US3364491A

US3364491A - Broadband ellipsoidal dipole antenna

Info

Publication number: US3364491A
Application number: US600108A
Authority: US
Inventors: Stohr Walter
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1958-12-10
Filing date: 1966-12-08
Publication date: 1968-01-16
Anticipated expiration: 1985-01-16
Also published as: DE1297167B; DE1109748B; FR1242647A; DE1290991B

Description

Jan. 16, 1968 w. STOHR BROADBAND ELLIPSOIDAL DIPOLE ANTENNA 5 Sheets-Sheet 1 Filed Dec. 1966 INVENTOR.

ifTORNEYS Jan. 16, 1968 w. STOHR BROADBAND ELLIPSOIDAL DIPOLE ANTENNA 3 Sheets-Sheet 2 Filed Dec.

INVENTOR. wzer 6%0722 ATTORNEYS Jan. 16, 1968 w. STOHR 3,364,491

BROADBAND ELLIPSOIDAL DIPOLE ANTENNA Filed Dec. 8, 1966 3 Sheets-Sheet 3 I N VEN TOR.

A TTORNE YS United States Patent 3,364,491 BRUADBAND ELLIPSOIDAL DIPOLE ANTENNA Waiter Stoln', Munich, Germany, assignor to Siemens Alrtiengesellschaft, Berlin and Munich, Germany, a corporation of Germany Continuation in-part of application Ser. No. 857,918,

Dec. 7, 1959. This application Dec. 8, 1966, Ser.

No. 600,108 Claims priority, application Germany, Dec. 10, 1958,

66,904; Dec. 30, 1958, S 61,171

5 Claims. (Cl. 343807) ABSTRACT OF THE DISQLOSURE An antenna which in the preferred embodiment comprises a pair of cigar-shaped radiators mounted side by side with their longitudinal axes parallel and fed by a matched balanced feed. A single relatively wide relative to its length radiator mounted adjacent a suitable reflector plane and with an eflicient feed system is also disclosed.

This is a continuation-in-part of application Ser. No. 857,918, filed Dec. 7, 1959, now abandoned.

The invention is concerned with an antenna arrangement for short and ultra short electromagnetic waves, comprising a dipole radiator of considerable thickness as compared with its length.

For the short wave range as well as for meter Waves and still shorter waves there are frequently required dipoles exhibiting within a relatively wide frequency range good matching and radiation properties which remain as uniform as possible. Most varied forms of dipoles are known for the realization of these requirements. Next to cone radiators and double cone radiators there are used for this purpose primarily cylindrical dipoles with a relatively low ratio of thickness to length. However, the results achieved in practical use are not very satisfactory. Moreover, ellipsoidal radiators with an axes ratio of 1:2 and greater have already been used for this purpose. In these known arrangements, the inner conductor of a coaxial line passes continuously into the ellipsoid and the outer conductor forms a bead of complicated spatial form. An antenna of this tF/Be is, for example, described in the German Patent No. 894,575. The feature which is in con nection with such antennae disturbing, is, that they are despite their form which is in part relatively complicated, sufficiently good in the matching to a high frequency line only within a relatively narrow frequency band of, for example, 121.5.

The object of the invention is to show a way which will make it possible to obtain over a considerably wider frequency band, for example, one octave, good matching and radiation properties as uniform as possible while avoiding complicated spatial forms such as shown, for example, in the German Patent No. 894,575.

This object is according to the invention achieved by the provision of a dipole radiator in the shape of a sphere or of an ellipsoid extending in the radiation axis, especially with an axes ratio of about 1.5: 1, and making the spacing between the neighboring ends of the dipole halves, in a non-symmetrical dipole, the spacing between a reflector plane and the neighboring dipole half, so small in the direction of the radiator axis that the impedance appearing between mutually most closely lying points is on the order of magnitude of the characteristic impedance of customary coaxial lines, especially between 50 and 60 ohms.

