U.S. patent number 3,906,514 [Application Number 05/363,029] was granted by the patent office on 1975-09-16 for dual polarization spiral antenna.
This patent grant is currently assigned to Harris-Intertype Corporation. Invention is credited to Harry Richard Phelan.
United States Patent |
3,906,514 |
Phelan |
September 16, 1975 |
Dual polarization spiral antenna
Abstract
An element antenna for use with a plurality of similar element
antennas in an array. The element antenna receives and reradiates
circular polarized electromagnetic energy such that the reradiated
energy is of the same polarity as the received energy,
independently of the geometric polarization element antenna. The
element antenna includes a plurality of elongated, electrically
conductive arms, each having an intermediate portion located in an
annular active antenna region where circular polarized
electromagnetic energy is received and reradiated. The arms of the
element antenna are configured so that they define a geometric
polarization element antenna of a given circular polarity so that
currents induced in the respective intermediate arm portions from
received energy, flow towards specific arm ends in dependence upon
the polarity of the received energy. The currents are acted upon so
that they re-enter the active region having their relative phases
controlled in such a manner that the reradiated energy is of the
same circular polarity as the received energy.
Inventors: |
Phelan; Harry Richard
(Indialantic, FL) |
Assignee: |
Harris-Intertype Corporation
(Cleveland, OH)
|
Family
ID: |
26888448 |
Appl.
No.: |
05/363,029 |
Filed: |
May 23, 1973 |
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: |
343/895;
343/754 |
Current CPC
Class: |
H01Q
3/46 (20130101); H01Q 15/22 (20130101); H01Q
23/00 (20130101) |
Current International
Class: |
H01Q
23/00 (20060101); H01Q 15/14 (20060101); H01Q
3/46 (20060101); H01Q 15/22 (20060101); H01Q
3/00 (20060101); H01Q 019/06 () |
Field of
Search: |
;343/895,754,854 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lieberman; Eli
Parent Case Text
This is a continuation-in-part of my previous application Ser. No.
192,869 filed Oct. 27, 1971, now abandoned, and which is assigned
to the same assignee as this application. The disclosure of that
application is incorporated by reference herein.
Claims
What is claimed is:
1. An element antenna for receiving and reradiating circular
polarized electromagnetic energy comprising a plurality of
elongated electrically conductive spiral arms spaced from each
other, each said arm having inner and outer ends and at least an
intermediate portion of its length between said ends located in an
annular active antenna region where circular polarized
electromagnetic energy is received and reradiated, said arms having
a common axis of rotation, said inner arm ends being rotationally
displaced about said axis relative to each other by a given angle
to achieve a given rotational phase progression about said axis,
said arms being configured so that when taken together they define
a geometric polarization element antenna of a given circular
polarity whereby the currents induced in said respective arm
portions from energy received in said active region flow towards
specific arm ends in dependence upon the polarity of the received
energy, and phase control means for controlling said element
antenna to reradiate circular polarized energy of the same polarity
as the received energy and for controlling the phase relationship
of the reradiated energy with respect to the received energy and
including interconnecting means for effectively interconnecting
selected ones of said arm ends of the same sense, for controlling
the phase relationship of said currents re-entering said active
region from said arm ends of both senses to effect reradiation from
said active region in such a manner that the energy reradiated in
the general direction of the received energy is of the same
circular polarity as the received energy independently of the said
geometric polarization of said element antenna and such that the
phase relationship of said reradiated energy relative to said
received energy is determined by said selected interconnection.
2. An element antenna as set forth in claim 1, wherein said arm
ends of one sense are inner ends located inwardly of said active
region and said arm ends of the opposite sense are outer ends
located outwardly of said active region.
3. An element antenna as set forth in claim 2, wherein said inner
ends are positioned relative to each other in a spacial
configuration so that the currents induced in said arms for
received energy of a given circular polarity initially flow toward
said inner ends and arrive at said inner ends electrically
displaced in phase by given amounts.
