US2505115A - Dipole antenna system - Google Patents

Description

April 25, 1950 HlLLs ETAL 2,505,115

DIPOLE ANTENNA SYSTEM Filed Sept. 11, 1944 FlG. i 'llb [Is 3b 1 I30, k u Ila, lOb W 12 I2 1 L b l "5 n E? AMPLIFIER I I0 55 16 DETECTOR a a FREQUENCY CIRCIUITS cf T SELECTOR 23 20a7 g923230 23b 20b 238 g J If I L! H J I 22!) 2. 210. dy (2H0 35b *2 4 J-l H6 3 ll 34bj:|l" "35d CONTROL SIGNAL l TRANSMITTER 1 l ATTORNEYS Patented Apr. 25, 1950 DIPOLE ANTENNA SYSTEM Elmer G. Hills and John A. Rankin, Chicago, Ill., assignors, by mesne assignments, to Belmont Radio. Corporation, Chicago, 111., a corporation of Illinois Application September 11, 1944; Serial No. 553,486

11 Claims. (01. 250--33) This invention relates to dipole antenna. systems and; while it is of general application, it is particularly suitable for embodiment in such systems of the type adapted totranslate any of a plurality of wavesignals of different frequencies within a wide frequency bandand incorporating an antenna of fixed physical dimensions suitable for mounting in the cabinet of a wavesignal receiver with which it is designed to operate. 3

It is customary to utilize a dipole antenna in connection with a wave-signal transmitter or a receiver operating in the high--frequency or ultra-high-frequency range because: of its superior response characteristics. However it is well known that the responseand terminal impedance of a dipole antenna of any" iven physical dimensions are rather critical with respect to frequency and vary rapidly with departure. of the operating frequency in either sense: from the frequency for which the antenna was designed. On the other hand; itis often desirable or necessary to adjust a high-frequency or ultra-highfrequency' wave-signal apparatus utilizing a dipole antennafor operation at any selected frequency within a wide frequency band.

In order to solve this problenuit has heretofore been proposed to utilize dipole antennas comprising extensible; antenna arms which may be adjusted to the appropriate length in accordance. with the frequency of the signal being translated. While such an arrangement is satisfactory for certain applications. it is difficult to adapt to a dipole antenna housed in a wavesignal receiver cabinet. which imposes a, limit onthe. physical. dimensions of the antenna. Also there are certain. applications for which the mechanical adjustment ofthe physical'length of the antenna may be difiicult. to. incorporate in the antenna syst em..

It is. an object of the invention therefore to provide a new and improvedv dipole antenna system of fixedphysicallength, theefiective electricallengthofwhich may be adjusted for operation at anyselectedone ot a. plurality of frequencl'es within awide frequency band.

It is another'obiect of the invention to provide a new and improved. dipole antenna. system of the type described which is particularly suitable for mounting in the cabinet. of. a. wave-signal receiver with, which it is designed to. operate.

In accordance with the. invention, a dipole antenna system adapted to translate any of a plurality of wave signals of, different trawli within a wide. frequency band comprises. a dipole.

antenna structure. including a pair of opposed arms of fixed physical length, and means disposed at the remote ends of. such. arms for effectively modifying its electrical length to adjust the frequency of optimum response.

Further inaccordance with the invention, the means for effectively modifying the electrical length of the antenna comprises apair of elongated conductive elements individually associated with the arms of the dipole antenna in fixed relation thereto and means for adjustably coupling each of the elongated elements. with associated dipole arms. In a preferred embodiment of the invention, such two elongated elements are embodied in a two-section elongated conductive operating shaft of an adjustable condenser including an insulating section at its midpoint. The condenser also comprises stator plate means mounted. at the outer-ends of the opposed arms and rotor plate means mounted at the outer end of the shaft and individually cooperating with the stator plate means to adjust the frequency of optimum response of the system.

For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in. connection with the. accompanying drawings while itsscope will be pointed out in the appended. claims. l

Referring now to the drawing, Fig. 1 is a schematic representation of. a dipole antenna system embodying the invention as applied to a wave-signal. receiver; Fig. 2 is a diagrammatic representation of an alternative form of the invention in which the adjustment is also mechanical-.as in. Fig. 1;.whi-le Figs.v 3 and 4 represent other forms of the invention to which the adjustment of the electrical. length of the antenna is effected by entirely. electrical means suitable for operation from a position remote from the antenna structure. 7

