U.S. patent number 3,925,784 [Application Number 05/440,182] was granted by the patent office on 1975-12-09 for antenna arrays of internally phased elements.
This patent grant is currently assigned to Radiation Incorporated. Invention is credited to Harry R. Phelan.
United States Patent |
3,925,784 |
Phelan |
December 9, 1975 |
Antenna arrays of internally phased elements
Abstract
An antenna array which receives radio waves and reradiates them
in a controllable direction. Direction of the reradiated wave is
controlled by controlling the phase relationship between waves
reradiated from individual antennas which are elements of the
complete array assembly. Phase control of the individual element
antennas is effected by altering the relative phase between the
received wave and the reradiated wave for each individual element
antenna. The phase of the received signal is controlled at
terminals on the individual antennas at which that received signal
arrives. The phase-altered signal is reapplied to those terminals
to serve as an excitation signal for the antenna for causing a
reradiated wave to be emitted. The difference between the direction
of the reradiated wave and the direction of the received wave is
controlled by diode switches or by varactor diodes (or by both)
which can be mounted integrally with the individual element
antennas of the array assembly.
Inventors: |
Phelan; Harry R. (Indialantic,
FL) |
Assignee: |
Radiation Incorporated
(Melbourne, FL)
|
Family
ID: |
26888449 |
Appl.
No.: |
05/440,182 |
Filed: |
February 6, 1974 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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192869 |
Oct 27, 1971 |
|
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Current U.S.
Class: |
343/754; 342/447;
342/374; 343/895 |
Current CPC
Class: |
H01Q
23/00 (20130101); H01Q 15/22 (20130101); H01Q
3/2647 (20130101); H01Q 3/46 (20130101) |
Current International
Class: |
H01Q
3/26 (20060101); H01Q 23/00 (20060101); H01Q
15/14 (20060101); H01Q 3/46 (20060101); H01Q
15/22 (20060101); H01Q 3/00 (20060101); H01Q
019/00 () |
Field of
Search: |
;343/754,854,895,797 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Lieberman; Eli
Parent Case Text
This is a continuation of application Ser. No. 192,869, filed Oct.
27, 1971, now abandoned.
Claims
What is claimed is:
1. A passive antenna for receiving and reradiating electromagnetic
waves comprising:
at least three electrically conductive arms each having an inner
end and an outer end,
said arms being spaced apart and symmetrically arranged in a plane
and having a common center such that AC electrical signals are
induced in said arms by a received electromagnetic wave and in such
a manner that said respective signals differ in phase among said
arms, and
interconnecting means located proximate to said inner arm ends at
said common center and in said plane for connecting a selected pair
of said inner arm ends together with essentially a short circuit
for reapplying said phase differing signals to the interconnected
arms in such a manner that an electromagnetic wave radiates from
the antenna with a phase relationship with respect to the received
electromagnetic wave that is determined by the selected
interconnections of said inner arm ends.
2. An antenna as set forth in claim 1 wherein the interconnecting
means comprises a plurality of switching diodes, and means for
selectively actuating said diodes into conduction or nonconduction
so that the relative phases of the reapplied signals are determined
by a choice made among received signals of differing phases to be
reapplied to the arms by the switching diodes.
3. An antenna as set forth in claim 2 wherein said plurality of
electrically conductive arms comprises frequencyindependent antenna
means having a frequency-independent phase shift between said
received electromagnetic wave and said received signals and between
said reapplied phase-differing signals and said radiated
electromagnetic wave, whereby said phase relationship between said
received and radiated electromagnetic waves is independent of
frequency of the waves over a range of frequencies.
4. An antenna as set forth in claim 2 wherein the means for
actuating said diodes comprises static switching means.
5. An antenna as set forth in claim 1 wherein the interconnecting
means comprises a plurality of switching means, and means for
selectively actuating said switching means so that the relative
phases of the reapplied signals are determined by a choice made
among received signals of differing phases to be reapplied to the
arms by the switching means.
6. A passive antenna for receiving radiated electromagnetic waves
and reradiating them, comprising:
a plurality of electrically conductive arms in which A.C.
electrical signals are induced by a received electromagnetic wave,
and
means for selectively changing the relative phases among the arms
of the signals and for reapplying the phase-differing signals to
the arms, by transmission and reflection, whereby the
phase-differing signals in the arms induce an electromagnetic wave
that radiates from the antenna with a phase relationship with
respect to the received electromagnetic wave that is affected by
the changes in the phases of the signals, said electrically
conductive arms being arms of a multi-arm spiral antenna, and the
means for selectively changing the relative phases and reapplying
the signals are proximate to the inner ends of the spiral arms, and
are controlled by a further element, namely, control means
connected proximately to the outer ends of the conductive arms.
7. A passive antenna for receiving radiated electromagnetic waves
and reradiating them, comprising:
a plurality of electrically conductive arms in which A.C.
electrical signals are induced by a received electromagnetic wave,
and
means for selectively changing the relative phases among the arms
of the signals and for reapplying the phase-differing signals to
the arms, by transmission and reflection, whereby the
phase-differing signals in the arms induce an electromagnetic wave
that radiates from the antenna with a phase relationship with
respect to the received electromagnetic wave that is affected by
the changes in the phases of the signals, said electrically
conductive arms being arms of a spiral antenna, and the means for
selectively changing the relative phases and reapplying the signals
are proximate to the outer ends of the spiral.
8. A passive antenna for receiving radiated electromagnetic waves
and reradiating them, comprising:
a plurality of electrically conductive arms in which A.C.
electrical signals are induced by a received electromagnetic wave,
and
means for selectively changing the relative phases among the arms
of the signals and for reapplying the phase-differing signals to
the arms, by transmission and reflection, whereby the
phase-differing signals in the arms induce an electromagnetic wave
that radiates from the antenna with a phase relationship with
respect to the received electromagnetic wave that is affected by
the changes in the phases of the signals, said electrically
conductive arms being arms of a multiple-arm spiral antenna, and
some of the means for selectively changing the relative phases and
reapplying the signals are proximate to the inner ends of the
spiral arms for affecting received signals having one direction of
rotation, and others of such means are proximate to the outer ends
of the spiral arms for affecting received signals having the
opposite direction of rotation.
