US2898590A - Multi-frequency antenna - Google Patents

Description

1959 A. M. PICHITINO 2,898,590

MULTI-FREQUENCY ANTENNA Filed March 25, 1955 v INVENTOR- ATIUF/Vf/S United States Patent @fiice Patented Aug. 4, 1959 MULTI-FREQUENCY ANTENNA Albert M. Pichitino, Waseca, Minn., assignor to E. F. Johnson Company, Waseca, Minn., a partnership Application March 25, 1953, Serial No. 344,571

2 Claims. (Cl. 343-722) This invention relates to multi-frequency antennas and more particularly to an antenna including a tuning net work which is capable of transmitting and receiving waves of more than one frequency.

It is a well known feature of radio operation that the antenna system in connection therewith be resonant at the frequency of operation. Although transmitters and receivers can operate with antenna which are not so resonant, it is desirable to secure the maximum rediation which the antenna is capable of delivering and this can be accomplished only under resonant conditions. Sometimes it is desired that the same antenna system be capable of transmitting or receiving signals selectively at one or more frequencies. Such is often the case with amateur radio operators and in the case of aircraft radio operation and, sometimes, military radio communication. In some cases, it is desired to transmit from an antenna system at one frequency and to receive on the same antenna system at another frequency. In the case of extra hazardous operations, such as in connection with military or naval campaigns, it becomes desirable to maintain ordinary communication at one signal frequency and to maintain a condition such that a distress signal or other urgent communication may cut in or be transmitted between two points at a frequency other than the regular operating one.

In these and many other situations where a multi-frequency operation is desirable, the conventional means of attaining such operation has generally been accomplished by several expedients.

The first of these is the obvious solution of maintaining a separate antenna system for each frequency. Obviously, such an arrangement is expensive and multiplies the maintenance problem in connection with both transmission and reception.

The second conventional means of multi-frequency transmission and reception requires mechanism for switching in the tuning network of an antenna system. Since the network is often located inconveniently at a midpoint of a vertical antenna, the mechanical switching must be accomplished by such means as relays which in turn must be remotely controlled. Here again the method of switching is costly and adds extra working mechanism subject to failure and requiring additional maintenance.

The third conventional means of attaining resonant transmission and reception at a plurality of frequencies lies in a tuneable network located at the transmitter or receiver and used in conjunction with a resonant conductor connecting with the antenna system. The latter requires a variable length antenna in order to obtain resonance at various frequencies and does not ordinarily lend itself to an efficient mode of operation. One common useage of the latter mode of frequency switching occurs in aircraft transmission and reception where an antenna is unreeled from the airplane and allowed to trail therebehind at a fixed distance. As the network is tuned, the antenna may be reeled in or reeled out to a preselected position such as to create a resonant condition. It will be noted that none of the foregoing conventional antenna systems provides for transmitting or receiving at more than one frequency without the use of a costly and cumbersome switching set-up to attain the desired resonant conditions at the various operating frequencies.

It is, therefore, an important object of the invention to provide for an antenna system which is capable of transmitting or receiving radio signals on more than one preselected frequency, the interchange between frequencies being accomplished without recourse to mechanical switching devices and without resorting to the use of a resonant transmission line.

It is another object of the invention to provide for a tuning network within an antenna system which will automatically provide for resonance at more than one preselected operating frequency.

It is a further object of the invention to provide for an antenna system which can operate on several preselected frequencies without resorting to the use of a resonant transmission line and without requiring physical switching at any position along the transmission line or within the tuning network, yet which will yield an ideal resonant condition whenever a transmitting or receiving signal of one of the preselected frequency values is applied to the antenna system.

These and other objects and advantages of the invention will more fully appear from the following description made in connection with the accompanying draw ings wherein like reference characters refer to similar parts throughout the several views and in which:

Fig. 1 illustrates a quarter-wave antenna using my system for resonating at two dilferent frequencies with out switching or otherwise changing the physical dimensions thereof;

Fig. 2 illustrates the system of Fig. 1 with extra circuit element added to clarify evolution of the system;

.Fig. 3 shows an extension of my invention in which the tuning network will provide for radio waves of three different frequencies, the system resonating at each of its frequencies; and

Fig. 4 shows still another application of my invention in which a parasitic element is included in the multifrequency antenna system also without requiring switching or change in the physical dimensions of the antenna in order to produce resonance at the various frequencies.

