US2634371A - Multichannel antenna system - Google Patents

Description

April 7, 1953 R. w. MASTERS MULTICHANNEL ANTENNA SY Filed June 30, 1949 Robert WWZJEZ Qrs 2,

Patented Apr. 7, 1953 MULTICHANNEL ANTENNA SYSTEM Robert Wayne Masters, Erlton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application June 30, 1949, Serial No. 102,266

Claims.

The invention relatesto antenna systems and it particularly pertains to transmitting antenna systems which are capable of simultaneous radiation of both television and frequency modulated broadcast signals.

In many television station installations it is desirabie both from an economic and esthetic viewpoint to have a single antenna serve for radiating both frequency modulation broadcast and television broadcast signals. The result is a saving not only in the cost of an otherwise necessary separate antenna but also in the additional transmission line which would be necessary to apply energy thereto.

There are few antennas known to the art which are capable of furnishing the required extremely wide band width necessary for successful high definition television. One of these few antennas is the so-called current-sheet radiator turnstile antenna Which is disclosed and described in copending U. S. patent applications of R. W. Masters, Serial Numbers 574,898 and 574,899, filed January 27, 1945, now U. S. Patents 2,480,153 and 2,480,154, respectively, issued August 30, 1949.

Models of this antenna which are designed for the 209 Mc./s. television band are not equally suitable for transmission at a frequency in the 83-120 Mc./s. frequency modulation broadcast hand because they have been found to be so reactive as to be unusable unless some means of tuning to resonance without appreciably altering the impedance at 200 Mc./s. is provided.

The known television antennas of the type described above, which are most often used, comprise six layers spaced at approximately wavelength intervals on a common metal supporting structure, each layer consisting of four currentsheet radiators of the type described and disclosed in the above-mentioned applications arranged in turnstile formation. The six pairs of currentsheet radiators in one vertical plane are excited in phase by equal length transmission lines from a common junction box and the other six pairs of current-sheet radiators in a vertical plane oriented at 90 with respect to the first plane are similarly excited all in phase but in phase quadrature withrespect to the first six pairs of ourrent-sheet radiators, which is the standard turnstile connection. In practice, each current sheet has its own individual transmission line from the junction box, but for purposes of clarity each pair of radiators may be considered as being connected to a single transmission line, bifurcated near the radiators having the sheath of one transmission line section bonded to one currentsheet radiator of the pair and the corresponding inner conductor connected to the supporting structure while the sheath of the other transmission line section is bonded to the supporting structure and the corresponding inner conductor is connected to the other current-sheet of the pair in the manner described in U. S. Patent 2,433,183, of Lester J. Wolf, issued December 23, 1947. This type of feed system is highly desirable for use with FM and television signal transmission.

Therefore, it is an object of the invention to provide an antenna system capable of radiating frequency modulation broadcast signals and television broadcast signals as well.

It is a further object of the invention to provide a network by means of which an antenna system designed for television broadcast band can be operated in the frequency modulation broadcast frequency band without noticeably altering the impedance of the antenna system at the television frequencies.

It is an additional object of the invention to provide components by means of which a standard television broadcast band antenna may be employed for frequency modulation transmission without materially altering its characteristics at television frequencies.

It is another object of the invention to provide a network capable of converting antenna systems primarily designed for operation at television signal frequencies for transmission with high efficiencies in the frequency modulation band.

It is still a further object of the invention to provide an antenna system for simultaneous operation in both television and FM bands which issimple in construction, pleasing in appearance, and efiicient in operation.

These and other objects which will appear as the specification progresses are attained according to the invention by means of two terminal coaxial transmission line networks having an arm providing a reactance characteristic equivalent to that of an open ended section of transmission line a quarter wavelength long at the video mid-channel frequency and another arm having the reactanoe characteristic of a length of short circuited coaxial cable of the same char-- acteristic impedance providing a reactance which in parallel with the reactance of the first arm wiil provide over-all reactance at the FM frequency of the correct value to compensate for that of the radiators with which it is connected. According to one embodiment of the inventlon, such a network is comprised of a length of coaxial transmission line arranged to be clamped to the vertical edge of the sheet radiator element or to the supporting structure, and according to another embodiment of the invention, the network is incorporated directly into a current sheet radiator or the supporing structure as required.