9. A passive antenna array for receiving radiated electromagnetic
waves and reradiating them, comprising:
a plurality of electrically conductive arms spaced from each other
and oriented relative to each other such that A.C. electrical
signals are induced in said arms by a received electromagnetic wave
and in such a manner that said respective signals differ in phase
among said arms, and
phase shifting means for selectively changing the relative phases
of said signals among the arms and including interconnecting means
for selectively interconnecting selected ones of the arm ends of
the same sense for selectively reapplying the phase-differing
signals to the arms, by transmission and reflection, in such a
manner that an electromagnetic wave radiates from the antenna with
a phase relationship with respect to the received electromagnetic
wave that is determined by the selected interconnection of said arm
ends,
an array of said element antennas wherein the impinging wave
strikes the array of element antennas on the same side of the array
as that from which the resultant reradiated array wave leaves the
antenna for propagation principally in the controllable
directions,
each of said element antennas comprises frequency-independent
antenna means having a frequency-independent phase shift between
said impinging wave and said received A.C. signals and between said
reapplied A.C. signals and said reradiated elemental antenna waves,
and wherein the array of element antennas forms a parabolic contour
having a focus for one of said impinging and reradiating waves on
the geometric axis of symmetry of said contour, and the array's
dimensions transverse to the axis of the parabolic contour are at
least as great as five wavelengths of the A.C. signals, whereby
said reradiated wave when propagating externally from said array
remains collimated substantially independently of the frequency of
the A.C. signals.
10. A passive antenna array for receiving electromagnetic waves and
reradiating them in a controllable direction, comprising:
a plurality of element antennas that receive A.C. signals from an
impinging wave, and
means for reapplying the received A.C. signals to the element
antennas with signal phases that differ controllably among the
element antennas, to excite the element antennas to reradiate
elemental antenna waves having signal phases that differ among
themselves by amounts that cause a resultant reradiated array wave
which the elemental antenna waves cooperate to form, to propagate
principally in controllable directions from the array, under
control of the means for reapplying the received A.C. signals, said
element antennas being multiple-arm spiral antennas, and the means
for reapplying the received A.C. signals are proximate to the inner
ends of the spiral arms, and are controlled by a further element,
namely, control means connected proximately to the outer ends of
the conductive arms.
11. A passive antenna for receiving radiated electromagnetic waves
and reradiating them, comprising:
a plurality of electrically conductive arms spaced from each other
and oriented relative to each other such that A.C. electrical
signals are induced in said arms by a received electromagnetic wave
and in such a manner that said respective signals differ in phase
among said arms, and
phase shifting means for selectively changing the relative phases
of said signals among the arms and including interconnecting means
for selectively interconnecting selected ones of the arm ends of
the same sense for selectively reapplying the phase-differing
signals to the arms, by transmission and reflection, in such a
manner that an electromagnetic wave radiates from the antenna with
a phase relationship with respect to the received electromagnetic
wave that is determined by the selected interconnection of said arm
ends,
said received and the reradiated electromagnetic waves have
rotating polarization and wherein said electrically conductive arms
are arms of a multi-arm spiral antenna, and wherein said
interconnecting means includes means proximate the inner ends of
the arms.
12. A passive antenna for receiving radiated electromagnetic waves
and reradiating them, comprising:
a plurality of electrically conductive arms spaced from each other
and oriented relative to each other such that A.C. electrical
signals are induced in said arms by a received electromagnetic wave
and in such a manner that said respective signals differ in phase
among said arms, and
phase shifting means for selectively changing the relative phases
of said signals among the arms and including interconnecting means
for selectively interconnecting selected ones of the arm ends of
the same sense for selectively reapplying the phase-differing
signals to the arms, by transmission and reflection, in such a
manner that an electromagnetic wave radiates from the antenna with
a phase relationship with respect to the received electromagnetic
wave that is determined by the selected interconnection of said arm
ends,
said received and reradiated electromagnetic waves have rotating
polarization and wherein said electrically conductive arms are arms
of a multi-arm spiral antenna and said interconnecting means
include means proximate the outer ends of the arms.
13. A passive antenna for receiving radiated electromagnetic waves
and reradiating them, comprising:
a plurality of electrically conductive arms spaced from each other
and oriented relative to each other such that A.C. electrical
signals are induced in said arms by a received electromagnetic wave
and in such a manner that said respective signals differ in phase
among said arms, and
phase shifting means for selectively changing the relative phases
of said signals among the arms and including interconnecting means
for selectively interconnecting selected ones of the arm ends of
the same sense for selectively reapplying the phase-differing
signals to the arms, by transmission and reflection, in such a
manner that an electromagnetic wave radiates from the antenna with
a phase relationship with respect to the received electromagnetic
wave that is determined by the selected interconnection of said arm
ends,
said received and reradiated electromagnetic waves are rotationally
polarized waves and wherein said plurality of spaced apart
electrically conductive arms comprises a plurality of rotationally
angularly spaced apart electrically conductive arms for receiving
and reradiating said rotationally polarized waves, whereby a change
in said phase relationship effectively electrically rotates the
antenna for said reradiated signals.
14. A passive element antenna comprising:
a plurality of electrically conductive spiral arms spaced from each
other, said arms having a common axis of rotation, each said arm
having inner and outer ends, said inner ends being rotationally
displaced about said axis relative to each other by a given angle
to achieve a given rotational phase progression about said common
axis; and
phase control means for effectively electrically rotating said
spiral arms about said axis to control the phase relationship of
electromagnetic energy to be radiated from said element antenna
comprising interconnecting means for interconnecting at least one
pair of said inner arm ends together so that electrical signals in
said respectively interconnected pair of arms are interchanged from
one arm to the other thereof with a relative phase change dependent
upon the rotational phase relationship between said interconnected
inner arm ends.
