US2278660A - Radiogoniometer - Google Patents

Description

April 1942- G. LEHMANN 2,278,660

RADIQGONIOMETER Filed Aug. 28, 1939 INVENTOR.

Gerard Le hma 71/71.,

Patented Apr. 7, 1942 Gerard Lehmann, Paris, France Appiication August 28, 1939, Serial No. 292,316 In France September 3, 1938 4 Claims.

The present invention relates to radiogoniometers of the kind described in my copending application Serial No. 276,014, filed May 26, 1939.

One object of this invention is to provide a radiogoniometer in which the 180 ambiguity in the determination of the direction of the transmitting station is removed.

Another object of this invention is to provide a radiogoniometer for accurate measurements of the direction to be determined.

The invention is particularly adapted for use on short and ultra short waves. Referring to the accompanying drawing briefly,

Fig. l is a schematic view of a radiogoniometer according to said copending application.

Fig. 2 shows a radiogoniometer with the improvements according to the present invention.

The goniometer according to Fig. 1 makes use of two symmetrical aerial elements which are constituted by two parallel sets of vertical wires close to each other, namely, wires I, 2, 3, 4 on one side, and 5, 6, l, 8 on the other side, connected as indicated by the drawing at their remote ends through loops and at their near ends on one side through impedances 9-40 proportioned to avoid setting up of reflected electric waves in the antenna elements. The wires 2, l and 4, of the antenna elements are connected to feed conductors ll-IZ, respectively. A feeder lS-M leading to receiver I5 is connected to conductors li--l2 substantially at their middle points it and H; the conductors ll-IZ leading to one of the systems (I2--3-- 5) are crossed at Na in such manner as to obtain the usual dephasing of 180 between the currents which feed or are generated in the two systems to produce the desired radio goniometric effect. Conductors ll-|2 and feeder [3-44 ar shielded to avoid any action thereon by external electromagnetic and electrostatic fields. Connection points l0ll between conductors ll--I2 and feeder iii-4i are preferably adjustable to obtain the correct dephasing of 180 between the currents in th aerial elements. The aerial ele- "ments incorporated in this apparatus are fully described in my other copending application Serial No. 211,860, filed June 4, 1938.

It is known that goniometers using a loop aerial or a system of two symmetrical dipoles have polar radiation diagrams which are themselves symmetrical and therefore give rise to the well known 180 ambiguity in the determination of the direction of the transmitting station. To remov this ambiguity use is ordinarily made of a supplementary nondirective antenna so as to obtain a nonsymmetrical polar diagram.

According to the present invention the desired dissymmetry is very simply obtained by the modification of the value of one of the impedances 9-40 which absorb th progressive waves. Ex-

perience shows that an adequate modification of this value permits discrimination between signals from the two directions in which the antenna is responsive thus obviating the necessity of an additional antenna.

This modification of value is made by means of a circuit breaker preferably remotely controlled and short circuiting all or part of one impedance during the operation of the goniometer for removing the ambiguity, or short circuiting a supplementary impedance during the taking of the bearings.

Therefore the determination of the bearing of a transmitting station comprises two operations:

1. Adjusting the antenna system to receive the signals transmitted, the two impedances 9 and it of the aerial elements being of equal values.

2. The removing of the 180 ambiguity by changing said impedances to unequal values- Fig. 2 shows diagrammatically a radiogoniometer incorporating the improvements according to the present invention. The aerial elements id entical to those shown in Fig. 1 are designated HlI9-28--2I and 22-3--2 i-25 with their impedances 32 and 33. Wire connections 26 and 2! are employed between these elements. These connections are crossed on one side at 26a to produce the desired phase opposition. Feeders 2829 are provided to connect these wires 26 and 21 to the receiver proper, the points of contact 30-3l being adjustable for the reason indicated above. The relay il modifies the value of impedance 33 for the purpose of removing of the 180 ambiguity. As described above this relay short circuits all or part of this impedance 83, and therefore it is opened during th determination of the bearing of the transmitting station and closed for the removing of the ambiguity. Or it may be used to short circuit a supplementary impedance connected in series with 33 and in this case it is closed during the taking of bearings and opened for removing the 180 ambiguity because including this supplementary impedance in series with impedance 33 destroys the symmetry of the antenna elements and makes the antenna system uni-directional thus e1im mating the so called 180 ambiguity.

