feeding technique for antipodal linearly tapered Slot Antenna Array,”
2005 IEEE MTT-S Int. Microwave Symp. Dig., pp. 1641 – 1643, 2005.
[5] A. Nesic, “Endfire Slot Line Antennas Excited by a Coplanar
Waveguide,” 1991 IEEE AP-S Int. Symp. Dig., pp. 700-702, 1991.
[6] C. Wu, L. Shen, G. Y. Deng, Y. Shen and J.Litva, "Experimental
Study of a Wide Band LTSA Which is Fed by an Inverted Microstrip
Line (IML)," 1998 IEEE Int. AP-S Symp. Dig., vol. 4, pp. 2328-2331,
1998.
[7] Z. N. Chen, K. Hirasawa and K. Wu, “A broadband monopole in a
parallel plate waveguide,” 1999 IEEE APMC., vol. 3, pp. 732-735,
1999.
[8] K. H. Chuang, S. H. Pyun, S. Y. Chuang and J. H. Choi, “Design of a
wideband TEM horn antenna,” 2003 IEEE Int. AP-S Symp. Dig., vol. 1,
pp. 229-232, 2003.
91](https://image.slidesharecdn.com/f2eb01f1-e626-49f0-9b7c-744c86d0e3c6-150814062849-lva1-app6891/85/Antipodal-linearly-tapered-slot-antenna-system-using-substrate-parallel-plate-waveguide-feeding-structure-4-320.jpg)
Antipodal linearly tapered slot antenna system using substrate parallel plate waveguide feeding structure
- 1. Antipodal Linearly Tapered Slot Antenna System Using Substrate Parallel Plate Waveguide Feeding Structure Fan Fan He#*1 , Ke Wu *2 , Wei Hong# 3 # Poly-Grames Research Center, École Polytechnique de Montreal Montreal, Quebec, H3C 3A7, Canada 1 fanfan.he@polymtl.ca 2 ke.wu@polymtl.ca * State Key Laboratory of Millimeter Waves, Southeast University Nanjing, 210096, P.R. China 3 weihong@emfield.org Abstract— An antipodal linearly tapered slot antenna (LTSA) structure fed by substrate parallel-plate waveguide is presented in this paper. First, propagation constant of the substrate parallel plate waveguide is analyzed by full-wave software CST. The simulated results show that this waveguide support TEM mode. Second, an LTSA element fed by our proposed parallel plate waveguide is designed, fabricated and measured. A very wide bandwidth is shown on the basis of the simulated and measured results. I. INTRODUCTION The linearly tapered slot antenna (LTSA) has attracted much interest in many practical applications due to its attractive features such as narrow beam width, high element gain, wide bandwidth and small transverse spacing between elements in arrays [1]-[3]. To design an LTSA, the most important part is how to develop the feeding structure which determines the performances of this antenna. So far, many feeding structures such as fin line, inverted microstrip line, coplanar waveguide, microstrip to slot line transition, balanced microstrip line and substrate integrated waveguide (SIW) have been proposed and designed [4]-[6]. Generally speaking, some of the above-mentioned feeding structures such as SIW and microstrip line transition have the limitation for wide bandwidth LTSA. As is well known, the parallel plate waveguide as a TEM mode transmission line has many applications in wide-band components [7]-[8]. Therefore, a wide-band LTSA excited by parallel plate waveguide is proposed in this work. The parallel plate waveguide is fabricated on substrate while it has a small size feature with finite ground planes. The propagation characteristics of the substrate parallel plate waveguide are relatively easy to analyze. This structure is found to be a good candiddate for microwave and millimeter-wave applications. Details of the LTSA with substrate parallel plate waveguide feeding mechanism including the prototype, simulated and measured results are presented in this paper. (a) (b) Fig. 1. (a) 3D schematic of the substrate parallel plate waveguide. (b) Electric fields over the cross section. II. SUBSTRATE PARALLEL PLATE WAVEGUIDE An The substrate parallel plate waveguide is inspired and