U.S. patent number 3,806,946 [Application Number 05/294,448] was granted by the patent office on 1974-04-23 for travelling wave chain antenna.
Invention is credited to Henry Stefan Tallqvist, Martti Eelis Tiuri, Seppo Ilmari Urpo.
United States Patent |
3,806,946 |
Tiuri , et al. |
April 23, 1974 |
TRAVELLING WAVE CHAIN ANTENNA
Abstract
A travelling wave chain antenna including a ground plane, having
a radiation beam, the direction of which can be varied by altering
the frequency, wherein the antenna consists of four-sided links
made of conducting material and of connection parts between the
links, these being located one after another, either in a straight
row, in such a manner that the connection parts are at right angles
to the longer sides of the links, or in an oblique row, in such a
manner that the connection parts are at an angle to the longer
sides of the links, the center points of the longer sides of the
links being electrically connected to the center point of the
longer side of the following link by means of the connection parts
which are parallel to the shorter sides of the links, and the
antenna being fed from either end by means of a cable, in such a
manner that one conductor is connected to one end of the chain
structure of the antenna and the other conductor is connected to
the ground plane, the end of the antenna opposite the feed point
being either open or loaded with a load impedance connected between
the end of the antenna and the ground plane.
Inventors: |
Tiuri; Martti Eelis (Tapiola,
SF), Urpo; Seppo Ilmari (Karakallio, SF),
Tallqvist; Henry Stefan (Helsinki, SF) |
Family
ID: |
23133472 |
Appl.
No.: |
05/294,448 |
Filed: |
September 28, 1972 |
Current U.S.
Class: |
343/731; 343/846;
343/853 |
Current CPC
Class: |
H01Q
21/12 (20130101) |
Current International
Class: |
H01Q
21/08 (20060101); H01Q 21/12 (20060101); H01q
011/02 () |
Field of
Search: |
;343/792.5,846,897,908,731,853 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lieberman; Eli
Attorney, Agent or Firm: Waters; Eric H.
Claims
What I claim is:
1. A travelling wave chain antenna having a radiation beam, the
direction of hwich can be varied by altering frequency,
comprising:
a. a ground plane;
b. a plurality of four-sided links made of conducting material and
being located in sequence to form a part of a chain structure, said
links including longer and shorter sides;
c. a cable for feeding the antenna from one end, and including a
first conductor connected to one end of the chain structure and a
second conductor connected to the ground plane; and
d. connection parts arranged between the links and electrically
connecting the center points of the longer side of each adjacent
link, said connection parts being parallel to the shorter sides of
the links and arranged in a common plane at least substantially
orthogonal to the ground plane.
2. A chain antenna in accordance with claim 1 wherein the end of
the antenna opposite said one end is open.
3. A chain antenna in accordance with claim 1 comprising a load
impedance and wherein the end of the antenna opposite said one end
is loaded with said load impedance which is connected between the
end of the antenna and the ground plane.
4. A chain antenna in accordance with claim 1 wherein the links are
arranged in a straight row, such that the connection parts are at
right angles to the longer sides of the links.
5. A chain antenna in accordance with claim 1 wherein the links are
arranged in an oblique row such that the connection parts are at an
angle to the longer sides of the links.
6. A chain antenna in accordance with claim 1 wherein the
connection parts are so constructed that the characteristic
impedance of the transmission line formed by the connection parts
and the ground plane is considerably smaller than the
characteristic impedance of the transmission line formed by the
sides of the links and the ground plane.
7. A chain antenna in accordance with claim 1 wherein, at the
middle frequency of the operating range, the electrical length of
the longer sides of the links is approximately one wavelength and
the electrical length of the shorter sides and the connection parts
between the links is approximately 0.25 to 0.75 wavelengths, and
the distance of the chain structure from the ground plane is
constant and approximately 0.1 wavelengths.
8. A chain antenna in accordance with claim 1 wherein the
characteristic impedance of the transmission line formed by the
connection parts between the links and the ground plane is half the
characteristic impedance of the transmission line formed by the
sides of the links and the ground plane.
9. A chain antenna in accordance with claim 1 wherein the radiating
structure, consisting of the links and connection parts between the
links and the ground plane are curved in relation to each
other.