4. An element antenna as set forth in claim 3 wherein said
interconnecting means includes switching means for selectively
interconnecting selected said arm inner ends together to vary the
phase relationship of the currents flowing from said inner ends
into said active region.
5. An element antenna as set forth in claim 3 wherein said
interconnecting means includes switching means for effectively
electrically interconnecting selected said arm outer ends together
to vary the phase relationship of the currents flowing from said
outer ends into said active region.
6. An element antenna as set forth in claim 3 wherein said phase
control means includes an extended arm portion of each said arm
extending outwardly from said active region to said outer ends so
that currents induced in said arms for receiving energy of an
opposite polarity from said given polarity will initially flow
outwardly along said arms toward said outer ends and be reflected
at said outer ends so as to then flow inwardly.
7. An element antenna as set forth in claim 6 wherein selected ones
of said outer arm portions are reactively terminated in such a
manner that as said currents are reflected to flow inwardly they
are shifted in phase so as to be out of phase as they enter said
active region, said interconnecting means including means
interconnecting selected said arm inner ends together such that the
currents which then flow outwardly along said arms are shifted in
phase relative to each other to be out of phase as they reenter
said active region and said interconnecting means being chosen and
said outer ends being reactively terminated in such a manner that
said phase shifted outwardly flowing currents are reflected from
said outer ends and then flow inwardly in phase with each other as
they re-enter said active region so that they reradiate
efficiently.
8. An element antenna as set forth in claim 7 wherein said outer
arm portions are reactively terminated by passive reactance
means.
9. An element antenna as set forth in claim 6 wherein said outer
arm portions are reactively terminated with active switching means
selectively actuatable for connecting said outer arm portions with
selected reactance means to effect desired phase shifting.
10. An element antenna as set forth in claim 6 wherein said outer
arm portions are configured so that the length of each arm portion
from said active region to the said outer arm end thereof is such
that said induced currents that initially flow outward are
reflected from said outer end to flow inwardly and out of phase as
they re-enter said active region, said interconnecting means
including means interconnecting selected said arm inner ends
together such that the currents which then flow outwardly along
said respective arms are shifted in phase relative to each other to
be out of phase as they re-enter said active region, and said
interconnecting means connecting selected said arm inner ends and
said outer arm portions being of lengths such that said phase
shifted outwardly flowing currents are reflected from said outer
ends and then flow inwardly in phase with each other as they
re-enter said active region so that they reradiate efficiently.
Description
BACKGROUND OF THE INVENTION
The present invention relates to the art of antennas and, more
particularly, to an improved phase controlled element antenna
adapted to be included in an array and which is particularly
applicable for reradiating circular polarized electromagnetized
energy of either polarity and of the same polarity of the received
energy.
The element antenna is particularly applicable for use in an array
suitable for reradiating energy received from a source of
electromagnetic energy. Alternatively, the element antennas may be
used in an array for reradiating electromagetic energy in a
controlled direction from a nearby feedhorn or other primary source
of excitation in front of it. Still further, the element antenna
may be used in an array for reradiating, in a lens fashion, a radio
frequency wave which excites the array assembly from behind it.
Whereas the invention will be described herein with respect to an
element antenna having a plurality of spiral shaped arms, the
invention is not limited thereto so long as the arms exhibit a
spacial configuration such that they receive signals from an
incoming wave in such a manner that the currents induced in the
arms flow to respective ends of the arms while differing in
electrical phase one from the other.
It is a specific object of the present invention to provide an
element antenna constructed for receiving and efficiently
reradiating circular polarized electromagnetic energy of either
polarity in such a manner that the reradiated energy is of the same
circular polarity as the received energy.
It is a still further object of the present invention to provide an
element antenna suitable for use in an array of like element
antennas for reradiating either left-hand or right-hand circular
polarized energy.
It is a still further object of the present invention to provide an
element antenna construction suitable for use in an array with like
element antennas and having phase shifting means internally
disposed within each element antenna for purposes of controlling
reradiation of electromagnetic energy in a desired direction
relative to the direction of the incoming energy and of either
circular polarity.
