XIV.
MICROWAVE COMPONENTS
Prof. L. J. Chu
Prof. J. B. Wiesner
Prof. H. J. Zimmermann
A.
L. D. Smullin
A. D. Berk
J. Fontana
M. Schetzen
J. Sciegienny
FERRITES AT MICROWAVE FREQUENCIES
This work will be presented in Technical Report No.
ERRATUM.
284.
In the Quarterly Progress Report of January 15,
1954, page 53,
second
line from end, C = 1. 4 should read C = 1. 04.
A. D. Berk
B.
T-RIDGE WAVEGUIDES
Some further results are given concerning the T-ridge waveguides that were
described in a previous report (1).
Figure XIV-1 is a plot of the cutoff wavelengths of
the dominant mode (KX 1) and of the next mode (Xc 3 ) that can be excited by a symmetric
electric probe, as a function of the normalized ridge gap g; the symbols used are defined
in Fig. XIV-2. Both curves were obtained experimentally with a standard S-band rectangular waveguide in which L/H = 2. 12, with a ridge having 2/3 of the guide width. The
single-mode transmission bandwidth ratio
'1
is plotted in Fig. XIV-3. For large
values of g, the curve falls somewhat below the value 3 corresponding to the TE
1 0 and
TE 3 0 modes of a rectangular guide, but for small gaps it increases rapidly to very large
values.
2/3 L
L
Fig. XIV-2
Cross section of T-ridge wave-auide.
I_
o
0
01
0.2
0.3
0.4
0.5
I
0.6
0.7
I
0.8
I
0.9
1.0
g=olH
Fig. XIV-1
Cutoff wavelengths of lowest symmetric
modes in a T-ridge waveguide.
-68-
~--
-- _~--_~____. _
-~=-~;+
12
II
10
6
5
4
I
0.1
0
I
0.3
I
0.2
I
0.5
I
04
I
I
0.6
0.7
I
I
0.8
0.9
I
g = o/H
Fig. XIV-3
Ratio of the cutoff wavelengths of the first and second symmetric modes.
0.8
06
O4
P,
X -It
I
0.2
I
I
0
0.1
0.2
G3
0.4
G5
G6
0.7
0.
0.9
LO
ga/H
Fig. XIV-5
Fig. XIV-4
Power handling capacity.
Coaxial cable to the T-ridge guide
broadband junction.
o
(-r
00
z
5
Ww
-1400
i
i
i
2200
i
3000
300
FREQUENCYIN MCPS
Fig. XIV-6
Photograph of junction shown in Fig. XIV- 5.
-69-
Fig. XIV-7
Test curve of the broadband junction.
(XIV.
MICROWAVE COMPONENTS)
The computed maximum power transmissible for a maximum allowable electric field
is plotted on Fig. XIV-4; P(O) corresponds to the rectangular guide without a ridge.
can be observed that the wider the single-mode band is,
It
the smaller the transmissible
power becomes.
Figures XIV-5 and XIV-6 show a junction designed to feed a T-ridge waveguide having
a characteristic impedance equal to that of a 50-ohm coaxial cable.
The low impedance
of the guide eliminates the necessity of impedance-matching devices and allows operation
over a large frequency band with low standing-wave ratios; the back section to the left
of the junction operates as an open circuit over the whole range.
experimental plot of the voltage standing-wave
Figure XIV-7 is
an
ratio in the ridge guide when a lossy
cable is connected to the coaxial output; the high-frequency limit of the range of operation is determined by the neighborhood of the next cutoff.
J.
Fontana
References
1.
Quarterly Progress Report, Research Laboratory of Electronics,
p. 51.
2.
J. Fontana, T-ridge waveguides,
neering, M.I.T., May 24, 1954.
Jan.
15,
1954,
M. Sc. Thesis, Department of Electrical Engi-
-70-