Referring now, to Fig. 1 of the drawings, there is represented a dipole antenna system adapted to translate any of a plurality ofv wave signals of different frequencies within a wide frequency band, and to supply them to a wave signal receiver. This system includes a dipole antenna I9 which may be of conventional construction including a pair of opposed arms la and, lflb means comprises an elongated conductive member I I comprising the conductive sections I Ia and III) individually disposed generally parallel and spaced from the arms IOa and Iflb, respectively, their adjacent or inner ends being electrically separated by means of an insulating section I Ie Adjustable capacitance means I2 and I3 are provided for individually adjustably coupling the outer ends of the elements I la, I Ib to their associated dipole arms Illa, I 01), respectively. In a preferred form, the two-section elongated conductive member I I, including the insulating section I la at its midpoint, may comprise the operating shaft of an adjustable condenser including the capacitance means I2 and I3. The capacitance means I2 and I3 comprise stator plate I means IZa and I3a mounted'at the outer ends of the opposed arms I (la, IIIb, respectively, and rotor plate means I 211, I31) mounted at the outer ends of the shaft sections I011, I01) and individj ually cooperating with the stator plates I 2a and I 3a, respectively. The adjustable condenser II,

j I 2, I3 may be provided with adjusting means,

' such as a manually operable knob I Id.

Signals intercepted by the dipole antenna it are translated by a co-axial cable I4 to the input circuit of a wave-signal receiver comprising a radio-frequency selector I5, an amplifier and resented schematically at I detector circuit unit I6, and a signal reproducer,

' of a unicontrol apparatus indicated at U.

The operation of the dipole antenna system of i Fig. 1 will be apparent from the foregoing de- 1 scription.

.lated by the dipole antenna Briefly, high-frequency or ultrahigh-frequency signals intercepted and trans- I i! are applied through the cable I4 to the input circuit of the radio frequency selector I5, wherein the desired signals are selected and undesired si nals rejected. The signals selected and amplified in unit I 5 are translated to the unit I6 wherein they are further ampified, selected and detected for application to the loud speaker I I for reproduction. It will be understood that. if the receiver I5, I6 is of the superheterodyne type, the adjustable tunable circuit of the local oscillator will also be included in unit I5, as represented schematically by the tunable circuit I5a.

By the connection of the adjustable element of the tunable circuit I5a to the shaft I I by means of unicontrol mechanism U, adjustment of the tuning of the receiver I5, I6 is eifective simul taneously to adjust the setting of the condenser II, I2, I3, which is effective to adjust the coupling between the outer ends of the antenna arms I Ib, respectively.

Illa, lb and the conductive shaft sections II a, These shaft sections when coupled, as described, efiectively comprise with the arms Illa, III!) a folded-back dipole antenna,

, the effective electrical length of which is adjus- 'able by the adjustment of the coupling between the outer ends of the antenna arms IB'a, I 9b and the elements Ila, Ilb, respectively. By the proper design of the unicontrol mechanism U, which may include cam means or other variable ratio 1 drive means, the adjustment of the condenser II I2, I3 may be related to the tuning of the re- .ceiver I 5, I6 in such a way that the characteristics of the dipole antenna system are always adjusted for optimumresponse at the frequency to which the receiver is tuned. 'It will be under-' stood that by optimum response is meant not only that the actual signal voltage picked up at the antenna is a maximum but also that its radiation impedance, as reflected at the input circuit of the receiver unit I5, approximately matches the input impedance of unit I5, it being well understood that approximate impedance matching at this point is required for effective translation of the received wave signal.

In the modified form of the invention illustrated in Fig. 2, the means for variably loading the outer ends of the dipole antenna arms comprise elongated conductive elements 22a and 22b individually extending from such opposed arms, together with adjustable capacitance means coupling each of such elongated elements to its associated dipole arm. For example, the dipole antennacomprises arms 20a, 20?) which support at their outer ends U-shaped brackets 2| a, 2ib

from which extend the elongated conductive eleinents 22a, 22?), respectively, the units 22a, 22?), preferably being co-axial with the antenna arms 20a, 28b. The brackets 2 la, 2 lb include sections 2Ie, 2| 1, respectively, of insulation material to isolate the extensions 22a, 221) from the arms 20a, 2%, respectively. The arms 20a, 20?) are hollow and enclose shafts 23a, 23b electrically separated at their inner ends by a section 23c of insulation material and provided at their outer ends with rotor plate means 23d, 23c, which cooperate with stator plate means 2 lo, 2 Id mounted in the brackets 2Ia and 2Ib, respectively, the stator and rotor plate means described comprising adjustable capacitance means for coupling the elongated conductive elements 22a, 22b to the outer ends of the antenna arms 20a, 2%, respectively. The insulation section 230 may be knurled as indicated and comprise a manually operable adjusting means for the antenna system.

The operation of the antenna system of Fig. 2 is substantially similar to that of Fig. 1 except that, as the elongated extensions 22a, 221) are adjustably coupled to the antenna arms 20a, 202;, respectively, the antenna system operates as an antenna of effectively increased physical length rather than as a folded-back dipole antenna, increased coupling of the elements 22a, 22b in creasing the wave length and decreasing the frequency of optimum operation of the antenna system.

