U.S. patent number 3,713,165 [Application Number 05/077,947] was granted by the patent office on 1973-01-23 for antenna for strip transmission lines.
This patent grant is currently assigned to Telefonaktiebolaget LM Ericsson. Invention is credited to Rolf Ove Esbjorn Lagerlof, Lennart Stig Sjoholm, Thomas Lars-Gustav Svensson.
United States Patent |
3,713,165 |
Lagerlof , et al. |
January 23, 1973 |
ANTENNA FOR STRIP TRANSMISSION LINES
Abstract
An antenna for strip transmission lines has slots of different
lengths in the planar outer conductors. The slots are situated so
that they intersect the planar inner conductor and each slot is
matched for transmission or reception of signals with a certain
frequency by the length of the slot and the distance from the slot
to the end of the planar inner conductor. In one embodiment of the
antenna the end of the planar inner conductor is formed to match
the distances to the individual slots. In another embodiment of the
antenna the slots merge to form only one cut-out in the planar
outer conductor.
Inventors: |
Lagerlof; Rolf Ove Esbjorn
(Vastra Frolunda, SW), Sjoholm; Lennart Stig
(Jakobsberg, SW), Svensson; Thomas Lars-Gustav
(Vaxjo, SW) |
Assignee: |
Telefonaktiebolaget LM Ericsson
(Stockholm, SW)
|
Family
ID: |
20299216 |
Appl.
No.: |
05/077,947 |
Filed: |
October 5, 1970 |
Foreign Application Priority Data
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|
|
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Oct 23, 1969 [SW] |
|
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14507/69 |
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Current U.S.
Class: |
343/771; 333/237;
333/238 |
Current CPC
Class: |
H01Q
13/106 (20130101) |
Current International
Class: |
H01Q
13/10 (20060101); H01q 013/10 () |
Field of
Search: |
;343/767,768,770,771,854,84M |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lieberman; Eli
Claims
We claim:
1. A wideband antenna comprising a strip transmission line having a
planar inner conductor and at least one planar outer conductor
separated from but electromagnetically coupled to each other by a
dielectric medium, said planar inner conductor having a terminating
end and said planar outer conductor being provided with a plurality
of slots whose projections intersect said planar inner conductor,
each of said slots having a length which is a multiple of one half
the wavelength of a different particular signal frequency and the
distance from each slot to the terminating end of said inner
conductor being an odd multiple of a quarter of the wavelength of
the associated particular signal frequency in such a way that the
slots are displaced from the terminating end of said inner
conductor in the order of increasing length with the shortest slot
closest to said terminating end.
2. The antenna according to claim 1 wherein the width of the
exterior part of said planar inner conductor decreases
symmetrically with respect to its central line.
3. A wideband antenna comprising a strip transmission line having a
planar inner conductor and at least one planar outer conductor
separated from but electro-magnetically coupled to each other by a
dielectric medium, said planar inner conductor having a terminating
end and said planar outer conductor being provided with a cut out
formed from a plurality of merged subslots whose projections
intersect said planar inner conductor; each of said subslots having
a length related to a different particular signal frequency and the
distance from each subslot to the terminating end of said inner
conductor being related to an odd multiple of a quarter of the
wavelength of its associated particular signal frequency in such a
way that the subslots are displaced from the terminating end of
said inner conductor in the order of increasing length with the
shortest slot closest to said terminating end.
4. The antenna according to claim 3 in which the ends of adjacent
subslots merge smoothly into the next to form at each end a
continuum of subslot ends.
5. The antenna according to claim 3 in which the adjacent sides of
adjacent slots are of different lengths to give at each end of the
subslots a stepped profile of slot ends.
Description
The present invention relates to an antenna for matching signals
from a transmission line to waves in the free space and vice versa
and comprising one end of a strip transmission line with a planar
inner conductor and one or two planar outer conductors, whereby the
planar inner conductor and the planar outer conductors are
insulated from each other by means of a dielectric.
In the following description consideration will only be given to
the case when the transmission line consists of a planar inner
conductor and two planar outer conductors, one on each side and
situated in parallel with the planar inner conductor. An antenna
according to the invention is, however, in fact also implemented
when the transmission line only has one planar outer conductor.
