US2515436A - Tuning device for true antennas - Google Patents

Description

July 18, 1950 F. B ABlN 2,515,436

TUNING DEVICE FOR TRUE ANTENNAS Filed Oct. 3, 1946 2 Sheets-Sheet 1 (REACTANCE) mss siAucz) 0 Y 1 (REACTANCE) (RESISTANCE) 0 X INVENTOR FRANCOIS BABIN July 18, 1950 F. BABIN 2,515,436

TUNING DEVICE FOR TRUE ANTENNAS Filed Oct. s, 1946 v 2 Sheets-Sheet 2 IN VENTOR FRANCOIS BABl N BY &

NEY

Patented July 18, 1950 TUNING DEVICE FOR TRUE ANTENNAS Y FrancoisBabin, Paris, France, assignor to La 'Radio-Industn'e, Paris, France, a. society of France.

Application October 3, 1946, Serial No. 701,043 In France October 4, 1945 .3 Claims. (c1. 250-33 The presentr'invention relates to tuning" devices for true antennas, the expression true-antennas being used :to: differentiate them from artificial orfdummy antennas, the invention being more especially concerned with the case when said antennas" are used to work on Wave-lengths shorterthan four timestheir length.

Itis known that an-antenna-when it is used to work.ondifierentiwavedengths, and in particular wave-lengthsrshorter than four times its length, has atotaliimpedancewhich consists of two portions, to wit: an active one (resistance to radiation)and alreactive one (reactance). The adjustment or tuning of this antenna is the operation. whichconsists in adding thereto circuits such that, with'little losses, the impedance'thereof is caused to assume a purely active form and a predetermined value. i

This result is generally-obtained by proceeding in two steps; the first-ste consists in reducing the reactance to-zero by inserting in series with the antenna inductance coils or capacitors, according to the direction of this reac'tance; the second step transforms the new impedance thus obtained, for instance by circuit coupling.

The -chief object of invention is to provide a tunin device of 'the kind above referred to which isbetter adapted to meet the various requirementsof practice'than those used up to this time, in particular which permits of tuning the antenna in a single'operation.

Preferred embodimentsof invention will be hereinafter described with reference to the accompanying drawings, given mer'ely'by way of example and inwh-ich: Y a

Fig, 1 showsa curve representing the-variation of the total impedance of an antennawhenthe wa-ve-length-varies; I i

Fig: 2- shows a portion of the same curve on-a difierent' scale;

Fig. 3, diagrammatically shows ,a: system of tuning circuits according to theinvention';

Fig. 4;; diagrammatically shows another system oftuning circuits'also. accordingto the invention.

It'is known thatjwhen an antenna is caused to work on wave-lengths shorter than i'our times its length, the variations of its impedance when the wave-length varies may be represented by a curve such asv that'of Fig. l, by plotting in abscissas the active resistance; and in. ordinates the reactance. The theoretical curve in question is a spiral which intersects thea-xis ofabscissas, at points grouped in two series, to wit: so-called'resonanc points, of low impedance, and so-called anti-resonance points, of high impedance.

' For practical purposes, this curve may be considered as constitutedby a Set of semi-circles, alternately located on one side and the otherof the axis of abscissas OX having their centers on this axis, and extending each from a resonance point to the next anti resona-nce point. On such a curve I (Fig. 1), the pointthat represents the antenna impedance travels in the direction of arrow F when the wave-length decreases, point A being the representative point for the antenna working in quarter-wave fashion. Theory and experience show that the geometrical power of origin point 0 with reference to all these circles is approximately equal to the characteristic impedance Z of the antenna that is utilized. a a 1 Being givenwan' antenna'of characteristic impedance Z, the point that represents its total impedance for the wave-length on which it is caused to work is for instance located atM,--'on a circle of center 33 (Fig. 2).

Up to now, tuning the antenna consisted in bringing the figurative point from M to N, then from N to a point P, upon the axis-"OX of the active resistances.

The essential feature of the present invention consists in providing, in series with the antenna, circuits including inductance coils and capacitors and adjusting the values of said inductance coils and capacities simultaneously and in such manner that the point that represents this total impedance travels along the impedance curve toward the first resonance point that is reached when turning in the clockwise direction.

This result can be obtained by making use of an adjustable feeder having like the antenna (to ensure the minimum of losses) a characteristic impedanceequal td-Z.

By varying the working length of this feeder without modifying its characteristic impedance, its inductance and its capacityare'caused simultaneously to vary. Consequently the. point M that represents the antenna impedance for the wave-length that its utilizedwill becaused to travel'on the circle above defined so as to come to the nearestresonance point Q.

Preferably, the feederincludes a pluralityof suitably grouped variable elements for adjustment thereof. I

' For instance,'as shown'by Fig. 3,'it. consists of a line including inductance coils Lin series with antenna Land capacitors C in shunt with the earth 3. All these elements are made variable andpaused to vary simultaneouslnby means o f'a single control 4', in such manner to'keepthe 3 characteristic impedance of this line constant during this variation, and equal to Z, to wit: the characteristic impedance of antenna 2.