10. A wide band chain antenna in accordance with claim 1 wherein
the lengths of the sides of the four-sided links and of the
connection parts between the links increase sequentially so that
each change in length is approximately 2 percent.
11. A wide band chain antenna in accordance with claim 1 wherein
the shorter sides of the links in the antenna chain and the
connection parts between the links are of length l + l.sub.1 in
every alternate link or link connection, and of length l - l.sub.1
in the other alternate links or link connections, and wherein, at
the middle frequency of the operating range, the longer parts of
the links have a length of approximately 1 wavelength, l having a
length of approximately half a wavelength and l.sub.1 generally
having a length of between 0.05 and 0.40 wavelengths, the larger
value of l.sub.1 giving an antenna of wide bandwidth and the
smaller value giving an antenna of narrower bandwidth.
12. A chain antenna in accordance with claim 1 wherein the links
are parallelograms.
13. A chain antenna in accordance with claim 1 wherein the distance
of the ground plane from the radiating structure increases in such
a manner that the distance is at its smallest at said one end and
at its greatest at the opposite end of the antenna, so that the
distance of the ground plane from the radiating structure can vary
from 0.05 wavelengths to 0.30 wavelengths depending on the total
length of the chain.
14. An antenna array comprising a plurality of chain antennas in
accordance with claim 1 wherein the adjacent antenna chains are
electrically connected to each other at the shorter sides of the
adjacent links so that the characteristic impedance of the
transmission line formed by the common sides of the links and the
ground plane is approximately half the characteristic impedance of
the transmission line formed by the longer sides of the links and
the ground plane and that the said one ends of the parallel chains
are connected to the generator when transmitting or to the receiver
for reception by means of conventional parallel coupling methods
for loads.
15. An antenna array in accordance with claim 14 wherein the
connection parts between the successive and adjacent links are
similar.
16. An antenna array consisting of chain antennas in accordance
with claim 12 wherein elliptical polarization, and its limit cases,
both circular polarization and linear polarization, are achieved
using two said antennas consisting of links of parallelogram shape,
in which the parallelograms are identical and the longer sides of
the parallelograms are parallel to each other, the shorter sides
being approximately perpendicular to each other and the antennas
being mirror images of each other in relation to an axis which is
perpendicular to the longer sides of the parallelograms, these
being parallel to each other, and in which the said one ends of the
antennas are connected to the connection point by means of
transmission lines, one of which includes a phase shift element
which causes a fixed or adjustable phase shift between the parts in
the antenna array having different directions.
17. An antenna array consisting of chain antennas in accordance
with claim 13 wherein elliptical polarization, and its limit cases,
both circular polarizations and linear polarization, are achieved
using two said antennas consisting of links of parallelogram shape,
in which the parallelograms are identical and the longer sides of
the parallelograms are parallel to each other, the shorter sides
being approximately perpendicular to each other and the antennas
being mirror images of each other in relation to an axis which is
perpendicular to the longer sides of the parallelograms, these
being parallel to each other, and in which the said one ends of the
antennas are connected to the connection point by means of
transmission lines, one of which includes a phase shift element
which causes a fixed or adjustable phase shift between the parts in
the antenna array having different directions.
Description
This invention relates to high gain travelling wave antennas having
a ground plane and in which the direction of the radiation beam
generally depends on the frequency.
When a high gain antenna is required, especially in the HF, VHF,
UHF and SHF ranges, dipole arrays are generally used. When the
number of dipoles is large, however, the feed system for the
antenna array becomes extremely complicated and expensive. Also the
band width of the assembly is in general seriously limited by the
feed system. The travelling wave antenna has the advantage of a
simple feed system. One disadvantage of previous antennas of this
type, such as the long-wire antenna, V-antenna and rhombic antenna,
is that the direction of the radiation beam is determined by the
length of the antenna, and therefore the beam from the antenna
cannot be freely directed in the desired direction. Also, in order
to achieve a narrow beam, the length of a long-wire antenna, for
example, must be several wavelengths. The resulting radiation
pattern is finger shaped, or in other words, has several side lobes
in addition to the main beam.
