US3015823A

US3015823A - Helical antenna null suppressor

Info

Publication number: US3015823A
Application number: US793822A
Authority: US
Inventors: Paul M Pan
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1959-02-17
Filing date: 1959-02-17
Publication date: 1962-01-02
Anticipated expiration: 1979-01-02

Description

Jan. 2, 1962 I P. M. PAN I 3,015,823

HELICAL ANTENNA NULL SUPPRESSOR Filed Feb. 17 1959 2 Sheets-$heet 1 Pk/OR ART I I 0 Z NW 55- V 26A 26B 0 d E za 0 180 300 AZIMUTH ANGLE SIGNAL SOURCE INVENTOR. Paul M. Pan

/11A BY SIGNAL SouRcE M ATTO EY Jan. 2, 1962 I P. M. PAN 3,015,823

HELICAL ANTENNA NULL SUPPRESSOR Filed Feb. 17. 1959 2 Sheets-Sheet 2 FIG. 9

I SIGNAL Z SouRcE 5:

10B O .J Lu LT. FIG. 7 o

AZIMUTH ANGLE INVENTOR.

SGML Paul M. Pan

SouRcE BY United States Patent Ofifice 3,015,823 Patented Jan. 2, 1962 Generally, electromagnetic radiation systems.'include I I an antenna and a signal source for exciting the antenna. Currents flowing through the antenna while under excitation cause electromagnetic waves to be radiated by the antenna. The direction and intensity of propagation of the electromagnetic waves is the radiation pattern of the electromagnetic radiation system. In many applications, such as the transmission of television signals from a transmitter to numerous receivers surrounding the antenna, a pattern in an azimuth plane is desired.

Often it is not only sufiicient to develop a radiation pattern in the azimuth plane, but the intensity-of the radiation at particular azimuth anglesmust be controlled. For example, if it is known that a substantial portion of the receivers are in a particular sector of the plane, it is ,de-

sirable to form the radiation in a beam directed towards that particular sector. On the other hand, when the receivers are generally distributed throughout the entire azimuth plane, and omnidirectional pattern is desired.

The form of the radiation pattern is generally determined by the geometrical and electrical properties of the antenna. In one particular case, an antenna with a particular helical geometry has been foundadmirably suited for omnidirectional propagation of electromagnetic radiation throughout the azimuth plane. Although such an antenna presents a radiation pattern that is substantially uniform throughout the azimuth plane, there is one narrow sector of the plane having an appreciable diminution of field strength. This sector may be termed the main null. The main null occurs because of the electromagnetic discontinuities at the coupling between the feed system and the antenna, introducing improper phase and amplitude distributions.

Heretofore, the main null has been cancelled by stacking a plurality of these antennas in a multi-bay system and by properly phasing each bay. However, it is more desirable to reserve the bay phasing to control the elevation pattern of the radiation. Further, the trend is toward the use of single bay systems because of the saving in apparatus and because of their smaller size. In single bay systems, there is no chance to cancel the main null by the proper phasing of the bays. In addition, these antennas have bandwidths of several percent of the operating frequency. Often this bandwidth is satisfactory but there are instances where broader beam bandwidths are desirable.

It is accordingly an object of the invention to provide an improved helical electromagnetic radiation system.

It is another object of the invention to provide an improved helical electromagnetic radiation system which transmits a modified radiation pattern which approaches a desired pattern.

It is a further object of the invention to provide an improved electromagnetic radiation system which includes an antenna having a particular helical geometry that minimiles the main null in the radiation pattern.

It is a still further object of the invention to provide means for increasing the beam bandwidth of a helical antenna.

Briefly, the invention is embodied in an electromagnetic radiation system which comprises a radiating transmission line, having a helical configuration means for exciting the radiating transmission line and means for introducing a discontinuity at a point along theradiating transmission line to modify the pattern of radiation transmitted by the electromagnetic radiation system.

Other objects, features and advantages of the invention will be evident from the following-detailed description when read with the accompanying drawings wherein:

FIGURE 1 is a diagrammatic representation of a portion of tin-electromagnetic radiation system, employing a-helical radiative element, which is useful in describing the theory of the invention;

' FIGURE 2 is a graph of field intensity (the abscissa) as a function of azimuth angle (the ordinate) of the radiation pattern of the electromagnetic radiation system of FIGURE 1;

FIGURE 3 is a diagrammatic representation of a portion of an electromagnetic radiation system employing a helical radiative element shown in-=perspective, inaccordance with one embodiment of the invention;

FIGURE 4 is a sectional, viewof the system of FIG- URE 3 taken along the line 4-4 of FIGURE 3;

