Dec. 3, 1946. P. J. KIBLER TURNSTILE ANTENNA Filed Feb. 14, 1944 N TO TRANSMTTER T OR RECEIVER - u-2 TO TRANSMTTER OR RECEIVER INVENTOR PAUL. J. KBLER ATTORNEY
Patented Dec. 3, 1946 UNITED STATES PATENT OFFICE TURNSTLE ANTENNA This invention relates to turnstile antennas and particularly to impedance matching and phasing means used in connection. With antennas of this type. According to conventional practice turnstile antennas comprising a plurality of radiator ele ments Symmetrically disposed with respect to one another in the same plane are employed for radi ating a rotating radio frequency field having a predetermined pattern. In order to establish such a field of substantially uniform intensity it is necessary to supply substantially equal currents to the respective radiator elements in a prede termined phase relation to one another. In the case of a turnstile antenna, comprising four radi ator elements, the elements are disposed at 90 angles with respect to one another and the ex citing currents are supplied thereto in time Paul J. Kibler, Fort Wayne, Ind., assignor to Farnsworth Television and Radio Corporation, a corporation of Delaware Application February 14, 1944, Serial No. 22,323 Claims. (C. -33) quadrature. In order to equalize the exciting currents it is necessary to match the impedances of the radiator elements to the transmission medium by Which the currents are impressed upon the radiators. It also is necessary to couple the current feeding transmission medium to the radiator elements in Such a manner that the ex citing currents are impressed. Successively upon the respective radiator elements in proper phase. In antennas of this character previously em ployed the impedance matching and phasing means have been of Such characters that it has not been possible to effect the required adjust ments for each radiator element individually. It, therefore, has been necessary to make these ad justments only after complete assembly of the antenna, array. Then, because of the mutual : interdependence of the antenna, components, the adjustments are relatively difficult to make. It is an object of this invention, therefore, to provide a novel impedance matching and phasing means for a turnstile antenna Which Will facili tate the preliminary adjustment of the imped ance matching and phasing means. In accordance with the invention there is pro vided a turnstile antenna, having four equal plane and disposed at 90 angles With respect to one another. Associated With each of the radi ator elements is an adjustable reactance device by means of which the radiator elements each may be tuned for parallel resonance at the oper atting frequency. Adjacent tuned radiator ele ments are connected to the respective ends of two quarter Wavelength concentric transmission lines. The extreme terminals of a full Wave concentric transmission line are connected respectively to O 2 0 3 2 two Oppositely disposed radiator elements and a third terminal of the full wave concentric line located three-quarters of a wave length distant from one of the extreme terminals and a quarter Wave length distant from the other extreme ter minal is connected to the apparatus to be used With the antenna. For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description, taken in connection with the accompanying draw ing, and its scope will be pointed out in the appended claims. In the drawing: Fig. 1 is a diagrammatic illustration of a four element turnstile antenna, embodying the pres ent invention; Fig. 2 is a diagrammatic representation of a concentric transmission line for use with the an tenna, array of Fig. 1; and, Fig. 3 is a schematic illustration of a network of lumped circuit elements also for use with the antenna, array of Fig. 1. Having reference now particularly to Fig. 1 of the drawing, there is shown a four-element turn stile antenna, comprising a north radiator element N, an east radiator element E, a south radiator element S, and a West radiator element W. These radiator elements are all disposed in the same plane and are located at 90 angles with respect to one another. The elements are of equal lengths. In the illustrated embodiment of the invention the radiator elements are each approxi mately equal to a quarter wave length which is related to the radio frequency at which it is de sired to establish the rotating field. Connected between the inner ends of each of the radiator elements N, E, S and W are adjustable condensers l?, 2, 3 and 4, respectively. The opposite ter minals of each of these condensers are connected to ground. There also is connected between the inner ends of the radiator elements N and W a concentric transmission line, the effective length of which is substantially equal to a quarter wave length. Similarly, there is connected be tween the inner ends of the Opposite pair of radir ator elements E and S a quarter Wave length concentric transmission line f6. The inner ends of any two oppositely disposed radiator elements Such as W and E constitute terminals A and B to which there may be connected apparatus for sup plying exciting currents of opposite phase to the antenna array. The outer conductors of the transmission lines and 6 are grounded, pref -
3 erably, adjacent the terminals A and B, respec tively. In Fig. 2 there is illustrated one type of trans mission medium Suitable for connection to the antenna, terminals A and B of Fig., as indicated by corresponding characters of reference in the two figures. This transmission medium coin prises a concentric transmission line of full Wave length between the terminals A and B. This concentric line is divided into a darter O Wave length. Section 8 and a three-quarter Wave length. Section 9. At the junction point of. these two line sections there is connected a concentric transmission line 2 of whatever length is required to couple the phasing trans mission line to a circuit C such as a trans mitter for use in connection with the antenna, array. Ihe Outer conductor of the transmis sion line 2 is grounded and also connected to the transmission line 7 as shown. Considering now the manner in which a turn Stile antenna in accordance with