U.S. patent number 3,747,102 [Application Number 05/208,301] was granted by the patent office on 1973-07-17 for electronically modulated tacan antenna.
Invention is credited to Herbert Warren Cooper.
United States Patent |
3,747,102 |
Cooper |
July 17, 1973 |
ELECTRONICALLY MODULATED TACAN ANTENNA
Abstract
A TACAN antenna array comprising a central radiating element,
providing carrier frequency f.sub.c radiation omnidirectionally in
the azimuth plane, which is surrounded by two or more concentric
arrays of 15Hz and 135Hz modulation radiating elements. The first
concentric array is preferably comprised of 4 elements used to
provide a f.sub.c .+-. 15Hz modulation and is comprised of two
orthogonally disposed antiphased subarrays which are excited with
the suppressed carrier sideband energy of a 15Hz modulated carrier
frequency f.sub.c with the two orthogonally arranged subarrays
being excited in phase quadrature with one another. The second
concentric array is preferably comprised of 36 radiating elements
divided into two subarrays of 18 elements each, which are excited
with 135Hz modulated suppressed carrier f.sub.c sideband energy.
The elements of the two 18 element subarrays are alternately
dispersed in a circular pattern. The two subarrays respectively are
fed in phase quadrature with adjacent elements of each subarray
being fed in antiphase relationship so that as the circumference is
traversed a +l, +j, -l, -j phase relationship exists in consecutive
sets of four elements around the 36 radiating elements.
Inventors: |
Cooper; Herbert Warren
(Hyattsville, MD) |
Family
ID: |
22774074 |
Appl.
No.: |
05/208,301 |
Filed: |
December 15, 1971 |
Current U.S.
Class: |
342/399 |
Current CPC
Class: |
G01S
1/02 (20130101) |
Current International
Class: |
G01S
1/00 (20060101); G01S 1/02 (20060101); G01s
001/46 () |
Field of
Search: |
;343/16R,1SA,1CS,854 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Stahl; Robert F.
Assistant Examiner: McCabe; Denis H.
Claims
I claim as my invention:
1. An electronically modulated TACAN antenna system for providing a
rotating radiation pattern, comprising in combination:
a TACAN transmitter generating and providing at least three output
signals having frequencies of f.sub.c, f.sub.c .+-. 15Hz, and
f.sub.c .+-. 135Hz, respectively, where f.sub.c is the carrier
frequency;
central radiation means coupled to said f.sub.c output signal and
providing an omnidirectional radiation pattern in the azimuth plane
thereby;
an array of at least four elements containg two pairs of mutually
orthogonal active radiation elements centrally located with respect
to said central radiation means;
circuit means coupling said array of at least four radiation
elements to said f.sub.c .+-. 15Hz output signal and including
circuit means feeding said f.sub.c .+-. 15Hz output signal to said
at least four radiation elements with respective f.sub.c .+-. 15Hz
output signals phased +1, +j, -1, and -j, consecutively where +1
corresponds to 0.degree. phase shift, +j corresponds to 90.degree.
phase shift, -1 corresponds to 180.degree. phase shift and -j
corresponds to 270.degree. phase shift whereby said +1 phase and -1
phase excited radiation elements are located on a common axis on
opposite sides of said central radiation means and said +j phase
and -j phase excited radiation elements are located on a common
orthogonal axis on opposite sides of said central radiation
means;
another array of 4 n radiation elements, where n>1, circularly
arranged concentrically with respect to said central radiation
means; and
circuit means coupling said circular array of 4n radiation elements
to said f.sub.c .+-. 135Hz output signal and including circuit
means feeding said f.sub.c .+-. 135Hz output signal to repetitive
sets of four radiation elements each with respective f.sub.c .+-.
135Hz output signals phased +1, +j, -1, and -j, consecutively
around the entire array.
2. An antenna system according to claim 1 wherein n is equal to 9
whereby the phase of f.sub.c .+-. 135Hz signal goes through a
360.degree. linear phase variation for each 40.degree. of direction
angle in azimuth.
3. The apparatus as defined in claim 1 wherein said output signals
of f.sub.c .+-. 15Hz and f.sub.c .+-. 135Hz comprise suppressed
carrier sideband signals.
4. The invention as defined by claim 1 wherein said feeding means
for said array of at least four radiation elements includes:
a f.sub.c .+-. 15Hz signal buss;
signal coupling means coupled from said signal buss to a first
radiation element of said four radiation elements and providing the
+1 phase radiation;
signal coupling means including a phase inverter coupled between
said signal buss and a second radiation element, said second
element being located on said common axis with said first radiation
means and providing the -1 phase radiation;
quadrature phase shifter means coupled to said signal buss;
signal coupling means coupled from the output of said quadrature
phase shifter to a third radiation element, said third radiation
element being located on said orthogonal axis and providing the +j
phase radiation; and
signal coupling means including a phase inverter coupled from the
output of said quadrature phase shifter to a fourth radiation
means, said fourth radiation means being located on said orthogonal
axis opposite said third radiation element and providing the -j
radiation.