FIGURE 5 .is a diagrammatic representation of a portion of an electromagnetic radiation system, employing a helical radiative element shown in perspective, in accordance .with another embodiment of the invention;

FIGURE 6 is a sectional .view of the system of FIG- URE 5 taken along the line-6-6 of FIGURE 5; i FIGURE7 is a schematic representation of a portion of an electromagnetieradiation system employing a helical radiative element; shown in perspective .in accordance with a further embodiment of the invention;

FIGURE 8 is a sectional view of thesystem of FIGURE 7- taken along the ;line 78-8 of FIGURE 7; and;

FIGURE 9 is a graph similar to the graph of FIGURE 2 to show the radiation pattern after the suppression of the-main null.

Referring to FIGURE 1, a portion of an electromagnetic radiation system 10 is shown comprising a signal source 11 feeding an antenna 12. The antenna structure 12 is a diagrammatic representation of an electromagnetic radiation structure useful in describing the theory of the invention and may be of the type disclosed in British Patent No. 724,795 Improvements in and Relating to Antenna Structures of the assignee of the present application, which is to be regarded as prior art with respect to this present application. The signal source 11 generates a signal having a given carrier frequency or operating wavelength. Theantenna 12 comprises a hollow cylinder 14 of an electrically conductive material, and

first and

second helices

16 and 18 of electrically conductive material developed about and spaced from hollow cylinder 14. Helix 16 starts from a point near a feed point or hole 22 .in hollow cylinder 16 and progresses in a series of turns towards one end of hollow cylinder 14, and helix 18 starts from the same point and progresses in a series of turns towards the other end of hollow cylinder 14. Each turnof both helices 16 and 1 8 is an integral number of operating wavelengths in length. It should be noted that although one turn of each of the

helices

16 and 18 is shown, these helices in general comprise a plurality of turns. Helix 16 and the portion of the surface of hollow cylinder 14 under helix 16 may be considered as a two-conductor transmission line. Similarly, helix 18 and the portion of the surface of hollow cylinder 14 under helix 18 may be considered as a two-conductor transmission line.

. conductive support structure.

In particular, the helix 16 and the helix 18 are helical radiative conductors which extend in axially progressive turns about the hollow cylinder 14, which functions as a The helix 18 is shown as a righthanded helix, that is, it is developed about the and bosses in the form of

screws

44 and 46 are fixed in hollow cylinder 1413 under helix 16B. It should be noted that screws have the added advantageo'f permitting fine adjustments of the lumped impedances. The

screws

40 and 42 are located under helix 183 at a point where there is a very great change in .the near field associated with the helix 1813. This change will be somewhere between one-sixth and one-quarterof an operating wavelength from hole 228. The

screws

44 and 46 are similarly located in hollow cylinder 14B under helix A further embodiment of the invention is shown in the electromagnetic radiation systemlOC of FIGURES 7 and 8. Electromagnetic radiation system 100 is similar to electromagnetic radiation system 10 of FIGURE 1 except for the introduced lumped'impedances and reference characters with a postscript C will be used to designate like elements and only the differences will be discussed in detail.

More particularly, a parasitic element 50 is interposed in the space between helix 18C and hollow cylinder 14C, and a similar parasitic element 52 is interposed in the space between helix 16C and hollow cylinder 14C. The parasitic element 50 is located between one-sixth and one-quarter of an operating wavelength from the hole 22C along the length of helix 18C. The exact position is determined by the above-mentioned near field measurements. Parasitic element 52 is similarly positioned.

The parasitic element 50 is a length of electrical conductor 54 supported'on dielectric standotf 56 (FIG. 8).

lectrical conductor 54 is disposed parallel to helix 18C. It should be noted that near field measurements will be required to determine the length of electrical conductor 54. That is, the length of electrical conductor 54 is correct when the near field phase and amplitude distribution measurements are proper.

It should be noted that by employing the various embodiments of the invention, it is possible to not only suppress the main null by 4.5 to 6.5 decibels but also to increase the beam bandwidth to greater than ten percent. FIGURE 9 shows such an improvement in the radiation pattern.

There has thus been disclosed improved electromagnetic radiation systems which transmit modified radiation patterns that approach a desired radiation pattern. In particular, the electromagnetic radiation systems, according to several embodiments of the invention, transmit radiation patterns in an azimuth plane that are omnidirectional with substantially constant field strength in all azimuth directions because the main null has been suppressed. There has further been disclosed, in electromagnetic radiation systems which include antennas having a particular helical geometry, means for minimizing the main null in the radiation pattern. In fact, by employing the embodiments of the disclosed lumped impedances it is possible to cause a diminution of the main null by up to eight decibels.