Some of the earlier resonant-type antennas used especially in the
short wave range can be fed at a single point. These include the
Franklin antenna, the Sterba array and the Bruce array (Jasik:
Antenna Engineering Handbook, Chapters 4 and 21 ). As these
antennas are of the resonant type, they operate efficiently only at
one frequency, and generally only as broadside arrays. Because of
the difficulties in controlling the radiation properties of these
antennas, their length is limited, in practice, to a few wave
lengths, and the beam width cannot be greatly reduced.
The wire mesh antenna described by J.D. Kraus (U.S. Pat. No.
3,290,688) consists of a wide network made up of rectangular wire
meshes and fed at a single point. A disadvantage of this antenna is
that it is not power matched. This causes a decrease in gain and an
increase in the back beam due to reflections. The distribution of
the current at the feed in end of the antenna is only good when
operating at the middle frequency, and, in addition, the antenna
cannot be used with circular polarization.
An object of the antenna provided in accordance with the invention
is to eliminate the aforementioned disadvantages. it is
characteristic to the invention that the antenna is a travelling
wave, chain shaped antenna located above a ground plate, the
radiation properties of which can easily be controlled. The
structure of the antenna is simple and it requires only one feed
point. By varying the frequency, the radiation beam of the antenna
can be rotated over a large area. A high gain can be achieved with
this antenna if required, and also a narrow beam, without the
occurrence of strong, interfering side lobes. The antenna can
easily be used as an element in large antenna arrays, and can be
used both for the transmission and reception of linear or circular
polarization.
The invention is described in detail in the following with
reference to the attached drawing in which:
FIG. 1 shows a plan view of the basic arrangement of the
antenna;
FIG. 2 shows a side view of the basic arrangement of the
antenna;
FIG. 3 shows an antenna having parallel-sided links;
FIG. 4 shows an antenna in which the distance from the ground plane
varies continuously;
FIG. 5 shows an antenna having a radiation structure of increasing
dimensions;
FIG. 6 shows an antenna in which alternate links are of equal
size;
FIG. 7 shows a parallel connection of two chain antennas;
FIG. 8 shows a parallel connection of two chain antennas; and
FIG. 9 shows a parallel connection of two chain antennas, to obtain
circularly polarized radiation.
As shown in FIGS. 1, 2 and 3, the basic arrangement of the antenna
consists of a chain shaped structure 1 made of electrically
conductive material, located above a ground plane 2 made of
electrically conductive material. The chain is made up of links 3
and connection parts 6 electrically connected to them. The
four-sided links 3, which are rectangular as in FIG. 1 or
parallelograms as in FIG. 3, are arranged in a row in such a manner
that the longer sides 4 of the links are parallel to each other and
the midpoints of all the longer sides lie on the same line. The
midpoints of the longer sides of adjacent links are connected to
each other by means of connection parts 6. Ground 2 is, for
example, a solid metal sheet, a perforated metal sheet, a wire net
having a mesh size of 0.1 wavelengths or a grid made up of wires
located side by side and parallel to parts 5 and 6. Typical
dimensions for the antenna, in wavelengths corresponding to the
middle frequency of the operating range, are as follows: the
shorter sides 5 of the links and the connection parts 6 between the
links, 0.4 wavelengths, the longer sides 4 of the links, one
wavelength, the distance from the ground plane, 0.1 wavelengths and
the total length of the antenna, for example, 10 wavelengths. The
antenna is fed at one end 7 of the chain by means of a coaxial
cable, for example, in such a manner that the center conductor 16
(16') is connected to the chain structure 1 and the outer conductor
15 (15') to the ground plane 2. Feeding can also be effected by
means of a twin conductor structure.
The antenna can also be fed at both ends. Several receivers or
transmitters operating at different frequencies can be connected
simultaneously to the antenna.
Measurements have shown that an antenna constructed in accordance
with the dimensions given above radiates in such a manner that the
maximum beam is directed at a backward elevation angle of .theta. =
75.degree. at the middle frequency. Alteration of the frequency by
.+-. 10 percent causes the rotation of the beam over the range
.theta. = 45.degree. - 85.degree. without the gain of the antenna
changing considerably.
It is essential to the operation of the antenna that there exist a
power wave moving away from the feed point of the antenna. For this
reason, in an ideally constructed antenna, the characteristic
impedance of the transmission line made up of parts 6 and the
ground plane must be half the characteristic impedance of the
transmission line made up of parts 4 and 6 and the ground plane.