the present in vention is adjusted to operate in the desired manner, reference will be made to Figs. 1 and 2. Inasmuch as each of the radiator elements, such 2 as the north radiator N, has a physical length equal to a quarter Wave, the radiator element Will exhibit a reactance at the related fre quency Which is slightly inductive. Consequent. ly, the condenser is adjusted suitably to pro vide the necessary capacitative reactance. So that the radiator element is tuned for parallel reso nance at the radio frequency related to the length of the radiator element. Thus, the in pedance represented by the radiator element N and the condenser may be made purely re sistive. Also, by Suitable adjustment of the ef fective length of the radiator element, together With a compensating adjustment of the tuning condenser, the effective impedance of the radia tor may be made equal to the characteristic.in pedance of a concentric transmission line. Similarly to the described adjustment of con denser, the condensers 2, 3 and 4 are ad justed. So that the respective associated radiator elements E, S and W have impedances, each equal to the characteristic impedance of a con centric transmission line. Thus, when the radi ator elements N and W. are coupled by the con centric line and the radiator elements E and S are coupled by the concentric line 6, these concentric lines are terminated at each end in their characteristic impedances. In such a case then the radiators N and W are effectively con nected in parallel by the quarter wave length line. Similarly, the radiators E and S are effectively connected in parallel by the quarter wave length line 6. In such a case the in pedance of the pair of radiators N and W at the point A and also the impedance of the pair of radiators E and S at the point B is equal to one-half of the impedance of one of the tuned radiator elements. The in pedance of the pair of radiators N and W at the point A comprises the load for the quarter wave length section 8 of the phasing transmission line fl. Since it is characteristic of the quarter Wave length line to invert impedances, the impedance looking into the quarter wave length section 8 of the phas ing line T from the point D, therefore, is equal to twice the impedance of one of the radiator elements. In like manner, the impedance at the point B looking into the parallel arrangement of the radiator elements E and S is one-half of the 30 3 4. 6. 4. impedance of One of the radiator elements. This impedance comprises the load connected to the B terminal of the three-quarter Wave length line Section 9 of the phasing line 7. Inasmuch as it is characteristic of a three quarter Wave length concentric transmission line to invert impedances at the terminals thereof, the impedance looking into the three-quarter wave length. Section 9 from the point D also is equal to twice the impedance of One of the tuned radiator elements. By connecting the phasing line sections 8 and 9 in parallel at the point D the impedance of the complete System looking toward the point D. from the connecting transmission line 2 is equal to the impedance of one of the tuned radiator elements, Inasmuch as originally this impedance was adjusted to correspond to the characteristic impedance of a concentric trans mission line, a line of this character such as 2 may be connected at the point D and there by will be terminated in its characteristic in pedance. Thus, by means of the described impedance matching arrangement the individual radiator elements may be excited by currents of equal magnitude. Also, by reason of the quarter wave length concentric line coupling between ad jacent radiator elements such as N and W, and E and S, the exciting currents for the two radia tors of each pair are in phase quadrature. Fin ally, by means of the quarter Wave length Section 8 and the three-quarter Wave length section 9 of the phasing transmission line, exciting currents are supplied to the points A and B, respectively, of the two pairs of radiator ele ments in phase opposition. In this manner the four radiator elements of the turnstile antenna, are excited by currents of equal magnitude in phase quadrature. Fig. 3 illustrates an alternative form of a phas ing transmission medium for supplying exciting currents of opposite phase to the two pairs of ra diator elements at the points A and B of Fig. 1. This medium comprises a balancing network formed of condensers 22 and 23 between which there is connected in series an inductor 24. The reactances of the condenser 22 and the inductor 24 are made numerically equal to twice the react ance of the condenser 23. The values of these re actances will determine the effective impedance of the network as seen from C. By suitably choosing the values of these reactances, the network in pedance may be matched properly to a transmis sion medium connected thereto. The condenser 22 is connected to the terminal A of the antenna array of Fig. 1 and the junction point between the inductor 24 and the condenser 23 is connected to the terminal B Of the antenna, array. The condenser 23 is connected to ground, as shown, and the junction point between the con denser 22 and the inductor 24 is connected to the apparatus With Which the antenna, array is to Op erate, A network in accordance with that illustrated in Fig. 3 is similar to one described by S. Frankel, in the Proceedings of the I.R. E. of September, 1941. Such a network functions to impress currents de rived from the utilization circuit C upon the ter minal points A and B in phase opposition and bal anced with respect to ground. The antenna array as shown in Fig. 1 then functions in a nanner similar to that described to produce a rotating radio frequency field of a substantially circular pattern, -
