U.S. patent number 3,696,433 [Application Number 05/055,848] was granted by the patent office on 1972-10-03 for resonant slot antenna structure.
This patent grant is currently assigned to Teledyne Ryan Aeronautical Company. Invention is credited to Derling G. Killion, Kent B. Roberts.
United States Patent |
3,696,433 |
Killion , et al. |
October 3, 1972 |
RESONANT SLOT ANTENNA STRUCTURE
Abstract
A resonant slot antenna composed of one or more elongated
coaxial type radiating elements, each having an inner conductor
supported within an outer conductor, the outer conductor having
longitudinally spaced slots which are shaped to provide phase
reversal between slots and spaced to avoid mutual coupling. This
permits a coaxial or strip line antenna to be made with the
desirable characteristics of a waveguide type. The antenna is
particularly adaptable to construction by printed circuit
techniques, with the slots and conductor elements etched in
conductive plating on dielectric supporting material, making it
possible to construct unitary arrays of multiple elements.
Inventors: |
Killion; Derling G. (San Diego,
CA), Roberts; Kent B. (El Cajon, CA) |
Assignee: |
Teledyne Ryan Aeronautical
Company (San Diego, CA)
|
Family
ID: |
22000548 |
Appl.
No.: |
05/055,848 |
Filed: |
July 17, 1970 |
Current U.S.
Class: |
343/770; 333/237;
333/238; 333/243; 343/771 |
Current CPC
Class: |
H01Q
13/16 (20130101); H01Q 13/22 (20130101); H01Q
13/10 (20130101) |
Current International
Class: |
H01Q
13/16 (20060101); H01Q 13/10 (20060101); H01g
013/10 () |
Field of
Search: |
;343/770,771,767-768 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Saalbach; Herman Karl
Assistant Examiner: Nussbaum; Marvin
Claims
Having described our invention, we now claim:
1. A resonant slot antenna structure comprising,
at least one elongated antenna element having a longitudinal inner
conductor,
a longitudinal outer conductor at least partially surrounding said
inner conductor,
supporting means for holding said inner conductor in spaced
relation to and coextensive with said outer conductor,
longitudinally spaced radiating slots in said outer conductor, each
slot having at least one longitudinally extending arm and a
transverse coupling portion at one end of the arm,
said support means is a dielectric material,
said slots are substantially Z shaped, with a pair of opposed arms
interconnected by said coupling portions, and alternate slots have
the arms thereof transposed.
2. A resonant slot antenna structure comprising,
at least one elongated antenna element having a longitudinal inner
conductor,
a longitudinal outer conductor at least partially surrounding said
inner conductor,
supporting means for holding said inner conductor in spaced
relation to and coextensive with said outer conductor,
longitudinally spaced radiating slots in said outer conductor, each
slot having at least one longitudinally extending arm and a
transverse coupling portion at one end of the arm,
said support means is a dielectric material,
and said slots are substantially L shaped, with the arm thereof
adjacent one side of the antenna element.
3. A resonant slot antenna structure comprising,
at least one elongated antenna element having a longitudinal inner
conductor,
a longitudinal outer conductor at least partially surrounding said
inner conductor,
supporting means for holding said inner conductor in spaced
relation to and coextensive with said outer conductor,
longitudinally spaced radiating slots in said outer conductor, each
slot having at least one longitudinally extending arm and a
transverse coupling portion at one end of the arm,
said support means is a dielectric material,
and a feed element having an array of antenna elements extending
therefrom in spaced parallel relation, an inner feed conductor in
said feed element coupled to the inner conductor of each antenna
element, the slots in alternate antenna elements having their arms
transposed relatived to the slots in adjacent antenna elements.
4. An antenna structure according to claim 2, wherein alternate
slots are transposed with the arms thereof adjacent the other side
of the antenna element.
5. An antenna structure according to claim 3, wherein said
dielectric material is a unitary structural support in said feed
element and antenna elements.
6. An antenna structure according to claim 5, wherein said outer
conductor is a conductive plating on the outer surfaces of said
dielectric material.
