US2405123A - Antenna system - Google Patents

Description

1945' c. w. FYLER 2,405,123

ANTENNA SYSTEM Filed Aug. 7, 1945 2.Sheets-Sheet l Inventor: George W. F leT,

Hus Attorney.

1946- I G. w. FYLER 2,405,123

ANTENNA SYSTEM Filed Aug. 7, 1943 2 Sheets-Sheet 2 Inventor: George W. Fyler',

TRANSMITTER. by.fi I His Attorney.

Patented Aug. 6, 1946 ANTENNA SYSTEM George W. Fyler, Stratford, Conn, assignor to General Electric Company, a corporation of New York Application August 7, 1943, Serial No. 497,813

8 Claims. I

My invention relates to high frequency antenna systems, and particularly to high frequency antenna systems designed to provide substantially circular radiation patterns.

In broadcasting radio programs within the higher frequency channels utilized for frequency modulation and television broadcasts, it is generally desirable to distribute the energy radiated from the transmitting antenna as uniformly as possible in all horizontal directions. At the same time, it is desirable to concentrate the radiated energy at low angles in the vertical plane. In other words, for most efiective service, the radiating system should have a high degree of vertical directivity and the horizontal field strength pattern should be as nearly circular as possible.

Accordingly, it is an object of my invention to provide an improved high frequency antenna which possesses these and other desirable electrlcal characteristics.

In general, simple two-terminal antennas, such as dipoles heretofore commonly used, have nonuniform radiation characteristics, It has heretofore been customary to resort to compound antenna arrangements in order to secure a reasonably uniform horizontal wave pattern with horizontal polarization. It is another object of my invention to provide an improved and simplified compound antenna structure which is capable of producing a substantially uniform radiation pattern and which is relatively economical to build and easy to adjust.

Still another object of my invention is to provide a new and improved antenna system which has only two connection terminals and which nevertheless provides a substantiall circular radiation pattern and the radiation of which is concentrated substantially in the horizontal plane,

The features of my invention which I believe to be novel are set forth with particularity in the appended claims. My invention itself, both as to its organization and manner of operation, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawings in which Fig. 1 is a perspective view of an antenna system embodying the principles, of my invention; Fig. 2 shows vectorially the relationship of the current and voltage present on the antenna of Fig. 1; Figs. 3, 4, 5, and 6 show modifications of the system disclosed in Fig. 1; Fig, '7 shows a different embodiment of my invention; Fig. 8 is a diagram illustrating characteristics of antenna systems of the type illustrated in Fig. and Fig, 9 shows another embodiment of my invention.

As is well understood in the art, a properly terminated transmission line does not have any standing waves. In Figs. 1 and 2 there is shown an antenna system in which a transmission line section is utilized as a radiator, the line section being formed into a circular loop and the ends coupled to a suitable source of signal voltage. Such an antenna has substantially uniform current and hence a substantially circular radiation pattern in the plane of the loop.

In Fig, 1 there is shown such a transmission line antenna or radiating transmission line. The antenna comprises a substantially closed circular loop l0 formed from electrically conductive material of any desired cross sectional shape. For example, the loop may be a suitably formed pipe disposed in a circular configuration, The loop is coaxially disposed around a suitable electrically conductive member such as a cylindrical grounded mast II to form therewith a short section of transmission line.

The loop H1 is suitably supported from the mast by means of a supporting member I2 of insulating material, suitably connected at its respective ends to the loop and to the mast and of such length that the loop and mast are spaced apart approximately a quarter of a wave length. Thus there is provided a transmission line conductor and a grounded mast, the mast serving as a reflector for the loop.

There is illustrated in Figs. 1 and 2 means for energizing a system in which the length of the loop i0 is an integral number of full wave lengths. There is provided a transformer I 3, having a primary l4 and a secondary [5, carried by the mast ll, Any suitable transmission line It may be utilized to elTect the transfer of energy between the primary l4 and a suitable source of signal voltage which may comprise the high frequency radio apparatus or transmitter represented by the box ll. One end of the secondary I5 is suitably connected to the mast H and the other terminal of the secondary is connected to the mast through a variable condenser 18. Thus winding l5 and condenser l8 constitute a tuned circuit which enables proper termination of the transmission line It. In installations where wide band operation is desired, this tuned circuit should have a low Q. In such a system, since the radiator operates as a transmission line rather than as a resonant dipole, no resonance effects are present, and the system exhibits relatively broad frequency band width characteristics.

The ends of the loop H) are connected to suitable points on the coil or winding l5 by means of suitable conductors is extending between the ends of the loop and the Winding through a suitable opening 26 in the mast.

