US2454768A - Direction finding antenna system - Google Patents

Description

Nov. 30, 1948. e. s. BuRRouGl-ls nnmc'rron FINDvING ANTENNA SYSTEM Filed .nine 25, 1945 .www

, QNUSWR maks atented 2,454,768 DIRECTION FINDING ANTENNA SYSTEM Gordon S. Burroughs. Forest Hills, N. Y., assignor to Federal Telephone and Radio Corporation,

` `New York, N. Y., a corporation oi Delaware Application June Z5, 1945, Serial No. 601,386

The present invention relates to direction ilnders and particularly to that type of direction nder which utilizes an elevated H" Adcock type antenna system.

Ii a perfectly symmetrical antenna system of the H Adcock type were located in free space remote from all objects, no polarization errors would be introduced. In attempting to approximate this condition, such arrays have been arranged on wooden towers high above the ground. While this has to some extent lessened the effect of proximity to ground, it` has not altogether obviated it. Furthermore the use of very high towers is, in many cases, impractical particularly. for portable direction finders. When waves having horizontal components impinge on the horizontal conductive membersfthey induce'voltages in said members. These members are capacitively coupled through many .stray capacitances to the antenna units and introduce voltages into said antenna units. If the introduced voltages balance, there will be no resultant output due to the horizontal wave components. straycapacitances are not symmetrical in the antenna system due to the proximity to earth and other bodies, as well as other factors, `these introduced voltages tend to be unequal and to introduce error. The problemv is further aggravated by-local conditions which are changing and require rebalancing of the system, and even more so when the system is moved from place to place as in portable units.

Since these 14 claims. (ci. 34a-11s) Y 2 so asto substantially eliminate polarization errors.

Another object of the present invention is the provision of apparatus and a method associated with a direction finder whereby such antenna systems may be readily balanced or rebalanced by relatively un killed personnel.

Still another object of the present invention is the provision of apparatus and a method for adjusting such antenna system to obtain a good null.

A further object of the present invention is the vprovision of a direction finder including an antenna system of the type referred to hereinabove including apparatus enabling the ready adjustmy invention.

Referring now to the ligure, the H" type Adcock antena system there illustrated, includes four antenna units I-t of which antenna units I and 2 are the upper pair and 3 and I are the lower pair, with antenna units I and 3 being on the left side and antenna units 2 and t being on the right side as viewed in said gure. Antenna In such systems another problem, which comincluding its leads is electrically substantially.

symmetrical.

An object of the present invention is the provision of apparatus and a method for adjusting an antenna system of the type described so as to produce substantially electrical symmetry therein.

Another object of the present invention is ,the provision of an apparatus and method for balancing an antenna system of the type referred to units I-- are cross-connected by transmission lines 5 and 6. However, in accordance with my invention, transmission lines 5 and 6, which may be in the form of coaxial lines, are not directly connected to said antennas but are coupled to said antenna units through couplers for antenna units I-t respectively.

In accordance with my invention, balancing is accomplished by controlling the relative gain of the coupling units 'l-I I prefer to employ coupiers which, while giving variable gain, are relatively constant in regard to their impedance as seen from the output line and which are also free of changes of phase. For this purpose I prefer to use anode-loaded circuitsas the couplers. A typical example of such an anode-loaded circuit is illustrated schematically in coupling unit 8, it

being understood that the other coupling units are similar in construction. In coupling unit il, it will be seen that antenna unit 2 is connected to the 'gridI II of an electron discharge device I2 whose anode I3 is connected through a suitable load resistor It to a source o f B power supply I5.

aecaree it being' understood that the negative side of said source is connected to ground. The radio frequency output of the coupling unit is taken from anode I3 to a coupling condenser I3 which is; in turn, connected to one end of transmission line i5. The other end of said transmission line 6 being connected to the radio frequency output of coupling unit 9. Similarly the radio frequency output of coupling unit 1 is connected with the radio frequency output of coupling unit I by line 3. The cathode I1 is connected through a by-pass condenser I9 to ground (the chassis of the coupling unit). Bias for the cathode is supplied through a cathode resistor which is likewise used to control the gain. For this purpose the cathode I1y is connected by a lead I9 touthe interior of the direction iinding receiver 20. Similar leads 2l, 22 and 23 connect the cathodes o coupling units 1, 9 and I0 respectively to the interior of the direction finding receiver.