In the foregoing description reference has been made to feeding or Supplying currents to an an tenna, array in accordance with this invention. This is the case where the antenna is to be used in conjunction with radiant energy transmitting apparatus. It is obvious, however, to those skilled in the art that such an antenna also is susceptible of use with receiving apparatus, in which case the radio frequency currents collected by the antenna, are transferred to the receiving apparatus. Ac cordingly, it is contemplated that the structures defined in the appended claims are suitable for use either with transmitting or receiving apparatus. Therefore, the term utilization circuit' used in this specification and in certain of the claims is intended to define a circuit associated with either transmitting or receiving apparatus. It also will be obvious to those skilled in the art that the invention is not limited to use with radiator elements Substantially of quarter wave lengths. It is contemplated that the invention may be embodied in antennas having radiator ele ments of substantially any desired lengths, pro Wided that in any one antenna, array all radiators are of the same length. In the case where the radiator lengths are such that the radiator re actances at the operating frequency are capacita tive rather than inductive, as in the case de scribed, the matching reactances required for tuning will of necessity have to be inductive. Hence, in place of the condensers, 2, 3 and 4, corresponding adjustable inductors will be required. From the foregoing description of one embodi ment of this invention, it follows that there is provided an antenna, System, each radiator ele ment of which is susceptible of individual pread justment of its effective impedance, whereby after complete assembly of the antenna array no fur ther adjustments are required. While there has been described what, at pres ent, is considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and rinodifications may be made therein without departing from the invention, and therefore, it is aimed in the ap pended claims to cover all such changes and modi fications as fall Within the true Spirit and scope Of the in Vention. What is claimed is:. A turnstile antenna. Comprising, four equal One another, a pair of quarter Wave length trans mission lines connected respectively between ad jacent radiator elements, individual means asso ciated with each of said radiator elements to natch the impedance of each element to the characteristic impedance of one of said trans mission lines separately and independently of the other radiator elements, and means for coupling two oppositely disposed radiator elements in phase opposition to a utilization circuit for said antenna. 2. A turnstile antenna comprising, four equal between adjacent radiator elements, a reactance element associated with each of said radiator ele ments and adjustable to match the impedance of each eleinent to the characteristic impedance of One of Said transmission lines, and opposed 0 0 60 7 6 phase coupling means for said antenna connect ed to two oppositely disposed radiator elements.. 3. A turnstile antenna, comprising, four equal between adjacent radiator elements, a tuning condenser connected to each of Said radiator ele inents to match the impedance of each element to the characteristic impedance of One of said transmission lines, and an opposed-phase coul pling medium for said antenna, including a pair of transmission lines of different lengths connect ed respectively to two oppositely disposed radiator elements. 4. A turnstile antenna, comprising, four equal plane and disposed at 90 angles With respect to One another, a pair of quarter Wave length con between adjacent radiator elements, a variable tuning condenser connected to each of Said ra diator elements to match the impedance of each element to the characteristic impedance of one of said transmission lines, and a coupling medium for said antenna, including a pair of concentric transmission lines differing in length by a half wave length connected respectively to two oppo sitely disposed radiator elements.. A turnstile antenna comprising, four equal plane and disposed at 90 angles with respect to one another, a pair of quarter wave length concentric transmission lines connected respec tively between adjacent radiator elements, a vari able condenser connected to each of said radi ator elements to tune each element for parallel resonance at the operating frequency and to natch the impedance of each element to the characteristic impedance of one of said trans mission lines, and a full wave concentric trans mission line having its two extreme terminals connected to two oppositely disposed radiator elements and having a third terminal three quar ters of a Wave length distant from one of said extreme terminals, and a quarter wave length distant from the other of said extreme terminals, Whereby currents of opposite phase may be ap plied to said opposed radiator elements from a Source connected to said third terminal. 6. A turnstile antenna comprising, four equal one another, a pair of quarter wave length trans mission lines connected respectively between ad jacent radiator elements, a tuning condenser con nected to each of said radiator elements to match the impedance of each element to the character istic impedance of one of said transmission lines, and an Opposed-phase coupling medium for said antenna, including a balancing network connect ed to two Oppositely disposed radiator elements and having an intermediate terminal connected to a utilization circuit for said antenna. 7. A turnstile antenna comprising, four equal between adjacent radiator elements, a variable Condenser connected to each of said radiator ele ments to tune each element for parallel resonance and to match the impedance of each element to the characteristic impedance of one of said trans
7 mission lines, and a coupling medium for said antenna, including a network comprising an in ductor connected in series between a first con denser having a reactance numerically equal to that of Said inductor and a second condenser having a reactance numerically equal to one-half that of Said inductor, Said first condenser and the junction point of said inductor and said sec s 8 Ond condenser being connected to two Oppositely disposed radiator elements, and Said second Con denser being connected to ground and the junc tion point of said inductor and said first cons denser being connected to a utilization circuit for said antenna. PAUL J, KBER,