In the case of a non-symmetrical dipole, the one of the mutually most closely adjacent points which lies at the ball or spherical radiator, is suitably connected with the inner conductor of a coaxial line, the outer conductor of which is carried from the side facing away from the radiator, to the reflector plane or the counterpoise, respectively.

It has moreover been found of advantage in such antenna, to make the spacing between the reflector plane and the half-dipole between 1 and 7 of the extent of the halt' dipole in the direction of its axis.

In the case of a symmetrical dipole, it will be of advantage to connect the mutually most closely adjacent points with a symmetrical high frequency line which preferably extends in the direction of the symmetry plane.

It is moreover in the case of a symmetrical dipole of advantage to connect the two mutually most closely adjacent points with a wide band symmetrizing device the essential extent of which lies in the symmetry plane and which passes into a high frequency line which is non-symmetrical to ground.

It is above all in the case of a non-symmetrical dipole supplied by way of a coaxial line in many cases of advantage to construct the arrangement so that the inner conductor passes smoothly with the half dipole and that the outer conductor passes with the reflector plane by way of a widening coaxial line of uniform characteristic impedance.

The various objects and features of the invention will appear from the description which will be rendered below with reference to the accompanying drawings showing embodiments thereof and illustrating essential details.

In the drawings:

FIG. 1 shows an antenna constructed in the manner of a dipole in accordance with the invention;

FIG. 2 shows an arrangement according to the invention having a normal dipole radiator consisting of two dipole halves;

FIG. 3 illustrates an embodiment in which the symmetrical dipole is supplied by a line which is non-symmetrical to ground;

FIG. 4 shows an embodiment comprising a transition part for gradually passing the spherical radiator to the inner conductor of the coaxial line;

FIG. 5 indicates the manner of constructing a half-dipole of ellipsoid shape;

FIG. 6 shows in partial and part sectional View a nonsymmetrical dipole disposed according to the invention aboye a conductive member serving as a counterpoise;

FIG. 7 represents a symmetrical dipole according to the invention; and

FIG. 8 indicates the manner of combining non-symmetrical dipoles according to the invention to construct an omnidirectional antenna.

Referring now to FIG. 1, the half-dipole 1 has the shape of an interiorly preferably hollow ball or sphere made of metal. The half-dipole is disposed above a metal plate 2, hereinafter referred to respectively as reflector plane or counterpoise. The connection of the corresponding directionai antenna with a non-symmetrical high frequency line formed as a coaxial line, is effected so that the coaxial line is carried to the point at which the spherical radiator 1 is nearest to its counterpoise 2, the inner conductor 3 of the coaxial line passing at such point into the half-dipole 1, while the outer conductor 4 merges into the metal plate 2.

The mounting of the half-dipole 1 with respect to the metal plate 2 can be effected in diverse manner. If the half-dipole 1 is of relatively slight weight, it may be sup ported by the inner conductor 3 of the coaxial line which may be made sufiiciently sturdy and held in its position with respect to the outer conductor 4 in known manner by means of substantially reflection-free supporting disks. In the case of greater wei ht or strong lateral stress of the half-dipole 1, it will be advantageous to provide support by means of a dielectric, above all a dielectric with low relative dielectric constant. The corresponding support may be ring shaped, disposed between the reflector 2 and the adjacent side of the sphere and surrounding the feed point. It is in some circumstances of advantage to embed the entire antenna, that is, at least the operatively active part of the reflector surface and including the sphere, in such a dielectric. It is particularly advantageous to use in such cases a so-called foam dielectric which prevents ingress to a disturbing degree of moisture into the space between the half-dipole and the reflector surface while at the same time permitting to keep the dielectric constant of the material, due to the foaming, very small, for example, almost to 6,:1.

The operation of the arrangement shown in FIG. 1 can be explained as noted below, assuming the use of the antenna as a transmitter antenna, although it may be used in similar manner as a receiver antenna.

