U.S. patent number 3,604,012 [Application Number 04/766,012] was granted by the patent office on 1971-09-07 for binary phase-scanning antenna with diode controlled slot radiators.
This patent grant is currently assigned to Textron Inc.. Invention is credited to Dale C. Lindley.
United States Patent |
3,604,012 |
Lindley |
September 7, 1971 |
BINARY PHASE-SCANNING ANTENNA WITH DIODE CONTROLLED SLOT
RADIATORS
Abstract
The present invention relates to an antenna having a plurality
of radiators energized to produce radiation in at least two
adjacent quadrants and having control means for selectively
reversing the phase of radiation of individual radiators to thereby
provide direction radiation from the array and to scan such
radiation.
Inventors: |
Lindley; Dale C. (Sunnyvale,
CA) |
Assignee: |
Textron Inc. (Belmont,
CA)
|
Family
ID: |
25075129 |
Appl.
No.: |
04/766,012 |
Filed: |
August 19, 1968 |
Current U.S.
Class: |
343/768; 342/371;
343/771 |
Current CPC
Class: |
H01Q
3/38 (20130101) |
Current International
Class: |
H01Q
3/30 (20060101); H01Q 3/38 (20060101); H01q
013/10 () |
Field of
Search: |
;343/768,771,777,778,854,754 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lieberman; Eli
Claims
That which is claimed is:
1. An improved antenna comprising a large plurality of radiating
elements aligned in strips, each strip comprising a waveguide
having pairs of slots therein with the slots of each pair being
diametrically disposed on opposite sides of the center of the
waveguide and diodes connected across each slot, means energizing
said elements to radiate energy in at least two adjacent phase
quadrants with the phase of elements of any group of adjacent
elements substantially different and establishing a nonperiodic
phase distribution across the array, and switching means
selectively reversing biasing of diodes of each pair of slots for
selectively reversing the phase of energy radiated by each radiated
element to thereby establish a predetermined radiation beam pattern
and further successively reversing the phase of predetermined
elements in predetermined order to change the direction or pattern
of a radiated beam in a preselected manner.
2. The antenna of claim 1 further defined by said diodes being
disposed across ends of said slots for selectively detuning said
slots from said waveguide.
3. In an antenna structure having at least one waveguide with
coupling slots in the wall thereof for coupling waveguide energy to
the atmosphere, the improvement comprising each waveguide having
pairs of slots spaced along the length thereof with the slots of
each pair disposed equidistant on opposite sides of the center of
the waveguide, diodes connected one across the end of each
waveguide slot with the diodes of each pair of slots being
connected in parallel opposed arrangement and being controllably
biased by opposite polarity voltage causing either one only of each
pair of diodes to conduct for selectively reversing the phase of
energy coupled to the atmosphere from each pair of slots.
Description
BACKGROUND OF INVENTION
In many fields such as that of radar it is common practice to
radiate a highly directional beam of electromagnetic energy and to
scan the beam so as to controllably vary the direction of beam
propagation. It is noted that there have been developed a large
number of antennas, antenna arrays and antenna feed-and-control
systems to achieve the above-identified result. It is stated, for
example, in U.S. Pat. No. 3,286,260 to Shirly La Var Howard that it
is conventional to employ phase shifting between adjacent elements
of an antenna array in order to produce scanning of the beam. By
incrementally changing the relative phase of energy radiated from
successive elements of an array, the direction of a beam from a
broadside array, for example, can be shifted. One manner of
changing the relative phase of energy radiated from adjacent
elements of an array is to vary the frequency of element
energization. Another manner of electronically scanning a beam from
an antenna array is to employ phase-shifting devices between
elements for changing the phase of energy radiated from separate
elements. In this latter category fall ferrite-loaded beam-shifting
antennas and the like. The prior art has relied upon some manner of
relatively continuously varying the phase between successive
elements of an antenna array in order to electronically scan a beam
radiated therefrom, and the above-noted patent employs both of the
phase-shifting techniques identified above.
While it is recognized that a directional beam can be
electronically scanned, it is generally accepted that such scanning
requires the utilization of some type of continuous or near
continuous phase variation at each of the radiating elements. This
requirement is highly disadvantageous in necessitating the
utilization of relatively complex structures and circuits.
The present invention provides for the scanning, or controlled
variation, in the direction of propagation of the beam by the
selective reversal of the phase of energy radiated from separate
elements of the antenna array. Thus, in accordance with the present
invention, it is not necessary to employ any type of continuous or
near continuous phase variation; there is consequently achieved a
material simplification of structures and circuits required for
electronic-beam scanning.
