US3906514A

US3906514A - Dual polarization spiral antenna

Info

Publication number: US3906514A
Application number: US363029A
Authority: US
Inventors: Harry Richard Phelan
Original assignee: Harris Intertype Corp
Current assignee: Harris Corp
Priority date: 1971-10-27
Filing date: 1973-05-23
Publication date: 1975-09-16
Anticipated expiration: 1992-09-16

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.

Description

1451 Sept. 16, 1975 [54] DUAL POLARIZATION SPIRAL ANTENNA Harry Richard Phelan, lndialantic, Fla.

[75] Inventor:

[73] Assignee: Harris-Intertype Corporation, Cleveland, Ohio [22] Filed: May 23, 1973 [2]] Appl. No.: 363,029

Related US. Application Data [63] Continuation-impart of Ser. No. 192,869, Oct. 27,

1971, abandoned.

3,725,943 4/1973 Spanos 343/797 Primary ExaminerEli Lieberman 57 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 [52] US. Cl 343/895; 343/754 portion located in an annular active antenna region [51] Int. Cl. H01Q 19/06 where circular polarized electromagnetic energy is re- [58] Field of Search 343/895, 754, 854 ceived and reradiated. The arms of the" element antenna are configured so that they define a geometric [56] References Cited polarization element antenna of a given circular polar- UNITED STATES PATENTS ity so that currents induced in the respective interme- 3,045,237 7/1962 Marston 343 895 arm recewed energy flow W 3 137 002 6/1964 Kaiser et al..... 343/895 SPeclfic arm ends dependence upon the Polamy of 3:229:293 1/1966 Lime et a1 343/895 the received energy. The currents are acted upon so 3,344,425 9/1967 Webb 343 895 that y re-enter the active region having their rela- 3,354,459 11/1967 Schwartz et al 343/796 tive phases controlled in such a manner that the rera- 3,373.433 1963 343/895 diated energy is of the same circular polarity as the re 3,508,269 4/1970 Snyder 343/895 ceived energy 3,562,756 2/l97l Kuo et al. 343/895 3,665,480 5 1972 Fassett 343/754 10 Clalms, l0 Drawmg Flgures I i r/ 2 x AVA ER COA TPOL Q fie 4-20 MIA/ER X 4 7 41/4/1274 5/245 3 M con/m2 COA/TAOL PATENTED SEP 1 8 I975 3,906,514

sum 1 UF 3 SHEET 2 [1F 3 DUAL POLARIZATION SPIRAL ANTENNA This is a continuation-in-part of my previous application Ser. No. 192,869 filed Oct. 27, 1971, now .abancloned, and which is assigned to the same assignee as this application. The disclosure of that application is incorporated by reference herein.

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. I and 2 two different applications of an array of element antennas constructed in accordance with the invention. In FIGv 1 there is shown a reflectarray system employing a parabolic array assembly which carries an array of element antennas I2 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 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 ofa 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 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 e1nployed. 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 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 different phase shift than that which exists when link 90 is conductive. The 180 phase shift occurs because changing the diode states effectively rotates the antenna 90 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 620. 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 62/) 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 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 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 620 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 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 seetor 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 the phase of current at point 73 on arm 38 within the angular sector 72, because point 73 is displaced 90 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 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 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 cur rents are instantaneously 180 out of phase electrically v with the currents in sector 72. However, because the portions of the arms in sector 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 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 aconductive link 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 from its previous value.

Alternatively, two of the inner terminals could be short-circuited to a small ground plane or common tic point at the center of the element antenna, in which case the currents propagating outward along the shortcircuited 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, 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 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 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.

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.

By operating

switches

100, 102, I04, 106 to achieve various biases asjust described, the phase of the reradiated wave can be changed in 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 countcrclockwise 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 ac tive 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 lefthand 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, 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 lefthand 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 onequarter 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 llOH is provided. This control is connected in parallel with the diode and is spaced therefrom by a quarter wave length. The switch control llOH 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 1 A through 110I-I 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 righthand 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 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 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 relative phase change, then only switching diodes C and G are short circuited and the remaining diodes are open circuited. A 270 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, I24 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 Xl to effect a 0 phase shift. However, arm ends T2 and T4 are each reactively terminated by a reactance X2 to effect a 180 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 phase shift, then the diodes are biased so that

