US2532176A - Antenna system - Google Patents

Description

Nov; 28, 1950 D. ca. c. LUCK 2,532,175

ANTENNA SYSTEM Filed Dec. 21, 1945 F17. 1 1'7. 2 j 7 95 7 1 7 I 1 ll 11 11 i REC.

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INVENTOR Dal 1'0 .dLuck ATTORNEY Patented Nov. 28, 1950 UNITED STATES ANTENNA SYSTEM of Delaware PATENT OFFICE Application December 21, 1945, Serial No. 636,531

6 Claims.

This invention relates to radio direction finding and more particularly to improvements in antenna systems of the Adcock type.

Various Adcock systems are described in chapter 7 of Keen, Wireless Direction Finding, 3rd edition, published in 1938 by Iliffe and Sons, London, England. A typical Adcock system includes one or more pairs of horizontally spaced vertical pickup elements, connected in opposition to each other to a receiver or other utilization device so that their resultant output is substantially proportional to the difference in phase between the individual antenna voltages. The necessary horizontal leads between the pickup elements and the utilization circuit are arranged to prevent, as far as possible, any pickup except by the vertical elements. This is done to avoid response to horizontal electric field components, which is the cause of so-called polarization error in direction finders.

It is found in practice that even with the most thorough shielding of horizontal elements of the antenna system, there is some response to horizontally polarized field components. One explanation for such response is that horizontally polarized radiation induces currents in the shields, the ground, and any other horizontal conductors. These currents induce corresponding currents in the antenna system, causing response to horizontally polarized fields and consequent polarization error.

The principal object of the present invention is to provide methods of and means for reducing polarization error in Adcock direction finders.

Another object is to provide methods of and means for counteracting the above-described horizontal response in Adcock type direction finder systems.

A further object is to provide, in antenna systems of the described type, means responsive to horizontal polarization in opposition to the normal undesired horizontal response of the system.

The invention will be described with reference to the accompanying drawing wherein:

Figures 1 and 2 are schematic diagrams of typical prior art Adcock antenna systems,

Figure 3 is a schematic diagram of one embodiment of the instant invention,

Figure 4 is a schematic diagram of another embodiment of the invention,

Figure 5 is a diagram of a modification of the system of Figure 3,

Figure 6 is a. diagram of a modification of the system of Figure 4, and

Figure 7 is a schematic diagram of a further embodiment of the invention.

The U antenna, shown in Figure 1, comprises spaced vertical pickup elements I and 3, connected at their lower ends to a radio receiver 5 by horizontal conductors 'l and 9 respectively. The-conductorsl and 9 are placed on the ground, or as close to the ground as is practicable, to minimize their operation as horizontal antenna elements. Since the earth may be low in concluctivity or non-homogeneous, a conductive screen or ground plane it is provided on the surface in the neighborhood of the antenna system.

The structure of Figure 1 is based on the theory that the lcw resistance screen (or ground, if the screen is not used) minimizes horizontal voltage gradients in the vicinity of the conductors l and 9 and thus prevents response to horizontally polarized field components. While this efiect does appear to some extent, it is by no means complete, and systems like that of Figure 1 exhibit considerable polarization errors.

In the system of Figure 2, the horizontal conductors l and 9 are provided with coaxial shields, are disposed beneath the ground plane H, and may even be buried in the earth. While this arrangement is less subject to polarization error than that of Figure 1, there is still substantial response to horizontal fields, because signals appearing on the ground plane are coupled into the antennas.

In accordance with the present invention, additional horizontalconductors are provided, in series with the leads l and 9 and exposed to the radiation field in such manner as to pick up voltages which oppose the normal, and. undesired, response of the system to horizontal polarization.

Referring to Figure 3, the shielded horizontal lead from the vertical element l extends along and beyond the midpoint of the line between the lower ends of the antennas l and 3, Where it is connected to an exposed horizontal conductorflfi, leading back to the receiver 5. The shielded lead 9 is extended similarly beyond the midpoint between the antennas, and connected to the receiver through an exposed horizontal conductor E3.

The lengths of the conductors it. and i i, and their height above the ground plane, are adjusted to provide minimum .overall response of the system to horizontally polarized waves. Although the shielded conductors and may be placed above the ground plane as shown in Fig" ure 3., it will be apparent Without further illustration that they may be located underneath it,

like those of the system of Figure 2.

Under some conditions, it may be found that the horizontal pickup provided by the conductors I3 and 15 in the system of Figure 3 is of such polarity as to aid, rather than oppose, the normal horizontal pickup by the remainder of the system. In this case, the modification shown in Figure 5 may be used. The diiTerence between Figures 3 and 5 is simply that the positions of the shielded leads 7 and 9 in the circuit are interchanged with those of the exposed leads l3 and 15. Thus the phase of the voltage introduced in the system by the exposed wires of Figure 5 is opposite to that introduced in the circuit of Figure 3.