SUMMARY OF INVENTION
The antenna of the present invention comprises a plurality of
radiators which may be physically embodied as dipoles, waveguide
slots or the like. These individual radiators are energized in some
predetermined or random phase relationship which satisfies the
following conditions:
1. phase distributed approximately uniformly over at least two
adjacent phase quadrants
2. phase of elements of any group of adjacent elements
substantially different
3. aperiodic phase distribution
Selective phase reversal of energy radiated from individual antenna
elements is herein employed to first produce a desired beam
pattern, and second to produce a desired scanning of, or change in,
such beam. In the following description of the present invention
the production of a highly directional beam of electromagnetic
energy is taken as an example, and the explanation of the invention
is referenced to the production of such a beam and to the scanning
of same, i.e., the controlled variation in direction of
propagation. It is, however, to be appreciated that the present
invention is equally applicable to the generation of substantially
any desired beam pattern and to controlled changing of the
pattern.
The antenna of the present invention produces an aperiodic phase
front which suppresses radiation in other than the desired
direction, and it is to be noted that this is quite contrary to
conventional systems or antennas normally generating a plane or
periodic phase front. In accordance with the present invention
there is derived a relationship for the relative far-field voltage
at a predetermined far-field point and containing a phase term. It
is herein determined that the far-field pattern is not determined
by a unique set of individual element excitation phases, but,
instead, is determined by the phase of the algebraic summation of
radiation from a number of elements. In accordance herewith the
excitation phases of separate elements are considered to be
distributed in a nonperiodic manner over the range of 0 to 2.pi.
radians. The phase of each element in the array is then compared in
the value of the phase term as described in more detail below, and
if the elements' excitation phase differs from this value by more
than .pi./2 radians, the phase thereof is reversed. Consequently,
the phase of the resultant of the summation of all elements in a
strip statistically approaches the above-noted term as the number
of elements is increased.
The present invention may be best described and most easily
understood in connection with a series of linear strips of
radiating elements, and is thus so described below. It is, however,
to be appreciated that the invention is equally applicable to
circular apertures, as is also discussed below.
DESCRIPTION OF FIGURES
FIG. 1 is a schematic illustration bearing notations employed in
theoretical considerations upon which the present invention is
based;
FIG. 2 is a schematic illustration of an octagonal antenna array in
accordance with the present invention;
FIG. 3 is a partial perspective view of a slotted waveguide as may
be employed in the present invention;
FIG. 4 is a schematic perspective illustration of a dipole radiator
as may be employed in the present invention; and
FIG. 5 is a simple circuit diagram of diode connections for
switching in accordance with the present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
The present invention may be best described and understood by
initially considering a planar aperture surface A and radiation in
a plane perpendicular thereto. In this respect reference is made to
FIG. 1 employing the conventions:
A = aperture surface
N = normal-to-surface at some reference point O
.theta. = angle between the straight lines O-N and O-P
L = line on aperture surface defined by the intersection of the
plane Q containing the lines ON and OP and the aperture surface
S = narrow strip on aperture surface perpendicular to line L and
containing a large plurality of radiating elements
The far-field radiation pattern in plane Q of the array of
radiating elements in FIG. 1 is determined by the relationship
##SPC1##
In the foregoing relationship the terms are defined as follows:
E(.theta.) = relative far-field voltage
f(d.sub.i, .theta.) = a phase term related to the difference in
path length from the reference point O to the far-field point P and
from the aperture point, i, to the far-field point P. This phase
term is a function of the location of the i.sup.th element relative
to the point O and of the angle .theta..
a.sub.i = complex voltage feeding coefficient for the element
located at position i.
Consider first that the point, P, toward which the peak of the
radiation pattern is to be directed has been chosen. This choice
determines the plane, Q, and therefore the intersection line L.
This, then, also fixes the orientation of the aperture strips such
as S. The orientation of these aperture strips may thus be
different for different positions of the main beam peak. Making use
of the fact that, once the strip orientation has been determined,
the elements lying on any strip are equidistant from the far-field
point P, the relative far-field voltage may be written as:
##SPC2##
where g(d.sub.s, .theta.) = a phase term that is the function of
the location of the strip and of the angle .theta..
