US2255520A - Directional antenna system - Google Patents

Description

Sept. 9, 1941.

H. SCH USTER DIRECTIONAL ANTENNA SYSTEM Filed May 29, 1940 A )FIN scu TER FIG.| FIG.2

l L 32 J FiG.3

l 46 5 INVENTOR Patented Sept. 9, 1941 UNITED 2,255,520 DIRECTIONAL ANTENNA SYSTEM Hermann Schuster, Berlin-Zehlendorf, Germany,

G. in. b. 11., Berlin-Zehlenassignor to Fernseh dorf, Germany Application May 29, 1940, Serial No. 337,909 In Germany May 13, 1939 4 Claims.

This invention relates to a directional antenna system and particularly to a system for simultaneously receiving signals of widely differing wave lengths.

For the reception of signals of relatively short wave lengths, such as television signals, it is often desired to provide a directional antenna, particularly if the receiver is located between two stations operating with the same wave length. Since it is generally necessary to erect an outside antenna for the reception of television signals, it is desirable to make use of such an antenna also for the reception of signals of relatively long wave length, such as conventional sound broadcast signals. Furthermore, it can also be of advantage simultaneously to employ the same antenna system for reception of signals of short and long wave lengths.

The object of the present invention, therefore, is to provide a new and improved'antenna system which has a directional effect for signals of relatively shortwave length and which can be used for simultaneous reception of signals of both relatively short and relatively long wave lengths.

In accordance with the present invention,

there is provided a receiving antenna system comprising a first half-wave length rod for intercepting radiated signals of relatively short wave length, and a second half-wave length rod disposed substantially parallel to the first rod and spaced substantially one-quarter wave length therefrom for reflecting the radiated signals. Additional means are provided for conducting the intercepted signals to a signal-reproducing means.

i In accordance with another feature of the present, invention, there are provided similar antenna systems intercepting signals of both rela-, tively short Wave length and relatively long wave length and a single means for conducting the intercepted signals. Further means are provi d for separating the conducted signals and for separately' applying the separated signals to signalreproducing means.

For a better understanding of the invention, together with other and furtherobjects 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.

' point is mismatched In the accompanylng drawing, Fig. 1 shows a schematic diagram of an antenna system embodying the present invention, while Fig.2 shows a modification thereof and Fig. 3 schematically shows a circuit for separating the signals of short and long wave lengths.

Referring now more particularly to Fig. l of the drawing, there is shown schematically a receiving antenna system comprising a solid conducting rod I- having a length substantially equal to one-half the wave length of the short Wave signal tov be received. A similar rod 2 of substantially equal length is. disposed parallel thereto. and spaced from thefirst rod by one-quarter wave length. Both rods are supported by a supporting means 3 of insulating material which is attached to a metallic antenna mast 4. .Attached to the antenna mast 4 and electrically connected thereto is a metallic housing 5 preferably disposed in the vicinity of the-lower ends of the rods l and 2, as shown in the drawing.

For the purpose of conducting signals intercepted by the antenna rods. I andv 2 to the signalreproducing apparatus, there is provided a concentric cablefi disposed within the hollow of the antenna mast 4, as shown. The outer conductor of the cable 6 is preferably connected to ground at the signalereproducing apparatus, as schematically indicated at 1. For reception of signals of relatively short wave length, the inner conductor of cable 6 is conductively connected to a point 8 of the rod 1 by way of the inner conductor of a concentric cable 9, Whose outer conductor and shield is conductively connected to the metallic housing 5. For reception of signals of relatively long wave length, the inner conductor of the cable 6. is also connected to a point It) on the antenna rod 2 by way of a first de-coupling resist.- or H, a matching transformer i2, and a second de-coupling resistor 13.

v In operation, signals of relatively short wave length are intercepted by the antenna rod l and conducted to the inner conductor of the cable t I by way of the concentric cable 8, whose inner conductor is connected to the rod 1 at the point 8. The position of point 8 is preferably sochosen.

of the antennarod at. that with respect'to the characteristic impedance of the cable 6 by an amount greater than 1 to 3, preferably approximately I to i. For a diameter of 22 millimeters for the rod I, a signal wave length of 2.92 meters and a characteristic impedance of the cable 6 of ohms, a preferred position of the point 8 for favorable side-band frequency response is 770 millimeters from one end of the rod l. o

For signals of relatively short wavelength, the antenna rod2 is substantially unloaded, as

that the impedance will be explained later, and therefore oscillates freely at this wave length. Hence, all signals arriving thereat in the direction from rod I toward rod 2 will be reflected by rod 2 with such a phase relation with respect to the oncoming wave, due to the quarter-Wave length spacing between rods I and 2, that the oncoming wave and the reflected wave will cancel each other. Thus, the rod I receives only signals which come in the direction from the rod 2 toward rod. I.