7. An antenna structure according to claim 5, wherein said
dielectric material is in two similar array shaped portions
separated on a common flat plane of the antenna elements, said feed
conductor and inner conductors comprising a unitary plated array on
one of said dielectric portions.
8. An antenna structure according to claim 3, wherein said
dielectric material is a unitary structural supporting member in
and between said feed element and antenna elements, said dielectric
material having elongated slotted openings therethrough, between
and parallel to said antenna elements, said outer conductor
comprising a conductive plating on the outer surfaces of the
dielectric material and on the surfaces of said slotted openings.
Description
BACKGROUND OF THE INVENTION
Waveguide type array antennas with spaced slots have highly
directional and controllable beam patterns, the spacing and phasing
of the slots determining the particular radiation pattern. Slots
with resonant impedance are preferable for efficiency. Slots have
been incorporated in coaxial transmission lines but, since the slot
should have a length of approximately one half wavelength of the
radiation, circumferential slots are not practical in small sized
coaxial lines. It is also difficult to obtain maximum radiation
orthogonal to the axis of the antenna element due to slot phasing
with circumferential slots.
SUMMARY OF THE INVENTION
The antenna structure described herein has an inner conductive
strip supported by a dielectric material within an outer tubular
conductor, which may be of rectangular, circular, or other cross
section which will support the TEM mode of the radiation. Slots are
made in the outer conductor, the slots being of Z, L or U shape
which causes phase reversal between slots. The slots can thus be
spaced at other than multiples of the half wavelength, the
effective slot length achieved by the special shaping allowing
resonant slots to be incorporated in an element of small cross
sectional size.
The slots of Z, L or U shape are arranged with arms extending along
the length of the coaxial element and a coupling portion transverse
or circumferential to the element. For maximum efficiency and to
achieve a standing wave array, the mean slot length necessary for
resonance is slightly greater than one-half wavelength, but may be
longer. The amount of power radiated from each slot is determined
by the area of the coupling portion. With the Z and L shaped slots,
phase reversal is obtained by transposing the arms of adjacent
slots, the U shaped slot having opposed phasing in itself.
The structure is particularly adaptable to printed circuit
techniques, the slots and conductors being etched in conductive
plating on dielectric substrate material, which forms the basic
supporting structure of the antenna. Multiple element arrays can
thus be made in unitary form in any desired configuration, with
feed connections, impedance matching and phasing elements all
incorporated in a printed circuit type layout. This results in a
considerable reduction in cost compared to the usual assembly
techniques, and permits the construction of a compact antenna
without separate joints and associated fittings.
An object of this invention, therefore, is to provide a new and
improved resonant slot antenna.
Another object of this invention is to provide antenna structure
which enables a resonant slot configuration to be incorporated in a
coaxial transmission line of small cross sectional size.
A further object of this invention is to provide a resonant slot
antenna which is adapted to construction by printed circuit
techniques.
Other objects and many advantages of this invention will become
more apparent upon a reading of the following detailed description
and an examination of the drawings, wherein like reference numerals
designate like parts throughout and in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view of a single coaxial element, with portions cut
away.
FIG. 2 is a perspective view of a portion of an element with a Z
shaped slot, and showing the phasing.
FIG. 3 is a similar view showing the Z shaped slot transposed and
the phase reversed.
FIG. 4 is a similar view showing the phasing of an L shaped
slot.
FIG. 5 is a further similar view showing a U shaped slot.
FIG. 6 is a top plan view of an element with three slot
configurations to show typical proportioning.
FIG. 7 is a perspective view of a portion of a cylindrical coaxial
element with a Z shaped slot.
FIG. 8 is a perspective view of a portion of coaxial strip
line.
FIG. 9 is a perspective view showing the Z shaped slot in a
collapsible antenna element.
FIG. 10 is a perspective view of a coaxial element made by printed
circuit technique.
FIG. 11 is a top plan view, partially cut away, of an array using
the structure of FIG. 10.
FIG. 12 is a top plan view of another type of unitary array.