As pointed out hereinbeiore, the antenna system symmetry is obtained by balancing the gain from the coupling units 1-I0, which in turn, is controlled by controlling the D. C. Abias applied to the cathode by controlling the relative value of the cathode resistors. Furthermore. the foregoing adjustments are made so simply that an unskilled person could readily make them. For this purpose the following arrangement is employed. Leads I9 and 2l are connected to the opposite ends of the resistor oi a potentiometer 24 while leads 22 and 23 are connected to the opposite ends of the resistor of a potentiometer 25.

A third potentiometer 26 is employed whose movable arm is connected to ground. The potentiometers 24, 23 and 23 are interconnected by means of a multiple contact rotary switch 21 consisting of two sections 2t and 29 each having three contacts 39-32 and 33-35 respectively and having switch arms 36 and 31 respectively, said switch arms 35 and 31 being ganged together. The movable arm of potentiometer 24 is connected to contacts 30 and 32 with contact 3i being a blank. The movable arm of potentiometer 25 is connected to the switch arm 31. Contact 33 is a blank while contacts 34 and 35 are connected together and to one end of the resistor yof potentiometer 23. The other end of said resistor being connected to the switch arm 33. The other connections of the direction finder may be conventional, that is, the transmission lines and 6 which interconnect the antenna units, in turn, are coupled to the direction iinding receiver at their midpoints over transmission lines 38 and 39. A sensing antenna llil with a coupler 4I and a transmission line 42 is coupled into the direction finding receiver and the direction finding receiver has at its output an indicator 43, which may be in the form of a vacuum tube voltmeter arrangement such as is described in my copending application, G. S. Burroughs, for Comparison system, Serial No. 592,401, iiled May '1, 1945, now abandoned, or any other suitable indicating device.

In adjusting the antenna system in accordance with my invention, a target transmitter 44 is employed which is optically sighted so that the direction of the wave transmitted from said transmitter will be transverse and perpendicular to the common plane of the antenna units. In the iirst operation, the antenna system is balanced as to reception from the two upper antenna units I and 2. In the second step the two lower antenna units 3 and 4 are balanced. In. the

third step the upper units are balanced against the lower units. In the first two steps, the balance is made as to vertcially polarized waves and in the third step the balance is made as to a horizontally polarized wave, the target transmitter 44 being turned around for this last step to transmit horizontally polarized waves.

For the first step the knob of the switch 21 is turned into a iirst position in which switch arm 33 is on contact 30 and switch arm 31 is on contact 83. It will be seen that in this position the couplers t and I9 will be inoperative due to the fact that the cathode circuit is not completed to ground and so energy from antenna units 3 and 4 will not be delivered to the receiver while at the same time it will be seen that the couplers 1 and 8 associated with antenna units I and 2 respectively will be connected to ground through potentiometer 24 and potentiometer 23, and since, as stated before, the negative side of the B" supply is connected to ground, a bias is provided on the cathode of coupling units l1 and 3. The relative bias on these two coupling units is then adjusted by adjusting the position of the potentiometer arm of potentiometer 24. This adjustment is made while observing the indicator 43 until a zero reading is obtained on said indicator, that is, a reading which will indicate that the input derived from antennas I and 2 is exactly equal.

For the second step the switch 21 is moved into the second position with arm 33 on contact 3l and arm 31 on contact 34. In this position cou- 'pling units I and 8 are inoperative and therefore antenna units I and 2 are disconnected from the receiver whereas antenna units 3 and 4 are coupled to the receiver. By adjusting the potentiometer arm oi potentiometer until the indicator 43 indicates a zero reading, the outputs derived from said antenna units 3 and 4 are then balanced.