For signals of relatively long wave length, the rod 2 cannot oscillate freely, wherefore these signals are intercepted and conducted to the inner conductor of cable 6 by way of the decoupling resistor I3, matching transformer I2 and de-coupling resistor II. For short wave lengths, the value of the ole-coupling resistor I3.

must be large compared with the impedance of the reflector rod 2 at the point I0, so that the rod 2 may be permitted to oscillate freely at' those wave lengths. On the other hand, the value of the resistor I3 preferably should be small compared with the input impedance of the transformer I2 as seen from the rod 2 to prevent substantial attenuation of the long wave signals applied to the transformer. Furthermore, it is then possible to use a standard commercial transformer, since a relatively low value of the resistor I3 does not considerably shift the frequency pass-band of the matching transformer. The value of the de-coupling resistor II must be small compared with the capacitive reactance of the cable 6 for sound broadcast frequency, so as not unnecessarily to attenuate these signals, and large compared with the characteristic impedance of this cable, so as not to load the rod I with the matching transformer I2.

In this circuit connection, the antenna rod I receives signals of relatively short wave length coming in the direction of rod 2 toward rod I, and the intercepted signals are conducted to the concentric cable 5. The rod 2 oscillates freely at the short wave length and reflects signals coming in the direction from rod I toward rod 2 in such a phase that the oncoming and the reflected signal waves cancel each other. The rod 2 also serves as a receiving antenna for signals of comparatively long wave length which are also applied to the concentric cable 6 by way of the resistors II and I3, and the matching transformer I2.

Fig. 2 shows a modification of the antenna system just described. In this system there is again provided a solid conducting rod of substantially one-half wave length. A similar rod 2I of substantially equal length is disposed parallel thereto and spaced from the first rod by onequarter wave length. Both rods are supported by a supporting means 23 which is attached to the upper portion 24 of a metallic antenna mast 25. The rod 2! is conductively connected to the supporting means 23, while the rod-20 is insulated therefrom by means of an insulator 22. Attached to the antenna mast 25 and electrically connected thereto, is a metallic housing 26 from which the upper portion 24 of .the antenna mast and the supporting means 23 are insulated by means of an insulator 21. The housing 26 is preferably disposed in the vicinity of the lower ends of the rods 20 and 2|, as shown in the drawing.

For the purpose of conducting signals intercepted by the antenna rods 20 and 2I to the signal-reproducing apparatus, there is again provided a concentric cable 28 disposed Within the hollow of the antenna mast 25, as shown. The

outer conductor of the cable 28 is preferably connected to ground at the signal-reproducing apparatus, as schematically indicated at 29. For the reception of signals of relatively short Wave length, the inner conductor of cable 28 is conductively connected with a point 36 on the rod 26 by way of the inner conductor of a concentric cable 3|, whose outer conductor and shield is conductively connected to the metallic housing 26. For the reception of signals of relatively long wave length, the inner conductor of the cable 28 is also connected to the center of the antenna rod 2I by way of a de-coupling resistor 32, a transformer 33, the upper portion 24 of the antenna mast, and the supporting means 23.

As can be seen readily by comparing Figs. 1 and 2, the only difference between the structures illustrated therein is that the transformer 33 of Fig. 2 is directly coupled to the center of the rod 2!, at which point the impedance of this rod is substantially zero for signals of short Wave lengths. Hence, the impedance of the transformer 33, when viewed from rod 2 I, always represents a value greater than Zero for the short wave signals and therefore makes superfluous the provision of a de-coupling resistor, otherwise necessary to permit the rod 2! to oscillate freely at the short wave lengths. In order to prevent oscillations from being developed in the supporting structures of the rod 2|, it is preferable to make the effective length of the upper portion 24 of the antenna mast equal to one-quarter of the short wave length.

