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Патент USA US3054079

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Sept‘. 11, 1962
3,054,075
J. R. LOHOAR
ANODISED HELICAL TAPE WAVEGUIDE FOR MODULATING ARRANGEMENTS
Filed April 29, 1960
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INVENTOR
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ATTQRNEYS
United States Patent 0
1 r.
ICC
1
3,054,075
AN ODISED HELICAL TAPE WAVEGUIDE FOR
,
MODULATING ARRANGEMENTS
John Ronald Lohoar, Steveuage, England, assignor to
Marconi’s Wireless Telegraph Company Limited, Lon
don, England, a British company
3,054,075
Patented Sept. 11, 1962
2
Within said length of waveguide and a winding external
to said length of waveguide and arranged and adapted to
provide a varying magnetic ?eld through said body to
modulate, in accordance with the variations of said ?eld,
high frequency wave energy transmitted through said
length of guide.
Filed Apr. 29, 1960, Ser. No. 25,573
Claims priority, application Great Britain Aug. 19, 1959
Claims. (Cl. 333-96)
Preferably the tape is aluminium tape anodised to pro
vide the insulation between the turns.
In order to reduce discontinuities between the helically
10 wound length of guide and the adjoining ends of wave
This invention relates to wave energy modulating ar
guides between which the length is inserted to form a
rangements and more speci?cally to modulating arrange
“run” of guide, it is most desirable, if not essential, that
ments of the kind in which very high frequency wave
the ends of the helically wound length be ?nished ?at,
energy is modulated by propagating it along a waveguide
i.e. that they terminate in planes at right angles to the
in which is a ferrite or similar body and subjecting said 15 axis. One way of doing this is to ?t each end of the
body to a modulated or varied magnetic ?eld produced by
helically wound length with a cylindrical collar which is
a coil system outside the guide.
flat at one end and shaped with a step at the other to mate
The object of the invention is to provide improved,
with the end of the helix proper, the tape of which is
simple and efficient modulating arrangements of the kind
cut oif square to the length of the tape. Another way is
referred to wherein, despite that the coil system is out 20 to solder together the last few turns of the helical guide
side the waveguide, there is minimum losses due to the
to permit it to be turned off square, i.e. ?at.
interposition of the walls of the guide in the path of the
Preferably also the outside of said length of guide is
magnetic ?ux and minimum interference with the proper
covered with a thickness of comparatively rigid insulating _
functioning of the waveguide as such.
material, e.g. resin, and the winding is positioned on the
It is common practice to effect modulation of a high 25 outside of this insulating material. ‘In one construction,
frequency electro-magnetic wave transmitted down a wave
the winding is a single layer winding of turns of conductive
guide by applying a magnetic ?eld which is varied in ac
tape wound directly on the insulating material.
cordance with modulation to vary the magnetisation of a
The ends of the length of waveguide may be ?tted
ferrite body inserted in the waveguide, the modulating
with flanges which must be so arranged that, when said
magnetic ?eld being generated by a coil system outside 30 length is inserted in a “run” of guide, it is insulated at
the guide. One of the dii?culties met with in modulators
least at one end from the adjacent guides. Accordingly,
of this nature is that, since the varying magnetic ?eld
if a ?ange on the end of the helically wound length is to
has to pass through the guide walls to reach the ferrite
be in metal to metal contact with a ?ange at the end of
body, it induces substantial eddy currents in said walls,
an adjacent length of guide, the former ?ange should be
especially if the modulating frequencies are relatively high. 35 insulated from the helix and a thin insulating shim is
These eddy currents of course constitute loss and tend in
inserted to avoid contact between the end of the helix and
effect to short circuit the magnetic ?eld and oppose proper
the adjacent guide.
and e?icient modulation. Various expedients have been
The invention is illustrated in the accompanying draw
proposed to meet this difficulty but it is by no means easy
ing which is a simpli?ed sectional view of a preferred
to do so without interfering with the proper functioning of
embodiment of the invention as applied to a frequency or
the waveguide as such, and without resulting in a struc
phase modulator of microwave energy. Although the in
ture which is mechanically unsatisfactory or unduly ex
vention is not limited to its use at any particular band
pensive or incapable of handling high power. For ex
of frequencies, it is very advantageous for phase or fre
ample, it has been proposed to use a guide in the form
45 quency modulation of microwave energy'at comparatively
of a very thin ?lm of deposited silver or aluminium on
high frequencies and the illustrated embodiment is suitable
the inside of an insulating tube, but this construction will
for use for phase or frequency modulating microwave
not handle high power satisfactorily and is, moreover, ex
energy of a frequency of the order of 10,000 mc./s. by a
pensive and mechanically weak. It has also been pro
modulating frequency of the order of l mc./ s. Practical
posed to slot the waveguide with a slot running parallel
principal dimensions for the illustrated embodiment when
to the axis, but here again such a slot tends to distort the 50 intended for the frequencies stated are: about91A2" overall
?eld, its provision results in an asymmetrical waveguide
length and about 0.81" for the inside diameter of the
and leakage of high frequency (microwave) energy tends
to occur through the slot. Another proposal which has
been made is to provide the waveguide with a helical slot,
guide, the guide being wound from anodised aluminium
tape about 1A0 of an inch wide and about 1/32 of an inch
thick.