The invention will be described in detail with reference to the accompanying drawing forming part of the specification and in which Fig. 1 is an illustration of a single pair of current sheet radiators as modified according to the invention;

Fig. 2 is a cross-sectional view of one of the networks according to the invention to show details of its construction; and

Fig. 3 is an illustration of an alternate embodiment of the invention showing the incorporation of the network according to the invention directly to the current sheet radiator and the supporting structure.

Referring to Fig. 1, there is shown a supporting member comprising a hollow conductive member II! on which groups of mounting structures I2 are arranged, only four of such structures being shown here. Current sheet radiators I4 and I6 of the type described in above-mentioned U. S. Patent 2,480,154 are mounted on structures I2. Each pair of radiators I4, I6 is electrically connected together at the upper and lower ends by means of conductive structures I2 and support I0. Radiators I4, I6 are energized by means of a transmission line I8 having bifurcated end portions 22 and 23. The sheath of section 22 is bonded to support III for a part of its length near radiator I4 and then is carried over and bonded to the lower end of radiator I4 at the point where it makes contact with supporting structure I0. It is understood of course that the sheath of section 22 is at the same potential as the lower end of radiator I4 and the support I because of the direct connection by member I4, it being necessary for obvious reasons to employ a less abrupt change of direction in the placement of transmission line 22. The remaining length of section 22 is bonded to radiator I4 and extends up the vertical edge to a point near the center thereof at which point the inner conductor is connected to support I8 by means of an impedance matching device 28 later to be described in detail. Section 23 of transmission line I8 has the sheath thereof bonded to the support structure I0 for its entire length and at a point opposite the end of section 22, the inner conductor of section 23 is connected to radiator I6 via another impedance matching device 28. Impedance matching devices 28 are mechanically fastened to support I0 and radiator I6 by any suitable means, such as welding, metallic straps, clamps, and the like, which also afford electrical connection of the outer sheath 34 of device 28 to the supporting element.

Referring to Fig. 2, there is shown a crosssection diagram of an impedance matching device 28 comprising a section of transmission line 38 including an inner conductor 32 and an outer coaxial conductor 34. Inner conductor 32 is electrically connected to outer conductor 34 at one end by means of a conductive member 36 and is mounted in space relationship at the other end of the arrangement by means of insulating spacer members 38. At a point intermediate the end of outer conductor 34, branch section comprising an inner conductor 42 and an outer conductor 44 is arranged. The inner conductor 42 is held in fixed relationship to surrounding conductor 44 by means of an insulating member 46, which extends into the interior of conductor 34 to serve as an additional spacing support and inner conductor 32 to which inner conductor 42 is electrically connected. Preferably the latter connection is made by means of a metallic sleeve 48 into which a stud constituting inner conductor 42 is threaded. Sleeve 48 and inner conductor 32 are preferably soldered together for additional strength. Inner conductor 42 is connected to inner conductor 32 at a point which is one quarter wavelength at the television midchannel radio frequency from the open end of the transmission line 30. The length of transmission line 30 between the junction of inner conductor 42 and conductor 36 is of such length that the reactance at point P is equal and opposite to that of radiator I4 or I6 for which the impedance device 28 is designed.

An alternate embodiment of the invention is shown in Fig. 3, wherein transmission line 38 is made an integral part of radiator 26, the outer conductor 34 constituting the vertical edge member of radiator 26. In order to provide maximum efiiciency, conductor 32 is made adjustable and can be adjusted from the top of conductor 34. The open end of transmission line 30 as constituted in this embodiment is also made adjustable by means of a close fitting auxiliary sleeve 52 which can be adjusted from the bottom of conductor 34 in order to provide more precise tuning. For esthetic reasons, as well as other practical reasons, a second impedance matching device 28 is mounted internally to support member III in this case. Mounting the device 28 internally to the support member I0 permits reduced cost of construction in that no individual protection from the weather is required for those devices so mounted. Transmission line I8 is preferably arranged within support I0 and emerges therefrom at aperture 54 in order to be connected to the bottom end of radiator 24 whose vertical conductor 56 forms a continuation of the outer sheath of section 22 and an extension of the inner conductor of section 22 is car ried up through the conductor 54 to aperture 51 through which it is connected to conductor 42 of impedance matching device 28. Section 23 of transmission line I8 is carried up through support ID to aperture 58 through which the center conductor of section 23 is carried over to inner conductor 42 of the impedance matching device integrally within radiator 26.

