US2165958A - Aperiodic antenna - Google Patents

Description

Julyll, 1939- I, P; s. CARTER 2,165,958

APERIODIC ANTENNA Original Filed Dec. 23, 1933 2 Sheets-Shem; 1

4 70 HIGH FREQUENCY 4 A APPARATUS? v F MT;

INVENTOR PHILIPS CARTER y 11, 1939- P. s. CARTER 1 2,165,958

APERIODIC ANTENNA Original Filed Dec. 23, 1933 Q 2 Sheets-Sheet 2 INVENTOR PHILIP SNCARTER ATTORNEY Patented July 11, 1939 UNITED STATES.

APERIODIG ANTENNA Philip S. Carter, Port Jefierson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Original application December 23, 1933, Serial No. 703,801, now Patent No. 2,099,296, dated November 16, 1937.

Divided and this application November 2'7, 1936, Serial No. 112,967

4 Claims.

This application is a division of my copending application Serial No. 703,801, filed December 23, 1933, now Patent No. 2,099,296, granted November 16, 1937, and relates to aperiodic antennae, and particularly to such of these which are of the open-ended type. v

The ordinary type of antenna as known in the art presents an impedance to the load which varies widely as the frequency varies throughout a band. In communication with short waves around three meters, particularly in television where the frequency band width is of the order of 1,500,000 cycles, a variation in impedance with change in frequency results in picture distortion, as a consequence of which it has been found to be highly desirable to obtain an antenna whose impedance remains constant over a wide range of frequencies. An aperiodic antenna, it is known, possesses this desirable characteristic since it eliminates any distortion which may be due to antenna tuning.

It is, therefore, an object of the present invention to provide in a simple and convenient manner ways and means by which an open-ended antenna may be made to have a fiat frequency band characteristic.

A further object is to provide an open-ended antenna which is both substantially aperiodic and unidirectional in nature.

- In general, these objects are attained by the provision of an energy or power absorbing device in the open-ended antenna, preferably in the form of a resistance.

A feature of the invention is a transmitting antenna which may be made to be unidirectional without the use of a reflecting system. This is effected by the dissipation of part of the power in the system in resistances which are connected near the end or ends of the transmitting antenna nearest the receiving station and/or by special design of the radiating arrangement whereby there is obtained high attenuation by radiation.

Other objects and features will appear in the subsequent detailed description which is accompanied by drawingswherein:

Fig. 1 shows an antenna of the V type provided with an arrangement in accordance with the invention for making it aperiodic;

Figs. 2 to 6 show various structures for accomplishing the invention; and

Figs. 7 and 8 show means for increasing the efliciency of systems constructed in accordance with the invention whereby the amount of power dissipation in the aperiodic antenna system is reduced.

Although the. invention will be described with particular reference to a V type antenna structure, it is to be understood, of course, that it is not limited thereto, since it is applicable to all types of transmitting and receiving antenna structures.

,Referring to Fig. 1, there is shown, by way of example only, an antenna of the V type comprising essentially a pair of wires 1, I which are a plurality of half wavelengths long and angularly disposed with respect to each other. These wires in the ordinary V structures are so energized that standing waves are caused to exist on the wires in phase opposition whereby there is obtained a radiation characteristic predominantly along the direction of the plane of the bisector of the angle of the conductors. For unidirectional radiation it has been customary to provide a similar structure composed of wires parallel to the wires in the first structure and spaced away an odd number of quarter wavelengths measured in' a direction along the bisector of the angle along the conductors. Such an arrangement is, adequately described in my United States Patent No. 1,974,387,

granted September 18, 1934.

Various methods have been proposed in the past for reducing the reflection of the waves on the antenna wires which cause the presence of standing waves, such as by the use of a stance between the antenna wires and ground. yever, in the case of a short wave transmitting antenna it is not feasible to avoid standing waves by closing the open ends of the antenna wires with re sistances because of the excessive losses which result. Another method of reducing the standing waves by radiating as much as possible the energy fed to the antenna is described in United States Patent No. 1,927,522, granted September 19, 1933 to Nils E. Lindenblad, wherein there is described a system comprising a plurality of pairs of diverging conductors arranged end to end so as to radiate accumulatively.

According to the present invention, traveling waves are achieved and the antenna is made substantially aperiodic over a wide range of fre quencies and unidirectional in character by providing, at or near the far end of the antenna wire or wires, one or more power absorbing circuit means for dissipating power. These circuit means, indicated as 2 in Fig. 1, may take any of the forms illustrated in Fig. 2 and Fig. 3. or, if

located substantially at the open end of the antenna, may take any of the forms illustrated in Figs. 4, 5 and 6, although it is preferred to employ the method of power dissipation shown in Fig. 2.