In Fig. 2, there is shown the vector currents flowing in the antenna IQ of Fig. l. The arrow heads on the circle H3 represent the directions of current flow within the loop and the arrows pointing inwardly from the circle l0 represent the voltage phase relationships at the indicated points. The loop I is energized from coil by means of conductors l9 connected to desired taps on winding 15. With this arrangement there exists a difference of voltage across the ends of the loop and the loop has a circulating current with only the radiated energy and heat loss being supplied from the feed line. It is apparent that currents are uniformly distributed around the loop and, at diametrically opposite points of the loop, are 180 out of phase and may be represented by vectors pointed in opposite directions. In effect, therefore, the currents are in phase at opposite points of the loop 16, in that these currents produce additive radiation fields along the axis of the loop, as well as radiation in all horizontal directions. Normal to the plane of the loop, therefore, is a concentrated beam of radiation.

In Fig. 3 there is depicted schematically an arrangement which enables the application of the abov principles to a loop having an electrical length equal to an odd number of half waves. A balanced input circuit to the loop is shown. The ends of the transmission line l6 are connected directly to the ends of the loop 26, a suitable condenser being used properly to terminate the line in conjunction with a short length of line joining the antenna 20 and the transmission line 16. The Vector voltage and current relationships are shown by means of arrows. The phase of the loop current and voltage changes uniformly and progressively throughout the length of the transmission line antenna and the vectors make a half revolution in approximately one half wave length of line. The amplitude does not change appreciably, however, and, as long as the spacing between the loop and mast 2| is not great enough to introduce substantial radiation resistance and, hence, attenuation, a uniform substantially circular radiation pattern results.

In Fig. 4 I have shown a modification of the antenna structure of Fig. 1, in which a pair of substantially circular loop elements l8, Ill each have an electrical length equal to an integral number of full wave lengths at the operating frequency of the antenna and, spaced from the conductive mast I! by a distance equal to a quarter wave length, are spaced apart vertically by a distance M2 equal to a half wave length. Positioned below the lower element ID by a distance M4 equal to a quarter wave length is a reflector II. The ends of loop l6 are connected to a source of signal II by means of conductors [9, IE and the ends of loop H) are connected to the source by means of conductors l9, It. The length of connection from the source to loop [0 is made half a wave length longer than the connection to loop I0 so that these coaxial loops carry currents which are opposite in phase. Since the loops are displaced axially by a distance equal to a half wave length, the horizontal radiation of the loops is substantially completely cancelled, while their vertical radiations are additive to give a concentrated highly directive beam of radiation. By means of the reflector II, this vertical radiation is confined to a single direction, namely, upwardly along the axis of the loops. Such an antenna is relatively small and simple in structure and is particularly useful where concentrated radiation in a small area is desired, for example, for better illumination of a Parabolic reflector, or for use for diathermy and therapeutic work. Any larger even number of loops spaced apart axially by a distance equal to a half wave length with adjacent loops energized in opposite phase may be used, of course, to obtain a desired strength of radiation beam.

Fig. 5 shows the system of Fig. 3 with the addition of a driven substantially circular director 22 coaxially disposed and outwardly spaced approximately a quarter of a wave length with respect to the loop 20, and mast 2| by which additional vertical directivity is achieved. With this arrangement a suitable phase delay line or matching section, indicated by the numeral 23, is required.

Still more vertical directivity can be obtained by using stacked elements with half wave vertical spacing and excited in-phase.

In Fig. 6, there is illustrated a modification of the arrangement shown in Fig. l. The mast H has disposed about it a helically wound radiator 2 the turns being uniformly spaced from the mast.

In Figs. 7 and 9 there is shown a different form of my antenna system which provides substantially uniform current therein and, consequently, a substantially circular radiation pattern. It is well known that a linear antenna which is actually one-half wave long at the operating frequency has a current distribution which is essentially sinusoidal, the current being maximum at its mid-point and zero at its ends. If the antenna is less than one-half wave long and capacity is added between the ends of the antenna loop in an amount such that the eifective electrical length of the entire system is equal to one-half wave, the current at the free ends of the antenna is not zero, but has some finite value and the current distribution is more nearly uniform.

Accordingly, in Fig. 7, the loop or radiator 30 disposed in a substantially closed, peripherally incomplete loop constitutes a coiled up dipole and preferably has either a length of substantially less than one-half wave or a nearly uniform current obtained as discussed in conjunction with the description of Fig. 2. The electrical length may be much greater than the actual length because of the stray and, where desired, added capacity 3| between the ends of the loop. If the actual length is so much less than onehalf wave that resonance is not reached even when the stray capacity is considered, the free ends of the loop may terminate in elements form ing a condenser 3! of substantial capacity.

In order to provide the desired capacity between the ends of the loop, blocks or plates 32! may be secured, as by welding, to the ends of the pipe and U-shaped plates 33 fitted over the opposing faces of the blocks. In order to provide an adjustable condenser, one or both of the plates 33 may be provided with slots (not shown) or other suitable openings registering with screws threaded into the blocks 32. Of course, any other desired means may be employed for vary ing or adjusting the eifective capacity.

A small loop does not radiate to any substantial degree in a vertical direction, provided the current is substantially uniform and in phase around the loop. This is represented in Fig. 8, in which the numeral 34 indicates the vertical directivity pattern of the loop 38.

