US2541021A - Antenna - Google Patents

Description

R. F. BAUM Feb. 13, 1951 ANTENNA 2 Sheets-Sheet 1 Filed June 4, 1945 TRANJFER INVENTOR. RICH/4P0 R B/IUM AHOR/EY Patented Feb. 13, 1951 I UNITED ANTENNA Richard F. Baum, New York, N. Y., assignor to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware Application June 4, 1945, Serial No. 597,409

3 Claims.

This invention relates to antennas and more particularly to aperiodic ultra-high frequency antennas of a special design which has a constant response characteristic over an exceptionally wide band of frequencies.

In various applications of the radio art such as direction finding in connection with air and naval craft, it is frequently desirable to employ a rather wide band of frequencies, for instance, ranging from 200 to 400 megacycles without experiencing a loss of efficiency in the transmission or reception of the signals.

An antenna ordinarily has an input impedance varying widely with frequency throughout the band. This not only is responsible for poor power transfer at frequencies at which the antenna is not properly matched but produces other undesired results in certain applications, as in some systems used for direction finding wherein it is responsible for errors in bearing. It is clear that matching networks cannot be used practically over such a wide frequency band as they necessarily would have to be quite involved. Numerous antenna forms have been tried heretofore to provide radiating means having the abovenamed characteristics.

Other requirements have been to the effect that the antenna for these applications shouldbe directive in one direction and be practically free from back radiation in order to avoid the 1nfluence of signals reflected from objects in the rear of the antenna. An ordinary terminated antenna is not free from back radiation, but usually shows minor lobes towards the rear. For this and other reasons it became desirable to mount the antenna system on a ground plate, thereby cutting off the possibility of receiving signals from the rear of said plate. The maximum of the signal was desired in a direction normal to said ground plate.

Rhombic and similar antennas were investigated but were soon discarded asnot having a suitably wide band characteristic for the aforementioned purposes, especially since the radiation characteristics of an antenna of this type in combination with a reflector was subject to considerable variation with frequency to an extent not desired for use contemplated by the instant.

invention.

It was found that antennae which fulfill most nearly these requirements are antennae the elements of which carry progressive waves and are arranged and constructed in a way such as to form a number of lines of constant characteristic impedance equal to the resistance which forms the termination thereof.

An additional consideration for direction finding applications was that a rather small directivity was necessary. as a substantial amount of radiation has to be present in substantially spherical form within an angle of 45 degrees from the normal of the reflector plane. Thi required a length for the antenna components of notexceeding a half wavelength at the upper limit of the frequency band.

In order to be able to use a reflector in the manner suggested with a wide band antenna, it was found that the connections to the antenna for energy transfer as well as the termination by a resistance would have to be arranged so as to result in two planes of zero potential in the antenna system which permitted the disposition of a reflector or ground plate in one or both of the electrical planes of symmetry while retaining the desired direction and characteristic of the radiation pattern of the antenna.

It is accordingly an object of the invention to provide an antenna which has a fiat radiation characteristic over an exceptionally wide frequency band.

It is also an object of this invention to provide an antenna the input impedance of which remains constant and purely resistive over a wide frequency band, and is equal to the characteristic impedance of the associated transmission lines.

t is a still further object to provide an antenna which ha two planes of electrical symmetry.

' A still further object is to provide an antenna which is terminated at two points and fed at two other points in counter-phase to thereby provide two planes of electrical symmetry.

A still further object is to provide an antenna which has two planes of electrical symmetry and wherein half of the antenna asdetermined by either of the two symmetry planes may be replaced by ground plates.

A still further object of the invention is to provide an antenna which may be operated with a ground plate in an electrical plane of symmetry thereof to obtain a radiation normal to said ground plate or in the direction thereof.

It is furthermore an object of the present invention to provide an antenna of simple design easily adaptable for any given input impedance in the range of the characteristic impedances of commercially available transmission lines.

Another object is to provide an antenna which is mounted on a ground plate, having a maximum directivity in a direction normal to said ground plate, the presence of which does not alter the inherent flatness of the characteristic of the input impedance over the desired frequency band.