While only a single pair of current sheet radiators I4 and I6 or 24 and 26 are shown in their proper relationship to support I8, it is to be understood that for each layer of the turnstile, an additional pair of such radiators arranged at an angle of with respect to the first pair and fed in exactly the same manner are to be supplied. The two pairs of cooperating radiators are then supplied energy at television and frequency modulation wavelengths by means of a triplexing arrangement, preferably of the type shown and described in U. S. patent application 723,217, filed January 11, 1947, to Lester J. Wolf, although it is not necessary to the invention that this specific system be employed.

Although the foregoing description has been confined to a transmitting antenna system, it should be understood that the underlying principles of the invention are equally applicable to antenna systems wholly devoted to the reception of signals.

While the invention has been described in terms ofexpress embodiments, it is to be understood that obvious modifications thereof will be suggested to those skilled in the art without departing from the spirit and scope of the invention.

The invention claimed is:

1. An antenna system for simultaneous translation of radio frequency energy at differing wavelengths, including radiator elements havin dimensions providing optimum translation at a given wavelength and providing a predetermined reactance at a predetermined wavelength discretely differing from said given wavelength, transmission lines having characteristic impedances matching the input impedances of said radiator elements at said given wavelength, and transformer devices interposed between said transmission lines and said radiator elements, said transformer devices comprising length of two conductor transmission line shorted at one end and open at the other, said lengths of transmission line each being tapped at a point located one quarter of said given wavelength from the open end thereof to connect said transmission lines in effect directly to said radiator elements at said given wavelength and the shorted end of each of said lengths of transmission line being removed from said points by a distance effective to interpose in series with said radiator elements reactances substantially of equal value and opposing sign to said predetermined reactance at said predetermined wavelength to match said transmission line substantially only at said given and said predetermined wavelengths.

2. An antenna system for simultaneous translation of radio frequency energy at differing wavelengths, including a radiator element providing optimum translation at a given wavelength and providing a predetermined reactance at another predetermined wavelength discretely differing from said given wavelength, means to couple a transmission line having a characteristic impedance matching the input impedances of said radiator element at said given wavelength, and a transformer device interposed between said transmission line and said radiator element, said transformer device comprising a tuned network having two branches connected in parallel, one of said branches being series resonant at said given wavelength to connect said transmission line in effect directly to said radiator element at said given wavelength and the other branch having a reactance component of value which in conjunction with the reactance of said one branch at said predetermined wavelength interpose in series between said radiator element and said transmission line a reactance of equal value and opposing sign to said predetermined reactance at said predetermined wavelength to match said transmission line substantially only at said given and said predetermined wavelengths.

3. An antenna system for simultaneous translation of radio frequency energy at differing wavelengths, including a radiator element having dimensions providing'optimum translation at a given wavelength and providing a predetermined reactance at'a predetermined wavelength discretely differing from said given wavelength, means to couple a coaxial transmission line having inner and outer conductors and a characteristic impedance matching the input impedance of said radiator element at said given wavelength to said radiator element, and a length of transmission line having a center conductor and a. sheath conductor connected together at one end thereof, said sheath conductor being connected to said radiator element and coupled to the outer conductor of said coaxial transmission line, the inner conductor of said coaxial transmission line being connected to the center conductor of said length of transmission line at a point one quarter wavelength at said given frequency from the open end thereof to connect said transmission line in effect directly to said radiator element at said given frequency, said point being spaced from the closed end of said length of transmission line at a distance effective to interpose a reactance of equal value and opposing sign to said predetermined reactance at said predetermined wavelength in series with said transmission line coupling means to match said transmission line-substantially only at said givenand' said predetermined wavelengths.