15. An element antenna as set forth in claim 14 for use in
receiving and reradiating electromagnetic waves and wherein said
arms are oriented such that AC electrical signals are induced in
said arms by a received electromagnetic wave in such a manner that
the respectively induced signals differ in phase among said arms
whereby the electromagnetic energy reradiated from said element
antenna exhibits a phase relationship with respect to the received
electromagnetic energy that is determined by said interconnected
inner arm ends.
16. An element antenna as set forth in claim 14, wherein said
plurality of spiral arms includes a plurality of pairs of said arms
and said interconnecting means includes means for selectively
interconnecting the inner arm ends of at least one said pair of
arms.
17. An element antenna as set forth in claim 16 wherein said
interconnecting means includes switching means located proximate to
said inner arm ends.
18. An element antenna as set forth in claim 17 wherein said
plurality of arms and said switching means define a coplanar
structure.
19. An element antenna as set forth in claim 14 wherein said
plurality of spiral arms includes N pairs of arms, wherein N is at
least one, and said interconnecting means includes switching means
arranged to selectively interconnect at least one of N pairs of
said inner arm ends, whereby said element antenna is selectively
operable at one of 2.sup.N phase states.
20. An element antenna as set forth in claim 19, wherein said
switching means is proximate to said inner arm ends.
21. An element antenna as set forth in claim 20 wherein said
switching means and said N pairs of arms define a coplanar
structure.
22. A passive element antenna comprising:
at least three elongated electrically conductive arms;
said arms being spaced from each other, said arms having inner and
outer ends, said inner arm ends being rotationally displaced about
a common axis of rotation by a given angle to achieve a given
rotational phase progression about said axis so that AC electrical
signals are induced in said arms from received electromagnetic
energy such that the respective signals in the plurality of arms
differ in phase from each other in accordance with said phase
progression; and
control means for controlling said element antenna to reradiate
electromagnetic energy phase relationship with respect to the
received electromagnetic energy and comprising interconnecting
means located proximate to said inner arm ends for interconnecting
selected ones of the inner arm ends with essentially a short
circuit so that at least one pair of said inner arm ends is
interconnected by essentially a short circuit so that the phase
differing signals in the two interconnected arms of said at least
one pair are interchanged from one arm to the other thereof such
that an electromagnetic wave radiates from the element antenna with
a phase relationship relative to said received energy in dependence
upon the selected interconnection.
23. An element anntenna as set forth in claim 22 wherein said arms
extend outwardly of said common axis from said inner arm ends to
said outer arm ends.
24. An element antenna as set forth in claim 23 wherein said arms
are coplanar.
25. A passive element antenna comprising:
at least three electrically conductive arms spaced from each other,
said arms being rotationally displaced from each other about a
common axis of rotation, each said arm having inner and outer ends,
said inner ends being rotationally displaced about said axis
relative to each other by a given angle to achieve a given
rotational phase progression about said common axis, and
control means for effectively electrically rotating said arms about
said axis to control the phase relationship of electromagnetic
energy to be radiated from said element antenna comprising
interconnecting means located proximate to said inner arm ends for
interconnecting at least one pair of said inner arm ends together
with essentially a short circuit so that electrical signals in said
respectively interconnected pair of arms are interchanged from one
arm to the other thereof with a relative phase change dependent
upon the rotational phase relationship between said interconnected
inner arm ends.
26. An element antenna as set forth in claim 25, wherein said arms
are spiral arms of the same winding sense.
27. A element antenna as set forth in claim 25, wherein said arms
are of like configuration.
28. An element antenna as set forth in claim 25, wherein said arms
are of like configuration both in shape and size.
29. An element antenna as set forth in claim 28, wherein said arms
are spiral arms of the same winding sense.
30. An element antenna as set forth in claim 28, wherein said arms
and said interconnecting means are coplanar.
Description
This invention relates to an antenna comprising a plurality of
individual element antennas assembled in an array. It particularly
relates to passive antenna applications in which no transmitter or
receiver is connected directly to terminals of the array assembly,
but rather in which the array assembly effectively reflects or
redirects the radiant energy from a primary radiator. The direction
of transmission of the reradiated wave is controllable, without the
use of moving parts.
The antenna array assembly may be circularly polarized. It is
suitable for reradiating, as a return signal, energy received from
a distance source of radio transmission (retrodirective array); or
for reradiating radio energy in a controlled direction from a
nearby feed horn or other primary source of excitation in front of
it, (reflectarray); or for reradiating in lens fashion a radio
frequency wave which excites the array assembly from behind it
(lens array).
Other antenna array assemblies capable of controlling the
reradiation angle of an impinging radio wave are known in the prior
art. One of them is an array of spiral individual antenna elements,
each of which can be rotated about its individual principal axis
perpendicular to the plane of the antenna in order to control the
relative phases among reradiated waves from the element antennas of
the array. The relative phases are changed by mechanically rotating
the individual element antennas if they are circularly
polarized.
In the present invention, no mechanical motion is required; instead
the phase of the wave that is reradiated from an individual element
antenna is changed by "electrically rotating" the antenna.
The basic scheme for controlling the amount of phase change
accomplished within an individual element antenna between the
received wave and the reradiated wave is to receive the wave on
element antennas of a type having a plurality of arms, such as the
arms of a spiral antenna. The arms must have a spatial
configuration such that they receive signals differing in
electrical phase from one another, although they are received from
the same incoming wave.
EACH ELEMENT ANTENNA OF THE ARRAY ASSEMBLY HAS SEVERAL ARMS. The
received signals on the various arms can be cross-connected to each
other so as to interchange signals among the arms. As a result, the
antenna arms have a different set of phase relationships to each
other for reradiation purposes than they had when receiving the
wave originally. The phase relationships among arms for reradiation
are controllable with respect to those of the received signals so
as to change the phase of the reradiated wave with respect to that
of the received wave. Thus, for purposes of reradiation, signal
phases exist on the arms that differ among the arms but which
collectively are appropriate to reradiate a wave having a
particular phase relationship to the received wave.