FIG. 13 is a sectional view taken on line 13--13 of FIG. 12.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The basic antenna element 10, shown in FIG. 1, comprises a tubular
outer conductor 12 of rectangular cross section, with a coextensive
inner conductor 14 supported therein by dielectric material 16.
Part or all of the element may be enclosed in a protective plastic
sheath 18 of suitable dielectric quality. At one end of the element
is a coaxial feed connector 20 and at the other end is a shorting
plate 22, making a complete antenna element. In one wide face of
the outer conductor 12 are longitudinally spaced slots 24, which in
this case are Z shaped with arms 26 extending in opposite
directions parallel to the length of the element and connected by a
transverse coupling portion 28.
As shown, the inner conductor 14 is a flat metal strip of copper or
the like, the outer conductor being a copper tube, which may be
rigid, or in the form of plating on the dielectric material, or
even a braided sheath. One particularly suitable dielectric
material is Teflon, reinforced with glass cloth, but other
materials may be used.
For maximum efficiency it is necessary for each slot to have a
resonant impedance. This is accomplished by making the mean slot
length, indicated by the broken center line 30 in FIG. 6, at least
one-half wavelength of the radiation for which the antenna is
designed. The amount of power radiated by the slot is determined by
the area of the coupling portion 28, within the broken outline 32.
The coupling portion is not limited to the rectangular shape shown,
but it is desirable to have the medial length thereof substantially
shorter than the length of arms 26, so that the majority of
radiation is from the arms, in order to polarize the radiation
properly.
In FIG. 2, the instantaneous phase of the voltage across the slot
24 is represented by arrows 34, and the phase of the instantaneous
radiated electrical field by arrows 36. By transposing the arms of
the slot, as exemplified in slot 24A in FIG. 3, the instantaneous
phase of voltage across the slot is reversed, as shown by arrows
34A. This results in a phase reversal of the electrical, or E
field, shown by arrows 36A.
The phasing can be controlled in a similar manner by using an L
shaped slot 38, with a single longitudinal arm 40 and a transverse
coupling portion 42, as in FIG. 4. Arrows 44 indicate the
instantaneous phase of voltage across the L shaped slot, and arrows
46 show the instantaneous phase of the E field. By transposing the
L shaped slot, the phasing would be reversed in a manner similar to
that shown in FIG. 3. For reference, the mean length 48 and
coupling area 50 of the L shaped slot are indicated in FIG. 6.
The U shaped slot 52, shown in FIGS. 5 and 6, has a pair of
adjacent parallel arms 54 and 56, coupled at one end by a
transverse coupling portion 58. The mean length 60 includes both
arms and the coupling portion and the coupling area is indicated at
62. In FIG. 5, the arrows 64 show the instantaneous phase of the
voltage across the slot, the polarity in the two arms 54 and 56
being opposed. This provides oppositely phased E field radiation
around the two arms, indicated by arrows 66 and 68. The resultant
radiation is effectively nulled at the axis between the arms, but
has broad beam width on each side.
In FIG. 7, a Z shaped slot 70 is shown applied to a cylindrical
coaxial element 72, with arms 74 extending axially and the coupling
portion 76 circumferential in the outer conductor 78. A further
configuration, shown in FIG. 8, is a strip line element 80, with a
thin flat rectangular outer conductor 82 in which a Z shaped slot
84 is formed.
The waveguide type element 86, shown in FIG. 9 is fully described
in copending application, Ser. No. 684,907, filed Nov. 20, 1967 and
entitled "An Extendable Radio Frequency Transmission Line and
Antenna Structure." The cylindrical outer conductor 88 has a Z
shaped slot 90, with axially extending arms 92 and a
circumferential coupling portion 94.
