US2622199A

US2622199A - Radio aerial system

Info

Publication number: US2622199A
Application number: US53806A
Authority: US
Inventors: Ramsay John Forrest; Peat John Dewar
Original assignee: Marconis Wireless Telegraph Co Ltd
Current assignee: Marconis Wireless Telegraph Co Ltd
Priority date: 1948-04-16
Filing date: 1948-10-11
Publication date: 1952-12-16
Anticipated expiration: 1969-12-16

Description

Dec. 16, 1952 J. F. RAMSAY ET AL 2,622,199

RADIO AERIAL SYSTEM Filed Oct. 11, I948 Patented Dec. 16,1952

RADIO AERIAL SYSTEM John Forrest Ramsay, Chelmsford, and John Dewar Peat, Great Baddow, England, assignors to Marconis Wireless Telegraph Company Limited, London, England, a company of Great Britain Application October 11, 1948, Serial No. 53,806 In Great Britain April 16, 1948 7 Claims.

This invention relates to radio aerial systems and more particularly to such systems incorporating dipole, unipole, half-wave, quarter-wave and similar aerial elements. For the sake of brevity in description dipole aerial elements will be almost exclusively referred to in this specification but as will be apparent later the invention also applies to systems incorporating unipole, quarter wave and like elements.

The electric field from a horizontal dipole contains a vertical component of polarization except at points in a vertical plane perpendicular to the dipole axis through the center of the dipole where the field is purely horizontally polarized. The existence of vertical components of polarization at points in space removed from this plane is a more or less serious disadvantage for many purposes; for example, with the so-called omni-directional range beacon method of radio navigation it is very desirable that the vertical component shall be absent at all angles both as regards the omni-directional beam and the rotating beam.

The present invention seeks to provide improved aerial systems whereby the vertical component of polarization in the field of a horizontal dipole or like aerial elements may be substantially eliminated. Though not limited to its application thereto the invention is, therefore, of particular advantage when applied to the aerial systems of so-called omni-directional range beacons.

According to this invention a dipole or like aerial element is mounted in a screen constituted by a tubular wave guide having its axis substantially at right angles to the element axis and provided with a plurality of resonant slots cut in the wall of the tube substantially parallel to the axis thereof. The screen thus constituted is substantially transparent to horizontal polarization and substantially opaque to vertical polarization with the result that the combination or the aerial element and screen provides for practically complete elimination of the vertical component.

The invention is illustrated in the accompanying drawings which show two embodiments in simplified schematic perspective. Like references are used for like parts in both figures.

Referring first to Fig. 1 a horizontal dipole I is mounted centrally within a tubular screen or wave guide 2 whose ends are closed by conductive plates 3, 4 and whose axis is vertical, said screen or wave guide being provided with equally spaced vertical slots 5 in its circumferential wall each slot being about half of a wave length (in free space) long. The axial length of the wave guide is preferably about half a wave length (in the wave guide) long, i. e. half a guided wave length long.

screen. Such a combination of dipole I loop 6' The number and width of the slots may be varied within fairly wide limits and preferably, though not necessarily, the horizontal dipole is substantially at the center of the vertical tubular radiating cavity constituted by the wave guide.

The dipole element excites an H mode as the dominant mode, the diameter of the tube 2 being so chosen that other modes-notably the E010 mode--liable to be produced by vertical support provided for the dipole are practically negligible. The slots are excited by the transverse currents associated with the H111 mode, those on or near the dipole axis being extremely weakly excited While those on or near the perpendicular to the axis being fully excited. The radiation pattern in the horizontal plane thus tends to form a figure-of-eight with the axis of the eight perpendicular to the dipole axis. By rotating the dipole the figure-oi-eight pattern may be rotated.

The vertical radiation pattern is substantially the magnetic plane pattern of a magnetic dipole and is substantially uniform in all vertical planes as the electric dipole is rotated. The combination rotating aerial element and wave guide screen may be regarded as equivalent to a cylindrical array of magnetic dipoles and accordingly the solid radiation pattern is substantially free from vertically polarized components.

The wave guide or screen is not of necessity half a guided wave length long nor need the dipole element be centrally situated with regard to the slots for itmay be above or below the ring of slots, the wave guide proper in that case being made longer. For example, the dipole element may be situated about a quarter of a guided wave length from the bottom or top plate of the guide proper (or from a transverse piston like closure member therein) and may excite a travelling H1 mode in the solid tubular guide. The distance between the dipole and the center of the slots may be varied within fairly wide limits but may conveniently be one half of a guided wave length.

If, as above set forth, the electric dipole is displaced with regard to the slots, i. e. is beyond their ends, a p source of radiation may be arranged horizontally with its axis coinciding with the axis of the tubular wave guide, said loop being arranged in the horizontal plane bisecting the lengths of the slots. Such an arrangement is shown in Fig. 2 in which I is the dipole and 6 is the loop. Since the diameter of the guide tube 2 is below cut oil for the H0 mode the screen constituted thereby will be purely reactive in nature. The radiation pattern of the loop 6 will therefore not be seriously affected by the presence of the 3 and screen 2 constitutes a very advantageous structure for an omni-directional range beacon.