It is to be particularly noted that in accordance with the equation
immediately above, the far-field pattern in the plane Q is not
determined by a unique set of individual element excitation phases,
but, instead, is determined by the phase of the algebraic summation
of all elements in the strip. Consequently in order to focus energy
toward the far-field point P, it is only necessary that the
elements in any strip satisfy the following relation: ##SPC3##
where C(t) is any spacial constant and may vary with time. In order
to satisfy the requirements of the phase relationship set forth
immediately above, the excitation phases of the elements in each
strip are considered to be distributed in a nonperiodic manner over
the range of 0 to 2.pi. radians. The phase of each element is then
compared to the value of the right-hand term in the phase equation
above corresponding to the strip in which the element lies. If the
excitation phase of the element differs from this value by more
than .pi./ 2 radians, the phase thereof is reversed. The phase of
the resultant of the summation of all elements in a strip thereby
statistically approaches -g(d.sub.s, .theta.) = C(t) as the number
of elements is increase. The amplitude of the resultant
approaches
It is to be appreciated that the requirements of the phase equation
above does not constrain the distribution of elements within a
strip; thus this distribution may be made such that the resultant
of the summation of all elements in a strip is considerably less
than
for all points outside of the plane Q. By making the distribution
different for each strip, it is possible to further reduce the
radiation outside of the plane Q, and by the proper variation of
C(t) it is possible to still further reduce this radiation. In
fact, the maximum minor lobe level can be made to be essentially
the same as would be generated by a planar phase-front antenna
having the same amplitude distribution. This is best understood by
considering the far-field electric field to be composed of two
components; one in phase with C(t) and one in quadrature with C(t).
The in-phase components thus produce a radiation pattern with
essentially the same minor lobe level as would be produced by a
planar phase-front. The quadrature components produce a pattern
which fluctuates about a spacial average power level given by
.pi..sup.2,/8 n where n = number of elements.
As the value of C(t) is varied, the quadrature pattern maxima and
minima are moved, while the in-phase pattern remains fixed.
Therefore, the time average quadrature pattern level approaches the
above spacial average at all points in space. This, by increasing
the number of elements in the array, the maximum quadrature pattern
level may be reduced to an arbitrary amount below the maximum
in-phase or planar phase-front level.
A practical embodiment of the present invention may be constructed
by the provision of a slotted waveguide with individual radiating
elements of the invention being comprised of slots cut in the broad
wall of the guide as schematically illustrated in FIG. 3. Energy is
propagated in the TE.sub.01 mode through the rectangular waveguide
11, and energy is coupled out of the waveguide through slots formed
through the broad wall thereof. There is shown in FIG. 3 one pair
of slots 12 and 13 in such a waveguide with the slots of each pair
being symmetrically disposed on opposite sides of the center line
of the guide. It will be appreciated that energy propagated through
the waveguide will be coupled out of the guide through these slots,
with pairs of slots being spaced longitudinally along the guide. In
accordance with the present invention, provision is made for
reversing the phase of energy coupled from any pair of slots. This
is herein shown to be accomplished by the location of diodes 14 and
16 in the slots 12 and 13, respectively. These diodes are
preferably electrically connected in parallel, as illustrated in
FIG. 5. Application of a bias voltage in one direction between the
terminals 17 and 18 of FIG. 5 will serve to cut off one of the
diodes, and oppositely poled bias voltage will cut off the other
diode. These diodes serve to open or close the waveguide slots for
coupling of energy from the waveguide.
It is possible in accordance with conventional practice to employ
diodes in the manner described above to short one or the other of
the slots of each pair, so that only the slot which is not shorted
will couple energy from the waveguide. It is, however, provided in
accordance with the present invention that the diodes 14 and 16
shall be employed only to detune the slots. With the diodes being
employed to controllably short the coupling slots, it is necessary
for these diodes then to carry a relatively heavy current, but with
the diodes placed as shown in FIG. 3 at the ends of the slots, it
is provided that conduction of a diode only detunes the slot,
rather than fully shorting it. It will be appreciated that a
detuned slot does not couple substantial energy from the waveguide.
It is to be further appreciated that employment of the diodes in
the manner described above materially reduces the rating required
of the diodes, so that it is possible to employ much less expensive
diodes for phase reversal herein. It was, in fact, found in one
application of the present invention that diodes having a normal
capability of operating at 2 billion Hz., when located at the ends
of the waveguide slots as shown, provided fully satisfactory
switching at 10 billion Hz. It is considered that this is a marked
and novel improvement.
Switching between waveguide slots 12 and 13 of each pair of slots
in the waveguide provides for reversing the phase of energy coupled
from each "element" of the waveguide. As noted above, the present
invention provides for beam scanning by selective phase reversal of
energy radiated from individual elements of a large plurality
thereof. Thus, the above-described slotted waveguide structure with
diode switching for selective slot detuning is capable of carrying
out the present invention.