In accordance with the invention, the element antenna includes a
plurality of elongated electrically conductive arms which are
spaced from each other. Each arm has an intermediate portion of its
length located in an annular active antenna region where circular
polarized electromagnetic energy is received and reradiated. The
arms are configured in such a manner that they define a geometric
polarization element antenna of a given circular polarity so that
the currents induced in the respective arm portions, from energy
received in the active region, flow towards specific arm ends in
dependence upon the polarity of the received energy. The arms are
acted upon to control the phase relationship of the currents as
they re-enter the active region from the arm ends of either sense
to effect efficient reradiation from the active region. The
currents are acted upon in such a manner that the energy reradiated
in the general direction of the received energy is of the same
circular polarity as the received energy independently of the
geometric polarization of the element antenna.
In accordance with a more limited aspect of the present invention,
phase control is achieved by effectively electrically
interconnecting selected inner arm ends together in such a manner
to vary the phase relationship of the currents reapplied to the
active region.
In accordance with a still further aspect of the present invention,
phase control is achieved by reactively terminating the outer arm
ends in such a manner that induced currents, due to electromagnetic
energy of one polarity, are caused to initially flow outwardly to
the outer ends where they are reflected and changed in phase in
dependence upon the manner in which the outer arms are reactively
terminated.
In accordance with a still further aspect of the present invention,
phase control is achieved by varying the relative lengths of the
outer arm portions in such a manner that the currents reflected
from the outer arm ends are changed in phase before re-entering the
active region.
The foregoing and other objects and advantages of the invention
will become more readily apparent from the following description of
the preferred embodiment of the invention as taken in conjunction
with the accompanying drawings which are a part hereof and
wherein:
FIG. 1 is an elevational view illustrating a reflectarray excited
by a primary horn radiator and wherein the array is composed of a
plurality of element antennas;
FIG. 2 is an elevational view illustrating a lens antenna array
illuminated from its back by a primary radiator and wherein the
array is composed of a plurality of element antennas;
FIG. 3 illustrates an element antenna in the form of a four arm
spiral construction and which is used in one embodiment of the
present invention;
FIG. 4 is an enlarged view of the center portion of an element
antenna illustrating two of the inner arm ends being
interconnected;
FIG. 5 is a schematic illustration of an element antenna
illustrating a portion of the operation in conjunction with the
active region of the antenna;
FIG. 6 illustrates one manner of employing phase control in the
form of diode switches for interconnecting the inner ends of a
multi-arm spiral element antenna by DC bias potentials applied
through the spiral arms;
FIG. 7 illustrates a spiral element antenna employing diodes at
both the inner and outer ends of the element antenna in such a
manner that the antenna may be employed for reradiating either
left-hand or right-hand circular polarized electromagnetic
energy;
FIG. 8 illustrates another version of a dual polarization spiral
element antenna similar to that of FIG. 7 but which does not employ
switching diodes connected to the outer ends of the spiral arms
and, instead, the outer arm ends are reactively terminated with
reactances to achieve phase control;
FIG. 9 is another version of a dual polarization element antenna in
which the outer ends are reactively terminated for phase control by
varying the lengths of the spiral arms; and
FIG. 10 illustrates a still further version of a dual polarization
spiral element antenna wherein the spiral arms lengths and the
spiral diameter are chosen and configured to achieve phase
control.