It will be noted that the invention enables two serious difiiculties encountered with known aerial systems, of the, nature, in question to be avoided namely (1) that of obtaining bi-directional and omni-directional aerial elements with identical zenithal polar diagrams and (2) that of avoiding pattern distortion due to phase differences caused by the physical separation of, thetwo aerial elements. These difficulties areovercome because, in carrying out the present invention (1) the, two aerial elements radiate identical zenithal polar diagrams and (2) the energy from the said two elements is radiated from the same apparent,

point source.

As already stated, instead of using a dipole a unipole or like element may be employed,

What we claim is:

1. An aerial system including ahdipoleiand a loopradiatoraerial. element mounted within a screen constituted by a tubular wave guide with its axis substantially perpendicular to the axis of said dipole andv parallel to the axis of said loop radiator, said guide havinga plurality of resonant slots formed in, its wall with their lengths substantially parallel to the guide axis, said dipole being positioned in the unslotted length of said guide and, said loopradiator being mounted substantially in a plane bisecting the lengths of said slots.

2. An aerial system including a dipole and a loop radiator aerial element mounted in a screen constitutedby a tubular wave guidewith its axis substantially perpendicular to the axis of said dipole and substantially parallel to the axislof saidloopradiator, said guide being of substantiallytubular section and having a length of substantially half a guided'wave length, measured in the guide at the operating frequency and having aplurality of resonant slots each substantially half a wave length long, in free space, at the operating frequency formed in its wallwith. their lengthssubstantially parallel to the guideaxis, and said dipole being positionedin the unslotted length of, said guide and, said, loop radiator being mounted substantially in a plane bisecting ,the lengthsof said slots.

3, Any omni directional radio beacon aerial system comprising in combination a linear aerial elementmounted withits, axis substantially hori: zo ntal in ascreen constituted by a substantially vertical tubular wave guidea loop aerial element,

mounted in said screen with its axis. substantially vertical, said guide having a plurality of narrow elongated substantially vertical, resonant slots formed in itswall said slots being of, equal length and disposed in a-singlerow and extending only along part of thelength of said screen, saidlinear aerial element being disposed within said screen and displaced'from the terminating ends of said resonant, slots whereby radiated vertically polarized components of the electricv st tuted bra-su stantial y vertical tubules-waves guide having a tubular wall portion and a plurality of narrow elongated substantially vertical resonant slots formed in the wall portion, each substantially a half wave length long, said slots being arranged with their directions of length parallel to the axis of the guide and in the form of a ring of slots extending around said guide, the lengths of said slots lying on the surface of an imaginary cylinder which is co-axial with said guide and withinsaid guide, a linear aerial element having its axis substantially horizontal and disposed Within the tubular wall portion of said guide displaced from the ends of the slots therein,

a loop aerial element having its axis substantially vertical andrdisposed within the slotted portion oi'saidywaveguide, whereby the radiating vertically polarized components of the electric field from, said elements are substantially eliminated while horizontally polarized components are radiated; substantially without, loss by the energization of, said, slots.

7. A radio beacon aerial system having a slotted guide comprising in combination a screen constituted byhasubstantially vertical tubular wave guide having a plurality of narrow elongated substantially vertical resonant slots formed in the wall portion-and an unslotted wall portion, each slot substantially a half wave length long, said slots being arranged with their directions of length parallel to theaxisof theguide and in the form of a ring of slots. extending around said guide, the lengths of said slots lying on-the surface of .an imaginary cylinder which is oo-axial with said guide, and. withinsaid. guide, a rotatable dipole having its axis extending transversely of saidguide in said unslotted portion of said guide remote from the terminating ends of said slots, a horizontally disposed loop aerial in the slotted portion of said guide in a plane half way between the, terminating ends of said slots, whereby the radiatingvertically polarized components of the electric field from said dipole and from said loop are substantially eliminated while horizontally polarized components are radiated substantially without loss by the energization of said slots.

JOHN FORREST RAMSAY. .JOHN DETWARPEAT.

- REFERENCES CITED Thefollowing references are of record in the file of. this patent;

UNITED STATES; PATENTS Num er Na Date 2,407,068 Fiske et al Sept. 3, 1946 2,414,266 'Lindenblad Jan. 14, 1947 2,415,094 Hansen et a1 Feb. 4, 1947 2,432,990 Hansen Dec. 23, 1947 2,433,924 Riblet Jan. 6, 1948 2,460,286 Hansenvet al Feb. 1, 1949 2,465,416 Aram Mar. 29, 1949 2,482,162, Feldman Sept. 20, 1949 2,489,288 Hansen Nov. 29,1949

FOREIGN PATENTS Number Country Date 5383;665 France July'12, 1943 OTHER REFERENCES Riblet: Microwave Omnidirectional Antennas-.:"Proc. IRE, vol. 35, May 1947, pages 4'74 to 478.

Benoit; Omnidirectional centimetre-Wave Aerial/I Proc.;IRE,,Abstr-act No. 957. Vol.36, May lfififinpal fiififii