US2421032A

US2421032A - Unidirectional antenna

Info

Publication number: US2421032A
Application number: US497877A
Authority: US
Inventors: Marchand Nathan
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC; Federal Telephone and Radio Corp
Priority date: 1943-08-09
Filing date: 1943-08-09
Publication date: 1947-05-27
Anticipated expiration: 1964-05-27
Also published as: ES178066A1

Description

N. MARCHAND UNIDIRECTIONAL ANTENNA Filed Aug. 9, 1943 5 Sheets-Sheet 1 ATTORNEY May 2?, 1947. N. MARCHAND 2,421,032

UNIDIRECTIONAL ANTENNA Filed Aug. 9, 1945 3 Sheets-Sheet 2 A T TOME Y 1947. N. MARCHl- ND UNIDIRECTIONAL ANTENNA Filed Aug. 9, 1945 '5 Sheets-Sheet :s

INVENTOR. NA THAN MARC/MM!) Arrow Patented May 27, i947 pairs STATES ATENT @FEEQE UNEHRECTIONAL ANTENNA Application August 9, 1943, Serial No. 497,877

15 Claims. 1

This invention relates to radio antennas and in particular to antenna systems having field patterns suitable for either direction finding or directional transmission purposes.

The objects of my invention are:

To provide an antenna system having a field pattern with a unidirectional null.

To provide an antenna system having a field pattern with a sharper unidirectional null than that associated with a cardioid field pattern.

To provide an antenna system which has a sharper directivity than that obtained in the prior art with the same antenna elements.

Other objects will become apparent from the following description taken in connection with the attached drawings showing several illustrative embodiments of my invention and wherein Fig. 1 represents, in plan view, an embodiment of my invention employing a horizontal dipole and a horizontal loop;

Fig. 2 represents in plan view, a second embodiment of my invention employing a pair of horizontal loops and a single horizontal loop.

Fig. 3 represents in plan view a third embodiment of my invention employing a vertical loop and a vertical dipole.

Fig. 4 represents in plan view a fourth embodiment of my invention employing two vertical dipoles and a single vertical dipole.

Figs. 5, 6, '7, and {5 represent various field patterns of the antenna systems of my invention wherein the electrical spacing between the centers of radiation of the non-directional and the directional antenna elements of the array are 45, 90, 180 and 390 respectively.

The manner in which a cardioid field pattern may be obtained from a plurality of antennas is well known in the prior art. For example, if the field pattern of a directional antenna such as a vertical loop is superimposed upon the field pattern of a non-directional antenna such as a vertical dipole and the magnitudes and phase relations of the currents in the loop and the dipole are of the correct value, a cardioid field pattern is obtained. This presupposes that, if the antennas comprise a radiating system, the centers of radiation of the loop and of the dipole coincide. Another of the requirements is that the phase of the current flowing in the dipole is in quadrature with the phase of the current flowing in the loop antenna. The magnitudes of the currents may be chosen such that in one direction in the plane of the loop the resultant field intensity of both antennas together is twice that of either antenna alone and in the other direction the field intensity is zero. In the direction of zero field intensity a null is said to occur. These are the conditions for obtaining a true cardioid field pattern. A variation in the relative magnitudes of the currents in loop and in the dipole results in a change in the field intensity in the direction where it was formerly zero to some finite value, thus destroying the sharpness of the null.

The sharpness of the null in a cardioid diagram is relatively poor or in other words the null is quite broad. It is for this reason that modern direction finding systems employing a cathode ray oscillograph as an indicating means seldom employ an antenna system having a cardioid field pattern. Field patterns having a broad null point are not used in a directional finding system where a high degree of accuracy is desirable, assuming of course, that the direction finding system is based upon the principle of receiving a minimum signal.

The sharpness of the null point of a direction finding system can be likened to the resolving power of optical instrument such as a parabolic mirror or convex lens. For example, it is well known that the resolving power of a mirror depends solely on the diameter of the mirror and not upon the area of its reflecting surface. Similarly the sharpness of a field pattern of an antenna array depends upon the separation of the two outermost antennas of the array and not upon the number of antennas in the array.

A null point in the field pattern of an antenna array is produced by interference between the waves radiated from the individual antenna elements of the array and is sharper when the relative phases of the radiated waves change rapidly with changes in direction of reception from the array. The relative phases change more rapidly with increased antenna spacing.

Applying this principle to the above mentioned loop and antenna system giving a cardioid field pattern it will be seen that the separation of the antennas of the combination is zero or substantially zero at right angles to the plane of the loop and therefore the sharpness of the null point is broad.

In accordance with my invention I increase the sharpness of the null point by providing a substantial separation or spacing between the antenna elements in a direction at right angles to the direction of the desired null.