A modified embodiment of the invention is shown in Figure 4. This arrangement is similar to that of Figure 3, except that the exposed conductors, instead of going outward from the receiver to the shielded lines 7 and 9, go out through the shielded lines and are connected back through shielded conductors H to the vertical conductors.

Like the system of Figures 3 and 5, the intentional horizontal pickup in the system of Figure 4 may be of the wrong phase under certain conditions. In this event, the connections may be rearranged as shown in Figure 6, with the positions of the horizontal pickup elements 13 and I5 interchanged to reverse the phase of the voltages introduced in the system.

Referring to Figure 7, the horizontal pickup element 55 is divided into two sections, l5a and and 151), at the top and bottom, respectively of the vertical element l. The vertical element 3 is similarly provided with top and bottom horizontal members 53a and i312. With the system of Figure 7, the amplitude and phase of the voltage introduced in the system by the exposed horizontal members may be adjusted for optimum compensation of the undesired horizontal response, by independent adjustment of the lengths of the upper and lower horizontal portions.

Although the invention has been described with reference to a single Adcock pair, it is to be understood that it may be applied similarly to each pair of an array of differently oriented pairs, such as is commonly used with a goniometer or other phase comparison device for providing directional indication.

I claim as my invention:

1. A U-type Adcock antenna system including two horizontally spaced vertical conductors, a pair of horizontal conductors each connected to the lower end of one of said vertical conductors and extending toward the other of said vertical conductors, shields surrounding said horizontal conductors, a utilization circuit having a pair of terminals, and a further pair of horizontal conductors, each connected in series with one of said first-mentioned horizontal conductors between the respective vertical conductor and one of said terminals, and extending in the direction opposite to that of the shielded conductor to which it is connected.

2. A U-type Adcock antenna system including a pair of horizontally spaced vertical conductors, a pair of exposed horizontal conductors each connected to the lower end of one of said vertical conductors and extending toward the lower end of the other of said vertical conductors, a pair of coaxial transmission lines, each connected in series with one of said horizontal conductors and extending in the direction opposite to that of the conductor to which it is connected, and a utilization circuit connected to said transmission lines.

3. A U-type Adcock antenna systemincluding a pair of horizontally spaced vertical conductors, a utilization circuit including two terminals, and substantially horizontal conductors connecting the lower ends of said vertical conductors to respective terminals of said utilization circuit, each of said horizontal conductors including a shielded portion extending from said utilization circuit in one direction along the line between said lower ends of vertical conductors in series with an unshielded portion extending in the opposite direction along said line.

4. A U-type Adcock antenna system including a pair of horizontally spaced vertical conductors, a pair of coaxial transmission lines each connected to the lower end of one of said conductors and extending toward the lower end of the other of said conductors, a pair of exposed horizontal conductors, each connected in series with one of said transmission lines, and extending in the direction opposite to that of the line to which it is connected, and a utilization device connected to said horizontal conductors.

5. A U-type Adcock antenna system including two horizontally spaced vertical conductors, a pair of horizontal conductors, each connected to the lower end of one of said vertical conductors and extending toward but not connected to the lower end of the other of said vertical conductors, a utilization circuit including two terminals, a further pair of horizontal conductors each connected in series with one of said first-mentioned horizontal conductors to one of said terminals, and shields surrounding at least a portion of each of the conductors of one of said pairs of horizontal conductors.

6. A U-type Adcock antenna system including a pair of horizontally spaced elements disposed above a conductive ground plane and responsive substantially only to vertical electric field compon nts, a utilization circuit including two terminals, and two horizontal conductors each connecting one of said terminals respectively to one of said elements, each of said horizontal conductors including a shielded portion extending from said utilization circuit toward a respective one of said elements and an unshielded portion in series therewith and extending toward the other of said elements.

DAVID G. C. LUCK.

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

UNITED STATES PATENTS Number Name Date 798,153 Artom Aug. 29, 1905 1,549,032 Squier Aug. 11, 1925 2,130,675 Peterson Sept. 20, 1938 2,195,232 Wells Mar. 25, 1940 2,248,800 Alford July 8, 1941 2,387,670 Luck Oct. 23, 1945 2,416,246 Wheeler Feb. 18, 1947 2,424,968 Busignies Aug. 5, 1947 FOREIGN PATENTS Number Country Date 198,522 Great Britain June 7, 1923 433,900 Great Britain Nov. 26, 1935 443,018 Great Britain July 12, 1935 887,955 France Nov. 29, 1943

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