Referring now to the drawings wherein the showings are for purposes
of illustrating a preferred embodiment of the invention only and
not for purposes of limiting same, there is illustrated in FIGS. 1
and 2 two different applications of an array of element antennas
constructed in accordance with the invention. In FIG. 1 there is
shown a reflectarray system employing a parabolic array assembly 10
which carries an array of element antennas 12 constructed in
accordance with the present invention. The array is illuminated
electromagnetically by a primary radiator in the form of a circular
horn 14 having a circular polarized element in its throat. The
electromagnetic energy from the horn strikes the array assembly and
is reradiated by the element antennas along a direction generally
designated by the arrow 16. The direction of the reradiated energy
is controlled by a suitable beam steering circuit which operates to
actuate the phase control switches, to be described in greater
detail hereinafter. The reradiated energy may be steered along a
different direction, such as the direction indicated by the dotted
arrow 18. In addition to controlling beam direction relative to the
direction of the received energy, the element antennas also
reradiate the energy so as to be of the same circular polarity as
that of the received energy, independently of the geometric
polarization of the element antennas.
The invention may also be employed with a lens array, such as the
planar lens array 20 illustrated in FIG. 2. This array also
comprises a plurality of element antennas 12. In this case,
however, the element antennas are subjected to circular polarized
radiation from a feed device, such as a horn 22, mounted behind the
array. The array behaves as though it were refracting the received
wave and directs it in a forward direction, such as is represented
by the arrow 24. The direction of radiation is controlled by phase
control switching diodes so that the radiated energy may be steered
along a different direction, such as that indicated by the dotted
arrow 26. Still further, the phase control is such that the
radiated energy will be of a desired circular polarization.
Having generally discussed two of the applications of the present
invention, attention is now directed toward the element antenna
structure employed herein. 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 currents
travel inwardly along the spiral arms which serve as transmission
lines 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 of 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 open-circuited, 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. and 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 the 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 four-arm 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 arms 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 90.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 value 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 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 smaller 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. The current on arm 38 at point 65 on the mean
circle of the active zone, lags by 90.degree. the phase of current
at 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.
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.
The currents 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. 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 mean 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 of the active zone. 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.
It can be shown that all four arms contribute currents of mutually
reinforcing phase at a sector 75 diameterically 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 instantaenously in the same space
direction, for example, from left to right, they reinforce each
other in producing an electromangetic wave for propagation into
space from the antenna.
When an element antenna such as 12 is utilized as an element of a
reflectarray, 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 comtemporaneous and
continuous, and therefore reception and reradiation 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
open-circuited 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
terminals 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. Ths 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.
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. 6 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 potentials 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. 6, 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 small 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 arbitrarily
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, T2 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.
In the embodiment described above with respect to FIG. 6, the
spiral arms are configured so that they define a geometric
polarization element antenna of counterclockwise or left-hand
circular polarity. If the received wave front is also left-hand or
counterclockwise circularly polarized, then currents induced in the
active zone will initially flow in an inward direction along the
spiral arms. Upon reaching the inner ends, the currents will either
be reflected back toward the active zones or be transmitted through
one or more switching diodes so as to flow outwardly along a
different spiral arm. With the proper phase insertion accomplished
by the centrally located diode switches, the currents which flow
outwardly in the spiral arms arrive at the active zone in phase so
as to cause reradiation of a left-hand or counterclockwise rotating
circular polarized wave. whereas the currents are in phase with
each other, they may all be shifted together in phase depending on
the diode switches in effect so that the reradiated energy is
shifted in phase from that of the received energy. By including the
several element antennas in an array, the reradiated
electromagnetic energy may be steered by appropriately controlling
the centrally located phase shifting switching diodes.
It is also desired that a left-hand circularly polarized element
antenna, such as that shown in FIG. 6, be employed to efficiently
reradiate a received right-hand electromagnetic wave, such that the
reradiated wave is also of right-hand circular polarization. When
such a wave is received by the element antenna illustrated in FIG.
6, the currents induced in the active zone will initially travel in
an outward direction to the outer ends of the spiral arms. In order
to effect efficient reradiation of right-hand circular
polarization, the currents flowing in the arms must be flowing in
an inward direction and in phase with each other as they enter the
active zone. The embodiments illustrated in FIGS. 7, 8, 9 and 10
serve to provide dual polarization operation in that, in each case,
a left hand circular polarization element antenna may reradiate
either an incoming left-hand circular polarized wave or a right
hand circular polarized wave with the reradiated wave being of the
same circular polarization as the received wave.
