US2235163A - Broad band antenna - Google Patents

Description

Patented Mar. 18, 1941 UNITED STATES BROAD BAND ANTENNA Harold 0. Peterson, Riverhead, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application December 15, 1938, Serial No. 245,839

9 Claims.

The present invention relates to short wave antennas and, more particularly, to antennas for receiving horizontally polarized waves over a wide band of frequencies.

An object of the present invention is to enable the reception of horizontally polarized signals over a wide band of frequencies such as is at present used in television.

Another object of the invention is to provide an antenna suitable for receiving horizontally pol-arized signals over a wide band of frequencies.

Still another object of my invention is to provide an antenna having a substantially circular directivity pattern in the horizontal planes.

Another object of my invent-ion is to provide a single antenna structure capable of either a circular directivity pattern or of a figure 8 directivity pattern.

A further object of the present invention is the provision of a single contact antenna suitable for the reception of television signals.

The foregoing objects, and others which may appear from the following description, are obtained by providing a horizontally disposed double loop antenna.

In order to make the antenna substantially aperiodic over a wide band of frequencies a damping resistance is provided at a point on the loop remote from the connection of the transmission line to the loop. A damping resistance should have a value equal to the surge impedance of the loop.

My improved antenna may be constructed of two parallel horizontal loops each loop having a damping resistance at one point in its circumference and having a transmission line connected at a directly opposite point. Preferably, the diameter of my improved loop antenna should be somewhat less than a half of the length of the operating wave If a circular directive pattern is desired the two loops are connected in an additive relationship and if some directional efiect is desired they may be connected in an opposed phase relationship. As a further modification a two turn horizontal loop antenna may be employed having a damping resistance connected at its midpoint.

Referring, now, for a more complete understanding of the invention to the following detailed description which is accompanied by a drawing in which Figure 1 illustrates one form of my invention, Figure 2 illustrates a modification thereof and Figure 3 illustrates still a further modification.

Figure 1 shows one form of my invention.com

prising a pair of loop antennas disposed in parallel horizontal planes. The upper loop is composed of twosemi-circularly disposed conductors I and 2 having a damping resistance 5 connected at one pair of adjacent ends. The lower loop is composed of a pair of semi-circularly disposed conductors 3 and 4 having a damping resistance 6 connected at one pair of adjacent ends. The damping resistance 6 should be located at the diametrically opposite side of the antenna assembly from the damping resistance 5. The transmission line TL is connected by means of conductors I, l to one of the loops of my antenna and by means of conductors 8, 8 to the other loop of the antenna.

It will be noted that conductors 8, 8 are crossed in order to obtain an additive relationship between the currents induced in the two antennas. To the remote end of the transmission line is connected a receiver Ill indicated by a conventional box, The diameter of each of the loops is preferably somewhat less than a half of the length of the operating wave. In an actual physical embodiment which I have tested each pair of conductors form a circle having a diameter of .966 meters. The loop conductors were constructed of half inch copper tubing and arranged to be practically self-supporting. The value of damping resistor 5 and 6 was in the order of 700 ohms.

It is believed that the circular directivity pattern is obtained by the antenna in somewhat the following manner: Assuming that the antenna is arranged in a horizontal plane and that a horizontally polarized wave is arriving at the antenna in the direction indicated by arrow A, a voltage is induced in branches l and Z of the upper loop in the portions nearest the damping resistor 5. The voltage induced in each elemental portion of the antenna causes current to start flowing in both directions. Due tothe damping resistance -5, the currents flowing toward the damping resistance are not reflected and never reach the transmission line TL over the conductors 1, I. The only energy in the upper loop that reaches the transmission line is that traveling toward c011- ductors I, I. As soon as the wave in space has progressed beyond points diametrically opposite and on each side of the upper loop, the direction of induced voltage is re ersed since beyond that point the conductors are sloped in a direction opposite to the conductors at a point nearer the resistor 5, Consequently, the voltage induced in portions of the conductors is equal to, and is degrees out of phase with the component of the voltage induced in the portions of the conductors nearer resistor 5 and which is traveling towards conductors I, 1. Hence, no voltage from the direction A reaches the receiver if! from the upper loop antenna for any frequency lower than a frequency for which the diameter is less than half the length of the operating wave.

Now consider a wave arriving at the antenna and traveling in the direction indicated by arrow B. The elemental voltages induced in the antenna conductor nearer conductors I, I now have to travel back through the conductor towards the transmission line in a direction opposite to the direction of travel of the oncoming Wave. This introduces a time delay which shifts the phase of the energy so that by the time the energy from the conductor portions adjacent resistor 5 reaches the conductors I, I it is no longer cancelled by the energy induced in the conductor portions nearest conductors 1, 1. In fact, when the length of the conductors l and 2 from the point of connection of conductors .1, I to their midpoints approaches a length equal to a quarter of the length of the operating wave, the energy from the two halves of the upper loop of the antenna are in phase for waves traveling in the direction indicated by arrow B. Exactly the opposite action takes place in the lower loop 3, 4, butsince the two loops are connected in an additive relationship the received energy arriving from all directions is combined in an additive relationship to produce a substantially circular directive pattern.