The coaxial line 3, 4 has at the feed point 5 a predetermined characteristic impedance. The space connecting with the feed point between the lower dipole half and the neighboring area of the counterpoise or reflector surface 2 forms a radial line with predetermined characteristic impedance course in radial direction. This radial line merges into the radiator continuously. The resolution of the radiation is thereby in part effected already in the outer marginal regions of the radial line. The diameter D of the half-dipole lies for the longest operating wave at least in the order of magnitude of one-fourth of the wave length in free space. An at least nearly reflection-free transition from the coaxial line 3, 4 to the radial line may be Obtained by suitable proportioning of the space d between the mutually most closely adjacent parts of the half-dipole 1 and the counterpoise 2. The radial line provides a continuous transition to the characteristic impedance of the free space in which is effected the radiation of the high frequency energy supplied by Way of the coaxial line 3, 4. When the antenna is dimensioned in this manner, it will be found that it has above a limit frequency, from which results the longest operating wave length, a certain measure of mismatching which is determined by the above mentioned dimensioning, and that this mismatching is decreased With increasing frequency, resulting in strong looping of the impedance diagram. The radiator has a length of about M4 for the longest operating wave (x/4=wave length in free space). The radiation properties thereby remain within the mentioned frequency range practically nearly the same. The dipole radiates approximately like a normal x/ 4 radiator which is disposed above a conductive surface, laterally to the longitudinal antenna axis as indicated in FIG. 1 in dot-dash line. It was with such antenna arrangement for example possible to maintain within a frequency range of about 500 to 2500 megacycles a value of reflection amounting to only a few percent and which was in preponderant part of this frequency range appreciably less. The characteristic impedance of the coaxial line 3, 4 amounted to 60 ohms and the spacing d to about ,6 of the dimension D. It is of importance in this connection that the locus curve of the impedance is with increasing ratio d/D extended at the point 5 and that this impedance contains a higher active component While the impedance curve is with increasing diminution of the ratio d/D more and more contracted, the active component becoming smaller. However, a further reduction of the ratio d/D below the value or is not productive of further advantages, producing indeed under some conditions even a worsening of the operation.

FIG. 2 shows an arrangement according to the invention operating as a normal dipole radiator consisting of two dipole halves. Illustrated in solid line in FIGURE 2 are a pair of spherical radiators. The diameter D of the sphere is indicated and the spacing between adjacent spheres indicated as cl. The radiators may also be cigarshaped. This is shown by dotted line in FIGURE 2. The elements are mounted side by side adjacent each other with their major axes parallel. A section on a right plane through such structures would show a circle such as shown in solid line in FIGURE 2. The D dimension indicated constitutes the diameter of the largest circular section of the radiating elements. The dimension [2 the diameter at the cigar-shaped radiator at any point along its length a. The rules given with reference to FIG. 1 for the dimensioning of D and 0. apply in this case as explained in connection with FIG. 1. The arrangement according to FIG. 2 has the great advantage that the supply and the connection with a high frequency line can be effected by a symmetrical line 6 extending in known manner in the symmetry plane 7 indicated in dot-dash line.

FIG. 3 illustrates an embodiment of the invention in which the symmetrical dipole is supplied by a line which is non-symmetrical to ground. There is in this case provided a known symmetrizing device 8 operating in the manner of a symmetrizing loop which is suitably made adjustable for the prevailing operating frequency, for example, by means of a movable short circuiting ring 9. What has been said with reference to FIG. 2 applies other' wise also for this embodiment.

It may also be mentioned that the mounting of the half dipoles 1 and 1', FIGS. 2 and 3, may be effected in the same manner as explained in connection with the halfdipole 1 and the counterpoise 2 of FIG. 1. This also applies for the mechanical construction of the half-dipoles which may be in accordance with the construction noted in connection with FIG. 1.