developed from the concept of substrate integrated waveguide with four additional air gaps, as shown in Fig. 1(a). Four air gaps allow isolating central flat plates from side metallic walls. Metallic walls can suppress any potential radiation of the signal on the fringes of the two central flat plates. Moreover, metallic walls can reduce the size of the central plates. Fig. 2(b) shows the electric fields over the cross section related to the working mode. Through 2D simulations, the propagation constant of this structure can be obtained, as shown in Fig. 3. The results show that this substrate parallel plate waveguide can support TEM mode. 978-2-87487-013-2 © 2009 EuMA 28-29 September 2009, Rome, Italy Proceedings of the 2nd European Wireless Technology Conference 88
- 2. Fig. 2. Qualitative dispersion behavior of substrate parallel plate waveguide mode. III. DESIGN OF THE PROPOSED LATA A. Operating Principle of the Proposed LTSA Fig. 3 depicts the physical 3D configuration of an LTSA with substrate parallel plate waveguide feeding structure and microstrip-to-parallel plate waveguide transition, where the dielectric constant and substrate thickness are denoted by İr and t, respectively. The transparent and yellow areas identify the substrate area and metal covers of the substrate. The parallel plate waveguide-microstrip transition is used for connecting 50ȍ measurement system, W50 and Wstrip are the widths at the both ends of the microstrip taper for matching the antenna impedance to 50ȍ, and Ltaper is the length of the taper. The parallel plate waveguide section simply transforms the unbalanced microstrip to the balanced parallel plate waveguide feeding system for the ALTSA, where D and S are the diameter and period of the metallic vias used as equivalent metal wall like SIW, Wh is the distance between tow rows of metallic vias, Wgap is the air gap width and Lp is the length of parallel plate waveguide section and. ALTSA has a flare angle of 2Į and a length of Lant. Fig. 3. Physical 3D configuration and parameters of the proposed LTSA. Fig. 4. Photograph of the proposed LTSA. In Fig. 3, the substrate parallel plate waveguide is designed to support TEM mode free from cut-off frequency. The TLSA is designed by gradually flaring the metallic covers on opposite sides of the substrate by an angle of 2Į. In order to match the high impedance of LTSA with the low impedance parallel plate waveguide, the flaring metal covers are overlapped each other. The metallic covers gradually stretch out on the opposite side of the substrate by angle 2Į. Linear tapers from the overlapped metallic covers to tapered slot antenna can change the vertical field polarization of the parallel plate waveguide to the horizontal field polarization of the LTSA. A good impedance matching can be obtained by adjusting length Lant and angle 2Į. If a good matching performance cannot be obtained, we may match the LTSA with air by adjusting width W1, consequently the entire LTSA matching can be adjusted to its optimal performance. The gain of an LTSA is mainly determined by length Lant [2]. In this work, the proposed LTSA is designed only for demonstration purpose. The parameters of the antenna are listed in Table. I. The antenna is designed and fabricated on Rogers Duroid 5880 substrate with İr=2.2 and t=0.254mm. Fig. 4 shows the photograph of the fabricated LTSA sample. TABLE II DIMENSIONS OF THE DESIGNED LTSA D(mm) 0.3 Ltaper (mm) 20 S (mm) 0.6 Lt (mm) 40 Lp (mm) 10 Wh (mm) 4.8 Wp (mm) 4 Į(degree) 19.8 W50(mm) 0.75 W1(mm) 5 Wgap (mm) 0.2 WA (mm) 5 B. Simulated and Measured Results The LTSA using substrate parallel plate waveguide as feeding structure is simulated by the full-wave CAD software (CST in our case). Simulated and measured return losses are shown in Fig. 4, which show a very good agreement. Measured return loss S11 is lower than about -10dB from 12 GHz to 50GHz. Actually simulated return loss is lower than -10dB from 12.5 GHz to 80 GHz. The highest measured frequency is limited by the 89