As alternatives, instead of having the phases of the arms
interchanged by crossconnecting the arms, the signals can be
individually phase shifted. Moreover, they can be both
crossconnected and phase shifted.
Accordingly, it is a principal object of the present invention to
provide an antenna capable of receiving a radio wave and
reradiating it, in which the phase of the reradiated wave relative
to the phase of the received wave is conveniently controllable.
Another object is to provide an antenna capable of operation over a
wide range of frequencies without readjustment because of frequency
differences, in which the phase of a reradiated wave relative to a
received wave is simply and inexpensively controllable without the
necessity for any mechanically movable parts.
Yet another object of the present invention is to provide a
phase-adjustable antenna having a simple phase adjustment method
and low insertion loss because of the elimination of extraneous
transmission lines.
A further object is to provide an antenna that is capable of
convenient deployment in an array with other like antennas for
portable use because the array may be cut between any element
antennas for folding and because the array is thin.
A further object is to provide a reflectarray type of antenna array
that is steerable as to direction of reradiation by controlling
externally applicable DC biasing voltages.
A still further object is to provide a retrodirective antenna array
whose principal direction of radiation of a response signal is
controlled by DC bias potentials.
And a still further object is to provide a lens antenna array whose
direction of reradiation is easily steerable by means of bias
potentials applied to it.
Other objects and features of the invention will become apparent
upon aa consideration of the following description of a presently
preferred embodiment taken in conjunction with the accompanying
drawings wherein:
FIG. 1 is a view of an array assembly of element antennas suitable
for use as part of either a retrodirective array or a reflectarray
or a lens array;
FIG. 2 is an edge view of the array assembly which illustrates the
steering of a reradiated radio beam by phasing of the element
antennas;
FIG. 3 shows one individual element antenna of an array assembly,
the element shown being a four-arm spiral antenna;
FIG. 4 is an enlarged view of the center of one element antenna
with two of the four spiral arms connected together at their inner
ends;
FIG. 5 shows an annular ring which is a portion called the active
zone of an element antenna;
FIG. 6A is a phasor diagram showing relative phases of currents
induced in arms of an element antenna at an active zone, by a
received radio wave;
FIG. 6B is a phasor diagram showing relative phases of induced arm
currents which have travelled spirally in an inbound direction, as
they exist at the inner ends of the arms;
FIG. 6C is a phasor diagram showing the relative phases of currents
reapplied to the inner ends of the arms for transmission out to the
active zone;
FIG. 6D is a phasor diagram showing the relative phases of arm
currents that cause reradiation of radio energy at the active zone
of an element antenna;
FIG. 7 shows two connection plans for interconnecting the arms of
an element antenna at the inner ends of the arms;
FIG. 8 shows an arrangement of switching diodes connected to the
inner ends of a four-arm spiral antenna and provided with external
means for switching DC biasing potentials to them via the outer
ends of the spiral arms;
FIG. 9 is another possible arrangement of switching diodes
connected to the inner ends of the arms of a spiral antenna;
FIG. 10 is a spiral antenna having diodes connected between outer
ends of the spiral arms and ground terminals;
FIG. 11 illustrates the use of a varactor diode for phase shifting
at the inner ends of spiral antenna arms;
FIG. 12 is yet another version of a phase control system showing
the use of a varactor diode together with a PIN diode connected to
ends of the spiral arms of an element antenna;
FIG. 13 shows a reflectarray antenna consisting of a primary
radiator and a planar reflectarray utilizing the present
invention;
FIG. 14 shows a version of the reflectarray, excited by a primary
horn radiator, wherein the spiral element antennas are mounted so
as to form a curved surface;
FIG. 15 is a lens antenna array illuminated from its back by a
primary radiator; and
FIG. 16 is a retrodirective antenna system for radiating a return
wave back to a remote transmitter from which a wave has been
received.
The principle of the invention can be implemented structurally in
one embodiment in the following way. A number of structural arms
are provided on each element antenna, geometrically so arranged
that a single incoming radio wave excites currents of differing
electrical phase in the various structural arms. These received
currents are routed, at terminals of the arms to different arms
from those upon which they are received, but still within the same
element antenna, or are reflected back along the same arm, so that
a different set of phase currents appears on the structural arms
for reradiation purposes. The current phases differ among the arms
but they are nevertheless, as a set, appropriate for reradiating a
single phase of wave because of the spatial relationship between
the arms. By changing the selection of arms to which the received
arm currents are routed for reradiation, the set of current phases
on the structural arms can be changed, thereby altering the phase
relationship of the reradiated wave to the received wave and making
it different from previous values of that phase relationship. This
control can be effected by diode switching or by varactor diodes,
or by both, at the terminals of the structural arms.
FIG. 1 is a front view of one embodiment of an array assembly 10
suitable for use as either a reflectarray, a retroreflective array
or a lens array. It is illustrated herein as a planar structure,
although other structures are contemplated, consisting of a number
of rows and columns of individual element antennas. The individual
element antennas are multiple-arm spiral antennas suitable for
transmitting and receiving circularly polarized radio waves. When a
radio wave is arriving from, for example, the front of the array
assembly 10, energy is being received by the element antennas 12.
The portion of the energy which the element antennas 12 accept is
conducted through their spiral arms to ends of the arms, usually
the inside ends, and then flows back along the arms to the same
portion of each antenna at which it was received, that is, to the
same annular ring region. There they reradiate radio energy so as
to launch a wave that propagates outward from the array assembly.
All of the element antennas of the array operate in this manner at
the same time, and collectively they cause a single electromagnetic
wave to be reradiated from the array assembly as though it had been
reflected from the array assembly.
The angle of departure of the reradiated wave from the array
assembly depends upon the angle of arrival of the incident wave and
upon the control settings of external DC biasing means which
controls switching diodes or phase shifters located near the center
of each element antenna. Changing the phase relationships among
element antennas of an array assembly causes a wave to be radiated
in a different direction. In FIG. 2 an array assembly 10 is shown
in edge view. It consists of a number of element antennas 12
deployed over a planar surface in a grid arrangement or any other
pattern in which the individual element antennas are close enough
together to give a suitably smooth antenna radiation pattern as
measured in the far field. A planar electromagnetic radio wave
symbolized by the vectors 14 and 16 is shown impinging normally on
the array assembly, having been propagated there from some
transmitting antenna not shown.