The first two steps serve to balance the antenna system in regard to vertical polarization so that the antenna system is effectively symmetrical in regard to such polarization and the system is so balanced that when it is transverse and perpendicular to the direction from which energy is being transmitted, no output will be produced thus providing a sharp null.

The purpose of the third step is to eliminate the difference between the currents induced by horizontal polarization in the upper and lower portions of the antenna system and thus minimize the polarization error. For the third step the transmitter 44 is caused to transmit horizontally polarized waves. Switch 21 is then moved to its third position with switch arm 38 on contact 32 and switch 31 on contact 35. It

will be seen that in this position all ofthe coupling units 1-i0 are operative and therefore their respective antennas are coupled to the direction iinding receiver. In this position the movable arm of potentiometer 23 is moved so as to produce a zero indication in the indicator 43. This balances the horizontal pick-up of theA upper portion of the antenna system against the horizontalpolarizatlon pick-up of the lower portion of said antenna system. After this third step has been completed, the antenna system is substantially electrically symmetrical a'nd is balanced in regard to horizontal polarization.

While I have described the details of one method and associated apparatus for balancing an antenna system of this type. it will be apparent to those versed in the art from my teachings departing! from the teachings of my invention.

For example, other types of circuits, including other anode-loaded circuits than that illustrated here may be employed. Furthermore the switch 21 may be provided with other sections and other contact arms, as well as with additional potentiometers and other adjusting means, to produce .various other adjusting operations in connection with the direction iinding receiver. The same sequence of operations, that is, the movement of the switch 21 from one position to a next and then the adjustment oi the associated control may be carried out in more complex form in regard to further adjustment of the receiver "such as balancing of ampliiiers therein as, for example, in my copending application C. S. Burroughs, for Comparison system," Serial No. 592,401, filed May 7, 1945, and various other adjustments known to those versed in the art. Accordingly, while I have described above the principles o1' my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope oi' my invention as defined in the accompanying claims.

I claim: A,

1. In combination, an antenna system having a plurality of upper and lower radiantacting elements mounted in the same plane, each of said elements having separate output circuits, and

means controlling the gain oi' said upper element circuits and separate means for independently controlling the gain of said lower element circuits for balancing said outputs.

'2. An arrangement as set forth in claim 1, wherein said circuits each comprise an electron discharge device having an anode load for providing constant impedance as seen from said outputs, and means controlling the relative gain of said devices balancing said outputs.

3. An antenna system comprisinga plurality of upper and lower antenna units, mounted in the same plane a plurality of circuits each having its output coupled toa separate one of said units,

and means controlling the relative gain of saidupper unit circuits and said lower unit circuits to balance the resultant output.

4. An antenna system comprising a plurality of upper and lower antenna units mounted in the same plane and providing a radiant action pattern having a null direction, a plurality of circuits each having its input coupled to a separate one of said units, and means controlling the relative gain of said upper and lower unit circuits to produce equal outputs from said upper and lower units with respect to electromagnetic waves received from the null direction.

5. In an antenna system comprising a plurality of vertical upper and lower antenna units mounted in the same plane and interconnected by horizontal lines and providing aradiant action pattern having a null direction for vertically polarized waves, a plurality of circuits each having its input coupled to a separate one of-said units and its output connected to one end of said lines, and means controlling the gain of said upper unit circuits and means separately controlling the gain of said lower unit circuits to produce equal 'outputs from said upper and said lower units respectively ywith respect to vertically polarized waves from thenull direction and means for controlling rthe relative gain of said upper unit circuits and said lower unit circuits to produce equal outputs from said upper d and said lower unit circuits with respect to horl zontally polarized waves from the null direction.