Attention is now directed to the embodiment shown in FIG. 7. This
embodiment, like that illustrated in FIG. 6, employs centrally
located switching diodes which serve the same purpose as the
switching diodes of FIG. 6. These switching diodes are biased, as
desired, by applying DC signals through the spiral arms. A received
left-hand circular polarization wave front is reradiated in the
same manner as described hereinbefore with respect to the
embodiment of FIG. 6. In addition, the embodiment of FIG. 7 employs
switching diodes which are connected from the outer ends of the
antenna arms to ground. These outer switching diodes may be biased
in the same manner as the inner diodes so as to provide either an
open circuited termination or a short circuited termination to
ground and thereby selectively effect a phase change. Consequently,
when the antenna receives a wave of right-hand circular
polarization, the induced currents propagate outwardly along the
spiral arms. The diodes connected to the outer ends of the spiral
arms are selectively biased, as desired, to vary the relative
phases of the currents reflected back inwardly along the spiral
arms.
By a correct adjustment of the line lengths between the active
region of the spiral arms and the outer terminals, the same phase
progression will be existent between the terminal currents on the
outer terminals as on the inner terminals, discussed hereinbefore.
However, switching performed on the outer terminals is apparently
frequency dependent because the line length between the active
region and the outer terminals of the spiral will change insertion
phase linearly with frequency. The phase shifting at the inner
terminals would still be frequency independent and is isolated and
independent of the diode switching at the outer terminals. Because
of this independence, both right-hand and left-hand polarization
beams may be controlled independently and, for example, an array
employing such an element antenna may receive a right hand
circularly polarized signal from one direction while simultaneously
transmitting a left-hand circularly polarized signal in another
direction.
Referring more specifically to the embodiment of FIG. 7, it will be
seen that the outer switching diodes A', B', C', D', E', F' and G'
are connected to a transmission line T1 and spaced from each other
by one-quarter of a wave length. Bias control is provided for each
of the outer switching diodes in the same sense as that provided
for the switching diodes of FIG. 6. For example, with respect to
diode H', a DC bias switching control 110H is provided. This
control is connected in parallel with the diode and is spaced
therefrom by a quarter wave length. The switch control 110H may
take the form of a simple single pole, double throw switch, as
illustrated in FIG. 6, for purposes of selectively connecting
either a B+ or a B- potential to diode H'. The B+ potential applied
to the diode serves to provide a short circuit to ground, whereas a
B- potential applied to the diode serves to effect an open circuit.
The extra switching diodes; to wit, diodes B', D', F' and H' are
positioned one-quarter wave length from associated spiral arm
switching diodes and serve to isolate the antenna end switching
diodes from each other.
In the operation of the embodiment of FIG. 7, the switching diodes
A' through H' are selectively short circuited or open circuited by
the switch controls 110A through 110H to effect phase insertion.
The currents induced in the spiral arms from a right hand circular
polarized wave are reflected from the spiral ends and shifted in
phase in accordance with which diodes are short circuited or open
circuited so that the reflected currents flow inwardly into the
active zone in phase with each other. Thus, electromagnetic energy
of right-hand circular polarization is radiated. The outer
switching diodes may be actuated so that there is a phase change
between the reradiated electromagnetic energy and that of the
received electromagnetic energy. If the desired relative phase is
0.degree. then switching diodes A', B', D', E', F' and H' are short
circuited whereas switching diodes C' and G' are open circuited.
If, on the other hand, it is desired to obtain a 90.degree.
relative phase change, then only switching diodes D' and F' are
open circuited and the remaining switching diodes are short
circuited. If it is desired to obtain an 180.degree. relative phase
change, then only switching diodes C' and G' are short circuited
and the remaining diodes are open circuited. A 270.degree. relative
phase shift may be achieved if switching diodes B' and F' are short
circuited and the remaining switching diodes are open circuited. It
is contemplated that the element antenna of FIG. 7 be employed in
an array together with suitable circuitry for selectively short
circuiting or open circuiting the various switching diodes to
effect beam steering.
