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Патент USA US2412055

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Dec. '3, 1946.
' 2,412,055
‘Filed Jan. 25, 1945
vHa‘rrg; R. Meahl,
Patented Dec. 3, 1946
Harry R. Meahl, Schenectady, N. Y., assignor to
General Electric Company, a corporation of
New York
Application January 25, 1943, Serial No. 473,501
6 Claims.
(01. 178—44)
My invention relates to ultra high frequency
to a coaxial transmission line and is associated
systems and more particularly to an attenuator
with oppositely disposed walls or sides of the guide
for utilization therein. It has been appreciated
for some time that ultra high frequency electro
in order to excite the guide in response to the en
magnetic waves, now referred to as microwaves,
discharge device comprising a part of the input or
excitation means is displaced an appreciable dis
tance from a closed end of the guide so that the
ergization of the concentric line.
may be transmitted dielectrically through guides
of the hollow-pipe type, that is through guides de
?ned by conductive members. The types of elec
The electric
attenuation characteristic of the guide is not af
fected appreciably by the re?ections from the
closed end, and an axially adjustable output elec
tromagnetic waves which may be transmitted
through guides of this nature have been generally
trode means which may be attached to an adjust
classi?ed as transverse electric, TE, and trans
verse magnetic, TM, depending upon the nature of
the electric and magnetic ?elds constituting the
electromagnetic waves.
In accordance with the teachings of my inven
tion described hereinafter, I provide a new and
improved attenuator for systems of this nature
able plunger is positioned at the other end of the
guide and serves to derive from the guide ac
curately predetermined voltages dependent upon
the distribution of the guide energization, and
more particularly upon the attenuation charac
teristic of the guide.
F01‘ a better understanding of my invention,
reference may be had to the following description
taken in connection with the accompanying draw
wherein accurately controllable and determinable
voltages may be derived upon energization or ex
citation of the guide.
It is an object of my invention to provide a new
ing, and its scope will be pointed out in the ap
pended claims. Figs. 1 and 2, which are respec
and improved system for the utilization of ultra
high frequency electromagnetic waves.
It is another object of my invention to provide‘
tively a plan view and .a cross-sectional vertical
view, represent one embodiment of my invention
a new and improved attenuator for ultra high 25 as applied to an attenuator excited from a co
axial transmission line, and wherein an electric
discharge device is employed for converting the
It is a further object of my invention to pro
energization of the transmission line into the de
vide a new and improved attenuator for an ultra
high frequency system which comprises a dielec
sired energization of the attenuator.
tric guide of the hollow-pipe type which is excited 30 Referring now to Figs. 1 and 2 jointly, my in
at a frequency below the critical or cut-off fre
vention is there illustrated as applied to an ultra.
quency, and in which means are provided for de
high frequency system for controlling the trans-l
riving therefrom voltages of predeterminable
mission of energy through a dielectric wave guide
of the hollow~pipe type which comprises a con
It is a still further object of my invention to 35 ductive or metallic guide I which may have a
rectangular cross section. For example, the top
provide a new and improved attenuator for a high
frequency system which comprises a dielectric
and the bottom of the guide may be de?ned by
wave guide of the hollow-pipe type which is en
conductive or metallic plates 2 and 3 and the side
ergized or excited at a frequency below the cut
walls by plates 4 and 5. One end of the guide is
off frequency and in which the exciting means for
closed by means of a metallic end plate 6.
the guide is positioned with respect to a closed
In order to excite the guide, I provide an elec
tric discharge device 1 comprising a plurality of
end thereof in order to minimize re?ections there
from, so that accurately determinable output volt
enclosed electrodes such as an anode 8 and a
cathode 9 arranged in relatively close proximity in
ages may be derived from the guide.
frequency systems.
order to utilize effectively ultra high frequency
Brie?y stated, in accordance with the illus
trated embodiment of my invention, I provide in
currents. A cathode heating element (not shown)
lies within the cylindrical cathode 9 and heating
guide of the hollow-pipe type which is excited at a
current is supplied thereto by means of lead-in
conductors and terminal‘ posts Hi. Terminals H
frequency below the critical or cut-off frequency
in order to produce a predetermined attenuation 50 and I2 may be employed for connecting the cath
of the excitation within the guide. The exciting
ode to an external source of uni-directional cur
an ultra high frequency system a dielectric Wave
rent for-energizing the discharge. device.‘ The
electrodes of the discharge device are enclosed,
means for the guide may comprise an electric dis
charge device, such as a diode. peculiarly adapted
for the utilization of ultra high frequency energy,
and the discharge device, in turn, is connected
within a vacuum-tight envelope, and the anode _B_ .
is provided with an extension 13 to‘ serve as an.
adaptor for connection to the central conductor
ductivity of the conductive material de?ning the
of a concentric transmission line to be described
guide. Stated in other words, the waves are prop
agated with a predetermined attenuation.
