U.S. patent number 3,766,558 [Application Number 05/181,453] was granted by the patent office on 1973-10-16 for raster scan antenna.
This patent grant is currently assigned to International Telephone and Telegraph Corporation. Invention is credited to John A. Kuechken.
United States Patent |
3,766,558 |
Kuechken |
October 16, 1973 |
RASTER SCAN ANTENNA
Abstract
A broadside array antenna arrangement capable of scanning
electronically in one or two planes, wherein the transmitted or
received frequency remains fixed although beam steering is effected
by progressive phase shifts introduced to the various array
elements as provided by the expedient of frequency variations. A
prime oscillator frequency f.sub.o is mixed with a variable
steering oscillator frequency f.sub.s to produce sum and difference
frequencies f.sub.o + f.sub.s and f.sub.o - f.sub.s. The latter is
fed to a delay line having a plurality of taps spaced apart in
accordance with the particular arrangement of array elements, the
delay line providing in the frequency signal f.sub.o - f.sub.s
progressive phase shifts from tap to tap. The individual tap
outputs are separately mixed with the sum frequency signal f.sub.o
+ f.sub.s, wherein N separate outputs are simultaneously derived
having the same frequency of 2f.sub.o but varying from one another
progressively in phase. Variation of f.sub.s, which causes the
phase relationship between the N outputs to change as they are fed
to the radiators in one-to-one correspondence, thus provides a
sweep of the beam in one plane. Raster type scanning is provided by
introducing a multi-tapped secondary delay line at each tap of the
primary delay line and mixing instead the tap outputs of each
secondary delay line individually with f.sub.o + f.sub.s and
applying the resultant 2f.sub.o outputs to individual ones of a
corresponding element row of a two-dimensional array. The tapped
spacings on each of the secondary delay lines relative to the
tapped spacings of the primary delay line is such as to provide
scanning of an order of magnitude more sensitive in one plane.
Inventors: |
Kuechken; John A. (Pittsford,
NY) |
Assignee: |
International Telephone and
Telegraph Corporation (Nutley, NJ)
|
Family
ID: |
22664345 |
Appl.
No.: |
05/181,453 |
Filed: |
September 17, 1971 |
Current U.S.
Class: |
342/375;
342/371 |
Current CPC
Class: |
H01Q
3/42 (20130101) |
Current International
Class: |
H01Q
3/42 (20060101); H01Q 3/30 (20060101); H01q
003/26 () |
Field of
Search: |
;343/1SA,113R,854 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Borchelt; Benjamin A.
Assistant Examiner: Berger; Richard E.
Claims
I claim:
1. An antenna scanning arrangement comprising:
a. first means for generating from a fixed prime frequency signal
f.sub.o and a variable steering frequency signal f.sub.s first and
second frequencies of f.sub.o + f.sub.s and f.sub.o - f.sub.s ;
b. second means operating on one of said first and second signal
frequencies to provide N simultaneous signal portions thereof of
the same frequency and each having a unique phase which varies
progressively from one another in predetermined increments;
c. third means separately coupling each of said N simultaneous
signal portions with the untreated other one of said first and
second signal frequencies for providing N separate output signals
each having the same harmonic frequency of f.sub.o and
progressively varying in phase from one another in said
predetermined increments; and
d. N radiating elements in an array of predetermined arrangement
coupled to said third means for radiating signal energy responsive
to said N separate output signals applied thereto in one-to-one
correspondence, wherein said second means is comprised of a primary
phase shifting device having a plurality of terminals for providing
simultaneous outputs varying in phase from one another
progressively in said predetermined manner, and a plurality of
secondary phase shifting devices each having a plurality of
terminals for providing simultaneous outputs varying in phase from
one another progressively in a predetermined manner, said secondary
phase shifting devices each being separately coupled between a
terminal of said primary phase shifting device and said third
means, and wherein said radiating elements are arranged in a
two-dimensional array and said primary and secondary phase shift
devices are comprised of delay lines having taps arranged
periodically thereon.