FIG. 4 represents a further embodiment of the inven tion in which the spherical radiator does not merge abruptly into the coaxial line 3 and 4 but by way of a transition part 9 merging gradually to the cross section of the inner conductor 3. The transition part 9 merges With its surface tangentially with the radiator 21. The outer conductor 4 of the coaxial line is cross-sectionally widened so as to merge similarly tangentially to the counterpoise, thereby avoiding a characteristic impedance leap in the transition range to the radial line. In such a case, the spacing between the root point of the half-dipole 1 and the plane determined by the counterpo-ise 2, indicated in FIG. 4 by an arrow, can be greater than in the arrangement according to FIG. 1.

FIG. 5 shows how an ellipsoid half-dipole is to be constructed. The ellipsoid can be considered as a degenerated sphere and can as such take the place of the sphere in the preceding examples including the embodiment according to FIG. 4. For the dimensioning of the short axis a with respect to the long axis b-whereby b shall coincide with the dot-dash dipole axis of FIG. 1-it was found advantageous to maintain the conditions 0.6 a/b 1.7. In an embodiment according to FIG. 4, the value 1.5 was found a particularly favorable ratio a/ b for a characteristic impedance of the feed line between 50 ohms and 60 ohms. For a clearer understanding, examples of the different ratios a/b are illustrated in isometric in FIGS. 2 and 3 illustrating the extreme in which a/b is approximately 0.6, and FIG. 2 the extreme in which a/ b is approximately 1.7.

The antenna arrangement according to the invention is advantageously applicable in many cases. For example, the symmetrical dipole can be used as an exciting radiator for a parabolic mirror antenna. As an individual radiator, it may be used above all for the radiation of meterand decimeter-waves primarily in connection with television bands. The radiator can moreover be used in groups for obtaining certain radiation characteristics in a similar manner as customary dipole radiators. The radiator may also take the place of a passive or as a supplied radiator in the manner of a reflector or a leading dipole. The wide-band action will thereby likewise become prominent.

The radiator must not necessarily have a rotation symmetrical cross sectioncross section perpendicular to the axis b, D of in FIG. 5 but can above all be in the axial relation of this cross sectional plane, ellipitical, for example, in the ratio of about 0.6 to 1.7. It is in such case advantageous to match the radial line or the transition, respectively, to the prevailing cross-sectional shape.

Concerning the matching of the radiator to a high frequency line, there are above all two advantageous possibilities. It is on the one hand possible to proceed from a predetermined characteristic impedance value of the line and to select the diameter D or the spacing d as well as the ratio a/b so that matching is obtained or, on the other hand, to secure with predetermined radiator shape and/or dimension d, the matching by an intermediate connection of a wide band transformer, for example, an exponential line.

The matching requirements can be further improved in connection with such an antenna by forming the mutually adjacent surfaces of the half-dipoles or of one dipole with respect to the associated reflector surface or the counterpoise so that the radial line extending from the connecting point in radial direction over its entire length to the exit region of the wave has at least the same characteristic impedance as at the connecting point and that the connecting point merges directly with one supply line the characteristic impedance of which is at least nearly equal to the characteristic impedance of the radial line.

In case the antenna arrangement is constructed as a symmetrical dipole in which a high frequency line is carried to the terminal point in the symmetry plane, it will be necessary to consider in the construction of the mutually neighboring halves of the dipole the symmetrizing device which may be provided at the connection or terminal point.

It has been found of advantage in the formation of the dipole halves to make the characteristic impedance at any point of the radial line equal to the value at the connection point, or such, that the averaged value of the characteristic impedance of the radial line in the circumferential direction is for any random radius equal to the characteristic impedance at the connecting or terminal point.

In case of a non-symmetrical dipole, the outer face of a non-symmetrical high frequency line or the conductive outer shell of an antenna mast may be advantageously used for a reflector surface or for a counterpoise. The formation of the mutually neighboring surfaces is thereby to be determined such that the characteristic impedance is at each point of the radial line equal to the value at the connecting point or that the averaged value of the characteristic impedance of the radial line is in the circumferential direction for a random radius equal to the characteristic impedance of the connection or terminal point.