The system may for instance include six cells consisting each of an inductance coil L in series and a capacitor C in shunt; the control means for varying 'thesevalues are coupled together in such manner that the expression remains constant and is equal to Z.

Any suitable means may be used for controlling the variable inductance coils and variable condensers from a Single control shaft (cams, coils and condensers of special shapes, etc.) for ensuring the constancy of expression Of course, the number of cells-including each a variable-inductance coil and a variable capacitor-may vary. Calculation shows that, in order to obtain a very fine adjustment, six cells are to be employed but that a lower number (as low as two in certain cases) may be suflicient for obtaining a rough adjustment.

The variations being more important for long These features are adapted to permit the adjustment of a dissymmetrical antenna 2 (Fig. 3). If now it issupposed that it is desired to act upon a symmetrical or doublet antenna 5, 5 (Fig. 4), the artificial line will include two sets of in ductance coils L in series connected two by two through balanced or split condensers C. In this case also the inductance coils and the capacitors will be varied simultaneously and in such manner as to comply with the condition (characteristic impedance of the antenna) that is to say, in fact, in such manner as to keep the values. of L and C in the same ratio to each other. l v I 1 I may further couple together, with a variable coupling coefiicient M, homologous inductance coils in the two branches of the artificial line. ,The values of L, C, M will be varied in such manner. as always to remain proportional to one another, in order to comply with the condition of constancy of the characteristic impedance of the artificial line thus constituted.

It is thus possible to act on a symmetrical or doublet antenna 5, 6 (Fig. 4) from a dissymmetrical transmitter or line such as a coaxial cable 1. Reciprocally, a dissymmetrical antenna might be j acted upon from a symmetrical transmitter or line.

; .It is to be noted that, in most cases, a slight adjustment variation occurs, due to the fact that 4 the value of the impedance of the point of resonance increases when the wave-length that is chosen decreases; but this increase is small and most often can be neglected. As a matter of fact, when the antenna is attacked directly through a transmitter, the tubes work with the maximum .of power supplied for the impedance that is utilized, and this power varies little with the wavelength, as any function close to a maximum; and when the antenna is attacked through a feeder with progressive waves which ends on its characteristic impedance-which ensures the minimum of losses-these losses will remain small, as any function close to a minimum, if a slight unbalancing takes place.

My tuning device has, over the already existing devices of the kind in question, among other advantages, that of performing the adjustment very'simply in a single operation.

The consecutive inductance coil elements could be coupled together, with a view in reducing the volumeof the apparatus.

In a general manner, while I have, in the above description, disclosed what I deem to be practical and efficient embodiments of my invention, it should be well understood that I do not wish to be limited thereto as there might be changes 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 accompanying claims.

What I claim is:

1. For use with a radio transmitter antenna, a tuning device which comprises, in combination, feeder means including at least two variable inductance coils in series with said antenna and two variable capacitors in shunt between the earth and said antenna, and control means for simultaneously adjusting said coils and said capacitors to keep'the approximate characteristic impedance of said feeder means, as expressed by the square root of the inductance to capacity ratio thereof, substantially constant and equal to the approximate characteristic impedance of said antenna. j

2. For use with a radio transmitter doublet antenna, a tuning device which comprises, in combination, feeder means including a line for each an tenna element with at least two variable inductance coils in series therein and at least two variable balanced capacitors inserted in shunt between said lines, and control means for simultaneously adjusting said coils and said capacitors to keep a given proportional relation between the respective inductances and capacities thereof, said control means being adapted to keep the approximate characteristic impedance of said feeder means, as expressed by the square root of the inductance tocapacity ratio thereof, substantially equal to the approximate characteristic impedance of said antenna. I

3. For use with aradio transmitter doublet antenna, a tuning device which comprises, in combination, feeder means including a line for each antenna element with at least two variable inductance coils in series therein and at least two variable balanced capacitors inserted in shunt between said lines, means for coupling together with a variable coupling coefilcient the respective inductance coils of said lines, and control means for simultaneously adjusting said coils and said capacitorsand varying said coupling to keep a given proportional relation between therespec tive inductances, capacities and couplin coeflicients, said controhmeansbeingadapted to keep the approximate characteristic impedance 'of Said-feeder means, as expressed by the square root o-f-the inductance to capecity ratio thereof,

" ta t q l to the, abproziimete character- 322 5 istic lfnpedance of said antenna 1,998,322 FRANCOIS BABIN. 5 71 7 2,438,116 REFERENCES CITED The following references are of record in the Number file of this patent: m 493,860

UNITED STATES PATENTS Name Date Muller May 8, 1934 Kaar Apr. 16, 1935 Roosenstein Dec. 26, 1939 Dodds et a1. Mar. 23, 1948 FOREIGN PATENTS Country Date Great Britain Oct. 17, 1938

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