The design and performance is presented of the following Coplanar Waveguides (CPW) microwave distribution networks for linear as well as circularly polarized microstrip patches and dipole arrays: (1) CPW/Microstrip Line feed; (2) CPW/Balanced Stripline feed; (3) CPW/Slotline feed; (4) Grounded CPW/Balanced coplanar stripline feed; and (5) CPW/Slot coupled feed. Typical measured radiation patterns are presented, and their relative advantages and disadvantages are compared

Lee, Richard Q.

Simons, Rainee N.

English

NASA Technical Reports Server

G 9
NASA Technical Memorandum 104467
AIAA-91-3422
Coplanar Waveguide Feeds for
Phased Array Antennas
Rainee N. Simons
Sverdrup Technology, Inc.
Lewis Research Center Group
Brook Park, Ohio
and
Richard Q. Lee
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio
Prepared for the
Conference on Advanced Space Exploration Initiative Technologies
cosponsored by AIAA, NASA, and OAI
Cleveland, Ohio, September 4 -6, 1991
NASA
https://ntrs.nasa.gov/search.jsp?R=19910018163 2020-03-19T16:37:04+00:00Z
COPLANAR WAVEGUIDE FEEDS FOR PHASED ARRAY ANTENNAS
Rainee N. Simons
Sverdrup Technology, Inc.
Lewis Research Center Group
Brook Park, Ohio 44142
and
Richard Q. Lee
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135
Ahctrart
This paper presents the design and performance of the
following CPW microwave distribution networks for linear
as well as circularly polarized microstrip patches and printed
dipole arrays: (1) CPW/Microstrip Line feed, (2) CPW/
Balanced Stripline feed, (3) CPW/Slotline feed, (4) GCPW/
Balanced coplanar stripline feed, and (5) CPW/Slot coupled
feed. Typical measured radiation patterns are presented,
and the ir relative advantages and disadvantages are compared.
Introduction
Coplanar waveguide (CPW) is a transmission line which
consists of a center strip and a semi-infinite ground plane
on either side of it l as shown in Fig. 1. This type of
waveguide offers several advantages over conventional
microstrip line, namely, it facilitates easy shunt as well as
series mounting of active and passive devices; it eliminates
the need for wraparound and via holes, and it has a low
radiation loss. Another important advantage of CPW which
has recently emerged is that CPW circuits render them-
selves to fast and inexpensive on-wafer characterization at
frequencies as high as 50 GHz. 2 Lastly, since the RF
magnetic fields in the CPW are elliptically polarized,3
nonreciprocal components such as ferrite circulators and
isolators4 can be efficiently integrated with the feed net-
work. These as well as other advantages make CPW useful
for a MMIC based microwave distribution network. Grounded
CPW (GCPW) is a variant of CPW which incorporates an
additional ground plane on the back side of the substrates
as shown in Fig. 1. This additional ground plane can serve
as a heat sink and provide mechanical strength. In addition,
the ground plane serves as a shield between stacked antenna
boards to improve isolation.
Several CPW fed antennas have been reported in the
literature. A GCPW fed coplanar stripline antenna con-
structed by widening the center strip of the GCPW to form
a rectangular patch (Fig. 2(a)) has been reported. 6 This
antenna produces a linearly polarized far field radiation
pattern in a direction normal to the plane of the substrate.
CPW fed slot antennas which are the complement to printed
dipole antennas (Fig. 2(b)) have also been reported. This
antenna also radiates in a direction normal to the plane of
the substrate.
This paper presents the design and performance of the
following CPW microwave distribution networks for linear
as well as circularly polarized microstrip patches and printed
dipole arrays: (1) CPW/Microstrip Line feed, (2) CPW/
Balanced Stripline feed, (3) CPW/Slotline feed, (4) GCPW/
Balanced coplanar stripline feed, and (5) CPW/Slot coupled
feed. Typical measured radiation patterns are presented,
and their relative advantages and disadvantages are compared.
CPW Microwave Distribution Network Design
Coplanar Waveguide/Microstrip Line Feed