5. The invention as defined by claim 4 and wherein said feeding
means for each set of 4n radiation elements of said circular array
includes:
a f.sub.c .+-. 135Hz signal buss;
signal coupling means coupling said last recited circuit buss to
the first radiation element of each set of elements and thereby
providing the +1 phase radiation;
signal coupling means including a phase inverter coupling said last
recited circuit buss to the third radiation element of each set of
elements and thereby providing the -1 phase radiation;
a quadrature phase shifter coupled to said last recited circuit
buss;
signal coupling means coupling the output of said quadrature phase
shifter to the second radiation element of each set of elements and
thereby providing the +j phase radiation; and
signal coupling means including a phase inverter coupling the
output of said quadrature phase shifter to the fourth radiation
element of each set of elements and thereby providing the -j phase
radiation.
6. The apparatus as defined in claim 5 wherein said 4n radiation
elements comprise 36 elements.
7. The apparatus as defined in claim 6 wherein said f.sub.c .+-.
15Hz and f.sub.c .+-. 135Hz output signals each comprise suppressed
carrier sideband signals.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronically controlled
antenna system and more particularly to one which is capable of
providing a rotating radiation pattern particularly adapted to
TACAN.
2. Description of the Prior Art
TACAN is a tactical air navigation system which provides bearing
and range information on direct reading instruments located in an
aircraft. The heart of the system lies in the ground beacon antenna
which generates a certain amplitude modulation in space in all
azimuth directions to provide bearing information. Essentially,
this is a shaped beam in the horizontal plane which rotates in this
plane. Course bearing information is generated by a rotating
limacon-shaped pattern which results in a 15Hz amplitude
modulation. Fine bearing information is generated by a nine-lobed
radiation pattern which is superimposed on the limacon pattern. To
provide vertical coverage, the antenna is shaped similar to a
cosecant-squared pattern.
In order to better understand the design of an array for TACAN, an
existing mechanically scanned antenna design and its operation will
be briefly described. The antenna consists of a stationary central
vertically polarized element or array to provide an omnidirectional
pattern in the azimuth plane. This is the only active element in
the antenna. All other elements are parasitically excited. A
rotating subassembly is placed around this stationary central
element or array to distort the omnidirectional pattern into a
scalloped pattern which is shaped to produce two amplitude
modulations when viewed from a distance.
This subassembly consists of two coaxial plastic cylinders or
radomes which are rigidly held to each other and rotated at a
controlled speed of 15Hz. In turn, these coaxial cylinders are
concentric with the inner central feed array which is stationary.
Two biconical horns which are stacked vertically are fastened
between the inner and outer rotating plastic cylinders and thus
rotate with them. These two biconical horns are fed by the
stationary array. The purpose of the horns is to shape the antenna
pattern in the vertical plane. In other words, these horns
determine the shape of the primary radiation pattern in the
vertical plane and so determine the vertical coverage.
The heart of the amplitude modulating mechanism lies in the
inclusion of small parasitic radiators which are fastened to the
two rotating cylinders. Without these parasitic radiators, the
antenna pattern is essentially omnidirectional in the azimuth
plane. A single parasitic reflecting element in the form of fine
wires is cemented on the inner cylinder. By placing these wires in
the electric field radiating from the central stationary array, the
omnidirectional pattern is distorted into a more directional one.
The shape of this distorted pattern is that of a limacon. Next nine
parasitic elements uniformly spaced at 40.degree. intervals are
cemented on the outer rotating cylinder. Thus placed in the
electric field of the dipoles, the azimuth plane pattern is
distorted by the reradiated energy from these plastic wires. With
the absence of parasitic wires on the inner cylinder, the pattern
resulting from the nine parasitics is that of a nine lobed one.
As noted above, these two dielectric cylinders with their parasitic
elements are rotated at the controlled speed of 15Hz. Because of
the radiation pattern distortion, the radiated energy goes through
periodic variations in amplitude when viewed from anywhere in
space. The amplitude variation produced by a single parasitic
element on the inner cylinder can be represented as a sine wave.
Obviously, the frequency of this modulation is 15Hz. The amplitude
variation produced by the nine parasitic elements on the outer
cylinder also produces a sine wave. Because the pattern is nine
lobed, the frequency of this modulation is 9 .times. 15 or 135Hz.
With the simultaneous modulation by both sets of parasitics, the
nine lobed pattern is superimposed on the limacon pattern. The
resultant wave radiated by the antenna thus contains two modulating
frequencies 15Hz and, its ninth harmonic, 135Hz.