It is well known that the field pattern of an antenna system or array is the same whether the antenna is employed as a radiating or as a receiving system and it is also recognized that a description of the field pattern of an antenna system can usually be more simply expressed in terms of a radiating rather than in terms of a receiving system. I will therefore describe my invention as it might be employed in a radiating system although it is to be clearly understood that my invention can also be described as it might be employed in a receiving system.

In any radiating or receiving system it is usually desirable to employ either horizontally polarized or vertically polarized waves, and, except in special cases, not a combination of the two. For example, in a direction finding system, where it is desirable to receive the vertical component of a transmitted wave, the reception of th horizontal.

component produces undesirable distortions in the field pattern. A distortion also occurs if a direction finding system is designed to operate on the horizontal component of the transmitted" wave and a portion of the vertical component is received. Furthermore, to assure symmetry of fieldpattern the relative phase of'the currents in th directional and non-directional antennas in the system referred to above should be 90 as is well recognized in the art.

Referring now to Fig. 1, I have illustrated in a plan view one embodiment of 'my invention as comprising a horizontal dipole l and a horizontal loop antenna A. The horizontal field pattern of the dipole l is. substantially two circles lands. Together they form a" figure-of-eight pattern. The horizontal field pattern of the loop 4 is a circle 5. The separation of the centers ofradi'ation of the loop and of the dipole is Ki where K is preferably less than unity and. A is the wave length of the operating frequency. In all figures of the drawingthe center of'radiation of the directional element of the array'is indicated at the point D while the center of radiation for the nondirectional element is indicated at the point. N. An energy translator 5, which may be either a source of radio frequency current in a transmitting system, or a receiver of radio'frequency energy in a direction finding'system, is connected to the dipole I through transmission lines 1 and 8 and is connected to the loop 4 through transmission lines 9 and i respectively; The phase charger I l is connected between the energy translator 6 and theloop 4 in order that the phasing of the currents: to or from the loop as the. case may be, may be controlled. The phase changer could also be placed between the translator Band the dipole I; In accordance with. my invention wherein either horizontally or vertically polarized waves are employed, the phase changer shifts the phase of the current by 90.

In Fig. 2 I have illustrated asecondembodiment of my invention as comprising. two horizontal loops i2 and it for the directive element of my array and a singlehorizontal loop M as the nondirective element. I have omitted showing the energy translator, the phase changer, and the transmission lines from this figure since they would be the samea'sshown in Fig, 1 and would operate in the same manner. The separationof centers of radiation Ki has the same significance as that described in Fig. 1. The distance between the two loop antennas is K'x/ wherein K is a constant less than unity and A is the wavelength at the operating frequency; In other words theseparation of the loops is referably less than a quarter wavelength or less than illl'electrical degrees.

In Fig. 8 Ihavev shown a thirdiembodiment of' my invention wherein the directive element'comprises the vertical loop l5 and the non-directive element comprises the vertical dipole It. Again I have omitted the energy translator, the phase changer, and the transmission lines as they are the same as illustrated in Fig. 1.

In Fig. 4 I have illustrated a fourth embodiment of my invention wherein the directional element comprises two vertical dipoles H and I8 and the non-directional element comprises the vertical dipole l9.

In the above embodiments of my invention, monopoles could be employed in place of the vertical dipole antennas.

Referring now to Fig. 5 I have illustrated by the cllrve 2%! the field pattern which results when the centers of radiation of the directional and non-directional elements of the antenna array are spaced apart a distance corresponding to 45 electrical degrees of the operating wave-length. It will be observed that the pattern has a null which is considerably sharper than that obtained from a system wherein the directional and nondirectional elements are substantially superimposed and wherein the fieldpattern is the wellknown cardioid. diagram..

In Fig, 6 I have illustrated by'curve 2| the field pattern which results when the directive and nondirective elements are separated by a distance corresponding to electrical degrees. It Will be seen from this curve that the null point is considerably sharper than that of the curve 20 of Fig. 5. It will also be observed that the sides of the diagram begin to pinch in.

In Fig. 7 the curve 22 represents the field pattern which results when the centers of radiation of the directional and non-directional antennas are spaced apart a distance corresponding to electrical degrees. Again it will be noticed that the sharpness of the null increases over that illustrated by the curve 21 in Fig; 6i The sides furthermore have been pinched in to a degree where other'nulls may besaid to be forming.