2. The arrangement according to claim 1 wherein said first means
includes a prime oscillator for producing said fixed prime
frequency signal energy f.sub.o, a steering oscillator providing
said variable steering frequency signal energy f.sub.s and a first
mixer coupling said f.sub.o and f.sub.s signal energies for
providing said f.sub.o + f.sub.s and f.sub.o - f.sub.s signal
energies.
3. The arrangement according to claim 2 wherein when operation of
the arrangement is in a receive mode, said first means further
includes a second mixer coupled between said second means and the
output of said steering oscillator wherein said steering frequency
signal energy f.sub.s and the difference frequency f.sub.o -
f.sub.s from said second means are coupled to provide the frequency
output f.sub.o.
Description
BACKGROUND OF THE INVENTION
This invention pertains to communications systems and more
specifically to electronic raster type scan antenna arrangements
particularly adapted to communications requirements calling for
fixed rediated and received frequencies.
In, for example, high directivity microwave applications, the use
of steerable array antennas has certain very substantial
attractions compared to the more conventional two or three-axis
gimbaled reflector. Potentially, the array will have a much smaller
swept or inscribed volume and will be capable of steering the
antenna beam in very short times compared with the mechanical
motion of the reflector. In addition the mechanical mount or
pedestal is heavy and expensive. Consequently, a great deal of
effort has been expended in developing array antennas which may be
steered in one or two planes by the expedient of applying linearly
progressive phase shifts to the array elements to obtain
"electronic" beam steering of planar arrays.
Whereas many of the problems have been solved in such arrays,
several fairly severe and rather fundamental limitations
remain:
1. It is extremely difficult for example to cause any planar array
to scan more than .+-.45.degree. from braodside; and
2. On large arrays the gain proceeds approximately as the number of
elements, with 10.sup.4 elements being required for instance to
obtain 43 db of directivity.
The first limitation implies that either four or five planar arrays
are required to cover a complete hemisphere if no mechanical motion
is to be used. The second implies that very large numbers of phase
shifters are required if two-directional scan or steering is to be
obtained. The latter problem is further compounded if a quantized
phase shift is to be obtained because of the phase ripple on the
aperture.
This phase ripple may be interpreted as constituting a second
superimposed antenna excited only with errors, whose radiation
pattern interferes with the "real" antenna pattern. If it is
assumed that the RMS excitation of the error aperture is equal to
one-half the quantum size error the following is obtained:
Approximate Error Phase Quantum Sidelobe Level .pi. radians 0 db
(two main beams) .pi./2 -8.3 db .pi./4 -13.3 db .pi./8 -19.3 db
The error sidelobes may coherently add (voltagewise) to the normal
sidelobe structure.
Accordingly, it may be seen that a fairly large number of quanta
may be required if a reasonable sidelobe level is to be maintained
at all scan angles. If an additive scheme is used for .pi./4
quanta, then a four bit switching is required (22.5.degree.,
45.degree., 90.degree. and 180.degree.). (In a completely
non-additive scheme 15 bits would be required.) This number appears
as a multiplier against the number of elements in two-dimensional
scanning antennas using an interacting scan scheme whereby the
phase to yield appropriate beam steering in both planes is
independently determined for each radiator. A row and column scheme
will simplify the logic at the cost of an extra row or column's
worth of phase shifters.
In radar work a great deal of this complexity can be avoided by
using a frequency scan scheme. Here the frequency is altered to
provide the requisite phase shifts between taps on a delay line,
thus each beam position is associated with a unique frequency. The
device is a microwave analogue of an optical diffraction grating.
Such arrays are most commonly built to scan in one plane and use
mechanical motion in the orthogonal plane. However, a raster type
scan motion could be obtained by using orthogonal delay lines where
the frequency scanning in one plane is arranged to be an order of
magnitude more sensitive in one of the planes with the successive
grating lobes of the rapid scanning plane being used as the main
lobe. The scan band would be discontinuous between successive
raster lines, however; each usable frequency would be uniquely
associated with a given point on one of the raster lines. This
scheme is acceptable in radar work where the exact frequency is
unimportant as long as the receiver local oscillator tracks the
transmitter frequency. Unfortunately, this technique is not
directly applicable for instance to satellite communications
wherein the up link and down link frequencies are uniquely
determined by outside requirements.