These mechanically rotated systems, although simple and reliable,
are bulky, heavy and consume relatively large amounts of primary
power. Because of this, great interest has recently arisen for an
electronically scanned TACAN antenna. Three electronically scanned
TACAN antenna systems are shown and described in the following
patents:
U.S. Pat. No. 3,474,446, L. N. Shestag et al.;
U.S. Pat. No. 3,474,447, L. Melancon; and
U.S. Pat. No. 3,560,978, L. Himmel et al.
SUMMARY
Briefly, the subject invention comprises, inter alia, an
electronically scanned TACAN antenna comprised of a first array
configured as a stationary central element or array which is
excited from a TACAN transmitter with a carrier frequency signal
f.sub.c. A second and third fixed array of n elements and 4n
elements, respectively, are concentrically positioned relative to
the first array. The second array is preferably comprised of four
elements configured as two orthogonally disposed antiphased
subarrays with the subarrays being excited by a f.sub.c .+-. 15Hz
suppressed carrier sideband signal in phase quadrature with one
another. The third array is excited with a f.sub.c .+-. 135Hz
suppressed carrier signal and preferably is comprised of 36
radiating elements. The 36 elements are excited in groups of 18
elements in phase quadrature respectively with adjacent elements of
each group being antiphased with one another. The two groups of
elements are interspersed to provide repeating sets of four
elements, each having relative phases of +1, +j, -1, and -j,
respectively.
BRIEF DESCRIPTION OF THE DRAWING
The DRAWING is an electrical schematic diagram of the preferred
embodiment of the subject invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the DRAWING, reference numeral 10 designates a
central radiating element excited by a carrier frequency signal
f.sub.c coupled thereto from a TACAN transmitter 12. The central
element 10 is comprised of a selected number of vertical elements
forming an array suitable to provide a desired vertical plane
coverage pattern which is omnidirectional in azimuth. An impedance
matching device 14 is shown coupled between the output terminal 16
and the junction 18 for providing a suitable impedance match
between the central element 10 and the TACAN transmitter 12 for
obtaining maximum power transfer.
A second array of at least four active radiating elements,
designated by reference numerals 20.sub.1, 20.sub.2, 20.sub.3 and
20.sub.4, respectively, are disposed around the central element 18
with the elements 20.sub.1 and 20.sub.3 being located on a common
axis equidistantly on opposite sides of the central element 10 and
with the elements 20.sub.2 and 20.sub.4 being located on an
orthogonal axis relative to the first axis and also being disposed
equidistantly on either side of the central element 10. The
elements thus located around the central element 10 are excited by
means of a suppressed carrier sideband signal having a frequency of
f.sub.c .+-. 15Hz appearing at output terminal 22. The four
elements 20.sub.1 . . . 20.sub.4 are excited as two subarrays which
each comprise two elements which are fed in antiphase relationship
relative to one another, i.e., 180.degree. out of phase with one
another. Moreover, the two subarrays are respectively excited in
phase quadrature with one another so that for example the elements
20.sub.1, 20.sub.2, 20.sub.3, and 20.sub.4 have a respective phase
of +1, +j, -1, and -j which ocrrespond to 0.degree. , 90.degree. ,
180.degree. and 270.degree. of relative phase shift.
More particularly, the f.sub.c .+-. 15Hz signal is applied from
output terminal 22 to a signal buss 24. Radiating element 20.sub.1
is coupled to signal buss 24 through the impedance matching devices
26 and 28 and is thus said to have a zero or +1 phase shift. Its
opposing radiating element 20.sub.3 is excited from signal buss 24
through the impedance matching elements 28 and 30 as well as a
phase inverter 32 which applies 180.degree. phase shift to the
signal. Thus elements 20.sub.1 and 20.sub.3 are said to have a +1
and -1 phase, that is a mutual antiphase relationship. The
radiating elements 20.sub.2 and 20.sub.4 which are orthogonally
disposed with respect to the first pair of elements 20.sub.1 and
20.sub.3 are excited from signal buss 24 after passing through a
90.degree. or quadrature phase shifter 34. Moreover, the radiating
element 20.sub.2 is coupled to the output of the 90.degree. phase
shifter 34 by means of the impedance matching devices 36 and 38 and
thus is said to have a +j or 90.degree. phase shift relative to the
phase of the signal appearing on the circuit buss 24 and the
radiating element 20.sub.1. With respect to the fourth radiating
element 20.sub.4, it is coupled to the output of the 90.degree.
phase shifter 34 through the impedance matching devices 36 and 40
as well as a phase inverter 42, thus making its radiated signal
180.degree. out of phase with respect to the signal radiated from
element 20.sub.2 and thus is said to have a -j phase.