It is advisable in some cases in connection with the last described arrangement, for obtaining a predetermined radiation diagram, for example, an omnidirectional radiation diagram, to arrange a plurality of non-symmetrical dipoles about a common antenna mast, preferably in axially symmetrical distribution.

FIG. 6 shows a partial and part sectional view of a nonsymmetrical dipole 1 arranged in accordance with the invention above a practically plane conductive member 2 serving as a counterpoise. The half-dipole 1 and the counterpoise are at closely adjacent points connected with a high frequency line constructed as a coaxial line 13, 14. It shall be assumed that this coaxial line has, for example, a characteristic impedance 2 60 ohms. The spacing d between the dipole half 1 and the surface of the counterpoise 2 is such that radial line beginning at the radius I -fOIII1d by the neighboring surfaces of the half dipole 1 and the counterpoise 2has a characteristic impedance Z which is at least nearly equal to the characteristic impedance Z of the high frequency line 13, 14. Moreover, the surface of the half dipole l is within the range of this radial line formed such that the radial line hasin the operation of the antenna as a transmitter antenna-at least nearly a constant characteristic impedance from the value Z to the exit point of the waves. The waves are as known taken off at the area where the length of the electric field lines between the neighboring surfaces of the half dipole 1 and the counterweight 2 have for the longest operating wave length a value corresponding to half the wave length. This is indicated in FIG. 6 by the field line shown in dotted lines marked by a".

The operation of the arrangement illustrated in FIG. 6 corresponds substantially to that of the antenna arrangement described before. The result of the particular construction above all of the radial line 15, is that the transformation properties of the radial line will remain practically unchanged within the operating range of the antenna. The matching is thereby considerably facilitated. (Moreover, it is in this manner with least expenditure possible to pass from the high frequency line 13, 14 directly into the connecting points of the non-symmetrical dipole. It is advisable to make the spacing d for the radius r (r =one half of the inner diameter of the outer conductor 14) about equal to r it being assumed thereby that the dielectric has in both ranges the same dielectric constant, above all air.

FIG. 7 shows a further embodiment of the invention, representing a symmetrical dipole comprising the radiator halves 16, 17 which are in known manner supplied from a coaxial line 13, 14 by way of a symmetrizing device. The symmetrizing device is constructed similarly as described before with reference to FIG. 3 and comprises two longitudinal slots 18, 19 which extend in the symmetry pane of the dipole halves and the electrical length of which amounts at the operating wave length to about one half wave length. The inner conductor 13 is interiorly connected to one of the outer conductor portions formed by the slots, at a point lying approximately midway of the ends of the slots. The two dipole halves 16, 17 are in the same symmetry plane disposed upon and connected with the respective outer conductor portions. In such arrangement, the spacing between the two most closely adjacent places of the dipole halves 16, 1'7 is to a certain measure determined by the smallest diameter of the outer conductor 14 and the latter which extends in the symmetry plane of the half-dipoles 16, 17 extends in certain measure into the characteristic impedance distribution of the radial line formed by the neighboring surfaces of the half dipoles 16, 17. The characteristic impedance is thereby conveniently represented as occurring within a differentially small spatial element a'R which extends approximately like a hose in the direction of the electrical field strength between the adjacent surfaces of the half dipoles 16, 1.7.

There are two advantageous possibilities for applying the teaching of the invention in connection with an antenna arrangement constructed as described above. The shape of the mutually adjacent or neighboring surfaces of the half dipoles 16, 17 is either such that the characteristic impedance corresponds in each spatial element within the radial line, that is, at each point of the radial line, at least approximately to that obtaining at the connecting point, or that the characteristic impedance averaged for a desired radius of the radial line (calculated from the connecting point) corresponds at least approximately to the characteristic impedance at the connecting point.