In Fig. 81 have illustrated by curve 23 the field pattern which results when the directive and non-directive antenna elements are separated a distance corresponding to 300' electrical degrees. The sharpness of the null is now well defined as will be'seen by comparison with the curves of the other figures showing different degrees of antenna separation. The curve 23 represents about the upper limit of practical separation of theantennas because at this separation the sides of the curve are such that two other minimums 24 and zebecome very prominent and an operator of a direction finding system might be confused by an apparent multiplicity of. nulls. However, a field pattern as shown by curve 23. might prove useful in'radiation'systems.

The lowerpractical limit of separation is not as well definedas the upper limit since with small separations there is only one null in the field pattern and the sharpness of. the null increases with the antenna spacing; However, an antenna separation of one-twelfth wavelength would provide a field: pattern having a marked improvement. in the. sharpness of the pull. over thatof a cardioid.

While I have described above the principles of' my 'invention' in conn'ectionlwith specific antenna types it is. to be. clearly understood that this description is made by way of example and not as a limitationon' the scope of my invention as set forth in the objects and the accompanying claims.

I'claim'r 1. An antenna system comprising a directional antenna element having a center of radiation, a non-directional antenna element having a center of radiation, said centers of radiation being spaced apart a distance between one-twelfth and one wave-length of the operating frequency in a direction normal to the principal plane of radiation of said directive antenna element.

2. An antenna system in accordance with claim 1 wherein said directional antenna element comprises a vertical loop and said non-directional antenna element comprises a vertical dipole.

3. An antenna system in accordance with claim 1 wherein said directional antenna element comprises a horizontal dipole and said non-directional antenna element a horizontal loop.

4. An antenna system in accordance with claim 1 wherein said directional antenna element comprises a pair of horizontal loops and said nondirectional antenna element comprises a single horizontal loop.

5. An antenna system in accordance with claim 1 wherein said antenna elements are of a type susceptible to the reception of horizontally polarized waves only.

6. An antenna system in accordance with claim 1 wherein said antenna elements are of a type susceptible to the reception of vertically polarized waves only.

'7. An antenna system in accordance with claim 1 wherein the distance between said centers of radiation is greater than one-twelfth of the wavelength.

8. An antenna system in accordance with claim 1 wherein said directional antenna element has a substantially figure-of-eight field pattern.

9. An antenna system comprising a directional antenna element having a center of radiation, a non-directional antenna element having a center of radiation, said centers of radiation being spaced apart at least one-twelfth of the wavelength of the operating frequency, said nondirectional antenna element lying in a plane passing through said center of radiation of said directional antenna element and being perpendicular to the plane in which the directivity of said directional antenna element lies.

10. An antenna system. comprising a directional antenna element and a non-directional antenna element spaced apart a distance equal to at least one-twelfth of the wavelength of the operating frequency in a direction normal to the plane of directivity of said directional antenna element whereby the antenna field pattern has a unidirectional null sharper than that of a cardioid obtained with similar non-spaced antenna elements.

11. A directional receiving antenna array comprising a directional antenna element and a nondirectional antenna element said antenna elements being spaced apart a distance equal to at least one-twelfth of the wavelength of the operating frequency in a direction normal to the plane of directivity of said directional antenna element, a receiver, coupling means coupling said antenna elements to said receiver, said coupling means comprising phasing means whereby the energy received by said antenna elements is applied to said receiver in a predetermined phase relation.

12. An antenna system comprising a directional antenna element having a center of radiation, a non-directional antenna element having a center of radiation, said centers of radiation being spaced apart a distance equal to at least one-twelfth of the wavelength of the operating frequency in a direction normal to the plane of directivity of said directional antenna element, a source of high frequency current, coupling means coupling said source to said directional and non-directional antenna elements, and phasing means whereby the phase of the current flowing in said non-directional antenna element bears a predetermined relation with the phase of the currents in said directional antenna element.

13. An antenna system in accordance with claim 11 wherein said predetermined phase relation is substantially 14. An antenna system in accordance with claim 1, wherein said directional antenna element is comprised of a pair of spaced antennae.

15. An antenna system comprising a directional antenna element having a center of radiation, a non-directional antenna element having a center of radiation, said centers of radiation being spaced apart a distance greater than 30 electrical degrees and less than 300 electrical degrees at the operating frequency.

NATHAN MARCHAND.

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

UNITED STATES PATENTS Number Name Date 2,286,839 Schelkunoflf June 16, 1942 2,030,181 Potter Feb. 11, 1936 1,296,177 Franklin Mar. 4, 1919 2,002,430 Chromy May 21, 1935 2,256,619 Luck Sept. 23, 1941 OTHER REFERENCES Directive Diagrams of Antenna Arrays, by Ronald M. Foster, Bell Telephone Laboratories, Inc., May 1926.

Aero Digest, November 1936, pages 32, 33, 34,36.