Referring now to the drawing, I show the simplest form of my invention in Fig. 1. However, for the purpose of clarification and depicting the evolution of the system, reference is made to Fig. 2, which is equivalent to Fig. 1 with the addition of inductor 37. The antenna shown in Figs. 1 and 2 is generally of the grounded quarter-wave type which is particularly adaptable to the very high frequency range of radio signals. The device comprises a coaxial transmission line 10 which is connected to the transmitter or receiver (not shown) and leads to the lower end of an antenna. conductor or segment 11 as shown. The coaxial transmission line comprises a conductor 12 encased in and insulated from a metallic tubular member 13 which, in turn, is grounded at 14. The conductor 12 connects with the antenna segment at a mounting insulator 15 as shown. A tuning network T is interposed in the antenna segment 11 and is preferably positioned so that a portion 16 of the antenna segment will extend above the tuning network T.

Referring to the form shown in Fig. 2, the tuning network T of itself comprises a first inductor 17a and a second inductor 17b which are connected to terminals 18 and 19 of the antenna segment 11. In shunting relationnwiththe inductors 17a and l7b-is a third inductor 20 and a capacitor 21 connectedin series combination. The

latter two elements are likewise connected toterminals 18. and 19, but sutliciently far away from the inductors 17a and 17b to prevent electrical coupling. The entire" antenna system is'so devised =as to resonate at-two' frequencies designated as Fl-at the lower -frequency and F2 atithe higher. The Iengthofthe conductor or segmentll, includingthe. upper portion 16, is so selected asto, be resonant at the higher frequency F2. The values;

of the reactances of capacitor 21 and inductor 20 are so selected th atseries resonance at the higher frequency F2 occursbetween the terminals 18; and'19i It will be observed that, since a series-resonant circuit offers a very low impedance (zerotheoretically) :at the resonant frequency, an electrical shortis providedacross the terminals-18 and '19.which willstill leave the conductor or segment 11 resonant at the higher frequency F2;

Because there is very lowimpedance across the terminals-18 and 19 of the-antenna conductor or segment 11 attherescnantfrequency F2, the circuitelements 17a and 17b will have no effect upon-the behavior of'th'e antenna system at the higher frequency F2. the inductor 17b is of such a value which, in conjunction. with theinductorZO-and' capacitor 21,- will'form a parallel.resonantcircuit across the'terminals l8and' 19 at:the lower frequency F1: Sincea-parallel resonant circuit presents infinite impedance across its terminals,

the ser-iescombinationof the inductor 20-and the ,capaci-' tor-21 is, to all intents and purposes, not effectively connected across the terminals 18 and 1;9'at the lower frequency F1.

antenna segmentll the-system isresona-nt at. its lower frequency F1; It should be noted that the parallel combinationsof inductors 17a and 17bwith inductor 20" and capacitor 21' is not; in itself; resonant at the lower frequency F1;

In-.the= practical application of my antenna system,

inductors 17a and 1712, are combined in their parallel quenciesin the light of surrounding factors which may vary to some degree the value of the settings, they-need" not be. altered until such time as 'it is desired 'to operate However,

- The magnitude of inductance value in. inductor. 17a is selected so thatin-conjunction with.

It is understood, however, that .when.

4 example; The network T comprised an inductor 17' which was physically one and seven-sixteenths inches in diameter and two and one-quarter inches long and has an inductance value of 2.21 microhenrys. The inductor 20 was physically one and seven-eighths inches long and seven-eighths inch in diameter, having an inductance value of 0.845 microhenry. The capacitor 21 had a capacitance 015,36 micromicrofaradslwhlen installed upon an automobile in conventional manner, the system resonated on a lower frequency F1.of14.2.megacycles.and likewise resonatedat a higher frequency F2 of 29'megacycles, the system 1 resonating, as, a quarter-wave; antenna working against a ground plane.

Referring nowto Fig. 3, Ihave there shown an example of a three frequency antenna system embodying my invention. In this case, I desire to resonate the antenna system at three frequencies designated as F1, F2 and FSin increasing-order. The connection. between the coaxial cable 10"With' the antenna conductor or segment 11" is the same as that disclosed in-the diagrammatic representation of Fig. 1,.the insulator 15 and ground connection 14 being similarly arranged. In the three frequency system, however, the tuning network may, be

theantenna conductor or segment '11. inductor 22and capacitor 23 are of such a Value as to resonate at the highest frequency F35. The inductor 24- and the capacitor 25"are of'such a value as to resonate also at the highest frequency F3. The inductor 26 "and the capacitor 2Tare of such values as to be series-resonant at the intermediate frequency F2." Inductor 28 is electrically shorted -on the intermediate and highest frequency FZ'Jand F3? by series circuits across terminals 29"30' and 31-32. The inductor 28 has an inductance value which will" resonate the entire system at the lowest frequency F1;

ontwo other frequencies orunder such" other circum-.

stancesaswill afiect the values of the physical dimensions in the system.