In accordance with the present invention, the
In order to facilitate the insertion of the dis
charge device ‘I into operative relationship with
respect tolthe guide and to maintain the dis
charge device ?rmly in position after insertion,
critical frequency de?ned by Equation 3 above,_
I employ a pair of metallic adaptors III and I5
designed to afford appreciable resilience for en
attenuated along the longitudinal axis of a guide;
that is, the propagation constant 7 contains no
gaging parts of the discharge device.
Discharge device ‘I, and particularly the elec
tric discharge path between anode 8 and cathode
9, is controlled in response to the potential pro
vided by a concentric transmission line I6 com
prising an internal conductor I ‘I, which is con
nected to the anode adaptor I3, and a tubular
wave guide is excited at a frequency below the
so that the electromagnetic waves are rapidly
imaginary component.
Furthermore, in accordance with my invention,
the excitation means for the guide including the
electric discharge device 'I and the concentric
transmission line I6 are positioned with respect
to the end wall 6 so that there is little or no
re?ection therefrom, in this way increasing the
outer conductor I8 which is inserted into adaptor
accuracy of the attenuated energization proceed
I4 and which is electrically connected to one side
ing from the electric discharge device toward the
.of the wave guide such as plate 2.
right of the guide. I have found that prevention
In accordance with my invention, the wave 20 of undesirable reflections from the closed end
guide is designed to attenuate the excitation in
wall Ii of the wave guide may be obtained by posi
troduced into the guide by the concentric trans
tioning the electric discharge device 'I from the
mission line I6 and electric discharge device ‘I.
end Wall 6 at a distance which causes an attenua
More particularly, the height a and the width b
of the guide are chosen with respect to the fre
quency of excitation so that the electromagnetic
energization is not propagated in wave form along
the longitudinal axis of the guide but is rapidly
tion therebetween of at least 10 decibels so that
the reflected excitation from the closed end 6
will be attenuated at least 20 decibels when it
arrives at the electric discharge device ‘I.
Considering now the attenuation of the elec
tromagnetic excitation in a dielectric wave guide
'Each type of electromagnetic wave, that is each 30 operated below the cut-off frequency, it may be
type of transverse electric or transverse magnetic
stated generally that the energy of the excitation
wave in a given dielectric wave guide can be
is attenuated in accordance with the exponential
propagated at a frequency only above the critical
64%, where or represents the attenuation constant
or cut-off frequency. Considering a rectangular
of the guide and 2 represents the axial or longie
type wave guide, the propagation constant 7 may 35 tudinal distance along the guide. This relation
be expressed as follows:
ship will be appreciated when it is considered
that the energy of the excitation which may pass
along the guide is a function of the cross product
of the electric ?eld intensity and the magnetic
where w is the angular velocity of the wave under 40 field intensity, and inasmuch as both. the electric
consideration, 5 is the dielectric constant of the
?eld intensity and magnetic ?eld intensity are
medium through which the wave is propagated,
each attenuated in accordance with 6-12. the
a is the permeability, m is the mode of propaga
energy follows the squared law. Furthermore,
tion of the wave, and n is the order of the wave,
from the above it will be appreciated that the
a is the height of the guide, and b is the width
magnitude of the electric field of the energiza
of the guide.
tion within the guide is a function of r“?
For frequencies below the critical frequency,
the ?rst term of Equation 1 is smaller than the
sum of the other two terms, and Y is real. Con
sequently, under this condition of operation the
electromagnetic wave is attenuated. For frequen
cies greater than the critical frequency, the ?rst
term is greater than the sum of the other two
terms; consequently, ‘Y is imaginary, thereby re
sulting in a real propagated wave.