In Fig. 3, there is represented a modified form of the invention in which the means for loading or adjusting the effective electrical length of the dipole antenna 30 is effected electrically so that it is particularly suitable for remote control. Specifically, the dipole antenna comprises arms 30a, 30b adapted to be adjustably coupled to coaxial elongated conductive elements 3Ia and 31?), respectively, effectively comprising extensions of the antenna arms. The adjustable coupling is effected by adjustable capacitance means such as the pairs of condensers 32a, 32b; 33a, 33b; and 34a, 34b, adapted to. be selectively connected as coupling elements between the antenna arms and their respective extensions by means of selector switches 35a and 35?), respectively, which are preferably of the step-by-step type. The selector switches are provided with windings, 35c and 35d, connected to be energized from a control-signal transmitter 36, provided with an adjustable contact element 3511, through a circuit including radio-frequency choke coils'31a and 31b, which are connected directly. .to theantenna arms 30a, 3%, respectively, sothat theyserveto conduct 16 both the translated high-frequency signal waves ecount and the control-signals, which are of a relatively lowfrequency or direct current. we

The operation of the antenna system, per se, of

nect selected pairs of condensers 32a, 32b; 33a,

: 33b; or34a, 34b "between the antenna arms 3M,

3% and their respective extensions 131d, .3 lb to "adjust the effective-electrical length of the "dipole antenna in accordance with the frequencyof' the signal being translated;

In the form of the invention represented in 1 Fig. 4, the meansfor variably loading the ends of the antenna armscomprises reactance means individually coupled to the remote ends of the 'antenna arms, the reactance means having a. negative reactance-f-requency characteristic,

"whereby the electrical length of .the antenna is effectively .modifiedwith respect to frequency to impart to the system the optimum response at 'any selected one of the different frequencies withthe operating irequency band- 'By the term "negative reactance-irequency characteristic as used herein and in the appended claims, is meant a reactance characteristic which is the opposite of that of the usual physicalreactance--elements2 1' for example, an. inductive reactance which decreaseswith frequency .or a capacitive reactanc which increases withfrequency.

Specifically, in the arrangement of ig. 4,'the

dipole antenna; comprises arms 40a, 40b which are variably loaded at their ends by means of variable reactance means 41a. and 4th, .respeetively. The reactance means 4! a, MD areidentical and their components are identified by the same referencenumerals. "Each of thereactance means Ma, 41b comprisesa vacuum tube 42.;preierably of the screen gr-id type, connected directly between the. end of its respective antenna arm and ground. The control grid of the vacuum tube. 42 isexcited fromaphase-splitting circuit compris- :inga condenser '43 in series with a resistor 44 also connected between theend of its respective antenna arm and ground, the control grid'being connected across the resistor portion of such series circuit. of the antenna arm and ground isa series cir- .Also connected between: the end cuit comprising an inductor 45 -in series with a condenser 46,..a diode rectifier 41 and a load resister 48 shunted by a filter condenser 49. The inductor 45 and condenser 46 are proportioned to resonate at or near the'lower end of the frequency range over which the antenna system is intended to operate. The signal developed across the load circuit 43, 49 is applied to the screen grid of the :tube. 62, as indicated. Operating potentials for the anode and screen of the tube 42 are supplied from a. a suitable source +B we through resistors 50 and 5!, respectively.

In the operation of the system of Fig. 4, the

d5, 48 is resonant at the lower end of lthe operating frequency band, its series impedance is a minimum and it passes a maximum current at such frequency, developing a maximum rectified voltage across the load circuit 48, 49 of diode 41 which is applied to the screen grid of the tube 42.. 'The tube 42, under such conditions, draws maximum current and is the equivalent of a capacitance of maximum value. As the operating frequency increases and the circuit 45, -46

departs from resonance, this circuit draws less currentand the rectified voltage across the load 48, 49 proportionately decreases, thus decreasing the bias on the screen grid of the tube 42. That a is, the tube 42 draws a maximum current, indicating a minimum capacitive reactance, at or near the low frequency end of the operating frequency range and such anode current decreases with increasing frequency, indicating an efiective in,- crease in capacitive reactance of the tube 42 with increase in frequency; that is, indicating a negative reaotance-frequency characteristic.

It can be shown both mathematically and experimentally that a dipole antenna, when loaded at the outer ends of its arms bya negative reactance means of the type described, the constants of which are proportioned to cancel the positive reactance component of the radiation impedance-frequency characteristic of the unloaded dipole antenna, has a substantially uniform and optimum response over the operating frequency range.

