US2412090A - Turnstile antenna - Google Patents

Description

P. J. KIBLER TURNSTILE ANTENNA Dec. 3, 1946.

Filed Feb. 14, 1944 OR RECEIVER TO TRANSMITTER OR RECEIVER INVENTOR PAUL J. K|BLER ATTORNEY Patented Dec. 3, 1946 TURNSTILE ANTENNA Paul J. Kibler, Fort Wayne, Ind., assignor to Farnsworth Television and Radio Corporation, a corporation of Delaware Application February 14, 1944, Serial No. 522,323

7 Claims.

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 elements symmetrically disposed with respect to one another in the same plane are employed for radiating a rotating radio frequenc 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, predetermined phase relation to one another. In the case of a turnstile antenna comprising four radiator elements, the elements are disposed at 90 angles with respect to one another and the exciting currents are supplied thereto in time 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 exciting currents are impressed successively upon the respective radiator elements in proper phase.

In antennas of this character previously employed the impedance matching and phasing means have been of such characters that it has not been possible to effect the required adjustments for each radiator element individually. It, therefore, has been necessary to make these adjustments 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 facilitate the preliminary adjustment of the impedance matching and phasing means.

In accordance with the invention there is provided a turnstile antenna having four equal length radiator elements located in the same plane and disposed at 90 angles with respect to one another. Associated with each of the radiator elements is an adjustable reactance device by means of which the radiator elements each may be tuned for parallel resonance at the operating frequency. Adjacent tuned radiator elements are connected to the respective ends of two quarter wave length concentric transmission lines. The extreme terminals of a full wave concentric transmission line are connected respectively to 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 terminal 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 drawing, and its scope will be pointed out in the appended claims.

In the drawing: I

Fig. 1 is a diagrammatic illustration of a fourelement turnstile antenna embodying the present invention;

Fig. 2 is a diagrammatic representation of a concentric transmission .line for use with the antenna array of Fig. l; and,

Fig. 3 is a schematic illustration of a network of lumped circuit elements also for use with the antennaarray of Fig. 1.

Having reference now particularly to Fig. l of the drawing, there is shown a four-element turnstile 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 approximately equal to a quarter wave length which is related to the radiofrequency at which it is desired to establish the rotating field. Connected between the inner ends of each of the radiator elements N, E, S and W are adjustable condensers ll, I2, I 3 and M, respectively. The opposite te'r 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 l5, the effective length of which is substantially equalto a quarter wave length. Similarly, there is connected between the inner ends of the opposite pair of radiator elements E and S a quarter Wave length concentric transmission line IS. 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 supplying exciting currents of opposite phase tothe antenna array. The outer conductors of the transmission-lines l5 and I6 are grounded, pref? erably, adjacent the terminals A and B, respectively.

In Fig. 2 there is illustrated one type of transmission medium suitable for connection to the antenna terminals A and B of Fig. l, as indicated by corresponding characters of reference in the two figures. This transmission medium comprises a concentric transmission line I I of full wave length between the terminals A and B. This concentric lineis divided into a quarter wave length section l8 and a three-quarter wave length section these two line sections there is connecteda concentric transmission line 2| of whatever length is required to couple the phasing transmission line I 1 to a circuit C such as a transmitter for use in connection with the antenna array. The outer conductor of the transmission line 2| is grounded and also connected to the transmission line I! as shown.

Considering now the manner in which a turnstile antenna in accordance with the present invention 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 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. Consequently, the condenser II is adjusted suitably to provide the necessary capacitative reactance so that the radiator element is tuned for parallel resonance at the radio frequency related to the length of the radiator element. Thus, the im pedance represented by the radiator element N and the condenser Il may be made purely resistive. Also, by suitable adjustment of the effective length of the radiator element, together with a compensating adjustment of the tuning condenser, the effective impedance of the radiator may be made equal to the characteristic-impedance of a concentric transmission line.

Similarly to the described adjustment of condenser l l, the condensers I2, l3 and I 4 are adjusted so that the respective associated radiator elements E, S and W have impedances, each equal to the characteristic impedance of a concentric transmission line. Thus, when the radiator elements N and W are coupled by the concentric line l5 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 connected in parallel by the uarter wave length line l5. Similarly, the radiators E and S are efiectively connected in parallel by the quarter wave length line Hi. In such a case the impedance 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 pointB is equal to one-half of the impedance of one of the tuned radiator elements. The impedance of the pair of radiators N and W at the point A comprises the load for the quarter wave length section l8 of the phasing transmission line l1. Since it is characteristic of the quarter wave length line to invert impedances, the impedance looking into the quarter wave length section l8 of the phasing line I! 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 I9. At the junction point of 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 IQ of the phasing line H. Inasmuch as it is characteristic of a threequarter wave length concentric transmission line to invert impedances at the terminals thereof, the impedance looking into the three-quarter Wave length section 1-9 from the point D also is equal to twice the impedance of one of the tuned radiator elements.