the slotted waveguide being formed by electro-forming it 55 Referring to the drawing, a circularly sectioned guide 1
on a special mandrel and then using the coil, which the
is made from anodised aluminium tape which is wound
slotted guide in fact constitutes, as the source of the mod—
in helical form with the edges of the turns in contact with
ulating magnetic ?eld. This expedient avoids the di?’iculty
one another as indicated by the parallel lines 1a shown
above mentioned by in fact dispensing with the external
at the ends of the guide length. It will be understood that
60
modulating ?eld source altogether (since the guide itself
the distance between any two adjacent parallel lines 1a
is now the ?eld source) but the construction is expensive
represents the width of the tape. The anodising of the
and again there is a tendency to microwave energy loss
aluminium provides insulation so that although the tape
through the helical slot. There is also an added limita
edges are physically in contact with one another and the
tion in design parameters because of the fact that the mag
65 ?nished guide has no gaps or substantially no gaps lead
netisation coil and the guide are now one and the same.
According to this invention an arrangement of the kind
ing to the exterior, the turns are effectively insulated each
from the next. The ends of the wound guide are ?nished
referred to for modulating very high frequency electro
off by ?anges which serve for coupling the length of
magnetic Wave energy comprises a length of waveguide
guide to other guide lengths (not shown). These ?anges
constituted by a helically wound metallic tape with the 70 should be insulated from the guide proper and may be
edges of the turns substantially in physical contact with
one another but insulated from one another, a ferrite body
?tted thereto in any convenient manner. The most prac
tical way of making the glide consists in winding the tape
-
A,
3,054,075
3
on to'a, mandrel so .that no gaps occur in the winding;
clamping it at the ends; and then, after trimming the
ends if necessary, ?tting the ?anges in position with suit
able insulation between them-and the guide proper. The
clamps may then be removed and the mandrel punched
out.
.
4
ium tape the turns of which are substantially in physical
contact with one another, said tape being anodised to
provide insulation between the turns whereby energy trans
mitted through said length of Waveguide is modulated by
the varying magnetic ?eld through said body.
2. An arrangement as claimed in claim 1 wherein the
In the illustrated embodiment the waveguide with its
end ?anges, which are marked 2, is “potted” with resin or
some other suitable insulating compound so that the guide
is externally coated to provide it with additional mechan
ical: strength and rigidity by a comparatively thick layer
of resin or other insulating compound 3. On this layer
is wound the modulating magnetizing coil which is con
ends of the helically Wound Waveguide terminate in planes
at right angles to the guide axis and wherein the last few
ends for avoiding sharp impedance discontinuities. The
ferrite rod 5 is supported in position in the guide by suit
able insulating supports 6, preferably aper-tured as indi
cated.
tape.
turns of said tape are soldered together.
3. An arrangement as claimed in claim 1 wherein the
said guide is covered with a layer of insulating material
and wherein said coil is positioned on the outside of said
insulating material.
4. An arrangement as claimed in claim 1 wherein each
ventionally represented at 4 and may conveniently con
sist in practice of a few turns of copper tape wound di 15 end of the helically wound length is ?tted with a cylin—
drical collar which is ?at at one end and shaped with a
rectlyon to the insulation 3. The coil 4 extends at least
step at the other to mate with the end of the helix proper,
over the length of a ferrite insert which is shown as of
the tape of which is cut oif square to the length of the
conventional form at 5, i.e. it is a ferrite rod with pointed
5. An arrangement as claimed in claim 1 in which said
waveguide length is ?tted at least at one end with a ?ange
insulated from the helical winding.
, An experimental arrangement as illustrated using ano—
dised aluminium tape 0.1" x 0.032” has been successfully
used at the frequencies hereinbefore mentioned to handle 25
500 watts C.W. power.
I claim:
1. ,A wave energy modulating arrangement in which
very high frequency energy is modulated comprising a
length of waveguide, a ferrite body located in said wave 30
guide, a magnetic coil positioned outside said length of
waveguide arranged and adapted to subject said body to
a modulated magnetic ?eld, said waveguide being of circu
lar cross-section and comprising ahelically wound alumin
References Cited in the ?le of this patent
UNITED STATES PATENTS
2,802,134
Fox _________________ __ Aug. 6, 1957
1,031,381
Germany _____________ __ June 4, 1958
FOREIGN PATENTS
OTHER REFERENCES
Brown, “Proceedings of the IRE,” April 1958, pages
722-726.
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