A CPW to microstrip line feed with post coupler$ is
shown in Fig. 3. The CPW and the microstrip line share a
common ground plane that has an aperture. The coupler is
formed by a metal post which passes through the aperture
connecting the strip conductors of the CPW and the microstrip
line. A pair of wire bonds located adjacent to the post tie
the CPW ground planes and the microstrip ground planes
to a common potential. The diameters of the aperture and
the metal post were experimentally optimized to obtain the
best insertion loss characteristics. The advantage of this
type of feed is that the thickness and relative permittivity
of the dielectric substrates for the feed network and the
antenna can be independently chosen. This allows the
individual components to be optimized for the best
performance.
Coplanar Waveguide/Balanced Stripline Feed
A CPW to balanced stripline feed also makes use of a post
coupler9
 as illustrated in Fig. 4. The mechanical features
of the coupler is similar to that described above. This
coupler in addition uses a tapered stub to improve the
bandwidth of the device. The advantage of this feed is
similar to that of the previous example. -
Coplanar Waveguide/Slotine Feed 	 trates the integration of a rectangular patch antenna with
the feed.
A CPW to slotline feed lo which uses a nonplanar CPW
T-junction is illustrated in Fig. 5. The circuit is formed
when a CPW on a separate substrate is placed perpendicular
on the CPW of the CPW/Slotline feed network. The advan-
tage of this type of feed is that it eliminates the need for
direct connection between the feed line and the feed net-
work of the array module.
Grounded Coplanar Wave uide Balanced Coplanar
Stripline Feed
Figure 6 shows a GCPW to balanced coplanar stripline
feed.'' Since the GCPW is an unbalanced structure, the
transition to a balanced coplanar stripline requires a balun.12
At the unbalanced end, currents of equal magnitudes but
opposite direction flow in the center strip conductor 2 and
in the ground planes I and 3 of the GCPW. At the balanced
end, currents of equal magnitude but opposite in direction
flow in the strip conductors 2 and 3 of the coplanar stripline.
The short circuit placed between conductors 1 and 2 at the
balanced end results in an open circuit between the conduc-
tors a quarter wavelength away at the unbalanced end
forcing all currents to flow between conductors 2 and 3.
In addition, the balun also provides impedance transfor-
mation. This transformation ratio is determined by the
characteristic impedance of the coplanar stripline formed
by conductors 2 and 3. This is because all of the microwave
energy propagates through this section of the transmission
line. The advantage of this type of feed is that it allows
construction of end fire arrays which are necessary for
building large two-dimensional phased arrays. The disad-
vantage is that it requires a bond wire to tie conductors 1
and 3 at equal potential which might impact reliability.
Coplanar Waveguide/Slot Coupled Feed
This circuit is formed by etching a narrow resonant slot
in the bottom ground plane of a GCPW. The slot is oriented
symmetrically and transverse to the center strip conductor
of the GCPW. The advantage of this type of feed is that the
microstrip patch antennas can be electromagnetically coupled
to the feed through the aperture thus making integration
easy.
Coplanar Waveguide Feed System Performance and
Antenna Integration
The measured return loss (S 11 ) and insertion loss (S21)
of the CPW/Microstrip line post coupler is shown in Fig. 7.
The return loss and insertion loss are better than 10 and
1 dB, respectively, over a wide band of frequencies extend-
ing from 0.045 to 6.5 GHz. Figure 8 schematically illus-
The measured return loss (S 11 ) and insertion loss (S21)
of the CPW/Balanced stripline post coupler is shown in
Fig. 9. The return loss and insertion loss are better than 17
and 0.25 dB at the design frequency of 2.2875 GHz. Fig-
ures 10(a) and (b) present the proof-of-concept model of a
seven patch hexagonal circularly polarized (CP) subarray