In the modification of my invention shown in Figure 2 wherein the two loops are so connected that the energies are combined in a bucking relationship, the resultant directivity pattern has the general form of a figure 8 with the minimum sensitivity in the direction of arrows C and D.

. v This obviously is due to the fact that from either of the directions C or D, there is some effective current from each of the two antennas supplied to the transmission line TL butthe phase relationship is 180 degrees out of phase and so cancellation takes place.

In the further modification of my invention shown in Figure 3, which comprises a pair of circular loops II and I2 each having a diameter somewhat less than a half the length of the operating wave and having one pair of ends connected together by damping resistor 5, the transmission line TL being connected to the other pair of ends. In this form substantially the same directivity pattern is obtained as by the modification shown in Figure 1. Due to the presence of the damping resistors 5 and 6, in each of the embodiments, the antenna is substantially aperiodic. A substantially uniform response is obtained over a wide band of frequencies making the antenna particularly useful for television reception. The antenna is quite small and light and can readily be supported on the top of a light tower or on the roof of a building.

Antennasconstructed according to the dimensions given above in thedescription of Figure l were found to have a substantially uniform directivity over a frequency range from 45 megacycles to 100 megacycles.

While I have particularly shown and described several modifications of my invention, it is to be particularly understood that my invention is not limited thereto but that modifications may be made within the scope of the invention.

I claim:

1. A broad band antenna comprising a plurality of horizontal loops disposed in parallel planes,

a transmission line, means for separately connecting said loops to said transmission line and means in each of said loops and remote from the connection of said transmission line to said loops for preventing reflection of currents in said loops into said transmission line.

2. A broad band antenna comprising a plurality of concentric horizontal loops disposed in parallel planes, each of said loops having a diameter less than half the length of the operating wave, a transmission line, means for connecting said loops to said transmission line in an additive phase relationship and a series resistance in each loop at a point remote from the point of connection of said transmission line to said loop for preventing reflection of currents in said loop into said transmission line.

3. A broad band antenna comprising a plurality of concentric horizontal loops disposed in parallel planes, each of said loops having a diameter less than half the length of the operating wave, a transmission line, means for connecting said loops to said transmission line in an opposing phase relationship and a series resistance in each loop at a point remote from the point of connection of said transmission line in said loop for preventing reflection of currents in said loop into said transmission line.

4. A broad band antenna comprising a plurality of horizontal loop conductors disposed in parallel planes, each of said loops having a diameter less than half the length of the operating wave, a damping resistance at the midpoint of each conductor, the damping resistance in one of said conductor loops being diametrically opposite the damping resistance in the adjacent loop, a transmission line and means for connecting said loops to said transmission line in an additive phase relationship.

5. A broad band antenna comprising a plurality of horizontal loop conductors disposed in parallel planes, each of said loops having a diameter less than half the length of the operating wave, a damping resistance at the midpoint of each conductor, the damping resistance in one of said conductor loops being diametrically opposite the damping resistance in the adjacent loop, a transmission line and means for connecting said loops to said transmission line in an opposing phase relationship.

6. An antenna comprising a plurality of pairs of conductors disposed in parallel horizontal planes, the conductors in each plane being formed into a loop having a diameter less than half the length of the operating wave, a damping resistance connected between a pair of adjacent ends in each loop, a transmission line and means for connecting the other pair of adjacent ends of each loop to each transmission line, said loops being connected in an additive phase relation ship.

7. An antenna comprising aplurality of pairs of conductors disposed in parallel horizontal planes, the conductors in each plane being formed into a loop having a diameter less than half the length of the operating wave, a damping resistance connected between a pair of adjacent ends in each loop, a transmission line and means for connecting the other pair of adjacent ends of each loop to each transmission line, said loops being connected in an opposing phase relationship.

8. An antenna comprising a plurality of pairs of conductors disposed in parallel horizontal planes, the conductors in each plane being formed into a loop having a diameter less than half the length of the operating wave, a damping resistance connected between a'pair of adjacent ends in each loop, the damping resistance in one of said loops being diametrically opposite the damping resistance in the adjacent loop, a transmission line and means for connecting the other pair of adjacent ends of each loop to said transmission line, said loops being connected to said transmission line in an additive phase relationship.

9. An antenna comprising a plurality of pairs of conductors disposed in parallel horizontal planes, the conductors in each plane being formed into a loop having a diameter less than half the length of the operating wave, a damping resistance connected between a pair of adjacent ends in each loop, the damping resistance in one of said loops being diametrically opposite the damping resistance in the adjacent loop, a transmission line and means for connecting the other pair of adjacent ends of each loop to said transmission line, said loops being connected to said transmission line in an opposing phase relationship.

HAROLD O. PETERSON.

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