The energy represented by vector 14 is received by an element
antenna 8 lying in the surface of the array assembly, and is
reradiated on a wave front 22. Similarly, energy captured by an
individual element antenna in the region of vector 16 is reradiated
in a hemispherical contour represented by the circle arc 24.
If the phase of wave 22 that is reradiated from element antenna 18
leads the phase of wave 24 which is reradiated from element antenna
20, the instantaneous phase of the radiated wave at circle arc 22
will be the same as the phase at that instant of the wave at circle
arc 24, but the wave from element antenna 20 has not then
propagated outward as great a distance as has that from element
antenna 18. Consequently, the dotted line 26 represents an
advancing phase front of a resultant wave being reradiated from
element antennas 18 and 20 together. If all of the element antennas
across the face of the array assembly are properly phased so as to
act in concert, they collectively create a wave front such as that
shown by dotted line 26 across the entire face of the array
assembly, which advances from the array assembly in a direction
shown by 28, 30 normal to that wave front line.
The direction of the reradiated wave can be controlled by
controlling the relative phases of excitation of the individual
element antennas of the array assembly.
One type of element antenna that is suitable for the array assembly
of this invention is a multiple-arm spiral such as that shown in
FIG. 3. This antenna consists of four spiral arms 32, 34, 36 and
38, all electrically insulated from each other. It may be
constructed by printed circuit techniques wherein the four
individual arms are conductive copper strips on the surface of a
plastic substrate. The arm 32 has an inner end 40 and an outer end
42. The inner and outer ends of arms 34, 36 and 38 are designated
by numbers 44 and 46, 48 and 50, 52 and 54, respectively, as shown
in FIG. 3.
As element antenna 12 is performing its receiving function currents
are induced in each of its four arms in a portion of the arms at a
distance from the center which depends upon the frequency of the
radio wave received. With a particular direction of rotation of
circular polarization of the received wave, the induced current
travel inwardly along the spiral arms which serve as transmission
line until they arrive at the inner ends having terminals 40, 44,
48 and 52 of the arms.
As the antenna is performing its transmitting function, antenna
excitation currents enter the arms at the same terminals 40, 44, 48
and 52 and are transmitted in spiral paths outwardly along the arms
until they arrive at a place on the antenna which is suitable for
radiating waves of the frequency of the excitation employed, as
described in more detail below. The receiving and transmitting
functions can occur continuously and simultaneously.
FIG. 4 shows one manner connecting the inner terminals of an
element antenna. The conductive link 90 between terminals 40 and 48
can, in practice be a switching diode. Another switching diode can
be provided to connect terminals 44 and 52 together at times when
link 90 is opencircuited, to create a 180.degree. different phase
shift than that which exists when link 90 is conductive. The
180.degree. phase shift occurs because changing the diode states
effectively rotates the antenna 90.degree. because the phase shift
realized is equal to twice the effective mechanical rotation. More
details of the switching of links are given later.
Energy is received on each spiral antenna and reradiated from a
portion of the antenna called the active zone, whose position
varies depending upon the frequency of the radiation. FIG. 5 shows
an annular ring 55 which represents one portion of an individual
element antenna 12; its boundaries are circles of radii 56 and 58.
The active zone or sensitive zone is not sharply defined; instead
the sensitivity of the antenna progressively increases with
increasing radius and then progressively decreases with further
increasing radius and has a maximum sensitivity at some radius such
as 60 on FIG. 5, which is termed the mean radius of the active zone
herein. Portions of the spiral arms of the antenna having smaller
radial locations than radius 56 or larger radial locations than
radius 58 do not radiate or receive energy very efficiently at the
particular frequency under discussion. Those portions do not serve
as an efficient coupling mechanism between the conductive circuit
of the antenna arms and the wave transmission medium, so that
radiation from such areas outside the active zone is
negligible.
FIG. 5 is useful for describing electrical and structural phase
relationship among the currents on the arms. Portions within the
active zone of all four arms of a fourarm antenna are shown in FIG.
5; other portions of these arms are omitted from FIG. 5 for
simplicity. When this antenna is receiving a circularly polarized
electromagnetic wave that falls upon it, the electric field vector
of the received wave at the plane of the antenna may be represented
at one instant of time by vectors 62a, 62b and 62c. Electric field
vector 62a induces a counterclockwise current in spiral arm 32
within the active zone and vector 62c induces a clockwise current
or negative current in arm 36 within the active zone. The current
induced by transverse vector 62b in arm 38 and 34 at that instant
is negligible at mean radius 60.
The current induced in the active zone portion of arm 32 propagates
spirally inward along arm 32 to its inner terminal 40. At the same
time and at the same velocity of propagation, the negative current
induced in the active zone portion of arm 36 by electric field
vector 62c propagates inwardly along spiral arm 36. It arrives at
the inner terminal 48 of arm 36 at the same time that the current
induced in arm 32 by electric field vector 62a arrives at terminal
40. Since the current directions induced in arms 32 and 36 were
opposite in sense, the arriving currents are 180.degree. out of
relative phase at terminals 40 and 48. Currents at terminals 44 and
52, which are the inner terminals of arms 34 and 38, respectively,
are 9.degree. out of phase with the currents at terminals 40 and
48.
Because the received electromagnetic wave is circularly polarized,
the electric field vectors 62a, 62b and 62c rotate so that the
maximum vlaue of induced current of one polarity is induced
sequentially in arms 32, 38, 36 and 34, for one sense of rotating
polarization. The maxima of current waves that are induced arrive
sequentially at the terminals 40, 52, 48 and 44 and, therefore,
those terminals have a rotating phase sequence of received
currents.