with the above feed system.
The above are typical characteristics of the feeds dis-
cussed in the previous section and the characteristics of the
other feeds will be presented at the conference.
Far Field Radiation Patterns of the Antennas
The measured far field radiation pattern of the microstrip
patch antennas shown in Fig. 8 are presented in Fig. 11.
The radiation is linearly polarized and is parallel to the
plane of the antenna.
The measured far field radiation patterns of the CP
subarray shown in Fig. 10 is presented in Fig. 12. These
patterns were measured at 2.325 GHZ. The on-axis axial
ratio for the LHCP is 1.5 and 3 dB beam widths are 36° in
both planes of the subarray. The gain of the subarray as
determined from the beam widths is 13 dB. The measured
return loss at the coaxial input port of the subarray is better
than 10 dB at 2.325 GHz.
The above are typical measured radiation patterns of the
antennas investigated and more results will be presented at
the conference.
Conclusions and Discussions
The paper presents the design and performance of several
CPW microwave distribution networks which have poten-
tial applications in phased arrays. Typical measured far
field radiation patterns of several antennas with the above
feeds have been presented and discussed.
References
1. Wen, C.P., "Coplanar Waveguide:A Surface Strip Transmission Line
Suitable for Nonreciprocal Gyromagnetic Device Applications,"
IEEE Transactions on Microwave Theory and Techniques, Vol.
MTT-17, No. 12, Dec. 1969, pp. 1087-1090.
2. Jones, K.E., Strid, E.W., and Gleason, K.R., "mm-Wave Wafer
Probes Span 0 to 50 GHz," Microwave Journal, Vol. 30, No. 4,
Apr. 1987, pp. 177-183.
3. Simons, R.N. and Arora, R.K., "Coupled Slot Line Field Compo-
nents," IEEE Transactions on Microwave Theory and Techniques,
Vol. MTT-30, No. 7, July 1982, pp. 1094-1099.
DIELECTRIC
SUBSTRATE
( E r)
ADDITIONAL
GROUND
PLANE
__H
i
} ^^ H
i
GROUND PLANES ^
STRIP
CONDUCTOR
4. Koshiji, K. and Shu, E., "Circulators Using Coplanar Waveguide,"
Electronics Letters, Vol. 22, No. 19, Sept. 11, 1986,
pp. 1000- 1002.
5. Shih, Y.C. and Itoh, T., "Analysis of Conductor-Backed Coplanar
Waveguide," Electronics Letters, Vol. 18, No. 12, June 10, 1982,
pp. 5 38 - 540.
6. Greiser, J.W., "Coplanar Stripline Antenna," Microwave Journal,
Vol. 19, No. 10, Oct. 1976, pp. 47-49.
7. Nesic, A., "Printed Slotted Array Excited by a Coplanar Waveguide,"
12th European Microwave Conference Digest, Microwave Exhibi-
tions and Publishers, Kent, England, Sept. 1982, pp. 478-482.
8. Simons, R.N. and Lee, R.Q., "Coplanar Waveguide/Microstrip Probe
Coupler and Applications to Antennas," Electronics Letters, Vol. 26,
No. 24, Nov. 22, 1990, pp. 1998 2000.
9. Simons, R.N., Lee, R.Q., and Lindamood, G.R., "A New Coplanar
Waveguide/Stripline Feed Network for a Seven Patch Hexagonal
CP Subarray," Electronics Letters, Vol. 27, No. 6, March 1991,
pp. 533-535.
10. Lee, R.Q. and Simons, R.N., "Electromagnetically Coupled Feed
Network for an Array Module of Four Microstrip Elements," 1988
IEEE International Symposium on Antennas and Propagation Sym-
posium Digest, Vol. 111, IEEE, 1988, pp. 1018-1021.
11. Simons, R.N., Ponchak, G.E., Lee, R.Q., and Fernandez, N.S., "Coplanar
Waveguide Fed Phased Array Antenna," 1990 IEEE International
Symposium onA ntennas and Propagation Symposium Digest, Vol. IV,
IEEE, 1990, pp. 1778-1781.
12. DeBrecht, R.E., "Coplanar Balun Circuits for GaAs FET High-Power
Push-Pull Amplifiers," 1973 IEEE G-MTT International Micro-
wave Symposium Digest, IEEE, 1973, pp. 309-311.
Figure 1.—Schematic illustrating the fields along the coplanar
waveguide and the optional lower ground plane.
(a)CPW patch antenna.
(b) CPW slot antenna.
Figure 2.—Coplanar wave guide antenna.
r Coplanar waveguide input/output (port #1)
i
Coplanar	 IW	 Microstrip ground planewaveguide	 S ^^	 (common ground plane)
S = 0.045 in. ground plane, W^^
W = 0.01 in.
W m = 0.03 in.	 Ti^ 	 Bond wires
D t = 0.04 in.
D2 = 0.1 in.
T 1 = 0.125 In.	 EOEr 1 -
Er1 =2.21n.
T 2 =0.01 in.	 r`
E r 2 = 2.2 in.	 T2	 ..	 y
	