It is in the first case necessary to make the radius of the curvature of the dipole halves, in the ranges neighboring on the high frequency line 13, 14, dilferent from that obtaining in the ranges more remote from the high frequency line. This will result in a cross sectional shape of the half dipoles 16, 17-as viewed perpendicular to the dipole axis indicated in FIG. 7 in dot-dash line 1t]- which is not rotation symmetrical. In the second case, the corresponding cross sectional shape of the dipole halves or radiators can be made rotation symmetrical but the characteristic impedance values for the individual sectors of the corresponding cross sections will be different. The averaged value obtained in accordance with the foregoing explanations will however correspond at least approximately to the characteristic impedance at the connecting point.

It is moreover possible to satisfy the characteristic impedance requirements in simple manner alone by the shaping of the high frequency line or if provided, of the shielding means, or utilizing the corresponding shaping in addition to the previously noted measures.

The explanations with reference to FIG. 7 in which the feed is effected by Way of a coaxial line with a symmetrizing device, also apply sensibly in connection with the feeding of a symmetrical dipole by way or" a symmetrical high frequency line which may if desired be provided with a shielding jacket.

FIG. 8 indicates how non-symmetrical dipoles according to the invention can be combined to construct, for example, an omnidirectional antenna utilizing as counterpoise the conductive skin or shell 11 of an antenna mast. The dipoles are for simplified representation shown as spheres 12 and arranged axially symmetrically distributed about the outer shell 11 of the antenna mast. It must be considered that the counterpoise of the individual dipole halves 12, which are supplied similarly as shown in FIG. 1, consist in such a case of the outer shell or skin 11 of the mast, forming a cylindrical surface. The curvature of the cylindrical surface accordingly enters into the characteristic impedance distribution of the radial line, and it is for this reason advisable to observe the construction rule, for the shaping of the mutually adjacent surfaces of the radial line of each non-symmetrical dipole, given with reference to FIG. 7. Accordingly, due to the configuration and above all due to the shaping of the corresponding surface of the half dipole 12, either the characteristic impedance at each point of the individual radial line will be equal to that of the connecting point or the value of the characteristic impedance averaged in circumferential direction for a desired radius of each individual radial line will be equal to the characteristic impedance at the connecting point of the individual non-symmetrical dipole.

The spatial arrangement of the individual non-symmetrical dipoles at the antenna mast or tower can also be provided in known manner in accordance with the predetermined diagram requirements corresponding to the phase position of the waves fed to the individual dipoles and in accordance with the energy conditions.

Changes may be made Within the scope and spirit of the appended claims which define what is believed to be new and desired to have protected by Letters Patent.

I claim:

1. An antenna comprising a pair of cigar-shaped radiators mounted side by side with their longitudinal axes parallel, a pair of feed lines spaced a distance d apart and extending parallel to each other between said cigarshaped radiators and respectively attached to said radiators at their point of maximum circular diameter D, and the spacing d between said feed lines and the radiators being such that said spacing is small relative to the maximum circular diameter D of said pair of radiators.

2. An apparatus according to claim 1, wherein the ratio of the maximum circular diameter D of the radiators to the longitudinal length of said radiators falls within the range of 0.6 and 1.7.

3. An apparatus according to claim 2, wherein the portion of the feed lines adjacent the radiators is formed into an impedance matching transition portion to provide matching between the feed line and the radiator.

4. An apparatus according to claim 3 wherein the impedance matching transition portion comprises a pair of tapered members.

5. An apparatus according to claim 4, wherein ratio of the distance d to the maximum circular diameter D falls in the range of 0.02 to 0.1.

References Cited UNITED STATES PATENTS 2,239,724 4/1941 Lindenbald 343807 X 2,683,808 7/1954 Shumaker 343-807 X 2,724,052 11/1955 Boyer 343--830 X 2,939,143 5/1960 Zisler 343-807 X OTHER REFERENCES Draus-Antennas, 1950 NOTK 7872 AGK7-C3, pp. 8 and 9.

The Radio Amateurs Handbook, 1954, pp. 320 and 321, No. TK6550, RI6WC2.

ELI LIEBERMAN, Primary Examiner.