This condition can be fulfilled in a manner of ways such as, for
example, by making parts 6 of considerably thicker sections than
parts 4 and 5, by making parts 6 of broad flat sections or of two
or more adjacent wires, by decreasing the distance between the
ground plane and parts 6 or in some other way in which the
inductance of parts 6 is decreased or the capacitance between parts
6 and the ground plane is increased. Tests with various antennas
have shown that the fulfillment of the above-mentioned impedance
condition within an accuracy of approximately 10 percent is
sufficient for the more usual antenna applications. In an antenna
of middle frequency 3 GHz, having parts 4 and 5 made of 0.5 mm
diameter round wire and parts 6 made of 0.5 .times. 10 mm flat
section, a power wave, ideal within the limits of measurement
accuracy, moving away from the feed point has been measured.
When the above-mentioned impedance condition is fulfilled the whole
antenna can be represented as a transmission line with losses,
having a constant impedance and with the size of the losses
depending on the radiation power per unit length of the antenna. If
the impedance condition is not fulfilled, power reflections occur
in the transmission line and the power wave reflected backwards
causes a back beam in the radiation pattern and a decrease in the
main beam. The back beam, caused by the power wave reflected from
the end opposite to the feed end of the antenna can be eliminated
by loading the further end of the antenna. This can be done, for
example, using a termination 17 equal to the characteristic
impedance of the antenna, by placing absorbing material between the
far end of the antenna and the ground plane or by making the
antenna sufficiently long.
The radiation properties of the antenna can be controlled by
varying the distance to the ground plane. An increased distance
gives greater radiation power per unit length of the antenna, and a
smaller distance to the ground plane means lower radiation power
per unit length of the antenna. A chain antenna which is long in
comparison to the wavelength is located near the ground plane such
as, for example, at a distance of 0.05 wavelengths from it, and
thus a high gain and a narrow beam is achieved. A shorter antenna
having a smaller gain and a wider beam is located further away from
the ground plane, for example at a distance of 0.15 wavelengths.
The radiation power per unit length can also be increased by
bending parts 5 and 6 into upward curved shapes in such a fashion
that the middle sections of the parts are further away from the
ground plane than their ends, or by otherwise arranging that parts
5 and 6 are further away from the ground plane than parts 4, over
their whole or partial length.
The distribution of the current in the antenna can be improved, at
the same time increasing the efficiency of the antenna, by
increasing the distance from the ground plane either in steps or
continuously when moving away from the feed point of the antenna. A
side view of such a chain antenna is shown in FIG. 4. The shortest
distance from the ground plane can be approximately 0.05
wavelengths and the maximum distance approximately 0.25
wavelengths. The total length of this type of antenna can be
approximately 20 wavelengths.
The current distribution and the radiation properties of the
antenna can be altered by making the ground plane or the radiating
antenna structure itself, or both of them curved. If, for example,
the ground plane and the antenna are both curved in the same
direction in the plane parallel to the longitudinal axis of the
antenna, and the antenna is on the concave side of the ground, the
beam from the antenna can be angled at the same direction over the
whole range of operating frequency and, if the antenna is on the
convex side of the ground, a circular radiating antenna of large
angular range is achieved.
The geometrical shape of the antenna has proved to be such that the
longer parts 4 of the links cancel each other out almost
completely, and the shorter parts 5 and connection parts 6 function
as efficient radiation elements. From a functional point of view,
parts 4 of the antenna are transmission lines which cause
additional phase shift when moving to the next radiation
element.
The direction of the main beam can be set at the desired angle at
the middle frequency by dimensioning the parts so that parts 4 have
a length of one wavelength and parts 5 and 6 are 0.25 - 0.75
wavelengths. The elevation angle .theta. of the radiation beam,
measured as shown in FIG. 2, is small when the length of radiation
elements 5 and 6 is small, and large when the elements are long.