SUMMARY OF THE INVENTION
It is therefore a principle object of this invention to provide a
simplified electronic scan facility which avoids the
above-mentioned drawbacks.
It is another principle object of this invention to provide
electronic beam steering of planar array antennas in one or two
planes by the expedient of applying (linearly) progressive phase
shifts to the array elements.
It is yet another principle object of the invention to provide an
electronic scanning technique for steerable array antennas whereby
the radiated and received frequencies are fixed while the mechanism
of frequency scanning is employed to provide requisite phase
shifts.
It is still another object to provide an electronic antenna
scanning technique predicated on phase shifts wherein a steering
frequency is varied to provide uniform variations in requisite
phase shifts between taps on one or more delay lines.
It is a further object of this invention to provide electronic beam
steering of array antennas by way of the mechanism of frequency
scanning wherein the long term stability of the steering frequency
is unimportant.
It is yet a further object of this invention to provide an
electronic scanning arrangement which is applicable to both
communications antenna scanning systems and radar scanning
systems.
According to the broader aspects of the invention there is provided
an antenna scanning arrangement comprising first means providing
signal frequencies of f.sub.o + f.sub.s and f.sub.o - f.sub.s from
a fixed prime frequency signal f.sub.o and variable steering
frequency signal f.sub.s ; second means operating on said f.sub.o -
f.sub.s signal frequency to provide N simultaneous f.sub.o -
f.sub.s signals each having a unique phase which varies
progressively from one another in predetermined increments; third
means separately coupling each of said N simultaneous f.sub.o -
f.sub.s signals of said second means with said f.sub.o + f.sub.s
signal frequency for providing N separate signals each having the
same harmonic frequency of f.sub.o and progressively varying in
phase from one another in said predetermined increments; and N
radiating elements in an array of predetermined arrangement coupled
to said third means and radiating signal energy in response to said
N separate signals coupled thereto in one-to-one
correspondence.
A feature of the invention is that a two-dimensional electronic
scanning array antenna arrangement is provided whereby the phase
shifts yielding appropriate beam steering in both planes is
independently determined for each radiator.
A further feature of the invention is that raster type scanning by
way of requisite phase shifts is provided from steering frequency
variations wherein orthogonal delay lines are employed to receive
the steering frequency and to provide phase shifts such that the
electrical length between adjacent taps on the one delay line are
arranged with respect to the lengths between adjacent taps of the
other, so as to provide scanning in the one plane to be in the
order of a magnitude more sensitive.
BRIEF DESCRIPTION OF THE DRAWINGS
The above mentioned and other objects and features of this
invention will become more apparent by reference to the following
description taken in conjunction with the accompanying drawings, in
which:
FIG. 1A is a schematic representation of an array antenna scanning
arrangement in the transmit mode according to the invention for
scanning in one plane;
FIG. 1B is an operational plot of the scanning facility of the
arrangement of FIG. 1A in terms of azimuth beam position and
steering frequency;
FIG. 2A is a schematic representation of a raster type scanning
array antenna arrangement according to the invention; and
FIG. 2B is a plot of the scanning facility of the arrangement of
FIG. 2A in terms of beam position elevation and steering
frequency.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIGS. 1A and 1B, there is illustrated therein
respectively an electronic scanning array antenna arrangement
according to the invention for scanning in the horizontal plane;
and a diagram of the scanning facility of FIG. 1A in terms of
azimuth angle of sweep and the steering frequency spectrum giving
rise to the requisite phase shifts for beam steering. In FIG. 1A
the transmit mode is depicted (primarily), although the inventive
arrangement is intended to be reciprocal in capability, and to that
end a switch connection is illustrated which pertains to the
receive mode.