The relative phases of currents in the antenna at the active zone
are shown in FIG. 6A. Phasor 64 represents a current at a point 63
on arm 32 where arm 32 crosses the mean circle 60 of the active
zone, and serves as a reference phasor for this diagram. Current
phaser 66 represents a current in arm 38 at a point 65 where arm 38
spirally crosses the mean circle 60 of the active zone. Similarly,
the phasors 68 and 70 represents currents induced in arms 36 and 34
at points where those arms cross the mean radius circle of the
active zone.
The circumference of the mean circle of the active zone is
approximately one wave length of the waves being propagated along
the arms, this wave length being slightly greater than a free space
wave length because the velocity of propagation on the arms is
slightly smaller than the free space velocity. In the active zone,
there is approximately a 360.degree. phase shift standing on any
arm of the spiral antenna around one complete loop of the spiral at
one instant of time.
If the currents within one angular sector, such as sector 72 of
FIG. 5 are examined as to phase, all portions of all arms therein
are found to have approximately the same phase of current, in and
near the active zone. Phasor 66, which represents the phase of the
current on arm 38 at the mean circle of the active zone, lags by
90.degree. the phase of current at a point 73 on arm 38 within the
angular sector 72, because point 73 is displaced 90.degree.
structurally clockwise around the spiral from the point 65 where
phasor 66 exists. Thus, the current in arm 38 at point 73 can be
represented in FIG. 6A by phasor 66' which is leading the current
phasor 66 by 90.degree.. Phasor 66' is seen to be in phase with
current phasor 64 of arm 32, within the angular sector 72.
Similarly, the current on arm 36 within angular sector 72 is
leading phasor 68 by 180.degree. and can therefore be represented
by phasor 68', which is in phase with phasor 64. In the same way,
the current on arm 34 within the angular sector 72 can be
represented by pahsor 70' which is leading phasor 70 by 270.degree.
because of the structurally-caused phase difference along arm 34,
spanning the three-fourths of a full turn from the point on arm 34
where it crosses the mean circle of the active zone, to the point
where that arm is within sector 72. All of the current within
sector 72 are therefore seen to be of the same phase, such as would
be induced by a single electric field vector 62a.
Moreover, for radii within the active zone, each arm may be
contributing to the effective coupling of energy from space from
the antenna by more than merely that portion of the arm which
crosses the mean radius of the active zone. Other convolutions of
each arm at smaller and larger radii within the active zone
contribute somewhat also, although they are not quite as effective
in contributing to the operation of the antenna as is the
particular convolution which crosses the mean radius of the active
zone.
FIG. 6B shows that current induced in the arms 32, 38, 36 and 34 of
the spiral antenna differ in phase by progressive 90.degree. steps
at the inner ends 40, 52, 48 and 44 of those arms, as shown by
phasors 74, 76, 78 and 80, respectively, of FIG. 6B, which
represent the received currents at those terminals. This relative
phase relationship is the same as the phase relationship between
currents on the respective four arms at the places where those four
arms cross the means circle of the active zone, because all four
currents travel inward along the spiral conductors with the same
propagation velocity from the active zone to the inner terminals of
the antenna.
When the spiral antenna element is considered as a transmitting
antenna, its operation is similar to that described above for
receiving purposes, except that the direction of propagation of
energy is outward along the spiral transmission lines from the
inner terminals to the active zone. The four phasors 74', 76', 78'
and 80' of FIG. 6C represent currents applied to the terminals 40,
44, 48, 52, respectively, of the antenna for purposes of radiating
energy into space. It should be noted that phasor 76' is applied to
terminal 44, not to terminal 52. The sequence of events is as
follows: The currents at the inner terminals which are in
90.degree. clockwise phase progression with respect to each other
around the four terminals, propagate outward, each along its own
arm, at equal propagation velocity. They arrive simultaneously at
the mean radius 60 of the active zone of the antenna and have, at
the radius, a relative phase relationship shown by phasors 82, 84,
86 and 88 in FIG. 6D. These are the relative phases at the active
zone of currents on the four arms 32, 34, 26 and 38, respectively.
Tracing a wave clockwise around the active zone on, for example,
arm 38, whose current on the mean radius is represented by phasor
88, there is seen to be a 90.degree. phase lag in traversing the
structural quarter-circle from point 65 to point 73 in zone 72.
Consequently, the phase of the current on arm 38 within sector 72
is represented by phasor 88', which is seen to be in phase with the
current 82 on arm 32 within that angular sector. Arms 36 and 34
contribute currents 86' and 84' in zone 72, which are also in phase
with current 82.
It can be shown in a similar manner that all four arms contribute
currents of mutually reinforcing phase at a sector 75 diametrically
opposite sector 72 in the active zone. Those currents are
instantaneously 180.degree. out of phase electrically with the
currents in sector 72. However, because the portions of the arms in
sector 75 are mechanically pointing in an opposite direction from
their direction within sector 72, the structural phase reversal due
to this change in mechanical direction of the arms cancels the
180.degree. electrical phase reversal. As a result, the currents in
sector 75 travel in the same space direction as those in sector 72
so that they cooperate with the currents in sector 72 to induce an
electromagnetic wave in space. That is, because the currents in
angular sectors 72, 75 are instantaneously in the same space
direction, for example, from left to right, they reinforce each
other in producing an electromagnetic wave for propagation into
space from the antenna.
When an element antenna such as 12 is utilized in the present
invention as an element of an array, it must function as both a
receiving antenna and a transmitting antenna. The manner in which
the spiral antenna functions as a receiving antenna was described
above, culminating in currents at the inner terminals of the arms
40, 44, 48 and 52. The transmitting mode of operation of the
antenna was also described, starting with the application of
currents to the inner antenna terminals 40, 44, 48 and 52 and
culminating in the radiation of an electromagnetic wave from the
antenna because of resulting currents in the active zone. Although
the receiving and transmitting functions of an element antenna were
described above as occurring in a time sequence, they can be
contemporaneous and continuous, and therefore reception and
re-radiation can occur simultaneously.
