U.S. patent number 3,648,172 [Application Number 04/848,125] was granted by the patent office on 1972-03-07 for circular leaky waveguide train communication system.
This patent grant is currently assigned to Sumitomo Electric Industries, Ltd.. Invention is credited to Hiroshi Kitani, Noritaka Kurauchi, Tsuneo Nakahara.
United States Patent |
3,648,172 |
Nakahara , et al. |
March 7, 1972 |
CIRCULAR LEAKY WAVEGUIDE TRAIN COMMUNICATION SYSTEM
Abstract
A circular leaky waveguide comprising a metal tube or of a helix
waveguide which is provided with a row or a plurality of rows of
leakage apertures, each aperture having maximum diameter smaller
than a half wavelength of the transmission wave, and spaced at
intervals P<.lambda.o.lambda.g/.lambda.o+.lambda.g, where
.lambda. is free the space wavelength, and .lambda.g the waveguide
wavelength.
Inventors: |
Nakahara; Tsuneo (Nishinomiya,
JA), Kurauchi; Noritaka (Suita City, Osaka,
JA), Kitani; Hiroshi (Osaka, JA) |
Assignee: |
Sumitomo Electric Industries,
Ltd. (Osaka, JA)
|
Family
ID: |
25302413 |
Appl.
No.: |
04/848,125 |
Filed: |
October 2, 1968 |
Current U.S.
Class: |
455/523; 246/30;
343/717; 333/237; 343/771 |
Current CPC
Class: |
H01Q
13/20 (20130101) |
Current International
Class: |
H01Q
13/20 (20060101); H01q 013/10 () |
Field of
Search: |
;343/711,712,713,717,770,771 ;325/51,130 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lieberman; Eli
Claims
We claim:
1. A vehicle communication system comprising a metallic circular
leaky waveguide positioned between inbound and outbound vehicle
tracks and having two pairs of axially extending rows of leakage
apertures with each pair having a circumferential spacing between
row pairs determined by the central angle .phi. within the range of
20.degree. to 80.degree., each of said apertures having a maximum
measure smaller than half the waveguide wavelength with an interval
between adjacent apertures which is less than
.lambda.o.lambda.g/.lambda.o+.lambda.g , wherein .lambda.o is the
free space wavelength and .lambda.g is the waveguide wavelength,
one pair of said aperture rows positioned for coupling with an
antenna on an outbound vehicle and the other pair positioned for
coupling with an antenna on an inbound vehicle.
2. The vehicle communication system of claim 1 wherein said
metallic circular leaky waveguide is a circular helix
waveguide.
3. The vehicle communication system of claim 1 characterized by an
antenna mounted on a vehicle on said track and coupled for leaky
wave transmission or reception with said leaky waveguide, said
antenna consisting of a waveguide section having a row of leakage
apertures spaced at an interval sufficiently shorter than the
waveguide transmission wavelength, said waveguide section having
the same waveguide wavelength as that of said circular leaky
waveguide.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
Train communication systems in which a leaky waveguide is installed
along a railroad track and wherein a wave radiated from the leaky
waveguide is received by the antenna aboard the train for
transmission of signals for train telephone and signals necessary
for train operation control in the frequence band from several
hundred MHz. to several thousand MHz. have been under research.
The present invention relates to circular leaky waveguides.
2. Description of the Prior Art
Train communication devices have been known to employ a main
circular waveguide for transmitting signal wave energy which
branches off through directorial couplers at appropriate intervals
into leaky waveguides of rectangular shape having leakage apertures
for leaking a portion of the transmitting wave energy along a
railroad track at an interval of about 1/2 the waveguide
wavelength. The rectangular waveguide is installed in parallel to
the track and an antenna aboard a train couples with the leaky wave
of the leaky waveguide.
When the transmission wave is transmitted with low attenuation in
the main circular waveguide, a portion of the transmission wave is
divided from the main circular waveguide and directed into the
branched leaky rectangular waveguide through the directional
coupler to be radiated uniformly along the track and coupled with
the antenna aboard the train. When the antenna aboard the train
radiates radiofrequency waves, the leaky rectangular waveguide
couples with the wave from the antenna and sends this wave through
the main circular waveguide to fixed communication stations
connected to the main circular waveguide.