The frequency f.sub.o of a prime oscillator 1 is combined in a
mixer 3 of conventional design with the frequency f.sub.s of a
steering oscillator 2, with the outputs respectively at 10 and 11
being the sum and difference frequencies f.sub.o + f.sub.s and
f.sub.o - f.sub.s. While prime oscillator 1 remains fixed in
frequency, steering oscillator 2 is intended to be capable of an
output which is variable in frequency over a predetermined range,
say f.sub.1 - f.sub.N. The difference frequency f.sub.o - f.sub.s
is fed to a delay line 6 having taps A, B, C, etc. at predetermined
points, the separations thereof being generally dependent upon the
arrangement of and specifically the separation between the array
elements. Delay line 6 provides phase shifts to f.sub.o - f.sub.s
at the points A, B, C, etc. in accordance with the following
relation:
Phase Shift (for example) A to B =.psi. =[2.pi.(AB)]/.lambda.d
radians (1)
where:
(AB) = d = the physical distance along the delay line in
meters.
.lambda..sub.d in turm may be considered as being the
following:
.lambda..sub.d = (3 .times. 10.sup.8)/(f.sub.o - f.sub.s) .times.
(V.sub.q /C.sub.o) meters
and
V.sub.q /C.sub.o = the velocity of propagation in the delay line
(numeric factor).
The various taps off of delay line 6 are in turn fed to individual
mixers 4 wherein f.sub.o - f.sub.s from each delay line tap or
terminal is mixed independently with the f.sub.o + f.sub.s output
from mixer 3. Mixers 4 are to be considered conventional in design
and operation. As delay line 6, via the periodic taps A, B, C,
etc., provides f.sub.o - f.sub.s with successive and, in the
illustrated example here, linear phase shifts, that same phase
relation between the respective outputs of mixers 4 will be
maintained in view of the well known principle that phase remains
undisturbed in a mixing process. By combining the f.sub.o + f.sub.s
output of mixer 3 with the phase staggered outputs at the taps A,
B, C, etc. of delay line 6, the steering frequency f.sub.s drops
out leaving the N outputs of mixers 4 each having the same
frequency, i.e. two times the frequency f.sub.o of the prime
oscillator 1, but with the respective phase differences preserved.
As the outputs are then coupled to radiators 5, the energy radiated
by each is, therefore, of the same frequency but at some relative
phase difference with adjacent and all other similarly radiated
energies. Thus, as f.sub.s is varied, only the beam moves while the
radiated frequency doesn't change. In the above and hereinafter as
well, it is to be understood that conventional selective filtering
accompanys each mixer defined in the arrangement in order to
provide the desired mixer output(s).
The array of elements 5 may conventionally take the form of a
broadside driven array wherein all the radiators are in a line (a
one-dimensional array), i.e. the antenna axis. The elements 5 may
be either monopoles or dipoles appropriately arranged and fed to
provide the preferred broadside operation. Delay line 6 may in
actuality be any suitable means which provides simultaneous outputs
of f.sub.o - f.sub.s each with a unique phase successively varying
from output to output in a predetermined manner depending on the
arrangement of array elements, the delay lines here envisaged,
however, being of conventional design. It is estimated that perhaps
100 elements 5, and therefore mixers 4 as well, are needed to
achieve a 1.degree. beam width.
In operation, the arrangement of FIG. 1A could for instance
commence a sweep with the beam at 0.degree., i.e. normal with
respect to the axis of the array. In this situation, the steering
frequency f.sub.s is such as to provide an integral wavelength
.lambda. in relation to the distances d, i.e. AB, BC, etc. An
increase in steering oscillator frequency f.sub.s will for instance
cause the beam to swing away from normal or broadside (0.degree.)
to some angle 0.degree.<.alpha. < 45.degree. to the right of
normal, as viewed in the direction of intended transmission. A
continued increase in f.sub.s would cause the highly directional
array beam to sweep finally to an angle .alpha..apprxeq.45.degree.
with respect to normal (broadside). At this point it is
advantageous to design into the system some facility wherein the
scanning is interrupted, thus preventing a sweep of greater than
45.degree.. This is desirable because the beam at angles greater
than 45.degree. in general becomes sloppy, irregular and inadequate
in directivity. Moreover, there is created from an increase in
f.sub.s at the 45.degree. beam sweep angle a new and second beam
directed substantially 45.degree. to the left of broadside as
viewed in the general direction of intended transmission. Thus with
the development of two beams, the advantages of electronic scanning
with a highly directional beam are lost in the absence of some
facility in the system for rejecting the now deteriorated initial
swept beam and concentrating instead on the newly created beam.