In the antenna of the present invention, the currents which are
applied to the terminals 40, 44, 48 and 52 for transmitting
purposes can be the same currents which are received at those
terminals from the same group of antenna arms in the receiving
mode, but shifted as to phase by a greater or less amount either by
phase shifting devices or by swapping currents among the arms by
interconnections. Phase changing can be accomplished in a variety
of ways, one of which is simply to leave inner terminals 44 and 52
open-circuited, and to connect terminals 40 and 48 together by a
link 90, as shown in FIG. 4. Then current waves that propagate
inward along the spiral arms reflect when they encounter the
opencircuited terminals 40 and 48, and cause current waves to start
to propagate outward along the same spiral arms. The received
current of arm 34 becomes, when it reaches the inner terminal 44,
the negative of the transmitting current of that same arm. In the
same way, the transmitting current of arm 38 is simply the negative
of the received current of arm 38. The negative relationship exists
at the central terminals and may be somewhat different at the
active zone.
The received current from arm 32 at terminal 40 is connected
through a conductive link 90 to terminal 48 of arm 36 so that the
received current of arm 32 becomes a transmitting current of arm 36
and conversely the received current of arm 36 becomes a
transmitting current of arm 32. There is a current cross-over
between the two arms through the link 90, which can be a switching
diode.
The direction of sequential phase rotation of transmitting currents
among the terminals is the reverse of the direction of phase
rotation of the received currents, as it must be if it is to
radiate when it reaches the active zone. When the outward
propagating wave arrives at the active zone of the antenna, it
causes radiation, and the originally impinging radio wave appears
to have reflected from the antenna. Reconnecting the link 90 across
termianls 44 and 52 instead of across terminals 40 and 48 would
cause a different phase shift between receiving and transmitting
currents, differing by 180.degree. from its previous value.
Alternatively, two of the inner terminals could be short-circuited
to a small ground plane or common tie point at the center of the
element antenna, in which case the currents propagating outward
along the short-circuited arms would have the same polarity at
their starting terminals as have the received currents.
The relative phase between inward-propagating currents when they
originate in the active zone, and outward-propagating when they
arrive back at the active zone, is a function of the round trip
distance from the active zone in to the inner terminals and back
along the spiral arms, and can be expressed in wavelengths on the
line. This phase difference between the received wave and the
reradiated wave can be altered by changing the connections at the
inner terminals 40, 44, 48, 52, as just described. The phase of the
reradiated wave can therefore be made different as between
different individual element antennas of an array assembly, even
though all of those element antennas are excited by the same
received radio wave, by simply making different connections at the
antenna terminals 40, 44, 48, 52 of the different element antennas
of the array. Not only may the reradiated wave be changed in phase
by 180.degree., as shown above, but by appropriate connections of
the inner terminals, other amounts of phase shift can be
accomplished.
FIG. 7 shows, by solid lines 92, conections that would give a
particular phase relationship between received and reradiated waves
in an antenna having eight spiral arms. The dotted lines 94 show
different connections at the same inner terminals 96 of the antenna
arms, which would result in a different phase shift for the same
eight-arm spiral antenna.
In a preferred embodiment of the present invention connections
between the various arms at their inner terminals are made by means
of diode switching. FIG. 8 shows a four-arm spiral antenna with
diodes connected to its inner terminals, having capability for
applying by means of external switches various positive or negative
DC biasing currents to the outer ends of the spiral arms. By
selective operation of the switches 100, 102, 104, and 106, various
diodes can be rendered conductive by being forward biased, thereby
effectively connecting together the inner terminals of certain
spiral arms. Other connections can be effectively opened by means
of voltage back-biasing of their switching diodes, or even by
applying zero bias voltage to them, which is insufficient to cause
efficient conduction of small signals.
In FIG. 8, when terminal T2 receives a positive voltage by having
switch 102 in its upper position, and terminal T4 is given a
negative voltage by having switch 106 in its lower position, and
terminals T1 and T3 have no bias voltage applied because switches
104 and 100 are in their center positions, the following diode
pairs are conductive for samll signals: B, D, E, F, G, H. Diode
sets A and C do not conduct then. The relative phase of the group
of transmitting currents for this condition can be arbitarily
called 0.degree., so that this is a reference phase condition.
When only terminal T1 is made positive and only T3 is negative,
only diode pairs B, D are nonconductive. The relative phase of the
transmitting currents is then 180.degree..
When T1 and T4 are positive and T3, T4 are negative, only diode
pairs F and H are nonconductive (because they have zero bias), and
the relative transmitting phase is 90.degree..
When T1 and T2 are positive and T3, T4 are negative, only diode
pairs E and G are nonconductive; the relative transmitting phase is
then 270.degree..
By operating switches 100, 102, 104, 106 to achieve various biases
as just described, the phase of the reradiated wave can be changed
in 90.degree. steps.
FIG. 9 shows another embodiment in which, instead of the inner ends
of the spiral arms being selectively connected only to each other,
they may either be connected to another arm or connected to a
common ground point near the center of the element antenna. Diodes
108, 110, 112 and 114 are employed to connect antenna arms
together, while diodes 116, 118, 120 and 112 are used to connect
arms to a common ground point. The switches 124, 126, 128 and 130
may be used selectively to control the bias voltages on the various
diodes.
The electromechanical switches represented by reference numerals
100, 102, 104, 106, 124, 126, 128, 130 are merely symbolic of any
means of controlling the potentials to be applied to the spiral
antenna arms and therefore to the switching diodes or varactor
diodes. In practice, these potentials would more probably be
controlled by static switching circuits and possibly by circuits
under computer control.
Digitally switched embodiments of the invented antenna are
frequency independent in their performance, because the phase
differences among the currents originate in frequency independent
structural phase differences among the arms at the active zone. For
operation at a lower frequency, the active zone automatically moves
out to a greater radius of the element antennas.