Another known leaky wave communications system, in which a circular
waveguide having leakage apertures on the circular waveguide at
much longer intervals than the wavelength in the longitudinal
direction, is installed along the track and leaky waves from said
leakage apertures are coupled with the antenna aboard a train.
The former system has several draw backs which are as follows. The
construction of the transmission line of this prior art system is
complicated and much higher in cost and uneconomical, because this
system is comprised of two types of waveguides.
The transmission loss of the leaky rectangular waveguide is very
large, because the transmission mode, that is TE.sub.10 mode, has
high heat loss characteristics. At a curved section of the track
the transmission mode of the TE.sub.01 mode of a circular electric
mode is readily converted into the unwanted TM.sub.11 mode, which
makes it necessary to provide a film coating of polyethylene on the
inner surface of the circular waveguide so as to prevent the mode
conversion.
The manufacture and installation of the leaky waveguide of this
system calls for a high degree of technique or skill in order to
keep the uniform distribution of the leaky wave along the track,
because the spacing between adjacent leakage apertures sharply
effects the distribution of the leaky wave.
By the thermal expansion and contraction of the leaky waveguide,
the relative distance between leakage apertures on adjacent
branches of leaky rectangular waveguides changes. This causes an
uneven distribution of the leaky wave which interrupts
communication signals.
It is hardly possible to exclude such thermal effects.
The latter mentioned system has the following disadvantages:
Since the distance between adjacent leakage apertures in the
direction of wave transmission is very long as compared with the
waveguide wavelength, the leaky wave radiated to the outside from a
leaky aperture is still in the state of a spherical wave in the
neighborhood of the leaky waveguide and produces a standing wave
between leaky waves radiated from the adjacent leakage apertures,
so that when a train moves therealong the coupling level between
the train antenna and leaky waveguide fluctuates greatly and
produces great signal distortion in the communication.
With respect to the interior of the circular waveguide, it is
observes that since the distance between adjacent leakage apertures
are long as compared with the waveguide wavelength, there is no
selectivity between modes which are easily excited and modes which
are hard to excite in connection with the generation of unwanted
modes, so that almost all unwanted modes, mainly the TE.sub.mn
modes (where m and n are integers, except m = 0, n = 1), are
excited in equal amounts, with the result that a great deal of
unwanted modes are generated in the waveguide. The generation of
unwanted modes makes the transmission loss of the TE.sub.01 mode
exceedingly great, and the communication distortion of the
transmission due to mode conversion and reconversion is exceedingly
great.
BRIEF EXPLANATION OF DRAWINGS
FIG. 1 shows a sectional perspective view of a circular leaky
waveguide illustrating one embodiment of the present invention.
FIG. 2 shows a view in side elevation explaining the relation
between the circular leaky waveguide and the antenna aboard a
train.
FIGS. 3 and 4 show sectional perspective views of the embodiments
of the present invention.
FIGS. 5 and 6 show curves of theoretical results of transmission
properties of the system of the present invention.
FIG. 7 shows a transverse sectional view of the circular waveguide
of the present invention for illustrating the radiation patterns of
the leaky wave at different central angles.
FIGS. 7a through 7d are graphical illustrations of the transverse
radiation patterns of the leaky waveguide at different central
angles of the waveguide shown in FIG. 7.
FIG. 8 shows curves of the vertical and horizontal gain of the
waveguide of the present invention at various central angles.
FIG. 9 graphically shows the experimental results of a transmission
loss.
FIGS. 10 and 12 are sectional views in elevation illustrating
embodiments of the train communication system of the present
inventions.
FIG. 11 shows a sectional perspective view of an antenna used in
the train communication system of the present invention.
FIG. 13 shows a sectional view of a circular leaky waveguide suited
to the train communication system as shown in FIG. 12.