One means of facilitating a substantially continual scan for
further increases in f.sub.s while eliminating the dual-beam
situation is to provide the steering oscillator 2 mechanism with
the capacity of having its output to mixer 3 interrupted at the
frequencies equivalent or corresponding to the 45.degree. scan
angle with minimal tolerance taken into consideration. In other
words as the beam closely approaches the +45.degree. sweep angle
(i.e. 45.degree. to the right of normal in broadside), f.sub.s is
interrupted in reaching mixer 3 for a very small frequency band,
wherein the steering oscillator output would be once more permitted
to reach mixer 3 as a continued increase in f.sub.s meanwhile
reached a frequency which would provide the new, highly directive
beam at the -45.degree. angle of sweep (i.e. 45.degree. to the left
of broadside). At this frequency of f.sub.s, the former beam would
have dissipated beyond consideration. Now, as f.sub.s is yet
continually increased the new beam would continue to sweep from the
-45.degree. angle through broadside and finally once again approach
the +45.degree. angle of sweep, at which time f.sub.s would once
again be interrupted for a short frequency span. It is to be noted
however, that the interrupted frequency bandwidth is intended to be
equivalent to that required to provide a beam sweep of less than
half the beam width.
It is also possible to arrange the array elements so as to allow
the beam to disappear at the +45.degree. sweep angle. In this
manner the periodic discontinuities demonstrated in FIG. 1B of the
variable steering frequency f.sub.s may be virtually eliminated. It
is to be understood also that the discontinuities of f.sub.s in
FIG. 1B (and also FIG. 2B) are not to scale, but rather have been
emphasized to illustrate the existence of same.
In the inventive arrangement, steering oscillator 2, in having an
arbitrary operative spectrum of f.sub.1 .ltoreq.f.sub.s
.ltoreq.f.sub.n, may be arranged to begin at f.sub.1 and
continuously vary upward in frequency to f.sub.n and then
immediately switch back to f.sub.1 to begin a span of the band
anew. Alternatively the operative design could instead be arranged
so as to provide for f.sub.s, in reaching f.sub.N, to reverse
itself and decrease in frequency back to f.sub.1. It is entirely
possible therefore in this latter consideration to shorten the
operating range f.sub.1 - f.sub.N of steering oscillator 2. The
variability of steering oscillator 2 may of course be provided by
any conventional automatic or manual means.
It is particularly noteworthy that the long range stability of
steering oscillator 2 is unimportant in as much as the frequency
f.sub.s thereof cancels out in the inventive process, leaving only
2f.sub.o to be transmitted.
In general, uniform spacing of elements 5 is contemplated in the
arrangement of FIG. 1A. However, unfilled aperture techniques for
example can be accommodated equally well by simply making the delay
line length between taps proportional to the respective radiator
spacings.
For a broader understanding of electronic beam steering by the
expedient of phase shifts or variations (primarily uniform) in
broadside array antennas see "Antennas and Transmission Lines" by
John A. Kuecken, published in 1969 by Howard W. Sams & Company,
Inc.
In considering the arrangement of FIG. 1A in a receive mode, the
connection 11 running from mixer 3 to the delay line 6 is to be
substituted by a new line 12 leading to an additional mixer 13 by
way of switch SW. The other input to mixer 13 is taken by way of
lead 14 from the output of steering oscillator 2. The output of
mixer 13 is in turn coupled to the receiver IF strip for providing
the output in readily usable form. In this mode, the incoming
signal of 2f.sub.o is received by the radiators 5. The received
signal is treated in mixers 4 to provide from each an f.sub.o -
f.sub.s output according to the relation:
2f.sub.o - (f.sub.o + f.sub.s) = f.sub.o - f.sub.s
where the f.sub.o + f.sub.s output of mixer 3 is supplied as before
to mixer 4.
The resultant f.sub.o - f.sub.s signal from delay line 6 is then
combined with f.sub.s in mixer 13 to yield an f.sub.o output. This
f.sub.o output may then be treated by a conventional IF strip to
provide the output in desired form.
Thus it is seen that the inventive arrangement of FIG. 1A is
capable of reciprocal operation.