The characteristic impedance of a strip transmission line is
determined by the breadth of the planar inner conductor and the
distance between the planar outer conductors and the dielectric
constant of the dielectric insulation material. A theoretically
ideal strip transmission line has infinitely large planar
conductors and an infinitely thin planar inner conductor. In
practice the planar inner conductor consists of for example a thin
copper foil. The width of the planar outer conductors are chosen so
that the planar inner conductor can have the same width as the
planar inner conductor in an ideal transmission line. The width of
the planar outer conductors are also chosen so that an extension of
undesired waveguide modes is made impossible. Waveguide modes exist
as soon as the symmetry is interrupted, which is caused for example
by a slot in the planar outer conductor. In order to simplify the
dimensioning of the transmission line it can often be suitable to
surround it by a metal shell, for example of aluminum.
It is known to produce an antenna by making a slot in the one
planar outer conductor near the end of the planar inner conductor
at right angle to the planar inner conductor and symmetrically
thereto. Such an antenna is poorly matched to the transmission
line. It has moreover low efficiency and is moreover narrow-banded.
It is furthermore known to combine a number of slots of different
length according to the logarithmic periodic principle in order to
obtain a wide banded antenna. Such antennae become, however,
proportionately large as a great number of slots are required in
order to obtain a sufficient good impedance matching. This means in
its turn that the use of this antenna as an elementary antenna in
an antenna array with this application is either difficult if not
impossible when these applications require that the distance
between adjacent elementary antennae be about half a wavelength. It
is an object of the invention to provide a slotted antenna which
does not have the above-mentioned drawbacks. The characteristics of
such an antenna are defined in the appended claims.
The invention will be described in greater detail by means of the
accompanying drawing which shows different embodiments of an
antenna according to the invention.
FIG. 1 shows an exploded view of an execution of an antenna
according to the invention.
FIGS. 2 and 3 show several embodiments of a detail of an antenna
according to the invention, and in particular the shape of existing
slot outline.
FIG. 4 shows an embodiment of another detail of an antenna
according to the invention, viz. the end of the planar inner
conductor.
In FIG. 1 a planar inner conductor, denoted by 1, has a terminating
end denoted by 8. This planar, inner conductor 1 is fastened on a
rectangular plate 2 of a dielectric material, for example plastic.
This plate 2 is provided with two outgoing arms 3 which laterally
extend in opposite directions. A further similar plate 4 with
outgoing arms 5 is produced of the same material as the plate 2.
These two plates are fastened to each other so that the planar
inner conductor 1 is between the same. The surface on each plate
remote from and parallel with the planar inner conductor 1 is
covered with a layer of conductive material to form planar outer
conductors 6 and 11 respectively. Thus, inner conductor 1 and outer
conductors 6 and 11 form a strip transmission line.
In the one or both of these planar outer conductors 6, 11 there are
slots 7a-7f positioned to intersect the planar inner conductor 1.
Each such slot, for example slot 7a is designed for transmission or
reception of signals with a certain frequency by making the length
of the slot 7a a multiple of half the wavelength and locating the
slot at a distance from the end line 8 of the planar inner
conductor which is an odd multiple of a quarter of the wavelength,
the wavelength being calculated from the frequency of the signal
with reference to the present transmission medium. The distance to
the end of the planar inner conductor is measured from the point
where the symmetry centerline of the slot crosses the symmetry line
of the conductor and in parallel with the conductor.
A slot made in the planar outer conductor of an antenna in the
above described manner can be adjusted to a certain frequency, but
it will send or receive signals also within a narrow band about
this frequency. Thus an antenna with such a slot is narrow-banded.
By making several slots in the planar outer conductor, each
adjusted to a certain frequency, and if the frequencies to which
the slots are adjusted, are so close to each other that the band
width of the slots in part overlap each other, a wide banded
antenna is obtained. This case is shown in FIG. 1 with further
slots 7b-7f.