FIGS. 14 a and b and 15 a and b sectional views of circular leaky
waveguides with their corresponding radiation patterns.
DESCRIPTION OF PREFERRED EMBODIMENTS
The present invention provides circular leaky waveguides and a
moving body communication system using said circular leaky
waveguides which eliminate the drawbacks of the aforementioned two
systems of the prior art.
An object of the present invention is to provide a circular leaky
waveguide in which leakage apertures are placed on the wall of a
circular waveguide of an electroconductive circular tube, such as
an aluminum tube, copper plated steel tube or a helix waveguide at
fixed intervals of P<.lambda..sub.o 0.lambda. g/.lambda.
o+.lambda. g, where .lambda. o is free space wavelength and
.lambda. g is waveguide wavelength) in one row of apertures or more
than two in the longitudinal direction.
Another object of the present invention is to provide a circular
leaky waveguide which has four rows of leakage apertures, two rows
of the four rows of apertures being provided for the in track, and
the other group of two rows being provided for the adjacent
parallel out track. The central angle of each pair of aperture rows
as measured from the horizontal at the central axis of the circular
waveguide is from 30.degree. to 50.degree., and they are placed in
the wall of the circular waveguide at the fixed interval P, defined
above, in the longitudinal direction.
Still another object of the present invention is to provide a
moving body communication system in which the circular leaky
waveguide of the present invention is installed along a railway
track and antennas mounted aboard trains, couple with a leaky wave
from said circular leaky waveguide.
FIG. 1 shows the perspective view of an embodiment of a circular
leaky waveguide of the present invention.
In FIG. 1, 1 denotes a circular waveguide constructed of an
aluminum tube, copper tube, copper plated steel pipe or a so called
helix waveguide having such construction that a fine enameled
copper wire is closely wound helically, this helix is surrounded by
an impedance transformer jacket of dielectric material and this
transformer jacket is further surround by a shielding conductive
layer. 2 denotes the leakage apertures of circular, rectangular or
elliptic shape having their largest measurement shorter than 1/2
wavelength of the transmission wave from which leaky wave radiates
to the outside of the circular waveguide.
Apertures 2 are provided on the wall of the circular waveguide 1 at
the interval P in the longitudinal direction in each row or two or
more rows.
In FIG. 1, an example of the circular leaky waveguide having two
rows of leakage apertures is shown. The aperture interval P
determines the properties of the leaky wave radiated through the
aperture of a part of the energy of the transmission wave of the
TE.sub.01 mode of the circular electric mode. P is defined as
follows:
P<.lambda. 0.lambda. g/.lambda. 0+.lambda. g, and
where .lambda. o is free space wavelength, and .lambda. g is
waveguide wavelength of circular waveguide. When the aperture
interval P is kept within the range defined above, the angle
.theta. between the axis of the waveguide and the direction of the
leaky wave is determined by the following equation.
.theta.= cos.sup..sup.-1 (.lambda. o/.lambda. g)= sin.sup..sup.-1
(.lambda. 0/.lambda. c),
where .lambda. 0 and .lambda. g are already explained. .lambda. c
is the cutoff wavelength of the circular waveguide.
It is very important to know the fact that the radiation angle
.theta. is not dependent on the interval P of the apertures. For
example, the radiation angle .theta. is taken as 23.degree. in the
embodiment of the present invention where the diameter of the
circular waveguide of aluminum tube is 132 mm., the frequency of
the waveguide having apertures aligned at the interval P = 14 mm.
is 7.5 GHz., and with .lambda. 0 = 40 mm. and .lambda. g= 43
mm.
FIG. 2 shows the radiation angle .theta. and the relative position
between a leaky waveguide and an antenna aboard a train. In FIG. 2,
5 is the antenna equipped aboard the train which runs in parallel
to the leaky waveguide, other reference numbers show the same parts
as shown in FIG. 1.
FIG. 3 and FIG. 4 show sectional views of the detail of the wall
structure used in the embodiments of the circular leaky
waveguide.