Referring to FIGS. 2A and 2B, a two-dimensional or raster type
scanning array antenna arrangement according to the invention is
illustrated, together with a diagram showing the operation thereof
in terms of elevation scan angle and the spectrum of steering
frequency oscillator 2. Though the arrangement in FIG. 2A is
depicted and to be described in terms of the transmit mode, it is
to be understood here also that the inventive arrangement may be
utilized in a receiver capacity, and therefore is reciprocal in
nature. Duplicated portions of the arrangement of FIG. 1A have been
given like reference designations in the arrangement according to
FIG. 2A. The latter arrangement differs from the former
particularly by inclusion of secondary delay lines 16, 16', 16",
etc. at the taps A, B, C, etc. of delay line 6. These secondary
delay lines are in turn themselves tapped at Aa, Ab, Ac . . . Ba,
Bb, etc. in predetermined fashion as illustrated at 17. The taps in
turn are coupled to mixers 18, wherein once again the coupled
energy from the delay lines is mixed conventionally with f.sub.o +
f.sub.s. However, in this arrangement the radiators 19, 19', 19",
etc. are arranged in a two-dimensional array of rows and columns,
thus requiring corresponding row and columns of mixers 18, 18',
18", etc. Thus each secondary delay line 16, 16', 16", etc. is
associated for instance with its own element row or column, with
the individual taps thereof being in one-to-one relationship with
the associated mixers 18 and radiators 19.
Whereas, FIG. 1A provides for the N taps A, B, C, etc. from the one
delay line 6 only, thus giving rise ultimately to the respective
radiations of 2f.sub.o, 2f.sub.o < .psi., 2f.sub.o < 2 .psi.,
2f.sub.o < 3 .psi. . . . 2f.sub.o < N .psi., the arrangement
according to FIG. 2A provides, bp way of the N secondary delay
lines 16, 16', 16", etc. operating from the taps of delay line 6,
ultimately for the radiations of 2f.sub.o (<.psi. .sub.A + <
.psi. .sub.a), 2f.sub.o (< .psi. .sub.A + 2< .psi. ) etc. for
the first row (or column), 2 f.sub.o (< .psi. .sub.B + <
.psi..sub.a), 2f.sub.o (< .psi. .sub.B + 2<< .psi.) etc.
for the second row, and 2f.sub.o (< .psi. .sub.N +< .psi.
.sub.n), 2f.sub.o (< .psi. .sub.N + N< .psi. .sub.n) for the
Nth row.
Similar to before, the lengths AB, BC, etc. and A.sub.a A.sub.b,
A.sub.b A.sub.c, etc. between taps on the respective delay lines
are proportional to the spacings of the elements in each row (or
column) and now the spacing between the rows as well.
In operation, the plots of both FIGS. 1B and 2B indicate the true
scanning operation provided by the inventive arrangement
exemplified in FIG. 2A when considered together. As f.sub.s is
varied between f.sub.1 and f.sub.N, the highly directional beam
will scan azimuthally as described previously for instance from
left to right in relation to the direction of intended
transmission. As the +45.degree. scan angle is finally reached, the
steering frequency f.sub.s in reaching mixer 3 is once again
rendered discontinuous over a small frequency span for the reasons
noted hereinbefore. As a result, the elevational scan, as showing
in FIG. 2B, is also rendered discontinuous. Thus, the pattern
plotted shows the beam to continually increase in elevation as it
sweeps from -45.degree. to +45.degree. in azimuth, with the next
sweep, in terms of elevation commencing at some yet greater angle
of elevation at which it would normally have arrived even if there
had been no discontinuity in the frequency spectrum of f.sub.s. It
is to be particularly noted, however, that the distance or length Z
in FIG. 2B, which represents the amount of elevation scan
corresponding to the discontinuity in f.sub.s, is such as to be
considerably less than one beam width in elevation. Therefore, as
f.sub.s continues to increase the elevation angle will continue to
increase proportionally in a linear manner in the example
illustrated here, with, however, the periodic discontinuities as
mentioned.
