US2375593A

US2375593A - Reception of signals on a loop antenna

Info

Publication number: US2375593A
Application number: US481406A
Authority: US
Inventors: Carl G Sontheimer; Robett S Doak
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1943-04-01
Filing date: 1943-04-01
Publication date: 1945-05-08
Anticipated expiration: 1962-05-08

Description

y 1945- c. G. SONTHEIMER ET AL 2,375,593

RECEPTION OF SIGNALS ON A LOOP ANTENNA Filed April 1, 1945 Isnnentors 68 M Gttorneg Patented May 8, 1945 RECEPTION OF SIGNALS ON A LOOP ANTENNA Carl G. Sontheimer, Haddonfield, and Robert S. Doak, Collingswood, N. J., assignors to Radio Corporation of America, a corporation of Dela- Application April 1, 1943, Serial No. 481,406

3 Claims. (01. 250-33) This invention relates to 100p antennas, and more particularly to a method of and means for providing increased signal pickup for a given loop inductance. The figure of merit of a loop antenna for use with radio receivers, direction finders, and the like, is the ratio of effective height to the square root of the loop inductance. The effective height of a loop represents the factor which, when multiplied by the field strength in microvolts per meter, gives a measure of the E. M. F. generated in the loop. The effective height, h=21r7 A/ meters, where n=number of turns, and A=area of each turn in square meters.

The inductance, L, of a loop antenna is approximately proportional to WA. Thus for a loop of given area, both the effective height and the square root of the inductance are substantially proportional to the number of turns, and

the figure of merit, h/ L, is substantially independent of the number of turns on the loop. The power extracted from a radiation field by a loop depends basically on the radiation resistance of the loop; but this effect is ordinarily masked by the inductance of the loop.

The principal object of the present invention is to provide an improved loop construction and method whereby the advantages of increased effective height may beobtained without corresponding increase in the inductance.

A further object is to provide loop antennas having a greater ratio of effective height to the square root of inductance than prior loop antennas. g E

Referring to the drawing, Fig. 1 illustrates the construction of one embodiment of the invention, and Fig. 2 shows a modified construction.

A closed core I, of magnetically permeable material such as comminuted iron oxide, powdered iron mixed with a suitable binder material, or the like, is provided with a

winding comprising coils

3 and 5 disposed on the legs 1 and 9 respectively of the core I. The coils are connected in series in reverse polarities to each other between terminal II and I3, so that the mutual inductance between the two legs of the winding is such as to diminish the net series inductance.

The arrows Hs on the drawing represent the magnetic flux of a radiation field linking the

coils

3 and 5. The voltages 8s induced in the two coils are additive, i. e. the output voltage of the loop is substantially twice that of either coil.

The series inductance of the two coils is:

=L1+L22K\/Ll L2 where L1 and L2 are the self inductances of the

coils

3 and 5 respectively, and K is the coefiicient of coupling between them. If the permeability of the core I were infinite, L would be zero, and the total voltage would still be the sum of the voltages induced in the two coils. The expression 2K\/L1 L2 represents the mutual inductance which is opposed to either of the self inductances. The effectiveness of loops constructed in accordance with the invention is thus largely dependent upon the permeability of the core material.

Referring to Fig. 2, a core iii of toroidal shape is employed. The windings are disposed on this core in a manner similar to the arrangement of the

windings

3 and 5 on the core of Fig. l. The operation of this structure is identical with that of the loop of Fig. 1. It should be apparent without further illustration that either of the windings may be wound in a reverse direction, provided the connections thereto are interchanged.

Thus the invention has been described as an improved loop antenna structure, comprising spaced coils coupled together by means of a closed magnetic core to provide mutual inductance which is opposed to the self inductances of the spaced coils. This arrangement provides an improvement in the ratio of effective height to inductance over prior artstructures.

We claim as our invention:

1. A directive antenna comprising a closed core of magnetically permeable material, and windings disposed on spaced axes on said core and connected in series with each other in such relationship that the mutual inductance between said windings is opposed to the self inductances thereof.

2. A directive antenna comprising a closed core of magnetically permeable material, and windings disposed on spaced parallel axes on said core and connected in series with each other in such relationship that the mutual inductance between said windings is opposed to the self inductances thereof.

3. A directive antenna comprising a substantially toroidal core of magnetically permeable material, and windings disposed on spaced arcs on said core and connected in series with each other in such relationship that the mutual inductance between said windings is opposed to the self inductances thereof.

CARL G. SON'I'HEIMER. ROBERT S. DOAK.