6. An H Adcock antenna system providing a directional pattern having a null direction, comprising a plurality oi antenna units including two spaced vertical upper units and two correspondingly spaced vertical lower units with each of the lower units substantially aligned with a separate one oi the upper units, a plurality of adjustable gain circuits each having its input connected to a separate one oi said units, and each positioned adjacent its lassociated unit, a pair of substantially horizontal transmission lines interconnecting the outputs of said circuits, the output o! said antenna system being taken across the midpoints oi said horizontal transmission lines, means controlling the relative gain of the upper circuits to balance the outputs derived from the upper pair of units with respect to vertically polarized waves from the null direction, means lcontrolling the relative gain oi the lower circuits to balance theA outputs derived from the lower pair of units with respect to vertically polarized waves from the null direction, and means controlling the gain of the upper circuits in relation to the gain of the lower circuits to balance the outputs derived from the upper pair of units with respect to that from the lower pair of units with respect to horizontally polarized waves from said null direction.

7.. In a direction finding receiver, an "HI Adcock antenna system providing a directionallpattern having a null direction comprising a plurality of antenna units including two spaced vertical upper unlts and two correspondingly spaced lower units, each of the lower. units being vertically aligned with a. separate one of the upper units a plurality of adjustable gain circuits each having its input connected to a separate one of said units, a pair of horizontal transmission lines interconnecting the outputs of said circuits, a direction `finding receiver, means coupling the midpoints of said linesv to said receiver, means con trolling the gain of the upper circuits with relation to the lower circuits to balance the outputs derived from the upper pairs of units relative to the lower pairs of units with respect to horizontally polarized waves in the null direction, means controlling the relative gain of the upper circuits to-balance the outputs derived from the upper pairs of units with respect to vertically polarized waves in the null direction, and means controlling the relative gain of the lower pairs of circuits to balance the outputs derived from the lower pair of units with respect to vertically polarized waves in the null direction.

8. An antenna system according to claim 6 wherein said circuits each comprise an electron discharge device.

' 9. A direction finding receiver according to` claim 7 wherein said variable gain circuits each comprise an electron discharge device.

10. The method of balancingv an antenna system of the type -providing a radiant action pattern with a directional null and having a plurality aanwas 7 tem oi' the type providing a radiant action pattern with a directional null and having a plurality of vertical upper and lower antenna units mounted in the same plane and each coupled to a separate adjustable gain coupler comprising arranging the antenna system in the null position with respect to a source of radiant energy transmitting vertically polarized waves and adjusting the gain of said upper unit couplers and separately adjusting the gain of said lower unit cou- Apiers until the upper unit and the lower unit coupler outputs are equal.

12. The method of balancing an antenna system of the' type providing a radiant action pattern with a directional null and having a pair of spaced vertical upper and lower antenna units mounted in the same plane and each coupled to a separate adjustable gain coupler comprising arranging the antenna system in the null position with respect to a source oi radiant energy transmitting vertically polarized waves and adjusting the gain of the upper unit couplers and separately adjusting the gain of the lower unit couplers until the upper unit and the lower unit outputs derived from said couplers are equal respectively.

13. The method of balancing an antenna system of the type providing a radiant action pattern with a directional null and having a plurality of vertical upper and lower antenna units mounted in the same plane and interconnected by a pair of substantially horizontal transmission lines comprising arranging the antenna system in the null position with respect to a source of radiant energy transmitting horizontally polarized waves and adjusting the relative gain of said upper unit couplers Vand said lower unit couplers until the outputs of said upper unit and said lower `unit couplers are equal.

14. The method of balancing an H" Adcock antenna system providing a directional pattern having a null direction and including two spaced vertical upper units and two correspondingly spaced vertical lower units, a plurality of variable gain couplers each having its input connected to a separate one of said units and positioned adjacent its associated unit and a pair of substantially horizontal transmission lines interconnecting the outputs of said circuits comprising arranging the antenna system in the null position with respect to a source of radiant' energy transmitting vertically polarized waves, adjusting the gain of the upper couplers until the output derived from the upper antenna units is equal, adjusting the relative gain of the lower couplers until the outputs derived from the lower antenna units are equal, causing the target transmitter to transmit horizontally polarized waves and in the same null position varying the gain of the upper couplers with relation to the gain of the lower couplers until the outputs are equal.

GORDON S. BURROUGHS.

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

UNITED STATES PATENTS

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