US2156661A - Wireless aerial - Google Patents

Description

May 2, 1939. NWELLS 2,156,661

WIRELESS AERIAL Filed Ap ril l9, 1937 INVENTOR NORMAN WELLS ATTORN EY Patented May 2, 1939 PATENT OFFICE I 2,156,661 WIRELESS AERIAL Norman Wells, Ardeevin, land, assignor to Radio Epsom Downs, Eng- Corporation of America, a corporation of Delaware Application April 19,

In Great Britain 2 Claims.

This invention relates to aerials for wireless signalling and more particularly to aerials of the type sometimes termed inverted aerials, i. e., aerials operating as half wave aerials but having a so-called artificial top terminating the upper end of a vertical aerial section.

The invention is illustrated in and further explained in connection with the accompanying diagrammatic drawing in which Figures 1, 2 and 1 i 3 illustrate different forms of half wave antennas for the purpose of explaining the present invention. Figure 4 illustrates an embodiment of the present invention, while Figures 5 and 6 illustrate modifications thereof.

Referring to Fig. 1, it is usualat the present time to constitute (in the manner shown in Fig. i) an aerial operating as a half wave aerial by a vertical down lead I having an artificial top in the form of a horizontal conductor 2a., 2b which is symmetrically disposed with relation to the down lead. This well known type of arrangement is satisfactory if the length of the down lead is of the order of three-eights or more of the working wavelength, that is to say, when the horizontal top 2a, 2b is equivalent to an artificial extension of the order of one-eighth or less of the working wavelength so as to make the total aerial length electrically half the working wavelength. If, however, the down lead isless than approximately three-eights of a wavelength long and particularly when it is one-quarter or less of a wavelength long, the dimensions of the horizontal artificial top become such that substantial radiation takes place therefrom. The dimensions marked on Fig. 1 illustrate a typical case of this nature, A in Fig. 1 representing the wavelength. It has been shown that for the case illustrated in Fig. l, where the vertical down lead is 025i, and 2a and 2b are each of about the same length, the radiation resistance due to additional and unwanted radiation from the artificial top amounts to about 9 ohms. As the radiation resistance of an ideal aerial of this type is 32.4 ohms, it will be appreciated that 9 ohms radiation resistance due to unwanted radiation represents an appreciable loss of energy.

Various expedients have been suggested to meet this difliculty. For example, it has been suggested to fold back each half 2a or 2b of the horizontal wire constituting the artificial top in zig-zag fashion in the manner represented in Fig. 2 (where the supporting masts are not shown), the two zig-zag halves of the top being similar and consisting of wire arranged in a horizontal plane and zig-zagging in the same general 1937, Serial N0. 137,703

April 29, 1936 direction for both halves of the top. This known arrangement in effect reduces the overall length of the top as compared to that which would be obtained where a simple horizontal wire used as a top. The arrangement has, however, the serious defect that symmetry is lacking, since in plan view the whole top lies to one side of the junction between the vertical down lead and the horizontal top. Moreover, the arrangement does not give, by any means, the most effective use of the conductor, as regards the distribution of inductance and of capacity.

Fig. 3 shows another known expedient. Here the central portion of the top consists of a single wire 20, 2d which divides or spreads out at each end into two parallel separated wires 2e or 2]. In this arrangement the central conductor 2c, 201 is relatively inductive while the portions 2e, 2; are relatively capacitive. This arrangement too, lacks efficiency.

According to this invention, a half wave aerial of the kind comprising a vertical or substantially vertical down lead (which is preferably though not necessarily a multiple wire or cage down lead artificial top, is characterized in that the said top is symmetrical and consists of a plurality of wires lying in a substantially horizontal plane,

or of a substantially horizontal cage of wires connected to the down lead through two equal, oppositely extending horizontal connections which form part of said cage and which meet at the junction pointto said clown lead, the outer ends of said connectors being symmetrical with regard to the whole cage or plurality of wires which constitute the top.

Referring to Fig. 4 which shows one way of carrying out this invention, the vertical down lead I of an aerial of the-kind in question is connected to the middle point 3 of a horizontal wire 4 which is between and equi-distantly spaced from two further wires 5, 6 of equal length and coplanar therewith. The outer ends of all three wires l, 5, 5 are joined together, as shown, by two cross wires i, 8 which are parallel to one another and at right angles to the wires 4, 5, 6 which they join. To give typical dimensions: For a wavelength of 98 meters, the length of lead I might be 65 feet; the length of each of the wires 4, 5, 6 might be 60 feet; and the length of each of the wires 1, 8 might be 4.5 feet. The arrangement thus dimensioned operated efiiciently as a half wave aerial on 98 meters. The instantaneous relative directions of current are indicated in Fig. 4 by arrow heads.

As will be appreciated the arrangement of Fig.

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