In order to obtain a greater degree of vertical directivity with this type of antenna, there may be provided a substantially circular director 35 spaced outwardly from the loop 30 and comprising a plurality of elements 36 having capacitors 31 between adjacent ends. The director is substantially concentrically arranged with the loop 30 and disposed in substantially the same plane.

The director is spaced apart from the loop a distance of the order of to A4 of a wavelength, preferably approximately A, wave. This is for the reason that the antenna system may tune too sharply if the spacing is too little and little gain in directivity is obtained if the distance is too great.

The length of the director elements 36 should be somewhat less than /2 wavelength so as to maintain relatively uniform current distribution and to permit correct tuning. Accordingly, the spacing from the loop and the length of the director elements are inter-related.

Any suitable form of transmission line 33 may be utilized to effect transfer of energy between the high frequency radio apparatus or transmitter, represented by the box 39, and the loop.

The above described system has a vertical directivity pattern as represented by the lobes 40 in Fig. 8.

In order to obtain still more vertical directivity, a plurality of assemblies may be employed, spaced apart vertically approximately wavelength.

Two such assemblies are shown schematically in Fig. 9. The assemblies are interconnected in the same phase by a suitable impedance matching line 4|. A suitable transmission line 42 may be used to transfer energy between transmitter 39 and is connected to the line 4! at a point midway between the assemblies. The directivity pattern for the system of Fig. 9 is represented by the lobes 43 in Fig. 8.

In order to support the assemblies in operative position, there may be provided a mast H as in Fig. 7. The loops may be secured to the mast by means of member 45 of insulative material and the director elements 36 may be supported from the loop 30 by similar supports 45 which are preferably connected to the elements 36 at points of minimum voltage.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention in its broader aspects, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A high frequency antenna system having a substantially circular radiation pattern, said system comprising a substantially closed loop coaxially spaced from an electrically conductive member and forming therewith a transmission line terminated for refiectionless transmission of energy thereover, a source of high frequency signals, a tuned circuit connected between said source and said conductive member, and means connecting the ends of said loop to spaced points on said circuit.

2. A high frequency antenna system having a substantially circular radiation pattern, said system comprising a substantially closed loop coaxially disposed with respect to an electrically conductive member to form therewith a section of transmission line terminated for reflectionless transmission of energy thereover, a source of high frequency signal, means connecting said member to said source through a tuned circuit, and means connecting the ends of said loop to spaced points on said tuned circuit to supply to said loop energy to be radiated therefrom.

3. A high frequency antenna system having a broad frequency band width and a substantially circular radiation pattern, said system comprising a substantially closed loop coaxially disposed with respect to an electrically conductive member and forming therewith a section of a transmission line, a source of signal voltage, means for impressing a portion of said voltage across said loop, and means for connecting said member to said source, said last means includin means terminating said line to provide substantially refiectionless transmission of energy thereover.

l. A high frequency antenna system having a broad frequency band width and a substantially circular radiation pattern, said system comprising a substantially closed loop coaxially disposed with respect to an electrically conductive member, means for energizing said loop, said means comprising a source of signal voltage and a tuned circuit, means for impressing a portion of the voltage existing across said tuned circuit across said loop, and means for connecting said member to said tuned circuit.

5. A high frequency antenna system having a broad frequency band width and a substantially circular radiation pattern, said system comprising an electrically conductive member and a helically wound coaxially disposed electrically conductive member around the first mentioned member and uniformly spaced therefrom to form therewith a section of transmission line, a source of high frequency signals connected to said first member through a tuned circuit, and means connecting the ends of said helical member to spaced points on said circuit.

6. A high frequency antenna system comprising a pair of substantially closed loop coaxially spaced from an electrically conductive member and forming therewith a plurality of sections of transmission line, said loops being spaced apart axially by a distance equal to a half-wave length at the operating frequency of said system, a source of high frequency signals, and means connecting the ends of said loops to said source for energizing said loops in opposite phase to produce a radiation beam concentrated along the axis of said loops.

7. A high frequency antenna system comprising a pair of substantially closed loops coaxially spaced from an electrically conductive member and forming therewith a plurality of sections of transmission line, said loops being spaced apart axially by a distance equal to a half-wave length at the operating frequency of said system, a r fleeting element coaxial with said member and spaced axially from the lower of said loops by a distance equal to a quarter wave length at said frequency, a source of high frequency signals, and means connecting the ends of said loops to said source for energizing said loops in opposite phase to produce a radiation beain concentrated along the axi of said loops.

8. A high frequency antenna system having a substantially circular radiation pattern in a first plane and directivity in planes transverse thereto comprising, a cylindrical electrically conductive member, a metallic loop-like member substantially encircling and coaxially disposed with respect to said cylindrical member to form there with a section of transmission line terminated for reflectionless transmission of energy thereover, said metallic member having a pair of ends spaced apart by a small angle with respect to a radius of said cylindrical member, a source of high frequency signals, and means supplying signals from said source to said ends.

GEORGE W. FYLER.

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