4. An antenna system for simultaneous radiation of radio frequency energy at two discretely separated frequencies, including a radiator element of the type having a rectilinear conductor having a length between one half and one wavelength at one of said frequencies and a number of conductive members connected to said rectilinear conductor and arranged normally thereto; said rectilinear conductor being grounded at points near the ends thereof and being adapted for the application of radio frequency energy at points intermediate the grounded points, including a length of concentric transmission line having its conductors connected together at one end thereof, the sheath conductor of said transmission line being connected for substantially the entire length thereof to said rectilinear conductor. and the center conductorhaving an input terminal point located at a distance from the closed end of said transmission line to provide a react ance value substantially equal in magnitude and opposite in sign to the reactance of said radiator element at the other of said frequencies, the remainder of said transmission line being a quarterwave long at said one frequency whereby the input impedance to said radiator is substantially a pure resistance substantially only at said discretely separated frequencies.

5. An antenna system for simultaneous radiation of radio frequency energy at two discretely different frequencies, including a radiator element of the type having a rectilinear conductor having a length between one half and one wavelength at one of said frequencies and a number of conductive members connected to said rectilinear conductor and arranged normally thereto, said rectilinear conductor being grounded at points near the ends thereof and being adapted for the application of radio frequency energy at points intermediate the grounded points, including a length of coaxial transmission line having center and sheath conductors connected together at one end thereof, said sheath conductor being connected to said rectilinear conductor along substantially the entire length of said sheath conductor, and said center conductor having a terminal point located at a distance from the closed end of said coaxial transmission line to provide a reactance value substantially equal inmagnitude and opposite in sign to the reactance of said radiator at the other of said frequencies,'the remainder of said coaxial transmission line being a quarterwave long at said one frequency whereby the input impedance to said radiator at said terminal is substantially a pure resistance substantially only at said two discretely different frequencies.

6. An antenna system for simultaneous 'radla tion of radio frequency energy at two difierent frequencies, including a radiator element of the type having a hollow rectilinear conductor having a length between one half and one wavelength at one of said frequencies and a number of conductive members connected to said rectilinear conductor and arranged normally thereto, said rectilinear conductor being grounded at points near the ends thereof and being adapted for the application of radio frequency energy at points intermediate grounded points, including a length of center conductor arranged within said hollow rectilinear conductor and connected thereto at one end thereof, said center conductor having a terminal point located at a distance from the junction with said hollow conductor to provide a. reactance value substantially equal in magnitude and opposite in sign to the reactance of said radiator at another of said frequencies, the remainder of said center conductor being a quarterwave long at said one frequency whereby the input impedance to said radiator between said point on said center conductor and the hollow rectilinear conductor is substantially a pure resistance at both of said frequencies.

*7. An antenna system for simultaneous translation of radio frequency energy at two discretely differing wavelengths, including a conductive support, a pair of opposed radiators of the current sheet type having dimensions providing optimum translation at a given wavelength and providing predetermined reactances at a predetermined wavelength discretely differing from said given wavelength, a bifurcated coaxial transmission line having inner and outer conductors and a characteristic impedance matching the input impedances of said radiators at said given wavelength, and a pair of transformer devices, each of said devices comprising a length of transmission line having a. center conductor and a sheath conductor connected together at one end thereof, terminals connected to said length of transmission line at a point one quarter wavelength at said given frequency from the open end thereof, and said point being spaced from the closed end of said length of transmission line at a distance effective to provide a reactance of equal value and opposing sign to said predetermined reactance at said predetermined frequency, one of said devices having its sheath conductor connected to said support and the other having its sheath conductor connected to one of said current-sheet radiators along the feeder edge thereof, the connections to said sheath conductors being made substantially along the entire length of said sheath conductor-s, one end of said transmission line having its outer conductor connected to said support and its inner conductor connected to said device on said one current sheet radiator, the other end of said transmission line having its outer conductor connected to the other current sheet radiator and its inner conductor connected to said device on said support, thereby to provide substantially pure resistive input characteristics to said radiations substantially only at both of said discretely differing wavelengths,