In Fig. 2 there is illustrated an antenna wire I whose open end is connected to the usual suspension support, not shown, through an insulator 3. A power absorbing resistance 4 of any convenient form shunts out a portion of the antenna wire at a point where the currentis a. maximum in the wire which is at a distance equal. to

. from the end of the wire, where x is the length v wire, as shown in Fig. 1, it is desirable, in order to absorb as much as'possible of thepower, to place at least one other absorbing resistance in the wire, and these may be located at substantially any odcl'rnultiple of a quarter wavelength of the mean frequency from the open end, as indicated in Fig. 2 by the resistance 4'. The length of the portion of the antenna shunted by the resistance i may be adjusted lay-varying the distances between the two vertical clamping strips 5 which are in contact both with the antenna and the resistance. This shunted portion of the antenna forms part of a closed circuit'including vertical strips 5 and horizontal resistance 43 and associated terminal connections. For a given frequency, the total voltage induced in thisclosed circuit is proportional to the area enclosed by the closed circuit, and the amount of current flowing through resistance t depends upon the voltage and the eflective impedance of the closed path. The value of resistance i may vary within wide limits, depending upon the type of antenna and the frequency of the working wave. A small variable condenser 8 serves to compen sate for the inductance formed by the loop com prised of the resistance, the metallic strips and the shunted portion oi the antenna.

The principles underlying the invention will be readily understood from a knowledge of transmission line theory, it being well known that the impedance of a wire having an effective length of is very nearly zero. Since the'larger portion of the total energy is associatedwith the primary wave which follows-transmissionline laws; it will ance.

be appreciated that the quarter wave section of wire beyond the loadingresistance acts like ashort circuit just beyond the resistance and makes possible the absorption of nearly all of the energy associated'with the primary wave in the resist- With proper adjustment, little or no re.- flection will take place at the tar end and the antenna will become aperiodic and unidirectional. f Fig. 3 shows another method ofloading; Here a variable resistance of convenient i'ormv shunts an insulator 6 placed at a distance of from the far end.

In Fig. 4 two resistances are placed in series with two quarter wave pointing in opposite directions and perpendicularto the antenna wire. This arrangement causes the radiationfrom the quarter wave segments be neg'ii disease gible inasmuch as the currents flow in opposite directions in the two branches.

Fig. 5 shows the antenna wire terminated through a resistanceto a sphere, and Fig. 6 through a resistance to a disc. Both disc and sphere form low capacity reactances. The arrangement of these two figures are for the purpose of obtaining as high a capacity as possible in order that the current at the end of the antenna be high. In such case the resistance will absorb power. The distance of the sphere or disc and resistance from the open end of the antenna and the insulator d is not important in this case, but ordinarily this distance will be very short.

As set forth above, the larger portion of the field energy may be considered as associated with a primary wave following ordinary transmission line laws. The remaining energy, which is responsible for radiation, is associated with a num-- ber of secondary waves. If the ratio between the energies-oi the primaryand the secondary waves can be decreased, the amount of power dissipation necessary to give an aperiodic an= tenna system will be reduced. This may be accomplished by fanning the wires i, i by a number of other wires i, l, as shown in Fig. "I, as a consequence of which there is obtained a decreasing characteristic'impedance to the primary wave as the latter approaches the far end of the antenna. The radiation resistance undergoeslittlechange over that for a single pair so that the ratio of power radiated to power dissipated is greatly increased.

Fig. 8 shows an arrangement similar to Fig. with the addition of a greater number of fannin wires.

Although the systems herein described in connection with the present invention are inherently unidirectional, it may be advantageous in many cases to employ energized or floating reflectors which when used increase the concentration of radiation and decrease the amount of newer dissipation.

What is claimed is:

1. The combination with an open-ended antenne which is at least as long as the length 0! the I operating wave adapted to function over a wide range of frequencies, of a power absorbing device located near the open end of said antenna, said device comprising a metallic body of appreoiable surface area and a resistance adjacent said body and serially connecting said body to said antenna, whereby said antenna is rendered substantially aperiodic over said range of frequencies. a v

2. The combination with an open-ended anterms. which is at least as long as the length of the operating wave, said antenna being adapted to function over a wide range of frequencies, of

a power absorbing device located near the open end of said antenna, said device comprising a metallic body of rotation of appreciable surface area, and a-resistance adjacent said body and is, a sphere. 4. An arrangement in accordance-with claim characterized i this that said body of rotation isaflat disc. 7

rims? acmrnn.

characterized in this that said body of rotation

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