The ultimate stated object of the example arrangement illustrated
in FIG. 2A is to scan electronically in two planes, i.e. the
vertical and the horizontal. Intended to be provided therewith
according to a feature of the invention is the facility that the
scan in one plane (in this example the horizontal plane) be of an
order of magnitude more sensitive. To this end there is provided
very rapid scan in the horizontal plane with respect to the
vertical plane scan, which is directly attributable to the
relationship between the lengths d and d' between taps on the
respective primary delay lines 6 and the secondary delay lines 16,
16', 16" etc. In this case the length AB for example is
considerably greater than the A.sub.a A.sub.b. Thus is realized a
very rapid scan in the horizontal plane while simultaneously the
beam is increasing continually in elevation but at a much slower
rate. The result is that from a single run through the f.sub.1 -
f.sub.N spectrum of the steering frequency oscillator 2, a very
substantial area of space has been electronically raster scanned at
great speed.
Both the primary delay line 6 and recording delay lines 16, 16',
etc. of course respond to the relation of equations (1) and (2)
above, but as stated the array of FIG. 2A will provide a beam of
sweep rapidly from side to side while moving slowly in the
vertical. It is to be noted that the phase shift of interest at
each element is in general
.psi..sub.s =.psi.-.eta..pi. radians
where .eta. is any even integer. In other words, the beam condition
repeats every 2.pi. radians of phase shift. Between successive
raster lines then, .psi. jumps by 2.pi. radians in giving rise to
the discontinuous frequency spectrum. Again, techniques may be
employed, such as the use of directive radiating elements, whereby
this discontinuity between raster lines could be virtually
eliminated.
While in the arrangements of FIGS. 1A and 2A the outputs of mixer
3, i.e. the sum and difference frequencies f.sub.o + f.sub.s and
f.sub.o - f.sub.s, were respectively fed to mixers 4 (or 18) and
delay line 6, it is entirely within the scope of this invention
that the sum and difference frequency applications here be
reversed. That is, the sum frequency f.sub.o + f.sub.s may just as
easily be arranged to be fed to the delay line 6 and in turn the
f.sub.o - f.sub.s frequency be fed to the row(s) of mixers 4 or 18.
The operation would be the same with the output of mixers 4 or 18
again having the steering oscillator frequency f.sub.s drop out
leaving the second harmonic of the primary oscillator frequency
f.sub.o to be radiated.
In the above there has been disclosed array antenna arrangements
providing electronic scanning in one or two planes capable of both
transmit and receive operation, wherein the beam steering is
accomplished by the expedient of progressive phase shifts applied
to the individual radiators as generated by frequency variations of
a steering oscillator in being fed to a multitapped delay line. The
embodiments disclosed are particularly adaptable for instance to
satellite communications wherein the frequencies of operation are
determined by outside requirements and must be considered fixed.
Thus the inventive arrangements provide electronic beam steering by
requisite phase shifts resulting from frequency variations in
applications which cannot tolerate such frequency variations in
communications operations. The variable steering frequency
oscillator output is mixed with a fixed prime oscillator output to
provide the sum and difference frequencies therefrom, with the
difference frequency being applied to a delay line having periodic
taps proportional to the radiator spacing of the array. The
tap-offs from the delay line are in turn mixed individually with
the derived sum frequency such that the steering frequency drops
out leaving N outputs to be fed to the radiators, arranged
essentially in a one-dimensional array, which outputs all have the
same frequency of two times the prime oscillator frequency but
which progressively vary from one another in phase as derived from
the delay line. A variation in the steering oscillator frequency
causes the phase relation between the N outputs to change thus
providing a corresponding change in aximuth angle of the highly
directional beam. For two-plane or raster type scanning, secondary
multi-tapped delay lines are applied to the tapped outputs of the
primary delay line, with the individual taps of each secondary
delay line in turn being individually mixed with the derived sum
frequency to eliminate the variable steering frequency and the
outputs thereof in turn being fed to an associated row of radiators
in a two-dimensional array.
While the principles of this invention have been described in the
above with regard to specific apparatus, it is to be understood
that this description is made by way of example only and is not to
be considered as a limitation on the scope of the invention, and
the objects and features thereof, as set forth in the appended
claims.
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