Note: Descriptions are shown in the official language in which they were submitted.
9U~5
1 The present invention relates to antennas, and more
2 particularly to an electronically sc~nned antenna sys~em
3 havlng a linear array of endfire elements. An endfire
4 elenent is deCi~ed as an elemer whose maximum ~ain is
obtained along the element axis.
S Electronically scanned lil1ear arrays of simple
- elements are well known. Such arrays are generally
8 character zed by relatively low gain, and a broad
9 elevation patter~. Arrays of endfire elements in which
scanning is accomplished mechanically by rotating the
11 entlre ar ay are also known. These arrays are unsatisfactory
12 when conform~l mounting in the plane of the array is required,
13 e.g., on or within airfoil surfaces (wings and horizontal
14 stabilizer) of an aircraft.
Various antenna element configurations are known.
16 United States Patent 2,236,333 (Beck et al.) discloses a
17 broad bandwlth endfire antenna. United States Patent
18 3,182,330 (Blume) discloses an antenna array having non-
19 unirorm spacing of the individual elements. United States
Patent 2,425,887 (Lindenblad) discloses an endfire antel1na
21 in which all t~e elements are energized with equal voltages
22 in proper ph2se. United States Patent 3,258,774 (Kinsey)
23` discloses a series-fed phased antenna array. See also
24 United States Patent 3,509,577 (Kinsey). United-States
Patent 2,4l9,502 (Kandoian) discloses a binomial array
26 for producing a clover leaf pattern having highly directive
27 properties. A conventlonal Yagi antenna is referenced
- 2 -
~ . . ~
~79~S~i
in United States Patent 3,466,655 (Mayes et al.).
Moreover, generally in known antenna array
constructions mu-tual coupling is regarded as detrimental
and means are taken to minimize its effect. In contrast
the present invention utilizes mutual coupling to enhance
antenna performance.
Endfire elements are known to produce high
density with narrow patterns in both planes (azimuth and
elevation), and are therefore, according to conventional
practice, considered unsuitable forwide angle electronic
scanning when multiple elements are arrayed. (The scan
angle limits being established by the width of the in-
array element pattern.) In contrast with conventional
practice, the present invention advantageously utilizes
arrayed multiple elements for wide angle scanning by
employing mutual coupling between the elements to broaden
the endfire element pattern in the plane in which
electronic scanning is desiredO
The present invention provides an antenna having
a linear array of endfire elements, comprising: a
plurality of laterally spaced endfire elements, said endfire
elements being spaced from about 0.3 A to 0.9 ~ apart
to enhance the effects of mutual coupling therebetween to
broaden the element pattern in the plane of the array.
5S
From another aspect, the present invention
provides an antenna system for conformal mounting on an
aircraft for generating an electronically scanned main
radiation lobe comprising: (a) a linear array of
Yagi antennas which are laterally spaced from one another
a distance of about 0.3 A to 0.9 A center to center,
each of said Yagi antennas including a driven element,
a reflector member and a director member, each of
which having a length less than the spacing between
each adjacent Yagi antenna, each of said Yagi antennas
being operative to radiate: (i) free space beam widths
Bx and By in the coordinate X and Y planes, respectively,
the values of Bx and By being substantially less than
90 ; and (ii) free space maximum gain in the direction
of the lengths of said Yagi antennas; and (b) means
for scanning the antenna sys-tem mai.n lobe in the X plane
ovèr an angle A substantially greater than Bx, while at
the same time maintaining a system main lobe beam width
in the Y plane which approximates By, said scan angle A
being able to be broadened to greater than 90 as a result
of enhanced mutual coupling between said Yagi antennas.
~79(~5~
,
"Electronic scanniny" as the term is used herein
entails adjustments in the excita-tion coefficients
(e.g., phase and amplitude) of the elements in the array
in accordance with the direction in which the formation
of a beam is desired.