The amplitude of the energy in the sidebands radiated from the
elements 20.sub.1 . . . 20.sub.4 is maintained below the amplitude
of the energy in the carrier radiated from the central element 10
which results in an amplitude modulated signal, where the phase of
the modulation varies linearly as the direction varies from
0.degree. to 360.degree. in azimuth which is one of the
characteristics in the TACAN system.
Concentric with the second array including the radiating elements
20.sub.1 . . . 20.sub.4 is a third radiating array comprised of 4n
active radiating elements and more particularly comprised of 36
radiating elements 46.sub.1, 46.sub.2 . . . 46.sub.35 and 46.sub.36
arranged in a circular configuration around the central array 10.
These 36 radiating elements are excited by means of a suppressed
carrier sideband signal having a frequency f.sub.c .+-.135Hz which
appears at output terminal 48 of the TACAN transmitter 12.
Moreover, the 36 radiating elements 46.sub.1 . . . 46.sub.36 are
divided into two groups of 18 elements which are interlaced with
one another, i.e., alternating. The first or even-numbered group of
radiating elements are comprised of elements 46.sub.2, 46.sub.4,
46.sub.6 . . . 46.sub.34 and 46.sub.36 while the second or odd
numbered group of elements are comprised of elements 46.sub.1,
46.sub.3, 46.sub.5, 46.sub.7 . . . 46.sub.35. The even numbered
elements are powered from a signal feed line 52 coupled to the
signal buss 50 by means of an impedance matching device 54 with
each succeeding even numbered element being excited in antiphase
relationship with the preceding even numbered element. Taking
element 46.sub.36 as an illustrative example, it is coupled to the
signal feed line 52 by means of an impedance matching element 56
and exhibits a +1 phase or 0.degree. phase shift with respect to
the signal appearing on circuit buss 50. The even numbered elements
46.sub. 2 and 46.sub.34 on either side of the +1 phase element
46.sub.36 are coupled to the signal feed 52 by means of impedance
matching elements 58 and 60 and phase inverters 62 and 64,
respectively, and thus exhibit a -1 phase or 180.degree. phase
shift relative to element 46.sub.36.
The odd numbered elements 46.sub.1, 46.sub.3 . . . 46.sub.35 are
powered from a signal feeder line 66 which has its f.sub.c
.+-.135Hz sideband signal applied thereto in phase quadrature or
90.degree. out of phase with the signal appearing on signal feed
line 52. This is provided by a quadrature phase shifter 68 and
impedance matching element 70 coupled between the signal buss 50
and the feeder line 66. Radiating element 46.sub.1 is coupled to
the feeder line 66 through the impedance matching element 72 and
thus exhibits a +j phase or 90.degree. phase shift between the
signal applied to its immediately adjacent elements 46.sub.36 and
46.sub.2 which are phased +1 and -1 respectively. Odd numbered
elements 46.sub.3 and 46.sub.35 succeeding and preceding odd
numbered element 46.sub.1 are coupled to the signal feed through
the impedance matching devices 74, 76 and phase inverters 78 and
80, respectively and thus provide a -j phase or 180.degree. phase
shift with respect to the signal applied to the element
46.sub.1.
The sequence of phasing of the f.sub.c .+-. 135Hz sideband energy
as the circular array including the elements 46.sub.1 . . .
46.sub.36 is traversed, is +1, +j, -1, and -j which is repetitive
in that order in each set of four elements and thus the radiated
signal from the 36 element array will provide in conjunction with
the carrier radiated from the central element 10 a 135Hz modulation
radiated signal in which the phase of the modulation goes through a
360.degree. linear phase variation for each 40.degree. of azimuth
direction angle which is the other characteristic of a TACAN
antenna system.
The choice of exact radius on which to locate the elements of the
second and third concentric arrays with respect to the central
element comprises a design detail; however, the vertical plane
pattern of the four element array comprising radiating elements
20.sub.1 . . . 20.sub.4 is approximated by J.sub.1
[(.pi.d/.lambda.) sin.theta.] while the 36 element array including
the radiating elements 46.sub.1 . . . 46.sub.36 is approximated by
J.sub.9 [(.pi.d/.lambda.) sin.theta.] where .lambda. is the
wavelength of the carrier frequency and .theta. is the angle
measured from the zenith and would be equal to 90.degree. on the
horizon. Normally the radius of the elements of the array would be
chosen so that the Bessel function is a maximum on the horizon
although for synthesizing specific vertical coverage patterns,
other values might be used as well as a combination of additional
four element and additional 36 element arrays to provide a desired
coverage pattern; however, these additional elements can be
arranged both in the vertical plane and the azimuth plane on
different radii.
What has been shown and described, therefore, is a TACAN antenna
system in which the modulation or scanning is introduced onto the
radiated signal electronically and except for this fact, provides a
radiated signal which is identical in all respects to that realized
from a mechanically rotating TACAN antenna.
Having thus described what is at present considered to be the
preferred embodiment of the subject invention,
* * * * *