When a counterclockwise-rotating circularly polarized wave is
received in the active zone shown in FIG. 5, the received signal
propagates inward along the spiral arms because of the manner in
which the received wave couples to all of the arms and reinforces
the flow of current induced in those arms throughout all of the
convolutions of those arms in the active zone. On the other hand, a
clockwise-rotating circularly polarized wave impinging upon the
element antennas causes outwardly propagating spiral waves which
travel along the spiral arms to their outside ends. FIG. 10 shows
an embodiment in which diodes H are connected from the outside ends
of the antenna 132 to ground. When the antenna receives a
circularly polarized wave having such direction of circular
polarization as to cause the induced currents to propagate
outwardly from the active zone to the outside ends of the spiral
arms, certain of the diodes can be biased to conduction to cause
currents of the same polarity as the received currents to reflect
back inwardly along the spiral arms. The diodes may be switched by
application of DC potentials to forward-bias or back-bias the
diodes, thereby changing the phase shift. This embodiment is
frequency-dependent. The usefulness of this technique is that both
senses of circular polarization may be operated on simultaneously
and independently.
In another frequency-dependent version of the invented antenna, the
switching diodes may be varactor diodes, as seen in the simplified
sketch of FIG. 11, and the capacitance of the diodes may be altered
by applying different DC potential biases to them. The phase shift
encountered by a current that propagates along an arm to the diode
and is then reflected, can be varied by varying the capacitance of
the diode under control of the DC potential bias. In this way, the
phase shift of the element antenna can be controlled as to the
reradiated wave.
FIG. 12 is a combination of an analog and digital form of phase
control at terminals of a spiral antenna. Element 136 is a varactor
diode and element 138 is a PIN diode which can be either
forward-biased to short-circuit the reactance 140 or else
back-biased to permit reactance 140 to come into play.
FIG. 13 shows a planar array assembly 10 of the type shown in FIG.
1 utilized in a reflectarray antenna wherein the array assembly is
illuminated electromagnetically by a primary radiator such as a
circular horn 142 having a circularly polarized element in its
throat. Power represented by the vectors 144 strikes element
antennas 12 of the array assembly and is reradiated. The direction
of reradiation is that shown by arrow 146 for one phasing condition
of the element antennas 12. The wave is reradiated in a different
direction 148 when the element antennas 12 are phased in a
different manner, by application of a different set of DC potential
biases to their diode switches as described above.
In an embodiment employing multi-arm spirals, the spiral elements
can be nominally 0.5 wavelength in diameter at the lowest operating
frequency and spaced 0.25 wavelength above a continuous reflecting
ground plane. The diameter of the reflectarray is related to the
antenna gain and beamwidth desired. For example, if a 1.degree.
antenna beamwidth is required, the reflectarray aperture must be
approximately 70 wavelengths in diameter. If D is the reflectarray
diameter and f is the distance from the reflectarray to the feed
horn, typical useful values of the ratio f/D are 0.5 to 1.0. The
feed horn is typically 1 to 2 wavelengths in diameter.
FIG. 14 shows a curved version 152 of a reflectarray antenna, in
which the element antennas 12 are placed so as to form a contour
especially suitable for collimating energy that is radiated upon it
from a focus 153 by a nearby feedhorn or other primary radiator 154
on an axis of geometric symmetry 155. When the contour is parabolic
and the element antennas 12 are a frequency-independent type, such
as spiral antennas, and the aperture of the array is large in terms
of wavelengths, e.g., 5 or more wavelengths, the collimation that
is realized is independent of frequency. The reradiated wave can be
made to propagate in a direction shown by the vector 156, for one
set of phase shifting conditions within the element antennas, or to
propagate in a different direction 158 for a different set of
internal phase shifts. The array is suitable for both transmitting
and receiving, as are the other antennas described herein.
FIG. 15 is a lens array antenna which is yet another embodiment of
this invention. An array assembly 10 comprising element antenna 12
is subjected to radiation 160 from a feed device such as horn 162
mounted behind it. The array 10 behaves as though it were
refracting the received wave and directs it forward in a direction
such as is represented by Poynting vectors 164 or 166. The
direction is controlled by DC biasing potentials on the
phase-shifting diodes of element antennas 12, with no moving
mechanical parts.
A retrodirective application of the invented antenna is shown in
FIG. 16. The purpose of this antenna is to receive a wave 168 from
a remote source and send it back in the reverse direction 170 as
that from which it came. The reflection behavior of the antenna
array assembly 172 is, as in the other embodiments, controlled by
phase-shifting the reradiated wave from the various element
antennas. The phase-shifting is, as before, under the control of DC
potential biases 174 which affect switching diodes or analog phase
shifters such as varactor diodes at points connected to either the
inner ends, outer ends, or both ends of the spiral arms of each
element antenna. The direction in which the reradiated wave is to
be transmitted is ascertained with a direction-finding antenna 176
which is shown separated from the retrodirective array antenna 172,
although conceivably their functions could be combined in a single
antenna. A direction-finding processor 178 controls the DC
potential biases by means of a beam steering processor 180, to
establish the desired direction of reradiation.
Another feature of the retrodirective version is that relative
phase shift between elements may be used to steer the direction of
reradiation, while the absolute phase of all elements may be used
to phase modulate the retrodirected signal. A typical application
is one in which some desired information is sensed near the
retrodirective antenna, converted to voltage sufficient for phase
drive and applied to the retrodirective antenna phase modulator and
then to processor 180. Phase drive and modulation equipment 182,
184 are in dotted lines in FIG. 16. The sensed information may be
obtained by addressing the antenna from a distance with an RF
transmitter, receiver, and antenna.
Although the invention has been described by examples of circularly
polarized embodiments, it is equally applicable to elliptically and
linearly polarized antennas of types having individual arms in
which are induced, from a single received radio wave, currents
having differing electrical phases. Expressing this requirement in
terms applicable to a transmitting mode of operation, the invention
is applicable to antennas whose radiated wave is created by
simultaneous cooperation of arms or sub-elements whose
instantaneous exciting currents are distributed in phase,
preferably over some appreciable fraction of 360.degree. or more.
Antennas of this type permit current signals that are received on
their arms to be interconnected among themselves to other such
arms, and/or phase shifted, and thereby to serve as transmitting
antenna currents, with the manner of interconnecting the various
antenna arms to each other being used to control the phase of the
reradiated wave.
* * * * *