- 3. measurement system. The results show that the proposed antenna has a very wide bandwidth. The antenna gain is measured from 10 to 40 GHz because some measurement equipment above 40 GHz is not available during this work. Fig. 5 shows simulated and measured antenna gain versus frequency. Both simulated and measured results indicate that the antenna gain slowly increases from 6 to 12 dBi as the working frequency is swept from 10 to 40 GHz. This trend with regards to these curves is coincident with the Zucker’s standard curves for TSA [2]. Fig. 4. Simulated and measured return losses of the proposed LTSA cell. Fig. 5. Simulated and measured gain versus frequency Fig. 6 shows the measured radiation patterns of the LTSA with substrate integrated parallel plate antenna feeding structure at 18GHz and 30 GHz respectively. The sidelobe is below than -10 Db at both frequencies. The E-plane radiation pattern has a 3dB beamwidth of 50 degree and 28 degree at 18GHz and 30 GHz, respectively. The H-plane radiation pattern has a 3dB beamwidth of 78 degree and 57 degree at 18GHz and 30 GHz, respectively. At these two frequencies, antenna gain is 8dBi and 9.5dBi shown in Fig. 5. (a) (b) Fig. 6. Measured normalized radiation patterns for the proposed LTSA.(a) Radiation patterns at 18GHz. (b) Radiation patterns at 30GHz. IV.CONCLUSIONS The antipodal linearly tapered slot antenna using the substrate parallel plate waveguide feeding structure has been designed, fabricated and tested. The proposed substrate parallel plate waveguide supporting TEM mode, can be used in not only wideband antenna but also other wideband components such as wideband divider, coupler, etc. For the purpose of demonstration, wideband LTSA using this feeding structure are measured. The results indicate that the LTSA using the proposed feeding structure can yield wideband characteristics. ACKNOWLEDGMENT The authors are grateful to Guohua Zai for his help during the test and to Liang Han and Jing Zhang for revision. 90
- 4. REFERENCES [1] K. S. Yngvesson et al., “Endfire tapered slot antennas on dielectric substrates,” IEEE Trans. Antennas Propag., vol. 33, pp. 1392-1400, 1985. [2] K. S. Yngvesson, T. L. Korzeniowski, Young-Sik Kim, E. L. Kollberg, and J. F. Johansson, “The tapered slot antenna- A new integrated element for millimeter-wave applications,” IEEE Trans. Microwave Theory Tech, vol. 37, No.2, pp. 365-374, 1989. [3] Y.-S. Kim, and K. S. Yngvesson, “Characteristics of tapered slot antenna feeds and feed array,” IEEE Trans. Microwave Theory Tech., vol. 37, pp. 1559-1564, 1990. [4] Z. C. Hao, W. Hong, J.X. Chen, X. P. Chen, and K. Wu, “A novel feeding technique for antipodal linearly tapered Slot Antenna Array,” 2005 IEEE MTT-S Int. Microwave Symp. Dig., pp. 1641 – 1643, 2005. [5] A. Nesic, “Endfire Slot Line Antennas Excited by a Coplanar Waveguide,” 1991 IEEE AP-S Int. Symp. Dig., pp. 700-702, 1991. [6] C. Wu, L. Shen, G. Y. Deng, Y. Shen and J.Litva, "Experimental Study of a Wide Band LTSA Which is Fed by an Inverted Microstrip Line (IML)," 1998 IEEE Int. AP-S Symp. Dig., vol. 4, pp. 2328-2331, 1998. [7] Z. N. Chen, K. Hirasawa and K. Wu, “A broadband monopole in a parallel plate waveguide,” 1999 IEEE APMC., vol. 3, pp. 732-735, 1999. [8] K. H. Chuang, S. H. Pyun, S. Y. Chuang and J. H. Choi, “Design of a wideband TEM horn antenna,” 2003 IEEE Int. AP-S Symp. Dig., vol. 1, pp. 229-232, 2003. 91