The operation of the system illustrated in Fig. 2 is substantially the same as that of Fig, 1, inasmuch as the rod 20 intercepts signals of relatively short wave length which are conducted to cable 28, while the rod 26 is permitted to oscillate freely and serves as a reflector cancelling all signals arriving in the direction from rod 25 toward rod 2 I and simultaneously serves to intercept signals of relatively long wave length which are also conducted to the cable 28.

Fig. 3 schematically illustrates the receiving station proper, where there is provided a grounded metallic housing 40 into which is inserted the end of a concentric cable 4|, whose outer confductor and shield is conductively connected therewith. This cable 4| may be identical with cables 6 or 28 of Figs. 1 and 2, respectively. The inner conductor of cable M is connected to the antenna terminal of a receiving and reproducing apparatus for short wave signals, such as receiver 42, by way of a coupling condenser 43, in order to apply relatively short wave signals thereto. The inner conductor of cable 4| is also connected to the input terminal of a receiving and reproducing apparatus for long wave signals, such as sound broadcast receiver 44, by way of a de-cou pling resistor 45 and a matching transformer 46, in order to apply relatively long wave signals thereto. In order to obtain proper separation of the signals of relatively short and relatively long wave lengths, the capacitive reactance of the condenser 43 for the short wave signals is preferably chosen to be much smaller than the impedance of the de-coupling resistor 45, while the value of the latter should be small compared with the input impedance of the transformer 46, in order to prevent undue attenuation of the long wave length signals.

Hence, a system comprising the apparatus shown in Figs. 1 and ,3 or 2 and 3, respectively, is

- adapted to receive signals of relatively short wave length from one direction only and simultaneously to receive signals of relatively long wave length from any direction, to conduct such signals over a single means, and to separate such signals at the end of this conducting means so that they may be applied to separate signalreproducing apparatus.

While there has been described what is at present 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 it is, therefore, 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 receiving antenna system comprising a first half-wave length rod for interceptingiradiated signals of relatively short wave length, a second half-wave length rod substantially parallel to said first rod and spaced substantially one-quarter wave length therefrom for reflecting radiated signals of a relatively short wave length and intercepting radiated signals of a relatively long wave length, a single means for conducting intercepted signals of said relatively short and long wave lengths from said first and second rods, means for separating said conducted signals, and means for separately applying said separated signals to signal-reproducing means.

2. A receiving antenna system comprising a first half-wave length rod for intercepting radiated signals of relatively short wave length, a second half-wave length rod substantially parallel to said first rod and spaced substantially one-quarter wave length therefrom, adapted to oscillate freely at said relatively short wave length and for intercepting radiated signals of a relatively long wave length, a single means for conducting intercepted signals of said relatively short and long wave lengths from said first and second rods, means for separating saidv conducted signals, and means for separately applying said separated signals to signal-reproducing means.

3. A receiving antenna system comprising a first half-wave length rod for intercepting radiated signals of relatively short wave length, a second half-wave length rod substantially parallel to said first rod and spaced substantially one-quarter wave length therefrom for reflecting radiated signals of a relatively short wave length and intercepting radiated signals of a relatively long wave length, a single means for conducting signals, first means for coupling said first rod to said signal-conducting means, second means for coupling said second rod to said signal-conducting means, said last-named means adapted to pass signals of relatively long wave length only, first de-coupling means connected between said second coupling means and said second rod, second de-coupling means connected between said second coupling means and said signal-conducting means, means for separating said conducted signals, and means for separately applying said separated signals to signal-reproducing means.

4. A receiving antenna system comprising a first half-wave length rod for intercepting radiated signals of relatively short wave length, a second half-wave length rod substantially parallel to said first rod and spaced substantially one-quarter wave length therefrom for reflecting radiated signals of a relatively short Wave length and intercepting radiated signals of a relatively long Wave length, a single means for conducting intercepted signals of said relatively short and long wave lengths from said first and second rods, means for conductively connecting said lastnamed means to the center point on said second rod, means for separating said conducted signals, and means for separately applying said separated signals to signal-reproducing means.

HERMANN SCHUSTER.

Images