Reference is now made to the embodiments of the invention
illustrated in FIGS. 8, 9 and 10. These embodiments, like that of
FIG. 7, are geometrically arranged to define left-hand circular
polarized element antennas. Each serves to receive either a
left-hand or a right-hand circular polarized wave front and to
reradiate electromagnetic energy of the same circular polarity as
the received wave. However, unlike the embodiment of FIG. 7, none
of these additional embodiments requires the use of switching
diodes connected to the outer ends of the spiral arms.
Referring now to the embodiment shown in FIG. 8, the element
antenna is illustrated as being substantially identical to that
illustrated in FIG. 7. It includes four spiral arms, as in the
previous embodiment, together with centrally located switching
diodes for interconnecting the various inner arm ends together in
the manner described hereinbefore. The bias control for the
centrally located switching diodes is achieved through DC bias
signals applied to each of the outer arms via a switching
arrangement such as that shown in FIG. 6. In the embodiment of FIG.
8, the inner bias control is illustrated simply as inner bias
controls 120, 122, 124 and 126 for respectively applying either a
B+ or a B- potential to arm ends T1, T2, T3 and T4. In addition,
the arm ends are reactively terminated in a manner to obtain
desired phase insertion. Arm ends T1 and T3 are each reactively
terminated by a reactance X1 to effect a 0.degree. phase shift.
However, arm ends T2 and T4 are each reactively terminated by a
reactance X2 to effect a 180.degree. phase shift.
In the operation of the element antenna shown in FIG. 8, the inner
switching diodes ar biased so as to present either a low radio
frequency impedance or a high radio frequency impedance in the same
manner as described hereinbefore with respect to the operation of
the switching diodes shown in FIG. 6. If the reradiation phase is
to have a 0.degree. phase shift, then the diodes are biased so that
terminal points 2 and 4 are effectively short circuited. If a
90.degree. relative phase shift is to be achieved, then the diodes
are biased so that inner terminal points 1 and 2 are shorted and
inner terminal points 3 and 4 are shorted. Similarly, if a
180.degree. relative phase shift is to be obtained, then points 1
and 3 are shorted. lastly, if a 270.degree. phase shift is to be
achieved then points 2 and 3 are shorted and points 1 and 4 are
shorted. The operation that takes place for reradiating a received
left-hand polarity wave front is the same as that described
hereinbefore with respect to FIG. 6.
Assume that a right-hand wave is received and that the reradiated
wave is to have a relative phase displacement of 0.degree.. In such
a case, the currents induced in the active zone will initially flow
in an outward direction to the terminal ends T1, T2, T3 and T4. The
insertion phase for currents reflected from the spiral ends is
0.degree. , 180.degree. , 0.degree. and 180.degree. at spiral ends
T1, T2, T3 and T4 respectively. Consequently, the relative phases
of the currents flowing from the arm ends into the active region is
0.degree. , 180.degree. , 0.degree. and 180.degree.. Since the
currents are out of phase, electromagnetic energy is not radiated
from the active region. The relative insertion phase from the
active region to the feed point is 0.degree. , 90.degree. ,
180.degree. and 270.degree. at terminal inner ends 1, 2, 3 and 4
respectively. Thus, the relative phases of the currents arriving at
the inner terminals is 0.degree. , 270.degree. , 180.degree.and
90.degree. respectively. Since current swapping takes place between
inner terminals 2 and 4, the relative insertion phase from the
inner terminals toward the active region is 0.degree. , 270.degree.
, 180.degree. and 90.degree. along arms 1, 2, 3 and 4 respectively.
