US2438680A - Loop antenna apparatus - Google Patents

Description

Original Filed March 11, 1945 Patented Mar. 30, 1948 Wladimir J. Polydorofi, Glencoe, 111.

Original application March 11, 1943, Serial No.

Divided and this application October 20, 1944, Serial No. 559,495

Claims. 1

The invention relates to directional loop antennae and has more particular reference to improvements in the construction and operation of antennae of this character for improving reception over a wide range of frequencies,

In my Patent No. 2,345,332, granted July 25, 1944, I disclose a loop antenna having coil windings in associated relation with an elongated core in the form of a long cylinder composed of finely divided iron particles. In order to make the greatest use of the iron, the coils as disclosed in said application have the maximum number of turns in close association with the iron and said coil windings are spread throughout substantially the length of the elongated core.

An object of the present invention is to improve loop antennae of this character and thereby materially increase their efiiciency in the reception of radio waves.

Another object of the present invention is to provide an improved construction of directional loop antennae for use as low impedance loops. An important advantage of this type of antenna is due to the fact that when a small inductance loop is fed into a receiver through a suitable input transformer a large range of frequencies can be covered. It'has been possible to employ such low impedance antennae to cover the frequency range from approximately 100 to 1500 kilocycles.

However, if it is desired to cover a larger frequency range another such antenna must be employed of either more or less inductance, which second antenna is switched on for the corresponding extended frequency range. If two such antennae are used in close vicinity to each other it has been found that the presence of an idle loop in the field of an active one causes absorption of the energy from the said active loop, resulting in considerable weakening of the signal. Also the use of two coils in close association with each other will produce deflection of the signal from its true direction, which efiect is known as deviation.

Another object of the invention, therefore, is to provide antenna construction comprising a plurality of loop windings and which antenna construction will receive radio waves of high and low frequencies and wherein the absorption loss and the deviation effect above described is substantially eliminated.

Another object of the invention is to provide metal shielding for antenna loops which will have the effect. of suppressing; the electrostatic component of the radio wave acting on the loops.

With these and. various other. objects in view,

the invention mayconsist of certain novel features of construction and operation as will be more fully described and particularly pointed out in the specification, drawings and claims appended hereto.

In the drawings which illustrate an embodiment of the invention, and wherein like reference characters are usedto designate like parts Figure 1 is a sectional view illustrating a loop antenna. wherein two loop windings are mounted in close associated relation on an iron core member;

Figure 2 is a Wiring diagram illustrating a ciredit for electrically connecting the loop windings on the core member in parallelby remote control;

Figure 3 is an elevational view showing. a preferred manner of electrostatically shielding an antenna loop; and

Figure 4 is an end. elevational view of Figure 3.

In Figure 1 an operative modification of the invention is disclosed wherein a low inductance loop winding and a high inductance loop winding are both wound on the same core. Winding the two loops on a common core has the advantage that the total weight and bulk of' the system is materially reduced.

Referring to said figure, the elongated core indicated by numeral It] is composed of finely divided iron particles. Since an iron core is used the effective permeability is increased. A form or shell H of insulating material is placed over the'iron core, the same having a close fit therewith and providing a plurality of recesses extending completely around the cylindrical shell for receiving the wire comprisin the respective windings. The shaft [2 has securement to the shell ll alsoextending into the core [0 substantially centrally thereof and said shaft may be suitably journalled to provide for rotation ofthe core. Said core i0 may have an opening for receiving the shaft :2. orthe core may comprise a plurality of sections as described. in my Patent No. 2,354,332 herein identified. The two coils I3,

located in the outside recesses provided by the insulating shell H, comprise a plurality of turns of relatively fine wire. The coil are connected in series by conductor it and therefore they constitute the loop of high inductance indicated by numeral I5 which is employed for the reception of radio waves of low frequency, The conductor M isprovided with a center tap which is grounded. at 16. The inside recesses provided by the shell I l contain a less number of turns of. heavy wire to form coils H which therefore have low inductance and comprise the loop indicated by numeral l8 for receiving radio waves of high frequency. The conductor l9 connects the two coils I! in series and said conductor is provided with a center tap grounded at 20.

In this preferred modification of the invention the coils l3 comprise the loop l of high inductance and coils I1 comprise the loop l8 of low inductance. Both are wound on the same iron core to save weight and reduce the bulk of the system. However, the loops are coaxial to each other and they are therefore subject to absorption and deviation. In accordance with the invention these undesirable effects are substantially eliminated by the provision of means for electrically connecting the high inductance loop I5 inparallel with the low inductance loop l8 during the operation of said low inductance loop. As a result the inductance of loop I8 is somewhat reduced but this can be compensated for by initially adding a few extra'turns of wire to coils H.

To accomplish the electrical connection of the loops for the purpose above described, the invention provides a plurality of collector rings indicated by numerals 2|, 22, 23, 24 and 25. The collector rings are suitably fixed to rotate with shaft [2, being insulated therefrom by means of the sleeve 26 of insulating material. lilach collector ring has contact with a metal brush 21, collectively secured to the support 28. The collector rings 2| and 22 are electrically connected by means of the conductors 30 and 3| with the inside winding of the coils II, respectively. The conductors 32 and 33 have connection with the brushes 2'! which contact with the collector rings 2| and 22 and the circuit from the coils I1 is thus continued to the double pole single throw switch 34. In a similar manner the coils l3 are electrically connected by conductors 35 and 36 with the collector rings 24 and 2-5, respectively. Likewise the circuit is continued by the brushes 21 in contact with these collector rings and by the may be connected in parallel as-above described by remote control. In place of the double pole 7 single throw switch a contactor 45 is provided which, as shown in said figure, is normally inoperative. Therefore the conductors 32 and 33 are normally disconnected from the conductors 31 and 38. The contactor is actuated by means of the solenoid 43 having electrical connection through switch 41 with a source of current 48.. When switch 41 is closed the solenoid 46 is energized and contactor 45 is caused to descend into its operative position. The contactor will therefore close the circuit to the conductors 32 and 33 leading to the coils comprising the loop [8 and the said loop is thus placed in operation, being automatically connected in parallel with the coils conductors 31 and 38 to the switch 34 previously mentioned. The conductors 40 and. 4| constitute the conductors enclosed within cable 42 which extends to within the airplane or other enclosure on which the present apparatus is mounted. The center collector ring 23 is suitably grounded at 43 and this :collector ring through its corresponding brush 2? is connected by conductor 44 to the sheath of the cable.