FIG. 3 shows a wall structure of a metal pipe, such as aluminum
tube, copper tube, etc., with holes properly positioned therein. In
FIG. 3, 1 denotes a circular waveguide 2 denotes the leakage
apertures.
When a circular waveguide transmits the wave of a TE.sub.01 mode,
the current flow at the inner surface of the waveguide has
substantially a circumferential current component alone. When a
circular waveguide has apertures, the current flow at the inner
surface of the waveguide has some perturbed axial current
components in the neighborhood of the leakage apertures.
This axial current component is caused by the fact that the
circumferential current component being disturbed by an aperture
changes the direction of a part of the current flow to go round the
aperture. This axial current component is apt to generate the
unwanted TM mode waves which slightly increase transmission
loss.
FIG. 4 shows the details of the wall structure of a helix waveguide
having a leakage aperture as in the circular leaky waveguide.
In FIG. 4, 1 denotes a circular leaky waveguide, 11 is a fine
insulated wire in the form of helix, 12 is an impedance matching
layer of a dielectric material which is well penetrated by unwanted
waves, 13 is a lossy layer for the purpose of absorbing the energy
of unwanted mode waves, 14 is a conductive layer of shielding off
unwanted modes, and 15 is outer protective covering made of a
dielectric.
The helix waveguide as shown in FIG. 4 is disclosed in the Japanese
Pat. No. 2677/1962. The helix waveguide as shown in FIG. 4 has many
favorable properties in that the attenuation of the TE.sub.01 mode
is little, the suppression of unwanted modes is very effective, the
transmission loss due to mode conversion is little, and the helix
waveguide serves as a filter to purify the TE.sub.01 mode and to
remove spurious mode components, particularly those of the
TE.sub.11 and TE.sub.12 modes, when used in a shorter length. If
the helix waveguide having an aperture as shown in FIG. 4 transmits
the wave of the TE.sub.01 mode, the current around the aperture
does not flow to avoid the aperture because the impedance in the
axial direction is very much larger than the impedance the
circumferential direction, and the axial component of the current
around the aperture which causes spurious modes is negligible.
The helix waveguide has more excellent properties than that shown
in FIG. 3, but it is extremely expensive to manufacture.
A combined type transmission line without leaky wave apertures for
the transmission of the TE.sub.01 mode wave, which is made of
circular waveguides consisting of metal tubes and helix waveguides
intermittently interposed among the circular waveguides of metal
tube, has been previously known.
According to the present invention, a combined type circular leaky
waveguide may be constructed by using the circular waveguides
constructed of metal tube as shown in FIG. 3 and the helix
waveguides as shown in FIG. 4 in combination, which not only
radiates a leaky wave along the sections of the circular waveguides
of metal tubing, but also radiates equally along the sections of
helix waveguides.
The experimental results of an actual embodiment of the present
invention will be explained as follows.
FIGS. 5 and 6 show the theoretical results of the transmission
properties of the leaky waveguide of the present invention.
FIG. 5 shows the transmission loss (dB/km) of the TE.sub.01 mode
wave versus diameter (mm.) of the leakage apertures of the circular
leaky waveguide where the circular leaky waveguide is made of an
aluminum tube having an inner diameter of 132 mm., a transmission
wave mode which is the TE.sub.01 mode, frequency for the
transmission wave as 8 GHz., a shape for the leakage aperture of
round, and an interval P between apertures of 14 mm. aligned in the
longitudinal direction. The curves .alpha.h , .alpha..sub.ha and
.alpha..sub.r represent the substantial heat loss of the circular
waveguide without leakage apertures, for the TE.sub.01 mode, the
additional heat loss caused by the leakage aperture and the
radiation loss by the leaky wave respectively.
It is noted from these curves that when the practical range of
diameter of the leakage aperture lies within 4-12 mm., the
additional heat loss .alpha..sub.ha by the leakage aperture is much
smaller than that of the conventional leaky waveguide. For example,
when the diameter of the aperture d is 4 mm., .alpha..sub.ha = 0.1
db./km. and d is 12 mm., and .alpha..sub.ha = 1.2 db./km.