It is well known to those skilled in the art
that the beam of an antenna points in a direction tha-t is
normal to the phase front. In phased arrays the phase
front is adjusted to steer the beam by individual control
of the phase excitation of each radiating element. Phase
shifters are electronically actuated to permit rapid
scanning and are adjusted in phase to a value between
0 and 2 ~ radians. While this method of electronic
scanning is perhaps the most commonly used, other means
may be employed to effect the same changes in the phase
front of the array to produce steerage of the beam.
Control of the excitation coefficients of the` elements
of the array is commonly known as "antenna feed", and
includes all means for independently or dependently
controlling the amplitude and phase of the signals to
or from the indivudual elements of the antenna array, and
dividing or combining means therefore.
~7~3~55
1 The present invention is ~llustrated ln the
2 accompanying drawings, in which: -
3 FI~JRE 1 is a top plan view of a linear array
of endfire elements according to the present invention;
FIGURE 2 is a perspective view of a Yagi
S endfire element for the llnear array of the present
7 invention;
8 FIGURE 3 is a top plan of a linear array of
9 Yagi endfire elements of the type shown in Fig. 2 in
which all the endfire elements have a co~non reflector;
11 FIGURE 4 is a top plan vlew of a linear array
12 of endfire elements similar to Fig. 3 being scanned at
13 an angle ~ ; and
14 FIGURE 5 is a perspective view of an aircraft
with parts broken away to indicate the mounting thereon
16 of linear arrays of endfire elements in accordance with
17 the present invention.
18 Referring to Fig. 1, an antenna according to the
19 present invention is generally illustrated at 10. It
should be understooc that the antenna 10 may be used with
21 acoustlc as well as electromagnetic waves, although in the
22 description the antenna will be described with reference to
23 electromagnetic waves. The antenna 10 includes a linear
24 array of endfire elements 12 electronically coupled to
an element driving network 14 which is conventlonally
26 known as an antenna feed.
27
11'79Q5S
1 Each endfire element 12 is laterally spaced a
2 distance (D) between abou~ 0.3 ~ and about 0.9 h apart~
preferably about 0.55 ~ apart (center-to-center) to
4 enhance the effects of mut~al coupling between the elements
12, resulting in a broadened element pattern of the mainbeam
in the plane of the array, see the dotted lines and arrows
7 in Fig. 1. The length (L) of each individual element 12
8 is approximately 1.25 ~ .
9 Referring to Fig. 2, a Yagi endfire element 12A
for use in the array of the present invention is shown. As
11 is well known, a Yagi endfire arLay includes at least two
12 parasitic elements in addit;on to the driven element. The
13 Yagi endfire element 12A includes six conductive elements 16,
-14 18, 20, 22~ 24 and 26. Such a multiparasitic array is known
1~ as a 6-element beam. Each element has a diameter of
16 approximately 0.01 ~ and a length of approximately 0.5 ~ .
17 The six elements 16, 18, 20, 22, 24 and 26 are
18 positioned in spaced parallel relationship along the same
19 line of sight (transverse axis) with the spacing between
adjacent elements being approximately .25 ~ . The six
21 elements lG, 18, 20, 22, 24, and 26 are supported on a pair
12 of non-conductive Plexiglas- suppcrts 28 and 30, e.g., by
23 inserting the elements 16~ 18, 20, 22, 24, and 26 into
24 mating holes in the Plexiglass suport. The supports 28 and
30 electrically insulate the elements 16, 18, 20, 22, 24 and
26 26 from one anotner, and advantageously are substantially
27 invisible to the resulting electromagnetic wavesf
~ f ~ s /~a~ f~ rk .
-
~7~ ~5 S
1 Element 16 is the reflector element, element 18 the
2 driven element, and elements 20, 22, 24 and 26 the director
3 elements. A coa~ial cable 32 is electrically coupled to
4 the driven element 18 for providing a signal thereto.