From the foregoing it is apparentthat each of the forms of the invention illustrated and described above comprises an antenna system in which the antenna structure is of fixed physical dimensions and therefore one which is suitable for embodiment in the cabinet of a wave-signal apparatus with which it is designed to operate. Furthermore, any of the difficulties attendant upon the construction of an antennaof physically adjustable length are eliminated.

While there have been described what are at present considered to be the preferred embodi- .ments of the invention, it will be apparent to and individually coupled thereto for effectively pair of opposed arms of fixed physical length, a

pair of elongated conductive elements individually associated with said' arms in fixed relation thereto, said elements being insulated from said arms and from ground and capacitive reactance means for 'ad'justably coupling each of said elongated elements to its associated-dipole arm to adjust the frequency of optimum response of the system.

3. A dipole antenna system adjustable to receive wave-signals of any'desired frequency within a wide band of frequencies comprising, a di- 1 relation thereto,

"pole antenna structure including a pair of op- ;posed arms, a pair of opposed elongated conductive elements individually disposed generally parallel to and spaced from said arms and having their adjacent ends electrically separated, and -capacitive reactance means for adjustably coupling the outer end of each of said elements to the outer end of its associated dipole arm to adjust the frequency of optimum response of the system.

4. A dipole antenna system adjustable to receive wave-signals of any desired frequency with- :in a wide band of frequencies comprising, a dipole antenna structure including a pair of opposed'arms, a two-section elongated conductivev member disposed parallel to and spaced from said opposed arms and including an insulating section at its mid-point, and capacitive reactance means for adjustably coupling the outer ends of allel to and spaced from said arms and havin their adjacent ends electrically separated, and

an adjustable capacitance for adjustably coupling the outer end of each of said elements to the outer end of its associated dipole arm to adjust the frequency of optimum response of the system.

- 6. A dipole antenna system adjustable to receive wave-signals of any desired frequency with in a wide band of frequencies comprising, a dipole antenna structure including a pair of opposed arms, and adjustable condenser means comprising a two-section elongated conductive operating shaft including an insulating section at its midpoint, said shaft being disposed parallel to and spaced from said opposed arms, said condenser means comprising stator plate means mounted at the outer ends of said opposed arms and rotor plate means mounted at the outer ends of said shaft and individually cooperating with said stator plate means to adjust the frequency of optimum response of the system.

7. A dipole antenna system adapted to translate any of a plurality of wave signals of different frequencies within a wide frequency band comprising, a dipole antenna structure including a pair of opposed arms of fixed physical length, a

' pair of elongated conductive elements individually extending from said opposed arms in fixed and adjustable capacitance means for adjustably coupling each of said elongated elements to its associated dipole arm to ad-. just the frequency of optimum response of the system.

-8. A dipole antenna system adjustable to receive wave-signals of any desired frequency within a wide band of frequencies comprising, a di-.

pole antenna structure including a pair of opposed arms, and reactance means individually I coupledto the remote ends of said arms, said reactance means having a negative reactance-frequency characteristic, whereby the electrical length of the antenna is effectively modified with respect to frequency to impart to the system optimum response at any of said different frequencies." t

9. A dipole antenna system adjustable to receive wave-signals of any desired frequency within a wide band of frequencies comprising, a dipole antenna structure including a pair of opposed arms, and a pair of reactance tubes individually coupled to the remote ends of said arms, each of said tubes including input and output electrodes and a regenerative coupling therebetween for imparting thereto a negative reactance-frequency characteristic, whereby the electrical length of the antenna is effectively modified with respect to frequency to impart to the system optimum response at any of said difierent frequences.

10. In a wave signal translating device which is tunable to a plurality of difierent frequencies, a dipole antenna system adapted to be contained in a housing with the translating device comprising, a dipole antenna structure including a pair of opposed rectilinear arms of fixed physical length, a pair of elongated conductive elements individually associated with said arms in fixed relation thereto, said elements being insulated from said arms and from ground, a pair of variable capacitive reactance means disposed at remote ends of said arms and individually coupled to said arms and said associated elements for effectively modifying the frequency response of said system, and means for simultaneously adjusting said variable reactance means so that the frequency response of said system corresponds to the frequency of said device. v

11. In a wave signal translating device which is tunable to a plurality of different frequencies, a dipole antenna system adapted to be contained in a housing with the translating device comprising, a dipole antenna structure including a pair of opposed rectilinear arms of fixed physical length, a pair of variable capacitive reactance means disposed at remote ends of said arms and individually coupled thereto for effectively modifying the electrical length of said arms, and means for automatically adjusting said variable reac tance means'in accordance with the tuning of said translating device so that the effective length of said arms is optimum for the frequency of said device.

ELMER G. HILLS. JOHN A. RANKIN.

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

'UNITED STATES PATENTS

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