Dielectric
	
,'	 r	 ^'^	 \ `
	
substrates
	
—Microstrip line
E OE r 2 J	 y	 output/input
IW	
(port #2)
	Aperture of	 m
diameter D 2 in the	 '	 \\
microstrip ground plane — Metal post of r 	 .\
diameter, D1
Figure 3.—Schematic of a CPWrmicrostrip line post coupler feed.
R,
2S
RZJCoplanar waveguide	 ^Linput/output (port it1) N,	 ^-- Bond wires
s
Coplanar waveguide 	 (comm on
ground plane
^	 ^9	 w	 i (common ground plane)ground plane
^ Shorting pin
i
Tt^
Focr1 %\ '
T2
^ 
	
ground
Plane
FoFr2 —L	 F=^	 \	 Stripline
7 -
Di	
output/input
e lectric	 WsI	 ^	 I	 ^	 (Port #2)
substrate	 M^- etal post of
l	 diameter, D t
Aperture of diameter
D 2 in the stripline ground plane J
s	 = 0.055 inch	 D2 = 0.1 inch	 F,2 = 2.2
	
w = 0.01 inch	 T 1 = 0.125 inch	 R t = 0.055 inch
Ws = 0.1 inch	 Fri = 2.2	 R2 =0.065 inch
	
DI = 0.05 inch	 T2 = 0.062 inch	 L = 0.235 inch	 ctu0-51487
Figure 4.—Schematic of a CPW/balanced stripline post coupler.
4
a = 2.07 in.
b = 1.745 in.
Dielectric:
substrate
Printed
dipole
X
4 balun
CPW port
1
a=2.07 in.	 E
b=1.745 in.	 OEr3^,
T 3	 0.01 in.
Era=2.2
Y
,T3,
I
S 11	 Log mag	 S21
Ref. 0.0 dB	 Ref. 0.0 dB
5.0 dB/	 1.0 dB/
2
1
Slot	 b 	 I	 I	 —_^
line
J_ — — J	 7— Coplanar
W8Yegulde
Figure 5—Schematic of a CPW/slot line feed. Start 0.04500000 GHz
Stop 6.50000000 GHz
Figure 7.—Measured return loss (S11 ) and insertion
loss (S 21 ) of a CPW/microstrip line post coupler
feed.
(a) Direct feed.
3
Al^
I
I
F—	 Coplanar
I
^^	 •^
Coplanar
waveguide
/(unbalanced)
twin strip
transmission line
(balanced) J
Figure 6.—Schematic of a CPW/balanced coplanar stripline
feed.
Proximity Coupled
` CPW port
(b) Proximity coupled feed.
Figure 8.—Schematic illustrating the integration of a patch
antenna with CPW/microstrip feed.
5
".4	 Abb— 4ftp^
(a) Antenna layer.
a
.00
142
0
-10
Log
-20
magnitude,
Sit,	
-30
db
-40
-50
0
Log
magnitude, - . 5
db	 -1.0 f —db
-1.5
	