The best results are obtained by constituting the impedances 3233 of simple ohmic resistances. In the cas of short waves when an adequate selection of the geometrical dimensions of the antenna elements may be had the correct values of these impedances is nil, that is to say wires l82il and 2325 are respectively direct- ,ly connected one to another, the resistance of radiation of th antennas being of sufiicient value to absorb the progressive waves. In this last case, experience shows that good results for removing the 180 ambiguity are obtained by connecting a supplementary ohmic resistance of to what is called an antenna effect that is to say the aerial of the goniometer behaving in part like an ordinary antenna and collecting an induced electromagnetic voltage whatever its position. This antenna effect is due for instance to constructional defects giving rise to a lack of symmetry. My original experience has shown that this antenna effect may be greatly diminished by creating a slight dissymetry in the transformer coupling between the windings 34 and 35 which compensates for the most important part of this antenna effect and therefore permits accurate determination of the bearings. This operation is called the compensation of the zero (or null) reading. According to the invention this compensation is obtained by variation of the coupling between the two windings 34 and 35 constituting the high frequency transformer interposed between the feeders 28 and 29 and the first stage of the amplifier 38, 39, shown in Fig. 2. Variable condensers 36-31 are used for the tuning of circuit 3635-3'l; these condensers are connected in series and the middle point 40 is grounded. This circuit supplies voltage to grids of tubes 36-3 connected in push pull and the i system 35-3 63'i3839 is balanced as well as possible. The windings 34-35 have their axes parallel as shown in the drawing.

The desired variation of coupling is obtained by moving one of the windings 34-35, parallel to its axis. a composite character, that is, part of it is due to an electromagnetic coupling and the other part to an electrostatic coupling between the wires of the windings. The electromagnetic coupling remains practically of'constant value during such a translation when the winding 34, for example, is moved axially with respect to winding 35 but the electrostatic coupling, the value of which is nil by reason of symmetry when winding 34 is exactly opposite to the center of winding 35 varies in magnitude when the winding 34 is moved or shifted from this central position in either direction indicated by the arrow 42.

Quarter wave aerials as described in my prior 5' copending application S. N. 211,860 might of course be used as aerial elements for the goniometers instead of half wave aerials as indicated above,

While I have, in the above description, disclosed what I deem to be practical and efficient embodiments of the present invention, it should be well understood that I do not desire to be limited thereto as changes might be made in the arrangement, disposition, and form of the parts without departing from the principle of the present invention as comprehended within the scope of the appended claims.

What I claim is:

1. A radiogoniometer which comprises in combination two antenna devices including each two parallel wires extending close to each other It is known that such a coupling is of 'middle points of said connecting conductors respectively and a relay for varying the value of one of said impedances.

2. A radiogoniometer which comprises in combination two antenna devices including each two parallel wires extending close to each other compared to the shortest wavelength employed and interconnected to form two vertical loops, and an impedance connected into the corresponding part of each of said loops adapted to permit substantially only progressive waves moving in opposed directions to flow through said wires, said two antenna devices being symmetrical with respect to each other, two connecting conductors interposed between said loops, a supplementary impedance in series with one of said impedances to produce a uni-directional signal pattern and a relay for short circuiting said supplementary impedance to alter said signal pattern.

3. A radiogoniometer, comprising; a pair of antenna elements responsive to a wide band of frequencies and each comprising a di-pole and a wire doubled back over a considerable length of said di-pole, said doubled back wire being close to the corresponding di-pole compared to the shortest wavelength employed, connecting wires for connecting the centers of said di-poles in phase opposition to form a bi-directional antenna system, feeder conductors connected substantially to the centers of said connecting wires, a transformer connected to said feeder conductors, impedance means connected into at least one of said wires doubled back over its corresponding di-pole, and means for changing the effective value of said impedance means to change the directional characteristics of said antenna system.

4. A directive antenna'system responsive to a wide range of frequencies, comprising: two antenna devices each comprising a conductor having a pair of separated arms, another conductor arranged parallel to said first conductor and substantially to the middle points of said connecting conductors, said two antenna devices being symmetrical with respect to each other and having a bi-directional signal pattern, said other conductor of one of said antenna devices having an ohmic resistor connected substantially in the center thereof, and means for varying the value of said ohmic resistor to change said bi-directional signal pattern to a uni-directional signal pattern,

GERARD LEI-IMANN,

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