By connecting the phasing line sections l8 and 19 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 transmission line, a line of this character such as 2| may be connected at the point D and thereby will be terminated in its characteristic impedance.

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 adjacent radiator elements such as N and W, and E and S, the exciting currents for the two radiators of each pair are in phase quadrature. Finally, by means of the quarter wave length section t8 and the three-quarter wave length section I9 of the phasing transmission line I1, exciting currents are supplied to the points A and B, respectively, of the two pairs of radiator elements 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 phasing transmission medium for supplying exciting currents of opposite phase to the two pairs of radiator 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 reactance of the condenser 23. The values of these reactances will determine the effective impedance of the network as seen from C. By suitably choosing the values of these reactances, the network impedance may be matched properly to a transmission 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 condenser 22 and the inductor 24 is connected to the apparatus with which the antenna array is to operate.

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 derived from the utilization circuit C upon the terminal points A and B in phase opposition and balanced with respect to ground. The antenna array as shown in Fig. 1 then functions in a manner 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 antenna 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. Accordingly, 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, provided 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 reactances at the operating frequency are capacitative rather than inductive, as in the case described, the matching reactances required for tuning will of necessity have to be inductive. Hence, in place of the condensers H, l2, l3 and I4, corresponding adjustable inductors will be required,

From the foregoing description of one embodiment of this invention, it follows that there is provided an antenna system, each radiator element of which is susceptibl of individual preadjustment of its effective impedance, whereby after complete assembly of the antenna array no further adjustments are required.

While there has been described what, at present, is considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and therefore, it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A turnstile antenna comprising, four equal length radiator elements located in the same plane and disposed at 90 angles with respect to one another, a pair of quarter wave length transmission lines connected respectively between adjacent radiator elements, individual means associated with each of said radiator elements to match the impedance of each element to the characteristic impedance of one of said transmission 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 length radiator elements located in the same plane and disposed at 90 angles with respect to one another, a pair of quarter wave length concentric transmission lines connected respectively between adjacent radiator elements. a reactance element associated with each of said radiator elements and adjustable to match the impedance of each element to the characteristic impedance of one of said transmission lines, and opposedphase coupling means for said antenna connected to two oppositely disposed radiator elements.

3. A turnstile antenna comprising, four equal length radiator elements located in the same plane and disposed at angles. with respect to one another, a pair of quarter wave length eoncentric transmission lines connected respectively between adjacent radiator elements, a tuning condenser connected to each of said radiator elements to match the impedance of each element to the characteristic impedance of one of said transmission lines, and an opposed-phase coupling medium for said antenna including a pair of transmission lines of different lengths connected respectively to two oppositely disposed radiator elements.

4. A turnstile antenna comprising, four equal length radiator elements located in the same plane and disposed at 90 angles with respect to one another, a pair of quarter Wave length concentric transmission lines connected respectively between adjacent radiator elements, a variable tuning condenser connected to each of said radiator 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 difiering in length by a half wave length connected respectively to two oppositely disposed radiator elements.

5. A turnstile antenna comprising, four equal length radiator elements located in the same plane and disposed at 90 angles with respect to one another, a pair of quarter wave length concentric transmission lines connected respectively between adjacent radiator elements, a variable condenser connected to each of said radiator elements to tune each element for parallel resonance at the operating frequency and to match the impedance of each element to the characteristic impedance of one of said transmission lines, and a full wave concentric transmission line having its two extreme terminals connected to two oppositely disposed radiator elements and having a third terminal three quarters 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 length radiator elements located in the same plane and disposed at 90 angles with respect to one another, a pair of quarter wave length transmission lines connected respectively between adjacent radiator elements, a tuning condenser connected to each of said radiator elements to match the impedance of each element to the characteristic impedance of one of said transmission lines, and an opposed-phase coupling medium for said antenna including a balancing network connected 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 length radiator elements located in the same plane and disposed at 90 angles with respect to one another, a pair of quarter Wave length concentric transmission lines connected respectively between adjacent radiator elements, a variable condenser connected to each of said radiator elements to tune each element for parallel resonance and 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 network comprising an inductor connected in series between a first condenser 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- 0nd condenser being connected to two oppositely disposed radiator elements, and said second condenser being connected to nd d-the J tion point of said inductor and-said first condenser being connected to a utilization circuit for 'said antenna.

PAUL J. KIBLER.

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