8. An antenna system for simultaneous translation of radio frequency energy at differing wavelengths, including a conductive support, a pair of opposed radiators of the current-sheet type having dimensions providing optimum translation at a given wavelength and providing predetermined reactances at a predetermined wavelength other than said given wavelength, a

bifurcated coaxial transmission line having inner and outer conductors and a characteristic impedance matching the input impedances of said radiators at said given wavelength, one of said current-sheet radiators having a hollow conductive structural member and an inner conductor member arranged therein and connected together near one end of said hollow structural member, a terminal connected to said inner conductor at a point one quarter wavelength at said given frequency from the end thereof remote from said connection to the hollow conductor, and said point being spaced from said connection to the hollow conductor at a distance effective to provide a reactance of equal value and opposing sign to said predetermined reactance at said predetermined frequency, a length of transmission line arranged within said support and having a center conductor and a sheath conductor connected together at one end thereof, terminals connected to said length of transmission line at a point one quarter Wavelength at said given frequency from the open end thereof, and said point being spaced from the closed end of said length of transmission line at a distance effective to provide a reactance of equal value and opposing sign to said predetermined reactance at said predetermined frequency, the sheath conductor of said length of transmission line being connected to said support, one end of said transmission line having its outer conductor connected to said support and its inner conductor connected to said terminal on said one current-sheet radiator, the other end of said transmission line having its outer conductor connected to the other current-sheet radiator and its inner conductor connected to said length of transmission line within said support, thereby to provide a substantially pure resistance input characteristic to said radiations at both of said wavelengths.

9. An antenna system for simultaneous translation of radio frequency energy at differing wavelengths, including a radiator element having dimensions providing optimum translation at a given wavelength and presenting a predetermined reactance at the feed point thereof at a predetermined wavelength discretely differing from said given wavelength, means to couple a coaxial transmission line having sheath and inner conductors and a characteristic impedance matching the input impedance of said radiator element at said given wavelength to said radiator element, the sheath conductor of said coaxial transmission line being directly connected to at least one point on said radiator element remote from said feed point, and a transformer device interposed between said coaxial transmission line and said radiator element, said transformer device comprising an elongated conductor arranged in proximity to said radiator element to effect a length of transmission line therewith open at one end thereof, the inner conductor of said transmission line being connected to said elongated conductor at a point one quarter of said given wavelength from said open end of said length of transmission line to connect the inner conductor of said transmission line in effect directly to the feed point of said radiator element at said given wavelength and the end of said conductor remote from said open end of said length of transmission line being short circuited to said radiator element at a distance from said point effective to interpose in series between said transmission line and said radiator element a reactance of equal value and opposing sign to said predetermined reactance at said predetermined wavelength, thereby to match said transmission line substantially only at said given and said predetermined wavelengths.

10. An antenna system for simultaneous translation of radio frequency energy at differing wavelengths, including a current sheet radiator having characteristics providing optimum operation at a, given wavelength and a predeterminable feed point reactance at a predetermined wavelength discretely difiering from said given Wavelength, an impedance transforming device having a central conductor and an outer conductor arranged along said radiator in electrical contact therewith, said device constituting a length of transmission line having one section thereof substantially equal to a quarter wavelength at said given frequency and open at both ends and another section short circuited at the end remote from said one section and having a length at which a reactance substantially equal to said predetermined reactance and of opposing sign is produced, and means to connect a coaxial transmission line to said system to couple a source of energy at said given wavelength and another source of energy at said predetermined wavelength to said current sheet radiator through said device, whereby each of said sources is eiiectively connected to the feed point of said radiator substantially only at said given and said predetermined wavelengths, said means connecting the inner conductor of said transmission line to the junction between said transmission line sections and connecting the sheath conductor to said radiator at a point remote from said feed point.

ROBERT WAYNE MASTERS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,138,906 Cork Dec. 6, 1938 2,267,445 Cork Dec. 23, 1941 2,284,434 Lindenblad May 26, 1942 2,433,183 Wolf Dec. 23, 1947 2,480,155 Masters Aug. 30, 1949

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