The slotted waveguide structure described above is only one example
of structure in accordance with the present invention. Insofar as
individual radiating elements are concerned, it is possible to
employ various types and structures. Thus, for example, there is
illustrated in FIG. 4 a dipole 21 having quarter-wavelength arms 22
and 23 extending outwardly from the outer conductor of a coaxial
cable 24 at the upper terminus thereof. This outer conductor is
longitudinally slotted from the upper end for a distance of
one-quarter wavelength to separate the outer conductor into two
portions of such length, with one of the arms 22 or 23 connected to
each side of the outer conductor. Switching is accomplished with
this structure by the provision of a pair of diodes 26 and 27
connected between a central conductor 28 of the coaxial cable and
the separate arms 22 and 23. These diodes are preferably connected
in parallel as indicated in FIG. 5, so that it is possible with
appropriate biasing to cause either of the diodes to conduct. By
the application of energizing voltage between inner and outer
conductors of the coaxial cable 24, there is thus applied
energization to the arms of the dipole with the phase of such
energization being reversible by control of the conduction of the
two diodes 26 and 27.
It is also possible to form the present invention as a pair of
spaced plates energized, for example, by a probe extending between
the plates at the center thereof and probes from individual
radiating elements extending through one of the plates at varying
distances radially outward from the energizing probe. Various other
conventional types of radiators and radiator-energizing means may
be employed in carrying out the present invention.
There is illustrated in FIG. 2 of the drawing an octagonal array of
radiators formed, for example, of strips of radiators 31, 32, etc.,
transversely thereacross, and each of such strips being comprised
of a plurality of successive individual radiators. Each strip
could, for example, be formed as a waveguide of the type
illustrated in FIG. 3, with the individual radiators being then
comprised as pairs of waveguide slots, as described above. This
configuration of FIG. 2 provides a substantially circular aperture
so that the distribution of phases in any strip located a given
distance from the center of the aperture, for example, will be
independent of the location of the point P at which the beam is to
be directed consequently, the far-field pattern shape is
independent of the choice of the plane Q of FIG. 1.
It is to be understood that the present invention employs a very
substantial number of radiators or radiating elements, and that the
elements of any strip or line thereof are energized to radiate in
at least tow adjacent phase quadrants so that phase-reversal
radiation is achieved in all four phase quadrants. Thus it is
possible by reversal of the phase of radiation from selected
elements to produce a desired beam direction; consequently, by
further selected reversals to scan such a beam. With regard to this
accomplishment of phase reversal, it is noted that the preceding
description references diode switching; however, it is believed
evident that alternative types of switching may be employed. It is
furthermore noted that the sequence of diode switching, or phase
reversal, and the manner in which such is physically accomplished,
is likewise open to wide variation. Electronic or electromechanical
means may be employed to control diode switching. With regard to
the establishment of a particular desired beam, it is possible to
locate a radiation source at a point P with phase C(t) toward which
such a beam is to be directed and to measure the radiation at each
element of the invention and then to proceed as described above by
reversing the phase of those elements differing from the phase of
energy received by more than 90.degree.. This may be repeated for
different locations of point P throughout a beam scan so as to thus
arrive at a phase reversal program, which, when repeated, will
direct a beam as desired and scan same in a desired manner. More
practically, the programming of reversal may be accomplished by a
computer.
With regard to the phase of energy radiated from the elements of an
antenna array in accordance with the present invention, it is noted
that one highly advantageous arrangement is a random phase
distribution between elements. It will be seen that any line 41
drawn across the array of FIG. 2 may be considered as a strip of
radiating elements in which elements of the strip radiate in all
four quadrants of phase relationship, so that it is possible in
accordance with the present invention to reverse the phase of
particular elements thereof to generate a beam directed to any far
point P. An antenna array of the general configuration of FIG. 2
and having of the order of 400 radiating elements was employed to
produce a highly directional beam which was readily and rapidly
scanned through a predetermined pattern by the successive reversal
of phase of radiation from individual elements of the array.
There has been described above an improved and simplified scanning
antenna formed of a large plurality of radiating elements energized
to produce radiation in all four phase quadrants and adapted for
reversal of phase of radiation from individual elements thereof. In
this manner there is produced a desired radiation pattern from the
array; and scanning of the beam so produced is accomplished by
appropriate switching of the phase of energy radiated by individual
elements of the array. There is also provided hereby an
advantageous arrangement for reversing the phase of radiation from
waveguide slots by the location of diodes at the ends of such slots
for detuning a predetermined one of a pair of slots located on
opposite sides of the center line of a waveguide. Prior art
requirements of frequency variation or substantially continuous
phase variations for electronic beam scanning are hereby
precluded.
Although the present invention is described herein with respect to
particular preferred embodiments thereof, it is not intended to
limit the invention to the exact terms of description or details of
illustration, but, instead, reference is made to the appended
claims for a precise delineation of the true scope of this
invention.
* * * * *