The reflector 16 and directors 20-26 interact in a conventional
S manner to provide increased gain and unidirectivity to the
7 radiated signal pattern. The free-space half-~ower beam-
8 widths of element 12A is 42 in the E plane and 48 in the
9 H plane.
Referring to Flg. 3, ten endfire elements 12A-J
11 of the type shown in Fig. 2 are arranged in a linear array
12 lOA. The endfire elements 12A-J have a common reflector
13 16A and are closely spaced laterally a distance of between
14 about 0.3 ~ and about 0.9 ~ apart, preferably about
0.55 ~ apart (center-to-center), to increase thè effects
16 of mutual~coupling therebetween~ With such an arrangement,
17 the in-array pattern, i.e., the angle over whlch the antenna
18 mainlobe can be electronically-scanned increases from 42
19 for the single endfire element 12A of Fig. 2, see the dotted
lines and arrows of Fig, 2, to greater than 90 in the
21 array lOA. The narrow H plane pattern of 48 for the
22 single endfire element 12A is maintained in the array lOA~
23 Thus, the effect of closely spacing the endfire elements 12A
24 in the linear array 10 is to broaden the element pattern in the
plane of the array lOA (E plane) while preserving the narrow
26 H plane pattern.
27
~- ~
~ .7~3()SS
.,
1 The broadened E-plane pattern o the in-array
2 endfire element may be demonstrated as follows: The elements
3 12A-D and 12F-J have individual terminating impedances 34A-D
4 and 34F-J coupled to ground 36 in the array lOA. The
terminating impedances 34A-D and 34F-J are chosen to match
S the antenna driving point impedance to an antenna scan angle
7 o~ 0 in the E-plane. In ~he embodiment illustrated in Fig. 3,
8 the terminating impedances 34A-D and 34F-J are 50 ohms.
9 Element 12E is monitored by meter 38 which measures the power
received by element 12E when ~he array lOA is used as a
11 receiving device to receive signals transmitted by a
12 radiating device (not shown) positioned at sufficient
13 distance fro~ the array lOA so as to be in the far field
14 of the array lOA. As the array lOA is rotated in angle
with respect to the radiating device, the power measured
16 in meter ~8 will vary in proportion to the in-array element
l? pattern of element 12E. This method of pattern measurement
18 is well known in the art. Moreover, it is also well known
19 in the art that the in-array element pattern measured in
this manner is approximately proportional to the gain of
21 the array lOA as a function of angle when the outputs
22 o all of the elements L2A-J are utilized to io m a beam.
25 11
27
_ g _
~1'7911~55
.,
1 Wlth reference to Fig. 4, the array lOA operates
2 as follows: A feed means (not shown) applies transmission
3 signals to a combining/dividing network 40 which splits
4 the signals for transmission by the individual elements
42 of the array 44 (N elements are shown). N phase shifters
46 shift the phase of the signals in accordance with the
7 direction in which a beam is desired. In applications
where une~ual amplitudes are desired for each antenna
9 element to provide lower antenna sidelobes (co~monly known
as amplitude taper), the combining/dividing network 48
11 advantageously provides such a distribution.
12 The antenna array lOA with its feed is linear
13 passive and ~ilateral and is subject to the law of
14 reciprocity so that when it is used in the receiving
mode its characteristics are unaltered.
16 Referring to Fig, 5, an aircraft 48 is illustrated
17 with antenna arrays 10 B, C and D in accordance with the
18 present invention positioned in the wing leading edges
19 50 and 52 and in the horizontal stabilizer 54. With
this arrangement 360 azimuthal coverage ls obtained by
21 electronically scanning the arrays lOB-D and conventional
22 side-looking antennas 56 and 58 mounted on opposite sides
23 of the ~uselage 60. Advantageously, such an arrangement
t4 avoids the need for a large dome mounted on the fuselage
60 which must be mechanically rotated to provide the same
26 360 azimuthal coverage.
27
~l1'7~)055
1 It should be apparent to those skilled in the
2 art that various modifications may be made in the present
3 invention without departing from the spirit and scope
4 thereof, as described in the specification and defined
6 ln t appended claims.
9 .
12
13 . ~ .
14
17
18 .
19
~0
24 .
27
__ __ _, _ _ __ __