FIG. 6 shows the curves for the total transmission loss (db./km.)
of the substantial heat loss .alpha..sub.h, additional heat loss by
leakage apertures .alpha.ha and radiation loss .alpha..sub.r versus
frequency (GHz.) by the parameter of the leakage aperture diameters
of the circular waveguide.
The result is that the additional heat loss .alpha.ha by the
leakage apertures shown in FIG. 5 is very small and this is
considered to be so as follows: The TE.sub.01 mode wave and other
unwanted mode waves are generated progressively by the apertures
aligned at intervals which are small as compared with the waveguide
wavelength in the axial direction of the waveguide, and the
TE.sub.01 mode wave newly generated reacts as a perturbed reactance
to the transmission wave of the TE.sub.01 mode while other unwanted
modes are set off and become smaller because their phases do not
coincide. In consequence, the transmission wave of the TE.sub.01
mode is shifted slightly in its phase in the waveguide and other
unwanted modes being generated contribute, to the additional heat
loss by leakage apertures .alpha..sub.ha. The advantages of the
leaky circular waveguide of the present invention will be explained
below.
Since the radiation direction of the leaky wave having the angle
.theta. with respect to the axis of the waveguide is determined by
.lambda.o and .lambda.g as aforementioned, it is not affected by
the interval P, and when the leakage apertures are provided on the
wall of the circular leaky waveguide in the direction of the axis
of the waveguide at the interval P. The radiation direction is not
affected by a deviation of the interval of the leakage apertures
when manufacturing the transmission line.
This condition is applicable also to the joints between leaky
waveguides, so that the installation of the waveguide of the
present invention becomes very facile. This is a remarkable
advantage of the present invention.
The coupling between the antenna aboard the train and the leaky
waveguide is considered in turn.
When n apertures radiating spherical waves are aligned from an
original point on a straight line, the electric strength E at a
point far from these wave sources in the direction of the angle
.theta. with respect to the straight line is generally represented
by following equation,
ln is the distance from the original point to the point of nth,
.lambda.o and .lambda.g in defined before,
.theta. is as aforementioned,
e is the base of the natural logarithm
If such wave sources are identified with the apertures of the leaky
waveguide, then the radiation angle is .theta., (here .theta.=
cos.sup..sup.-1 (.lambda.o/.lambda.g) and .PSI..sub.n .tbd. 0.
In consequence, the electric field of the point P is given as
follows:
E=E.sub.1 +E.sub.2 + --- +E.sub.n
It is noted that the maximum radiation of the leaky wave would be
obtained within the radiation angle .theta. with respect to the
waveguide axis.
In other words, the radiation in this direction has no connection
with the pitch of the leakage apertures. Even if the sizes of the
leakage apertures are different, they merely affect the magnitude
of the aforementioned E.sub.1, E.sub.2 ......., E.sub.n, so that
only the intensity of the electric field of the point P changes,
while the direction of radiation remains unchanged.
Moreover, since the leakage apertures are arranged at shorter
intervals than the wavelength and the radiation directions of the
leaky waves are uniform in the longitudinal direction, standing
waves do not appear around the circular leaky waveguide so that the
coupling between the antenna and the leaky wave is
unfluctuable.
According to the present invention, the directivity in a plane
perpendicular to the waveguide axis of the leaky waveguide is
affected by the number of the rows of the apertures and distance
between rows.
The beam of the leaky wave is diverged broadly when the waveguide
has a single row of apertures, but concentrated more when it has
double rows.
FIG. 7 shows the directivity in a plane perpendicular to the
waveguide axis of the leaky wave in the situation where the central
angle .phi. on the two rows of the leakage aperture changes from
0.degree.-60.degree..
FIG. 8 shows two curves illustrating the gain in the vertical
direction and horizontal direction when .phi. changes from
0.degree.-80.degree. as seen in a plane passing through centerline
between the two rows of apertures and the central axis of the
waveguide which is hold vertically.