terminal points

2 and 4 are effectively short circuited. If a 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 relative phase shift is to be obtained, then points 1 and 3 are shorted. lastly, if a 270 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. 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, 180, 0 and 180 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, 180, 0 and 180. Since the currents are out of phase, electromagnetic energy is not radiated from the active region. The relative insertion phase from the TABLE I RIGHT HAND CIRCULARLY POLARIZED CURRENT STATES O DEGREES PHASE SHIFT CURRENT STATE/ CURRENT RELATIVE PHASE INSERTION PHASE FLOW OF WINDINGS l. Induced in Active Region OUT 0 0 O 2. Insertion phase for Reflection +0 180 0 180 reflection from spiral ends.

3. Reflected back into Active IN 0 180 0 180 Region from spiral ends,

4. Relative Insertion Phase- IN +0 90 180 270 Active Region to Feed point.

5. Phase of Currents IN 0 270 180 90 arriving at Terminals 6. Relative Insertion Phase- OUT +0 270 180 90 Terminal to Active Region 7. Phase of Currents Arriving OUT 0 180 0 180 at Active Region 8. Insertion phase for Reflection +0 180 0 180 reflection from spiral ends 9. Resultant phase at IN 0 0 0 0 Active Region active region to the feed point is 0, 90, 180 and 270 at terminal inner ends 1, 2, 3 and 4 respectively. Thus, the relative phases of the currents arriving at the inner terminals is 0, 270, l80and 90 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. 270, 180 and 90 along

arms

1, 2, 3 and 4 respectively. The currents TABLE II RIGHT-HAND CIRCULARLY POLARIZED CURRENT STATES 90 DEGREES PHASE SHIFT CURRENT STATE/ CURRENT RELATIVE PHASE INSERTION PHASE FLOW OF WINDINGS l 2 3 4 1. Induced in Active Region OUT 0 0 0 0 2. Insertion phase for REFLEC- 0 I80 0 I80 reflection from spiral ends TION 3. Reflected back into Active IN 0 180 0 180 Region from spiral ends 4. Relative Insertion Phase- IN 0 90 180 Active Region to Feed Point 5. Phase of Currents Arriving IN 0 270 180 90 at Terminals 6. Relative Insertion Phase- OUT 270 180 90 0 Terminal to Active Region 7. Phase of Currents Arriving OUT 270 90 270 90 at Active Region 8. Insertion Phase for REFLEC. I 0 180 O reflection from spiral ends 9. Resultant phase at Active [N 9O 90 ")0 Region which are flowing outwardly have a relative phase as they arrive at the active region of 0, 0 and 180 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, 180, 0 and 180. Hence, the currents now flow back into the active region in phase with each other at 0 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 ter- Similarly, it may be shown that the 270 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, at 0 phase reradiation requires that

points

2 and 4 be short circuited. a 90 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 phase change is desired between the incoming wave and the reradiated wave, then inner2

terminals

2 and 3 are short circuited. If a 270 relative 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.

TABLE V POLARIZATION l 3 1. .3 DIODE STATE 2 3 2 1 2 2 LEFT-HAND o 90 I80 270 RIGHT-HAND 270 180 90 phase change is desired, then

terminals

2 and 3 are short cireuited and

terminals

1 and 4 are short circuited.

Table III summarizes the operation for left-hand circularly polarized current states for the 0 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 Reference isnow made to the embodiment of FIG. 9.

5 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 phase shift. Consequently if 180 LEFT-HAND CIRCULARLY POLARIZED CURRENT STATES O DEGREES PHASE STATE Active Region Similarly, it may be shown that the 180 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 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 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. The arm terminals T1, T2, T3 and T4 are respectively connected to inner bias controls 120, I22, I24 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.

Referenceis 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 termi- LEFT-HAND CIRCULARLY POLARIZED CURRENT STATES DEGREES PHASE STATE Region Similarly, it may be shown that a 270 phase state corresponds to terminal ends 1 and 4 being shorted and 2 and 3 being shorted.

nated 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 phase change whereas the currents reflected from terminal ends T2 and T4 exhibit a 180 phase change. For this frequency range the, the element antenna of FIG. 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.

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 arfn 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.

I l l=

Claims

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.