While only several representative embodiments of the invention have been disclosed in detail, there will be obvious to those skilled in the art many modifications and variations accomplishing the foregoing objects and realizing many or all of the advantages but which do not depart essentially from the spirit of the invention.

What is claimed is:

1. An electromagnetic radiation system comprising a first electrical conductor, said first conductor being substantially linear, a second electrical conductor developed about said first electrical conductor in a helical configuration, said first and second electrical conductors cooperating to provide a radiating transmission line, a source of signal of given operating wavelength for exciting said radiating transmission line, coupling means for coupling said source of signal to said radiating transmission line, and loading means for introducing a cancelling discontinuity positioned in a region along the length of said radiatingtransmission line to minimize the main azimuth null in the radiation pattern caused by the electromagnetic discontinuity introduced by said coupling means.

2. The electromagnetic radiation system of claim 1 wherein said means for introducing the cancelling discontinuity is snug of electrically conductive material developed about said second electrical conductor. 3. The electromagnetic radiation system of claim 1 wherein said means forintroducing the cancelling discontinuity is a ring material of high dielectric constant developed aboutsaid second electrical conductor.

The electromagnetic radiation system of claim 1 wherein said means for introducing the cancelling discontinuity is a screw fitted in said first electrical conductor.

5. The electromagnetic radiation system of'claim 1 wherein said means for introducing the cancelling discontinuity is a parasitic element disposed between said first and second electrical conductors.

6. The electromagnetic radiation system of claim 1 wherein the region of introduction of said cancelling discontinuity along said radi-atable transmission line is where there is a very large change in the near field.

7. The radiation system of claim 1 wherein the region of introduction of said cancelling discontinuity along said radiatable transmission line is between one-sixth and onequaiter of an operating wavelength from said coupling means.

8. An electromagnetic radiation system comprising a first electrical conductor, said first electrical conductor being substantially linear, a second electrical conductor developed about said first electrical conductor and extending toward a first end of said first electrical conductor, a third electrical conductor developed about said first electrical conductor and extending toward the second end of said first electrical conductor in a helical configuration, said first, second and third electrical conductors cooperating to provide a radiata-ble transmission line system, a source of signal of given operating wavelength for exciting said radiatable transmission line system, coupling means for coupling said source of signal to said radiatable transmission line system, and loading means for introducing cancelling discontinuities positioned in regions along said radiatable transmission line system to minimize the main azimuth null in the radiation pattern caused by the electromagnetic discontinuity introduced by said coupling means.

9. The electromagnetic radiation system of claim 8 wherein said means for introducing cancelling discontinuities are rings of electrically conductive material developed about said second and third electrical conductors.

10. The electromagnetic radiation system of claim 8 wherein said means for introducing cancelling discontinuities are rings of high dielectric constant material developed about said second and third electrical conductors.

11. The electromagnetic radiation system of claim 8 wherein said means for introducing cancelling discontinuities are screws fitted in said first electrical conductor.

12. The electromagnetic radiation system of claim 8 wherein said means for introducing cancelling disc0n tinuities are parasitic elements inter-posed between said first and second electrical conductors and between said first and third electrical conductors.

13. The electromagnetic radiation system of claim 8 wherein the regions of introduction of said cancelling discontinuity along said transmission line system is where there is a great change in the near field.

14. The electromagnetic radiation system of claim 8 wherein the regions of introduction of said cancelling discontinuities along said radiatable transmission line system are from :between one-sixth and one-quarter of an operating wavelength from said coupling means.

15. An electromagnetic radiation system comprising a cylindrical conductor, a first radiative conductor, said first radiative conductor being a ri ghthanded helix of given pitch developed about said cylindrical conductor toward a first end of said cylindrical conductor, a second radiative conductor, said second radiative. conductor being a lefthanded helix of the same given pitch developed about said cylindrical conductor toward the other end, each of the turns of each of the helices of said radiative conductors having the same integral number of. operatin'g wavelengths, said cylindrical conductor andfsaidfir'st and second radiative conductors cooperatively disposed ,to

irig means coupled to said first and second "radiative con ductors to, feed signal energy to said first and 'Seepnd radiative conductors, and means for introducing cancelling discontinuities at regions along said radiatable transmission line system to minimize the main null-in the radiation .1 provide a radiatable transmission line system, signal fe'd- 8 pattern caused by the electromagnetic discontinuity introduced said coupling means. 7

j References Cited in thefile of this patent UNITED STATES PATENTS