It is noted from these graphs that the directivity of the leaky
wave becomes sharp where .phi. is around 50.degree. so that this is
advantageous to increase the coupling between the antenna aboard
the train and the leaky waveguide. The directivity of the leaky
wave becomes broader where .phi. is around 20.degree..
This is, however, convenient for the use of a parabolic cylindrical
reflector or elliptic-cylindrical reflector which reflects between
the leakage aperture and the antenna. Around 40.degree. of .phi.,
the horizontal gain of the leaky waveguide becomes minimum so that
this decreases the interference noise between this leaky wave
system and another outside microwave communication system using the
same microwave frequency, if present.
According to the present invention, since many leakage apertures
are arranged along the waveguide axis, a difference appears in the
transmission phase constant between the TE.sub.01 mode and the
TM.sub.11 mode, so that the degeneration relation between them is
released and the mode conversion from the TE.sub.01 mode to the
TM.sub.11 mode and its reconversion are exceedingly reduced at a
bend of the waveguide where they would inherently occur.
In consequence, the circular leaky waveguide of the present
invention has little thermal loss due to mode conversion. For this
reason, it makes it possible to make the distance between repeaters
longer than that in the conventional system and also to intensify
the coupling between the train antenna and the leaky waveguide.
It is to be especially noted that, the longer distance between
repeaters makes it possible to reduce the number of repeaters
required, so that the increase in thermal noise due to the
additional use of repeaters may be reduced and the cost of
construction may be lowered.
This has been a major cause for the lowering of the signal to noise
ratio in the communication system.
The experimental results of the circular leaky waveguide of the
present invention in which the transmission loss of the TE.sub.01
mode wave over the frequency range 7GHz. to 10GHz. is measured, was
shown in FIG. 9 in comparison with the theoretical values of
thermal loss without the apertures.
In FIG. 9, the curve a shows these experimental results and the
curve b the theoretical values.
In this experiment, a circular leaky waveguide made of an aluminum
tube which has a diameter of 132 mm., has two lines of leakage
apertures made at an interval of 14 mm. and has a central angle
.phi. on the two alignments of the apertures of 20.degree..
In FIG. 9, the curve a shows the experimental results of the
transmission loss of the circular leaky waveguide of the present
invention to be nearly 4 to 6 db./km. over the frequency range of
7.5 GHz. to 10 GHz., and the curve (b) shows the theoretical values
of the transmission loss of the circular waveguide without the
apertures 2 to be 1 dB/Km over the same frequency range.
It is supposed that the radiation loss of the leaky wave is
considered to be approximately 2-3 db./km. on this frequency range
and the additional heat loss is about 1 db./km.
A train communication system according to the present invention
will be explained hereinafter.
FIG. 10 shows a train communication system in which a circular
leaky waveguide as shown in FIG. 1, is connected to repeaters and
other communication stations and is installed along the railroad
track and the antenna aboard the train is coupled with the leaky
wave from the leaky waveguide.
In FIG. 10, 1 denotes a circular leaky waveguide, 21 is track rail,
22 is a train and 5 is the antenna aboard the train.
FIG. 11 shows an antenna which is very suitable for the train
communication system as shown in FIG. 10.
In FIG. 11, 5 denotes an antenna of rectangular waveguide, section
23 denotes apertures provided on the narrower wall of the
rectangular waveguide, and q is the interval between apertures
which are sufficiently smaller than the wavelength of transmission
wave.
This antenna is a type of travelling wave antenna. In the
rectangular waveguide shown in FIG. 11, if the waveguide wavelength
.lambda.g is selected to be equal to the waveguide wavelength
.lambda.g of the circular leaky waveguide, then the radiation
directivity of the leaky wave from the apertures of the rectangular
waveguide having the angle .theta. with respect to the axis of the
waveguide would be coincident with the radiation directivity of the
leaky wave from the circular leaky waveguide.
.theta. satisfied following relations.
.theta. = cos.sup..sup.-1 (.lambda.o/.lambda.g) = sin.sup..sup.-1
(.lambda.o/.lambda.c),
where .lambda..sub.c is the cutoff wavelength of the rectangular
waveguide.