045	 3.0Frequency, GHz 
Figure 9.—Measured return loss (S11) and insertion loss (S21 )
of a CPW/balanced stripline coupler feed.
C-90-14443
(b) CPW power divider layer.
Figure 10.—Proof-0f-concept model of a seven patch hexagonal
CP subarray.
6
	E-plane
	 E-plane
H-plane	 H-plane
	
Feed	 Feed
Frequency = 2.2 GHz	 Frequency = 2.2 GHz
p ^ E-plane E-plane
–10 -
r(a) I	 I	 I	 I	 1 (b)a –20
ti
E	 0Ea
H-plane
-^-
H-plane
–10
^
-20  1	 1	 1	 1
–90 60	 –30	 0	 30	 60	 90 –90	 60	 –30	 0	 30	 60	 90
Angle, deg
(a) and (c) Antena excited directly (b) and (d) Antena excited by
by CPW/microstrip feed. proximity coupled CPW/micro-
strip feed.
Figure 11.—Measured far field radiation pattern of the microstrip patch
antenna.
	
Amplitude,	 11^vY	 I'll
 –20--IY.^ J ffdB	 '	 't^
V
M ^I	 r l
	–30	
I	
^ ^ I I Yl,
	
II	 I	 I	 –40	 I	 V^
(a)(b = 0` plane.
,' h –to--IIVn'i'
	Ampllitude,	
–20it 
' '	 I	 Nei, I	 , ^, V^
–30
	
I	 I	 1	 –40	 1	 I	 I	 1
	
–90	 –60	 –30	 0	 30	 60	 90
Angle, deg
(b)d) = 90° plane.
Figure 12.—Measure far field radiation pattern of the subarray.
r
7
NASA
National Aeronautics and	 Report Documentation Page
Space Administration
1. Report No.	 NASA TM-104467 2. Government Accession No. 3.	 Recipient's Catalog No.
AIAA-91-3422
4. Title and Subtitle 5. Report Date
Coplanar Waveguide Feeds for Phased Array Antennas
6. Performing Organization Code
7. Author(s) 8.	 Performing Organization Report No.
Rainee N. Simons and Richard Q. Lee E-6315
10. Work Unit No.
506-44-2C
9. Performing Organization Name and Address
11. Contract or Grant No.National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135 - 3191
13. Type of Report and Period Covered
Technical Memorandum12. Sponsoring Agency Name and Address
National Aeronautics and Space Administration
14. Sponsoring Agency CodeWashington, D.C. 20546-000 1
15. Supplementary Notes
Prepared for the Conference on Advanced Space Exploration Initiative Technologies cosponsored by AIAA, NASA, and
OAI, Cleveland, Ohio, September 4-6, 1991. Rainee N. Simons, Sverdrup Technology, Inc., Lewis Research Center
Group, 2001 Aerospace Parkway, Brook Park, Ohio 44142. Richard Q. Lee, NASA Lewis Research Center. Responsible
person, Rainee N. Simons, (216) 433-3462.
16. Abstract
This paper presents the design and performance of the following CPW microwave distribution networks for linear as well
as circularly polarized microstrip patches and printed dipole arrays: (1) CPW/Microstrip Line feed, (2) CPW/Balanced
Stripline feed, (3) CPW/Slotline feed, (4) GCPW/Balanced coplanar stripline feed, and (5) CPW/Slot coupled feed.
Typical measured radiation patterns are presented, and their relative advantages and disadvantages are compared.
17. Key Words (Suggested by Author(s)) 18.	 Distribution Statement
Phased arrays Unclassified - Unlimited
Microstrip antennas Subject Category 33
19. Security Classif.
	 (of the report) 20. Security Classif. (of this page) 21. No. of pages 22. Price'
Unclassified Unclassified 4 A03
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Coplanar waveguide feeds for phased array antennas

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