The currents which are flowing outwardly have a relative phase as
they arrive at the active region of 0.degree. , 180.degree. ,
0.degree. and 180.degree. so that energy is not radiated from the
active zone. As the currents reach their outer arm ends at terminal
points T1, T2, T3 and T4 they are again relfected with a relative
insertion phase of 0.degree. , 180.degree. , 0.degree. and
180.degree.. Hence, the currents now flow back into the active
region in phase with each other at 0.degree. so that energy is
efficiently radiated from the active zone. This operation may be
more readily understood from considering Table I which summarizes
the operation for right-hand circularly polarized current states
obtained when terminal ends 2 and 4 are shorted to achieve
0.degree. relative phase shift with respect to the incoming wave
front.
TABLE I
__________________________________________________________________________
RIGHT HAND CIRCULARLY POLARIZED CURRENT STATES O DEGREES PHASE
SHIFT CURRENT STATE/ CURRENT RELATIVE PHASE INSERTION PHASE FLOW OF
WINDINGS
__________________________________________________________________________
1 2 3 4 Induced in Active Region OUT 0 0 0 0 Insertion phase for
Reflection +0 180 0 180 reflection from spiral ends. Reflected back
into Active IN 0 180 0 180 Region from spiral ends. Relative
Insertion Phase- IN +0 90 180 270 Active Region to Feed point.
Phase of Currents IN 0 270 180 90 arriving at Terminals Relative
Insertion Phase- OUT +0 270 180 90 Terminal to Active Region Phase
of Currents Arriving OUT 0 180 0 180 at Active Region Insertion
phase for Reflection +0 180 0 180 reflection from spiral ends
Resultant phase at IN 0 0 0 0 Active Region
__________________________________________________________________________
Similarly, it may be shown that the 180.degree. relative phase
shift state is realized for right hand circularly polarized signals
when terminal ends 1 and 3 are shorted.
Table II summarizes the operation for right-hand circularly
polarized current states obtained when terminal ends 1 and 4 are
shorted and 2 and 3 are shorted to achieve 90.degree. relative
phase shift with respect to the incoming wave front.
TABLE II
__________________________________________________________________________
RIGHT-HAND CIRCULARLY POLARIZED CURRENT STATES 90 DEGREES PHASE
SHIFT CURRENT STATE/ CURRENT RELATIVE PHASE INSERTION PHASE FLOW OF
WINDINGS
__________________________________________________________________________
Induced in Active Region OUT 1 2 3 4 0 0 0 0 Insertion phase for
REFLECTION 0 180 0 180 reflection from spiral ends Reflected back
into Active IN 0 180 0 180 Region from spiral ends Relative
Insertion Phase- IN 0 90 180 270 Active Region to Feed Point Phase
of Currents Arriving IN 0 270 180 90 at Terminals Relative
Insertion Phase- OUT 270 180 90 0 Terminal to Active Region Phase
of Currents Arriving OUT 270 90 270 90 at Active Region Insertion
Phase for REFLECTION 180 0 180 0 Reflection from spiral ends
Resultant phase at Active IN 90 90 90 90 Region
__________________________________________________________________________
Similarly, it may be shown that the 270.degree. phase state for
right-hand circularly polarized signals is obtained when terminal
ends 1 and 2 are shorted and 3 and 4 are shorted. The element
antenna of FIG. 8 is controlled by the inner bias controls such
that the same interconnection of the spiral inner ends to the
switching diodes is provided for both left-hand circular polarized
waves as well as for right-hand circular polarized waves. That is,
a 0.degree. phase reradiation requires that points 2 and 4 be short
circuited, a 90.degree. relative phase reradiation requires that
inner terminals 1 and 2 be short circuited and that inner terminals
3 and 4 be short circuited. Similarly, if 180.degree. phase change
is desired between the incoming wave and the reradiated wave, then
inner 2 terminals 2 and 3 are short circuited. If a 270.degree.
relative phase change is desired, then terminals 2 and 3 are short
circuited and terminals 1 and 4 are short circuited.
Table III summarizes the operation for left-hand circularly
polarized current states for the 0.degree. relative phase
condition. For this state, terminal ends 2 and 4 are shorted as was
the case for the right-hand circularly polarized currents.