As a result, maximum coupling gain between the train antenna and
circular leaky waveguide is obtained for transmitting and
receiving.
In the train communication system as shown FIG. 10, since the train
shakes or vibrates severely in general, the mutual distance between
antenna and waveguide greatly fluctuates.
This system, however, has the advantage that the variation of the
coupling coefficient of this system in smaller than that of
conventional systems.
It is explained as follows:
The variation of the distance between the train antenna and the
leaky waveguide caused by vibration of train in a direction
perpendicular to the waveguide axis is defined as d.
The leaky waves from the apertures radiate in the direction of the
angle .theta. with respect to the waveguide axis by the free space
wavelength .lambda.o and the transmission wave in the circular
waveguide transmit in the direction of waveguide axis by the
waveguide wavelength .lambda.g, so that the apparent wavelength in
the direction perpendicular to the waveguide axis is equal to the
cut off wavelength .lambda..sub.c where .lambda..sub.c =
.lambda.o/sin.theta. .
In consequence, the coefficient of the coupling variation C is
obtained by the formula; C =d/.lambda..sub.c , here .lambda..sub.c
is the cutoff wavelength of the circular waveguide which is known
as .lambda..sub.c =90 D/ 3.832, where D is diameter of the circular
waveguide. If D=132 mm., then .lambda..sub.c =108 mm.
The coefficient of the coupling variation c= d/.lambda..sub.c of
the system of the present invention is improved by 2.5 times in
comparison with that of C.sub.o =d/.lambda..sub.o of the
conventional system which radiates the leaky wave in the direction
perpendicular to waveguide axis with a free space wavelength of
.lambda..sub.0 =40 mm. at 7.5 GHz.
Another embodiment of the train communication system of the present
invention is shown in FIG. 12. In general, in and up travelling
train tracks are laid in parallel to each other, so that a circular
leaky waveguide having two aperture rows for use of the in-and-out
travelling train tracks respectively is installed between the two
tracks and it is used at the same time for the communications of
in-and-out travelling trains.
The circular leaky waveguide suitable for such train communication
system is shown in FIG. 13.
In FIG. 12, 1 denotes a circular leaky waveguide, 20 and 20' are
leaky waves of two directions, 22 and 22' are in-and-out travelling
trains, 5 and 5' are antennas aboard in-and-out travelling trains
and 21 21' are in-and-out railroad tracks.
In FIG. 13, 1 denotes a circular leaky waveguide, 2 denotes leakage
apertures of two rows for the in track and two rows for the out
track and 3 is the outer jacket of the circular leaky
waveguide.
Let us consider the relation of the leaky wave and the
apertures.
FIG. 14a shows a sectional view of a circular leaky waveguide 1
which provides two rows of apertures 2 and 2' for in and out tracks
made at the interval P aforementioned.
Lines drawn in parallel to the in-and-out rows of apertures through
each aperture center make a central angle .phi. of 30.degree. in
the circular waveguide with respect to the horizontal axis h.
FIG. 14 b shows a pattern of radiation of a leaky wave emitted from
the circular leaky waveguide as shown in FIG. 14a. It is noted that
the unwanted vertical lobe appears.
FIG. 15a shows the sectional view of a leaky waveguide 1 which
provides four rows of apertures 2 made at the interval P, two being
for the in track and two for the out track.
In FIG. 15a the parallel centerlines passing between the in rows of
apertures and the out rows of apertures each make a central angle
.alpha. of 30.degree. with respect to the horizontal axis and the
central angle .phi. between each set of two aperture rows for the
in and .phi. for the out rows are both 40.degree..
FIG. 15b shows a pattern of radiation of a leaky wave emitted from
the circular leaky waveguide as shown in FIG. 15a.
It is noted that the unwanted vertical lobe disappears, so that the
radiation of the leaky wave in the direction of the angle .alpha.
is made more effective.
From our experiments, it has been observed that the most suitable
values for these angles for the in and out track system is obtained
within the range .phi.=20.degree.-60.degree., and
.alpha.=0.degree.-40.degree. .
* * * * *