The critical or cut-off frequency f0 for a rectan
gular wave guide may be expressed as:
I provide within the guide output electrode
means which is adjustable along the longitudinal
axis of the guide in order to derive therefrom
voltage of predeterminable magnitude in accord
ance with the attenuation characteristic of the
guide. For example, the output electrode means
may take the form of a loop of Wire I9 constitut
ing an extension of an inner conductor 2| of
a concentric transmission line 20 which com
prises the inner conductor 2! and an outer tubu
lar conductor 22. As a means for positioning
the loop I9. the concentric transmission line 2!!
and consequently the loop I9 may be supported
by an axially 0r longitudinally positionable
In order to simplify still further the presenta
plunger 23 adapted to engage closely the top,
tion of the subject matter, it will be assumed
bottom and'side walls of the guide. The plunger
that the dielectric is air and that the system is
23 may be actuated by means of a suitable me
arranged for the transmission of an H01 type
chanical expedient such as a rod 24.
wave where the electric component of the ?eld 65
If it be considered that the guide is energi'led
is perpendicular to the base I), in which case the
at a substantially constant excitation by means
critical frequency may be expressed as:
of the concentric transmission line I6, there will
be established within the guide an excitation of
constant value, the electric discharge device
where c is the velocity of light. Of course, in any
practical: wave guide operated at a frequency
above the cut-off frequency, electromagnetic
waves are propagated with attenuation, the mag
nitude of thelatter being determined by the con
70 serving to periodically control the potential dif
ference between plates 2 and 3 of the guide tov
establish this excitation. The attenuation of the
excitation within the guide is determined in ac
cordance with the above described principles so
that by the positioning of the loop I9 with re
While I have shown and described my inven
tion as applied to a dielectric wave guide of par
' excitation of said member at a frequency below
conductive wave guide having a closed end, ex
spect thereto, I provide a system for obtaining
citation means displaced from said closed end
accurately and precisely determinable ultra-high
for exciting said guide at a ‘frequency below the
frequency voltages. The magnitude of the volt
critical cut-off frequency, and means displaced
age supplied to the concentric transmission line
from said excitation means for deriving pre
20 is, of course, determined by the position of
determinable amounts of energy from said guide
the loop I 9. As the loop I9 is moved toward
determined by the position thereof with respect
the electric discharge device 1, the magnitude
to said excitation means.
of the voltage obtained is increased; and the
4. In an attenuator, the combination compris
relationship of this voltage with respect to the
longitudinal dimension of the guide follows the 10 ing a hollow conductive member having a closed
end, excitation means connected to said guide
exponential relationship r”, where a is measured
and displaced from said closed end for e?ecting
from discharge device 1.
’ the cut-off frequency thereby imparting to the
ticular con?guration and as employing various 16 electro-magnetic energization of said member a
elements diagrammatically illustrated, it will be
obvious to those skilled in the art that changes
and modi?cations may be made without depart-.
ing from my invention and I, therefore, aim in
the appended claims to cover all such changes 20
predeterminable attenuation characteristic, and
adjustable means comprising a plunger having
output electrode means for deriving predeter
minable voltages from said member.
5. In an attenuator, the combination compris
ing a hollow conductive member having a closed
end, means for exciting said member at a fre
quency below the critical cut-off frequency com
prising an electric discharge device including a
and modi?cations as fall within the true spirit
and scope of my invention.
What I claim as new and desire to secure by
Letters Patent of the United States, is:
1. A dielectric wave guide system of the hol 25 plurality of enclosed electrodes, said discharge
device being positioned from said closed end at
a distance to minimize the re?ection therefrom,
and axially adjustable output electrode means at
the other end of said member for deriving from
prevent the re?ection of appreciable energy 30 said member a voltage of predetermined magni
tude determined by the excitation and the at
therefrom, and output electrode means opposite
tenuation characteristic of said member.
the excitation means for deriving energy from
6. In an attenuator, the combination compris
said guide.
ing a hollow conductive member having a closed
2. In an attenuator, the combination compris
ing a hollow conductive member having a closed 35 end, means for exciting said attenuator at a fre
quency below the critical cut-off frequency and
end, means for exciting said member at a fre- .
positioned from said closed end at a distance to
quency below the critical cut-off frequency and
prevent appreciable re?ection therefrom, and
positioned a distance from said closed end to
axially positionable means comprising an adjust- '
minimize the reflection therefrom, and axially.
positionable means at the other end of said 40 able plunger supporting output electrode means
at the other end of said member.
member and including output electrode means.
low-pipe type comprising a conductive member
having a closed end, means for exciting said
member below the critical cut-oil frequency and
positioned a distance from said closed end to
3. In an attenuator for a dielectric wave guide
system, the combination comprising a hollow
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