It should be understood that any of the slot shapes may be used in
any of the antenna element structures shown, and in any suitable
number and spacing, according to the beam pattern and performance
required. Different slot shapes may be combined in the same antenna
for some purposes. In each instance, the provision for phase
reversal between adjacent slots makes it unnecessary to have the
slot spacing at multiples of a half wavelength. As a result the
slots can be extended axially by means of the arm portions, to
obtain a large radiation area with minimum transverse or
circumferential extension of the slots. Thus the various slot
arrangements can be incorporated into antenna elements of small
cross section, with efficiency comparable to much larger waveguide
type structures.
The small size in which an efficient antenna can be built, makes
the structure adaptable to printed circuit techniques, a typical
arrangement being shown in FIG. 10. In this structure, an elongated
dielectric element 96 of rectangular cross section has an outer
plating 98, of copper or the like, on one wide flat surface and an
inner strip conductor 100 on the opposite surface. The strip
conductor can be etched by conventional printed circuit methods
from a plating on the entire surface of the element 96,
facilitating the manufacture from stock material plated on opposite
surfaces. A second similar dielectric element 102 has an outer
plating 104 on one flat surface and is bonded to the other
dielectric element 96 by suitable low loss adhesive 106, with the
strip conductor 100 sandwiched between the dielectric elements. The
unplated sides of the assembly are covered by conductive side
plates 108, or may be plated over by conventional methods to form a
complete outer conductor around the element. The radiating slots
are formed in the outer plating 104 by etching, or similar means.
In this form L shaped slots 110 and 110A are shown in transposed
pairs as an example, but any other slot arrangement is
applicable.
The printed circuit technique makes it practical to construct a
unitary, multiple element array of any desired configuration, in
flat form or curved to fit a supporting or surrounding surface,
such as the skin of an aircraft or space vehicle. A typical array,
shown in FIG. 11, has a plurality of spaced parallel radiating
elements 112, 114 and 116 extending from a common feed element 118.
Each radiating element has an inner strip conductor 120, embedded
or sandwiched between two similar array shaped pieces of dielectric
material 122, separated on a flat common plane of the array,
similar to the basic structure of FIG. 10. A feed conductor 124 in
feed element 118 is coupled to each inner conductor 120 in a
unitary printed circuit type combination. The entire outer surface
of the array is plated over to form an integral outer conductor
126, in a common surface of which the slots 128 and 128A are made.
The number spacing and type of slots, and the number and spacing of
the radiating elements are arranged to suit the specific beam
pattern desired. With resonant slots the array will have efficient
standing wave characteristics. Impedance and phase matching means
can be incorporated in the feed conductor 124 as part of the basic
assembly, the nature and function of such means being well
known.
It should be noted that, with proper spacing of the radiating
elements, two such arrays could be interfitted to form a continuous
planar array.
A further form of multiple element array, with inherent structural
strength, is shown in FIGS. 12 and 13. A plurality of spaced
parallel inner strip conductors 130 are sandwiched between
dielectric elements 132 and 134, and extend from a common feed
conductor 136 with a suitable feed connection 138. Impedance
transformers and other such means may be incorporated into the feed
elements as necessary. Between and parallel to the strip conductors
130 are elongated slotted openings 140 completely through the
array, the openings being separated by pillar portions 142 of the
dielectric material. The structure is thus lightened, without
unduly reducing the structural strength. When the outer surface of
the array is plated over, the interior of each opening 140 will
receive a wall plating 144, effectively forming outer conductors
about the individual inner conductors 130 and making spaced
radiating elements 146 within the array.
Each radiating element has slots in a common surface, the
arrangement shown utilizing Z shaped slots 148 and 148A along each
element, in the outer conductor plating 150. In one element the
slots have one orientation and in the next adjacent element the
orientation is reversed to obtain the desired phase reversal.
It will be evident that complex arrays can be made by low cost and
established techniques and with consistent accuracy. The resultant
structure is light weight, rigid and, with a dielectric material
such as the glass fiber reinforced Teflon mentioned, or a
comparable material, is more resistant to damage than a typical
thin wall waveguide assembly. While the conductive elements in
FIGS. 10-13 are shown as having substantial thickness, it should be
understood that the actual thickness will be on the order of a few
thousandths of an inch, the dielectric material providing the
structural support.
* * * * *