When'used on a mobile vehicle, the quarter-wave antennamay use thefrarne-of the vehicle suchas an. automobile. fora mirrorreflectingsurface which will: complement the quarter-wave antenna system so as to effectively produce thehalf-wave WhlCh'iS requisite for resonance.-- Where thetransmission line 12*is very shortandj constant in nature, it may-enter into the antenna system.

However, in-orderto-prevent introducing unnecessary. variables mto my device, I prefer-the grounded coaxial againuto. Fig. 1, the-transmission line which I employed;

was an. R.G.-8 -Bar U- coaxial (Slobms) grounded 'at the .outer end: and the-conductor of the transmission lineconnected tov the bottomof an insulatedrantenna conduc-- tor, o1: segment. one-quarter inch in diameter and thirtyseyen.andrseveneeighths. inches iong to-the terminal 18.

h em nder .of -.the antenna-conductor. or. segment 1.11

h; iii-diame e ould/ ct d tha u he diagram? maticrepresentation in Fig 1 does notnecessarily corre; spond proportionally to the values given in this specific preselected frequency.

ment are selected so. as. to have a correct corresponding:

The foregoing illustration resonates the entire system uponthe application ofeach' of the above mentioned threefrequencies, operating as a quarter-Wave antenna against either ground or -a ground plane.

Referring now to Fig. 4, I show therein .an extension.

of my network technique to. a parasitic system. In this case, the, parasitic or driven elementicomprises a pair of arms 37 and a network T3"in, spaced relation with'anantenna 36, the transmission line and'ground system be-v ingsimilar to that shown in Figs. 1 and '2'. Thetuning network T3, however, comprises a slightly different arrangement of conductors. In this instance, T3"has as.one

of its conductors, an inductor 33 and a capacitor 34 in.

reflectoras is common in theart. The. inductance'33 and.

capacitance,34 are made series resonant at the lower The arms 37 of the parasitic eleelectrical length, thus shorting the element across the networkterminals; The combination ofvalues of inductance 33,capacitance 34 and capacitance 35 "is chosen to present the proper value of reactance at a higher preselected frequency so as to tune the parasitic element at the higher frequency. In the special case where the lower frequency is exactlyhalf'of 'the higher frequency, the combination results in parallel resonance across the terminals of the tuning networkTS "at'the'higher-ofthe' two frequencies: The capacitors 34 and 35 aremade variable 'to facilitate adjustment of tuningon'th'e lowerand 1 higher frequencies respectively.

It may thus-beseenthat I have devised a simple-and.

troublefree antenna. system which is. capable of trans-.-

mittinggor receiving signals of more than one preselected;

frequency without providing separate antennasandme chanical switching mechanism for activating one or the other of several such antennas. In accomplishing the foregoing, I have maintained a resonant condition for each of the preselected operating frequencies.

It will, of course, be understood that various changes may be made in the form, details, arrangement and proportions of the parts Without departing from the scope of my invention.

What I claim is:

1. An antenna system adapted for connection with a coaxial cable for automatically accommodating a plurality of radio signals of preselected frequencies, comprising an antenna segment having a plurality of adjacent sections, one of which is connected to the coaxial cable, a plurality of tuning networks each providing series interconnection between adjacent sections of said antenna segment, each of said networks including an inductance of preselected value and each also including a first series connected inductance and capacitance of preselected value and connected in shunting relation with said first-mentioned inductance, one of said networks being connected into the antenna segment between the coaxial cable and another of the networks and also including a second series-connected inductance and capacitance of preselected values connected in shunting relation with said first mentioned series-connected inductance and capacitance, said preselected values of inductance and capacitance creating a resonant condition at each of said preselected frequencies without requiring mechanical switching or change in physical dimension of said antenna system, whereby a plurality of signals of different frequencies may be supplied to and transmitted by said antenna segment,

2. An antenna system for automatically accommodating a plurality of radio signals of preselected frequencies comprising an antenna segment having first, second and third sections, said first section being connected to the coaxial cable, a first tuning network connected between said first and second antenna sections, a second tuning network connecting said second and third antenna sections, each of said networks including an inductance of pre-selected value and each also including a first series inductance-capacitance circuit resonant at a first frequency and connected in shunt relation with said first mentioned inductance and said first tuning network also including a second series inductance-capacitance circuit resonant at a second frequency and connected in shunting relation with the inductance of the first network, said second tuning network being resonant at said second frequency and the first tuning network being resonant at a third frequency whereby to permit signals of three frequencies to be supplied to and transmitted by said antenna segment.

References Cited in the file of this patent UNITED STATES PATENTS 1,604,981 Elsasser Nov. 2, 1926 2,096,782 Brown Oct. 26, 1937 2,282,292 Amy et al May 5, 1942 OTHER REFERENCES Abstract of Application 132,876 printed in the Oflicial Gazette, vol. 644, page 305, Mar. 6, 1951.

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