X.
MICROWAVE COMPONENTS
Prof. L. J. Chu
Prof. J. B. Wiesner
Prof. H. J. Zimmermann
A.
L. D. Smullin
J. R. Fontana
P. H. Rose
M. Schetzen
J. Sciegienny
STRIP ABOVE GROUND PLANE TRANSMISSION SYSTEM
In order to study and evaluate some of the new ideas continuously being introduced
in the microwave field, the Research Laboratory of Electronics has recently organized
a Microwave Laboratory.
One of the first problems studied was
the microwave printed circuit (I, 2, 3).
The transmission system shown in
Fig. X-I was investigated.
This system
consists of a conducting strip separated
from a ground plane by a dielectric sheet.
STRIP--ttti:Bi~~D~~:~;:IC
L GROUND PLANE
The upper dielectric sheet was used
mainly for holding the strip. Polystyrene,
teflon, and synthane were used as dielectrics.
Fig. X-I
A pure TEM mode of propaga-
tion was assumed in all calculations.
The strip above ground plane
transmission system.
Measurements were made in the X and
S bands with the equipment shown in
Fig. X- 2.
In this apparatus the probe
can be moved in both the longitudinal and transverse directions.
The substitution method (4), the line voltage-distribution method (2), and the twoprobe power reversal method (5) were used to measure the insertion loss.
The
measured attenuation of the system was found to be of the same orde"!' of magnitude as
that of a coaxial cable.
The measured wavelength along the strip was longer than that
calculated under the assumption of TEM propagation. Some results are shown in Table 1.
Some typical measured patterns of the fields both in the transverse and the longitudinal
directions are shown in Figs. X-3, X-4, and X-5.
These results indicate that the
assumption of propagation of the TEM mode alone is, at best, only an approximation.
The following rf components were developed (see Fig. X-6): (a) transition to
the coaxial cable, (b) transition to the x-band waveguide, (c) x-band ring structure,
(d) x-band power divider, (e) x-band crystal holder, (f) silicon crystal, and (g) x-band
balanced mixer.
A new application of the quarter-wavelength technique for the printed circuits is
illustrated in Fig. X-7.
The movable short circuit in this tuning device can be placed
at such a distance from the strip, that the left part of the tuner presents an effective
open circuit.
The single strip tuners, the variable quarter-wavelength transformers,
-53-
Fig. X-2
The standing-wave detector.
1.0
0.9
MAGNETIC PR08E
0.8
c
0.7
STRIP
STRIP WIOTH 3/8 IN .• THICKNESS 0.002 IN.
POLYSTYRENE THICKNESS 1/8 IN.
FREQUENCY 3000 MC/SEC
STRIP WAVELENGTH 7.44 CM
.J
"'
ii:
<.:>
;::
0.6
"'e>Z
""::E
...0
GROUND
PLANE
0.5
:I:
l-
e>
z
"'
0.4
II:
I-
lJ)
"'>
;::
0.3
""
-'
"'II:
0.2
0.1
2.0
3.0
4.0
OISTANCE FROM THE STRIP AXIS (CM)
Fig. X-3
Relative strength of magnetic field in the transverse direction
for strip above ground plane transmission system.
- 54-
5.0
a
1.0
..J
W
ii:
STRIP WIDTH 3/8 IN., THICKNESS 0.002 IN.
POLYSTYRENE THICKNESS 1/8 IN.
FREQUENCY 3000 MC/SEC
POWER FED TO STRIP# I
STRIP# I
0
i=
w
z
STRIP#2~
0.8
~
MAGNETIC
PROBE
<t
::E
u.
0
0.6
POLYSTYRENE
I
I-
~
z
w
a:
IVl
GROUND PLANE
04
W
>
~
0.2
..J
W
a:
4
GROUND
PLANE
6
10
/2
DISTANCE FROM STRIP AXIS (CM)
Fig. X-4
Magnetic field distribution for two parallel strips above
ground plane transmission systems.
MAGNETIC
PROBE
STRIP WIDTH 3/8 IN .• THICKNESS 0.002 IN.
POLYSTYRENE THICKNESS 1/8 IN.
FREQUENCY 10,000 MC/SEC
POLYSTYRENE
a
LiJ
G:
0
i=
w
z
~
<t
:;;
u.
0
I
I-
~
z
w
a:
0.4
IVl
w
>
0.2
i=
<t
..J
W
a:
a
DISTANCE ALONG THE STRIP (CM)
Fig. X-5
Distribution of magnetic field in the longitudinal direction for the
strip above ground plane transmission system.
-55-
(b)
(0)
(d)
(el
(g)
Fig. X-6
Radiofrequency components developed in the laboratory.
-56-
(c)
(f)
(x.
MOVABLE)
SHORT
~
MICROWAVE COMPONENTS)
DIELECTRIC
A
GROUND
PLANE
(2n-I)"4
SHORT
SECTION A-A
OPEN
Fig. X-7
Double strip tuner (llHll -tuner).
Table 1
The Strip Wavelength For Strip Above Ground Plane Transmission System
Thickness of
dielectric material
(inches)
Measured
strip
wavelength
(em)
Calculated
strip
wavelength
for TEM
propagation
Polystyrene
0.13
7. 15
6.26
O. 38
Polystyrene
O. 13
7.44
6.26
8762
0.38
Polystyrene
O. 13
2. 52
2. 15
9200
0.21
Teflon
0.06
2.85
2.05
O. 1
2.42
2.13
Strip
width
(inches)
Dielectric
material
3000
0.56
3000
Frequency
(Me/sec)
8815
0.38
Polystyrene
Remarks
No upper
dielectric sheet
and the variable directional couplers using the above idea were investigated.
Different types of loads, attenuators, tuning devices. and antennas were investigated.
The performance of these devices indicate their practicability.
J. Sciegienny
References
1.
D. D. Grieg. H. F. Engelmann: Microstrip - A New Transmission Technique for
the Kilomegacycle Range. Proc. LR.E. 40. 1644. 1952
2.
F. Assadourian. E. Rimai: Simplified Theory of Microstrip Transmission Systems.
Proc. 1. R. E. 40. 1651, 1952
3.
J. A. Kostriza: lVIicrostrip Components. Proc. LR.E. 40. 1658. 1952
4.
C. G. Montgomery: Technique of Microwave Measurements, Radiation Laboratory
Series. Vol. 11, McGraw-Hill. New York, 1947
5.
A Laboratory Manual for Microwave Electronics. Dept. of Electrical Engineering.
M.LT. 1950
-57-