When parts 5 and 6 have a length of 0.3 wavelengths, for example,
the angle of elevation .theta. is approximately 48.degree., and
when they are 0.4 wavelengths long the angle is 75.degree.. The
mathematical formula which gives the approximate direction of the
beam is
.theta. = arcos [(n.sup.. .lambda. - 0.5.sup.. l.sub.2)/l.sub.1
]
where n is an integer, .lambda. is the wavelength, l.sub.1 is the
length of parts 5 and 6 and l.sub.2 is the lengths of parts 4.
A certain phase shift takes place between two adjacent radiating
elements 5 and 6 due to the physical dimensions of the antenna. The
electrical length between the beginning point of part 5 and the
beginning part of the following part 6 can be increased or
decreased artifically, thus altering the direction of the main beam
at a certain frequency. Conventional electrotechnical methods of
altering the phase shift can be used, such as using a variable
series inductance or a shunt capacitance. The additional phase
shift can also be made adjustable so that the direction of the beam
can be remotely controlled without altering the frequency.
The frequency band of the antenna or, in other words, the frequency
range over which the gain of the antenna is at its maximum can be
increased by increasing the dimensions of links 3 and connection
parts 6 continuously, so that the dimensions at one end of the
antenna are smallest and they increase by approximately 2 percent
in each link and in each intermediate element when moving towards
the other end. Such a structure is shown in FIG. 5.
The range of operating frequencies can also be increased by using
the design shown in FIG. 6. In every second link 3 and intermediate
element 6 the lengths of the parts are 10 percent larger than in
the adjacent links.
The width of the beam of the antenna, in the plane of the
longitudinal antenna axis, can be adjusted by altering the total
length of the antenna. A longer antenna gives a narrower beam than
a short one. The width of the radiation beam in the direction
perpendicular to the longitudinal axis can be narrowed
conventionally, by connecting antennas in parallel to give an
antenna array. The feed points of the various antenna elements are
connected to each other using conventional parallel connecting
methods for loads, for example with cables of equal length.
Parallel antenna elements can also be located quite close to each
other and interconnected electrically as shown in FIG. 7. In this
figure, the elements are connected by means of cables 8 of equal
length to connection point 9, to which point generator 10 or the
receiver is also connected. The parallel links 3 are connected to
each other at points 11 in such a way that the distances between
the parallel parts 5 are such that the characteristic impedance of
the transmission line 12 made up of the parallel parts 5 and the
ground plane 2 is half the characteristic impedance of the
transmission line made up of parts 4 and the ground plane. The
connections and the impedance requirements can also be achieved by
the method shown in FIG. 8, in which the connections are made using
parts 12 which have the same physical shape and dimensions as the
connection parts 6 between the adjacent links.
The antennas shown in FIGS. 1 and 3 operate with linear
polarization. Using two antennas in accordance with FIG. 3, in
which the links 3 are parallelograms, elliptical polarization can
be achieved, and two types of circular polarization as limit cases,
as shown in FIG. 9. With two chain antennas in which the links 3
are parallelograms of similar shape but are inclined in opposing
directions, the feeding points 7 are connected to connection point
9 by means of connection transmission lines 8 so that there is an
additional phase shift element 13 in one of them. Measurements have
shown that the radiation pattern of the antenna array shown in FIG.
9 is in the plane through the mirror image axis 14 of the antenna
and, in general, is elliptically polarized. In the case where the
acute angle .alpha. of the parallelograms is 45.degree. and the
additional phase shift is 13.degree. .+-. 90.degree., the radiation
is circularly polarized. For other values of .alpha. and additional
phase shift, the radiation is elliptically or linearly polarized.
Both of the oblique chains shown in FIG. 9 can also be replaced by
antenna arrays formed, by means of parallel connections, of
corresponding chain antennas.
When pure circular polarization is required, the direction of the
radiation beam must also be taken into account. In general, the
acute angle .alpha. of the parallelograms can be computed from the
formula cot .alpha. = sin .theta., where .theta. is the angle of
elevation of the main radiation beam. For the antenna shown in FIG.
9, for example, the radiating elements 5 and 6 have a length of 0.4
wavelengths, parts 4 have a length of one wavelength, the angle of
elevation .theta. is approximately 70.degree. and the angle of
inclination .alpha. is approximately 47.degree.
According to FIG. 7, the parts 5 are interconnected at the end
points 11 thereof whereas, according to FIG. 8, said parts 5 are
interconnected along their entire length 12.
* * * * *