In accordance with the invention I provide a crosswise arrangement of 4 pairs of antenna elements forming l properly terminated radiating transmission lines. The system forms a double broken V which I refer to as a double-V, four cornered antenna which is terminated at two ends and fed at the two other ends in phase opposition whereby the antenna system is given two planes of electrical symmetry. Each arm of the V is preferably a double cone arrangement the diameters of which are proportional to the distance of their center lines from the two respective planes'of symmetry or an equivalent ground plate where the radiant energy fields are zero. thus double-V antenna may be replacedby a-suitable ground plate so that an inverted V or only a'single arm of the V will be retained. In another embodiment two symmetrical halves of two antennae in accordance with the invention'rnay be used such that one forms the termination for the other resulting in .an arrangement showing a gain in radiation efficiency.

These and other features and objects of the invention will become more apparent upon consideration or the following detailed description to be read'in connection with the accompanying drawings" in which:

1 represents an antenna of the" invention in its most general form;

Fig; 2' is a representationof an antenna based on that shown in Fig. 1 wherein the single condoctors of the former have been replaced by cones; I I Figs. 3 and {i are alternative forms of the antennacr Fig. 2 illustrating antennae having different angular relationsbetweeri the Varrhs and between'adjacent portions of the two V sections;

Figs. 5 and 6 illustrate two forms of antennae of the" invention wherein half of the basic system has been replaced by're'fiectors or grounds;

Fig. 7 is an antenna bas'e'd ori'tlie' fornr shown inFig. 5', wherein another half, that is a total of three fourths of the original antenna hasbeen replaced by the reflector or ground; and

Fig. 8 shows-in schematic form an array of two antennae s'i'rni'iar' to those shown in Fig; 5; the antennae being connected in series.

The basicform' of the antenna in accordance with the invention shown in Fig. 1 comprises four doiibleielement transmission lines' designated as A; B, C and D which are arrangedto' form, two broken V- sections 1' and 2, each of which consists'of two conducting arms 3; 4 and 5, and 6,

respectively.. Each arm consists of two radiating elements 3a, 3b; 4a, 4b; 5a, 5b; and Set, 579. Element pairs 3a, ia and 5a, 6a, include an angle fiEWhi-le an angle a is included by element pairs 3'21, Eb'and 4b, 6b; respectively; Angles a and ,B may have'any suitable value from zero to 180 degrees'as will appear hereinbelow. The hori- Znta1 and vertical axis of the antenna may have the lengths L1 and L2, as indicated respectively, which may also assume different values from one another, as will be explained. A source of high frequency energy at 'Isupplie's energy to a feed line 8, 9 which splits into two branches; it and l twhich in turn are connected to the terrhinals l2 and" I3 and I4 and I of the two sec tions of the antenna respectively. It willbe understood; of course, that the antenna may be used for receiving signals in which case the source may be replaced by a suitable receiving apparatus. The branch I0 contains a cross over at It where by-the phase of the energy therein is 180 degrees 4 along their entire length, it is necessary to in crease the diameter of the radiating elements in proportion to the distance of their respective center lines from the adjacent plane of symmetry. This leads to an embodiment of the antenna in accordance with the Fig. 2 which differs from Fig lonly by the fact that the single conductors of the four transmission lines A, B, C and D making up the arms have been replaced by conductive conic formations as shown at 2| and 22 for the arm 3. In Figs. 3 and 4 two alternative forms of the antenna of Fig. 2 are shown in schematic form the terminating impedance and input circuits being omitted for simplicity;

These forms are similar to the antenna of Figure 2 except that in Fig. 3 the relation of the included angles a and c is such that:

whereby the axis of two adjoining cones becomes identical.- InFig. 4 the angles'arerelated such that =p=l80-". In Fig. 5 a plane type conductor 23 of infinite dimension has been provided in the electrical plane'of symmetry thr'u 28 (Fig; 3), thus making possible the suppression of the lower half of the system, that isthe transmission line D and half of the lines A and B. Accordingly, thelow'er V sectionl is dispensed with" and is replaced by the image of theeenter terminated v section I m the groundplate 23. The terrriinating resistor is again insertedat l T: and the system is fedby two c oneentriecaples- 2'4" and each ofwhich ha's'a eharacteristidimpedance of half or the terminating resistance R at H in' order to be matched. Lines 24 and 25" are 180 degrees out-'of -pliase and may join to forr'n one balanced feed line 26.- The relative direction of the currents in the centerconductors of i lilies 2d aid- 25 is indicated by arrows-21 3110113 respectively.

Inthe antenna of Fig. 6 a plane type conducelectrical symmetry I9 and 20 of zero potential which equals the'terminating resistor z 7 between the radiating arm 3 and ground at H.