FIG. 2a shows how several slots together form only one cut-out with
two opposite step shaped arms. The cut-out has been formed by
laying a number of slots in parallel so close to each other that
there is no outer conductor material between the slots i.e., the
slots merge. The different slots can clearly be interpreted as they
have different lengths and their ends give a step form to two of
the opposite sides of the cut-out. In FIG. 2a a cut-out is shown
consisting of four slots 12a, 12b, 12c and 12d, where the ends of
the longest slot have been denoted reference numeral 12a and the
ends of the shortest slot have been denoted reference numeral 12d.
FIG. 2b and 2c further show two conceivable designs of the cut-out.
These executions are often suitable for mass-produced antennas when
separate slots otherwise will lie very close together.
FIG. 3a shows a variant of a cut-out according to FIG. 2. The
cut-out in FIG. 3 has two sides situated just opposite each other
which are symmetrically decreasing in step form from the central
line and out towards the edges of the sides. In this case the
cut-out can be thought to be formed by a long slot, the ends of
which in FIG. 3a are denoted by 13a, and of two equilength shorter
slots 13b and 13c, one on each side of the long slot 13a . There
are furthermore two even shorter slots 13d and 13e, one on each
side of the other slots. The shortest slots 13d and 13e also have
the same length. Further slots can in the same manner be situated
on each side of the other slots. FIG. 3b, 3c and 3d show further
three conceivable embodiments of the cut-out. The cut-out can also
be designed so that only one end agrees with any of the figures
while the other end is cut, as is shown in FIG. 3d.
In connection with FIG. 3a it can be pointed out that starting from
this point of the form of the cut out a configuration can be built
up of several separated slots, where the longest slot is situated
in the middle and where shorter slots are situated on each side of
this longest slot. Whereby several slots will with it exterior
outline together remind about the cut-out in FIG. 3a.
FIG. 4 shows an example of how the edge of the planar inner
conductor 1 can be designed with a symmetrical decreasing step
form. With such a conductor the distances of the slots to the end
of the conductor are determined so that the first step 9 is counted
as the end of the conductor when the position of the slot is to be
determined which is adapted to the longest wave length.
Consequently the exterior step 10 on the planar inner conductor is
the starting-point for calculation of the distance to the slot
which is adapted to the shortest wavelength. By designing the end
of the conductor in this manner a longer distance is obtained
between the slots with maintained band width. The figure shows a
conductor with three steps, which is adapted to three slots.
Besides the design shown in FIG. 4 the planar inner conductor can,
as is shown in FIG. 1, be squarely cut or it can have a design
analogous to the one end of the cut-out in FIG. 3b, 3c and 3d. A
further alternative is that the planar inner conductor is increased
in step form so that it gradually or continuously becomes broader
towards its end.
An antenna according to the invention is impedance matched to the
transmission line by rotating the slots with respect to the
conductor or by moving them at right angle to the conductor.
However, the slots must not be displaced so much that they do not
intersect the conductor and they must not be rotated to the point
that they are in parallel with the conductor as the antenna then is
quite choked. By combining the methods of rotation and displacement
of the slots a good match between the antenna and the transmission
line is obtained in an easy manner.
An advantage in the construction of an antenna according to the
invention is that it is possible to mass produce the same by photo
engraving techniques. One can start with two plates of a dielectric
material, which plates on both sides are covered with a thin copper
foil. The copper is removed from one side of one plate while on one
side of the other plate the planar inner conductor is engraved. The
plates are put together, so that the sides which are still
completely covered by copper will be directed outwards. These outer
sides constitute the planar outer conductors and in the one or both
of these planar outer conductors the slots are engraved. Of course
one can start with one plate with both sides covered with copper
and one plate with only one side covered with copper.
As an example of the dimensioning of an antenna consider one built
up according to FIG. 1, but provided with 11 slots. In such an
antenna the distance from the central 6 slot to the end of the
planar inner conductor is about 15 millimeters, the length of the
longest slot about 12.5 millimeters and the length of the shortest
slot about 10.5 millimeters. The width of the slots is about 0.1
millimeters and the distance between them is 0.2 millimeters. Such
an antenna has, at a standing wave ratio of better than 2, a
frequency range covering 9.5 - 12 GHz.
* * * * *