TABLE III
__________________________________________________________________________
LEFT-HAND CIRCULARLY POLARIZED CURRENT STATES O DEGREES PHASE STATE
CURRENT STATE/ CURRENT RELATIVE PHASE INSERTION PHASE FLOW OF
WINDINGS
__________________________________________________________________________
1 2 3 4 Induced in Active Region IN 0 0 0 0 Insertion Phase -
Active IN +0 90 180 270 Region to spiral terminals Relative Phase
of Current IN 0 90 180 270 Arriving at spiral terminals Insertion
Phase - Terminal OUT +0 270 180 90 to Active Region Resultant Phase
at 0 0 0 0 Active Region
__________________________________________________________________________
Similarly, it may be shown that the 180.degree. relative phase
state is realized when terminal ends 1 and 3 are shorted.
Table IV summarizes the operation for left-hand circularly
polarized current states for the 90.degree. relative phase
condition. For this state, terminal ends 1 and 2 are shorted and 3
and 4 are shorted. These conditions are the inverse of those
required for the right-hand circularly polarized currents. Thus,
when a single, centrally located set of switching diodes is used to
phase shift both left-hand and right-hand circularly polarized
signals, the phase shift operation on both cannot occur
simultaneously.
TABLE IV
__________________________________________________________________________
LEFT-HAND CIRCULARLY POLARIZED CURRENT STATES 90 DEGREES PHASE
STATE CURRENT STATE/ CURRENT RELATIVE PHASE INSERTION PHASE FLOW OF
WINDINGS
__________________________________________________________________________
1 2 3 4 Induced in Active Region IN 0 0 0 0 Insertion Phase -
Active IN 0 90 180 270 Region to spiral terminals Relative Phase of
Current IN 0 90 180 270 Arriving at Spiral Terminals Insertion
Phase - Terminal OUT 90 0 270 180 out to Active Region Resultant
Phase at Active OUT 90 90 90 90 Region
__________________________________________________________________________
Similarly, it may be shown that a 270.degree. phase state
corresponds to terminal ends 1 and 4 being shorted and 2 and 3
being shorted.
To summarize, Table V below indicates the diode states
corresponding to a given phase state for both left-hand and
right-hand circularly polarized signals. ##EQU1##
Reference is now made to the embodiment of FIG. 9. This element
antenna is essentially the same as that illustrated in FIG. 8 in
that all of the spiral ends T1, T2, T3 and T4 are reactively
terminated. However, the spiral ends are reactively terminated by
cutting the spiral arms to different lengths. For example, for a
specific length the current reflected from terminal ends T1 and T3
may provide a 0.degree. phase shift. Consequently if 180.degree.
phase shift is required for arm ends T2' and T4' then these arms
would each be shorter than the other two arms by a quarter wave
length. By shortening these two arms by a quarter wave length, the
currents reflected from the terminal ends T2 and T4 will be changed
in phase by 180.degree.. The arm terminals T1, T2, T3 and T4 are
respectively connected to inner bias controls 120, 122, 124 and 126
for controlling the switching states of the switching diodes in the
manner as described hereinbefore with respect to the embodiment of
FIG. 8.
Reference is now made to the embodiment shown in FIG. 10. This
embodiment is similar to the embodiment of FIG. 9 except that all
of the spiral arms are of the same length. The arm ends are not
reactively terminated by passive or active reactances. Instead, the
spiral diameter DI is chosen and the length of the spiral arms is
chosen such that over a given frequency range, the currents
reflected from terminal ends T1 and T3 exhibit a 0.degree. phase
change whereas the currents reflected from terminal ends T2 and T4
exhibit a 180.degree. phase change. For this frequency range the,
the element antenna of FIG. 10 will operate in the same manner as
that described hereinabove with respect to FIGS. 8 and 9.
Whereas the invention has been described with respect to preferred
embodiments the invention is not limited to same as various
modifications and arrangements may be made without departing from
the spirit and scope of the invention as defined by the appended
claims.
* * * * *