In the embddiments described herei'n'above. part of the power appliedto the antenna is uselessly dissipated in the terminal resistance R;

' whereby the effectiveness of the antenna is imaired. In places where the desired radiation pattern indicates the possible use of an array, two or more antennaeniay be connected in series aw cording to Fig. 8. This figure shows two antennae I and 2 each as described in connection with Fig. 5. The terminating resistance of antenna l is removed and a balanced line 40 is connected at H instead. Line 40 is shown feeding the antenna 2 which itself is properly terminated in a resistance at M. The input impedance of antenna 2 thus becomes the terminating resistance for antenna I.

In practice, the forms of antennae shown in Figs. 5 and 7 are preferred, of which that of Fig. 5 will result in a reasonably spherical pattern normal to the ground plate 23. Each arm of the V sections is essentially a double cone arrangement which may take the form of a hollow sheet metal structure or one of conductive wire or mesh netting. The overall length of the double cone portions is preferably M4 at the lowest frequency and equal to M2 at the highest frequency of the operative band. The band itself as mentioned above may have an exceptional width. The possibility exists for the band being several hundred per cent of the low frequency. The choice of angles a. and B and that of the dimensions L1 and L2 is largely dependent upon the desired radiation pattern while the apex angle of the various cones is dependent on the desired characteristic impedances of the lines.

In connection therewith, it is well to point out that the characteristic impedance of a transmission line is determined by the ratio of the distance between two points on the line conductors and the diameter of the line conductors at those points. This is approximately true even if the transmission line consists of two wire conductors which include an angle therebetween. If E is the distance between two corresponding points on the axes of the two transmission line elements 13-13 (Fig. 3) equally distant from the point of intersection of the two axes at 4|, and if the diameter of the elements at the above points is equal to c, then the radius of the conductors will progressively vary such as to make the conductors conical whereby the ratio of E/e will equal the ratio corresponding to a parallel wire transmission line of the same characteristic impedance.

In the actual design, consideration should be given to the not necessarily equal distribution of the radiation resistance along the cones, as well as to the effect of discontinuities at the junction points of any two lines of the arrangement produced by the change of direction of wave propagation, and also to the effect of sharp edges. Thus, at the points where the terminating resistances are inserted a certain end effect will take place. An improvement in this direction may be observed as the apices of the cones are separated by about one inch from one another which in turn calls for an adjustment in the value of the resistances and in the diameter of the cones.

An advantage of the present invention over a number of other terminated antennae is that the terminating resistances may be connected directly between the ground plate and the antenna elements or between two antenna elements without the use of coupling elements such as end capacities, which may disturb the matching properties and the radiation pattern, .especially where, as in the present case, the antenna elements are relatively short with respect to the wavelength.

As alread pointed out a great variety of radiation patterns may easily be obtained by changing the length and the inclination of the antenna elements.

It will be seen from the above that I have provided an antenna which by being designed to have two electrical planes of symmetry at right angles to one another for reference of its constituent portions, has a constant impedance characteristic over an exceptionally wide range of frequencies.

It will also be apparent that by introducing reflecting grounds in one or both of the electrical planes of symmetry, electrical equivalents have been provided for part of the original radiating portions and elements.

While I have described above the principles of 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 of my invention as defined in the objects and the accompanying claims.

I claim:

1. An antenna comprising two double cone radiating elements forming substantially an inverted V formation, the two cones of each element being placed base to base, the two far ends of said V formation forming each a terminal for connection to one of the two ends of an energy transfer device associated with said antenna, a terminating impedance disposed between the two adjacent ends of said V, and an image forming ground reflector for said formation adjacent to said far ends and in a plane normal to that in which the three corners of said V are disposed.

2. An antenna comprising two radiating elements forming substantially an inverted V formation, each of said radiating elements being of increasing cross sectional area from both ends toward an intermediate point thereof, the two far ends of said V formation forming each a terminal for connection to one of the two ends of an energy transfer device associated with said antenna, a terminating impedance disposed between the two adjacent ends of said V, and an image forming ground reflector for said formation adlacent to said far ends, and disposed substantially normal to the plane in which the three corners of the V are disposed.

3. An antenna comprising two double cone radiating elements forming substantially an inverted V formation, the two cones of each element being placed base to base, the two far ends of said V formation forming each a terminal for connection to one of the two ends of an energy transfer device associated with said antenna, a

. terminating impedance disposed between the two adjacent ends of said V, and an image forming ground reflector for saidformation adjacent to said far ends and disposed substantially normal to the plane in which the three corners of the V are disposed.

RICHARD F. BAUM.

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

UNITED STATES PATENTS

Images