During operation of the apparatus as disclosed in Figure 1 it will be understood that switch 34 will be in open position for the reception of radio waves in the low frequency range since these frequencies are picked up by the winding l3 comprising the loop l5 of high inductance. This loop is electrically connected at all times to the collector rings 24 and 25 which in turn have connection with the conductors from cable 42.

Therefore when this loop I5 is in operation it will be understood that the switch 34 is open and loop l8 remains idle. However, in accordance with the invention the high frequency low inductance loop I8 is always operated in parallel with the low frequency high inductance loop 15. Loop l8 having connection with collector rings 2| and 22 can only be connected to conductors 40 and 4| of the cable 42 by closing the switch 34. Closing of said switch automatically connects the loop I5 in parallel therewith. By connecting the loops in parallel it will be understood that the high inductance loop is in effect short circuited through the low inductance loop. 7

, Figure '2 discloses apparatus whereby the loops comprising loop l5. Therefore whenever the high frequency loop is used it is in parallel with the idle low frequency loop. For best results the above described switch structure should be placed as close to the connector rings as possible.

In direct findin loops the direction of the transmitter is indicated by a sharp zero signal when the loop axis points toward the transmitter. In order to obtain sharp directional bearings only the electromagnetic component of the radio wave should act on the loop, the electrostatic. component being suppressed by electrostatic shielding of the windings. Preferred structure for carrying out the above is shown in Figures 7 3 and 4 wherein the loop antenna is enclosed by special cloth into which metal wires are woven in one direction. After the coils are placed 'in the insulating form H another insulating tube is placed over the windings in order to protect them from the atmosphere, said tube being indicated in Figure 3 by numeral 50, The cloth having the wires 5! is then placed around the exterior surface of the tube Siland in accordance with V the invention the cloth is provided with a gap 52 so that the wires extendin inthe same direction circumfercntially of the'loop antenna are not joined but are left open circuited at the top.

However, all the Wires are electrically connected in the vicinity of the lower'portion of the casing and the same is grounded at 53. Each loop antenna is also closed at its respective ends by the disc 54 which is covered with cloth providing the vertically disposed wires 55. These wires are also electrically connected at their lower ends and which connection is suitably grounded at 56.

An electrostatic shield may also be made from thin metal foil or metal leaf, preferably metal such as copper, which is a good conductor of electricity. A gap is provided so that the metal foil does not extend completely around the loop antenna and also in a manner as disclosed the various parts of the metal shield are grounded;

This application is a division of my co-pending application Serial No. 478,748, filed March 11, 1943, and entitled Loop antenna apparatus, now Patent No. 2,383,415, issued August 21, 1945.

The invention is not to be limited to or by detubular ferromagnetic core made in sections of finely dividedand compressed magnetic particles,

coil windings spread substantially over the length of said core and serially connected in aiding sense to increase the efiective permeability of said core in said windings, a supporting form common to said core and coil and in close association with the core, means supporting the core and coil combination for rotation, said means having securement to the supporting form and having provision for carrying the terminal connections of said coil windings.

2. In a loop antenna system, an elongated ferromagnetic core member, a plurality of coils coaxially wound on said core member, one set of said coils forming a low impedance loop antenna for the reception of high frequency radio waves, the other of said coils forming a high impedance loop antenna for the reception of low frequency radio waves, said two sets of coils being connected in parallel for the reception of high frequency radio waves to prevent the absorption of energy from low impedance loop by the high impedance loop, and switching means to disconnect the low impedance loop while receiving on the high impedance loop.

3. A directionalloop antenna system for the reception of electromagnetic waves comprising a hollow ferromagnetic core member of finely divided and compressed magnetic particles, coil windings substantially spread over said core member, a supporting form common to said core and said coil, an electrostatic shield of conductive material for suppressing the electrostatic component of the radio Waves acting on said windings, said shield incompletely surrounding said coil windings in close relation thereto and forming an integral part of said loop antenna, thereby permitting simultaneous rotation of said loop and said shield.

4. A directional loop antenna according to claim 3 wherein the electrostatic shield comprises cloth with wires woven therein, said wires forming incomplete loops around said coil.

5. A directional loop antenna according to claim 3 wherein the electrostatic shield covers the ends of said core member and said shield and wherein said ends are grounded.

WLADIMIR J. POLYDOROFF.

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

UNITED STATES PATENTS Number Name Date 1,077,319 Tatum Nov. 4, 1913 1,655,931 Langs'troth Jan. 10, 1928 1,942,575 Shapiro Jan. 9, 1934 2,266,262 Polydorofi Dec. 16, 1941 2,316,623 Van B. Roberts Apr. 13, 1943 2,328,024 Limb Aug. 31, 1943 2,339,234 Polyd-oroif Jan. 11, 1944 2,343,306 Lear Mar. 7, 1944 2,354,332 Polydorofl July 25, 1944 2,375,418 Johnston May 8, 1945 FOREIGN PATENTS Number Country Date 517,982 Great Britain Feb. 14, 1940

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