US2989746A

US2989746A - Scanning antenna system utilizing polarization filters

Info

Publication number: US2989746A
Application number: US677693A
Authority: US
Inventors: Ramsay John Forrest
Original assignee: Marconi Co Ltd
Current assignee: Marconis Wireless Telegraph Co Ltd; BAE Systems Electronics Ltd
Priority date: 1956-08-21
Filing date: 1957-08-12
Publication date: 1961-06-20
Anticipated expiration: 1978-06-20

Description

June 20, 1961 .1. F. RAMSAY 2,989,746

SCANNING ANTENNA SYSTEM UTILIZING POLARIZATION FILTERS Filed Aug. 12, 1957 2 Sheets-Sheet 1 J. F. RAMSAY June 20, 1961 SCANNING ANTENNA SYSTEM UTILIZING POLARIZATION FILTERS 2 Sheets-Sheet 2 Filed Aug. 12, 1957 F/GJ.

INVENTOR jrrfirv 70% ATTORNEY! United States Patent 2,989,746 SCANNING ANTENNA SYSTEM UTILIZING POLARIZATION FILTERS John Forrest Ramsay, St. Laurent, Quebec, Canada, as-

siguor to Marcouis Wireless Telegraph Company, Strand, London, England, a company of Great Britain Filed Aug. 12, 1957, Ser. No. 677,693 Claims priority, application Great Britain Aug. 21, 1956 1 Claim. (Cl. 343-761) This invention relates to aerials and has for its object to provide improved aerials suitable for use for example in radar systems for projecting or receiving radio beams which are scanned in azimuth and/or elevation or in radio communication systems, such as microwave links, for transmitting or receiving one or more directional radio beams in one or more different directions.

The specification accompanying co-pending application Ser. No. 485,055, now abandoned, describes aerial systems which may, for the sake of brevity, be referred to as barrel aerials and in which there is a plurality of plane polarized radiator elements arranged on a surface of revolution embracing at least 180 of arc, the planes of polarization of radiator elements substantially diametrically opposite each other across the axis of the surface of revolution being mutually substantially perpendicular. In the simplest embodiments of the prior invention the barrel axis is vertical and the radiator elements are wires running at 45 to the horizontal. A 45 polarized beam of radio waves is projected from a point inside the barrel towards the inner surface thereof. As explained in the said co-pending specification the radiator elements first struck by the beam of radio waves act as substantial total reflectors to reflect the said beam diametrically across the barrel where they encounter other radiator elements which are substantially transparent to the beam which accordingly is projected into space.

The aerial structures described in the said co-pending application Serv No. 485,055, now abandoned, present certain practical disadvantages from the point of view of manufacture, more especially in those cases in which the radiator elements are wires and the height of the aerial, i.e. the dimension along the length of the axis, is considerable. These practical disadvantages from the point of view of manufacture arise by reason of the fact that the curve which has to be followed by a radiator element along the surface of revolution in order to satisfy the requirement that one radiator element shall be a substantially total reflector and the opposite one substantially transparent to a given polarized wave, is a very complex one and it is accordingly a long and tedious process to make such an aerial. Particularly is this the case if the aerial is of substantial axial height as it is commonly required to be. The present invention seeks to overcome the aforesaid defect and to provide aerial structures operating on the same principles as those described in co-pending application Ser. No. 485,055, now abandoned, and which shall be easier to make while being of closely comparable performance.

According to this invention an aerial structure comprises a plurality of ring-like sections each of which is composed of a plurality of plane polarized radiator elements arranged on a surface of revolution embracing an arc of more than 180, the planes of polarization of radiator elements arranged diametrically opposite one another in the same direction being mutually substantially perpendicular, the axes of the surfaces of revolution of the sections being co-linear and the said surfaces of revolution adjoining one another on a common surface of revolution.

Preferably the common surface of revolution is para- See bolic but it may, in some cases be preferred to make it elliptical. It may also take other shapes, e.g. spherical.

Preferably the arc embraced is 360.

The invention offers its maximum advantages, from the practical point of view, when the radiator elements are wires.

In the preferred constructions in accordance with the invention each radiator element is a wire shaped to follow the direct projection, on the surface of revolution of the section to which it belongs, of a line which is at 45 to the tangent to the mid-circular arc of that section at said line and which is in the common plane of said tangent and said line. In these constructions the radiator elements of each section may be readily constituted by parallel wires in a woven cloth strip which is bent to follow the surface of the section and which is composed of wires and insulating material (e.g. glass thread) the wires running at 45 to the length of the strip when the latter lies flat.

It will be appreciated that the preferred constructions last mentioned do not comply with theoretical requirements since, theoretically, the angle of each radiator element in any given section will be precisely correct only at the point where it crosses the middle circular arc of that section the departure from the theoretical angle increasing with distance from the point of intersection of a radiator element with the mid-circular arc. However, since the height of any particular section may be kept small, the maximum deviation from theoretical requirements in any section may be also kept small and by suitably choosing the number of sections there may be obtained a relatively easily made aerial of considerable axial height which, though not complying precisely with theoretical requirements, will depart from those requirements by only a small tolerable extent.

The invention is illustrated in the accompanying drawings which show diagrammatically and schematically one embodiment thereof and wherein:

FIG. 1 is a diagrammatic elevation of one form of aerial embodying my invention;

FIG. 2 is a diagrammatic plan view of the form of aerial shown in FIG. 1; and

FIG. 3 shows a modified form of my invention in which strips of wire are woven in cloth and employed as part of the aerial system.

Referring to the drawings, the aerial therein shown may be termed a half barrel aerial mounted with its axis vertical. The bottom on the aerial is shown at 1 and the top, which is a circular hole, is represented at 2. The aerial consists of six sections laid vertically on top of one another and each consisting of a plurality of polarized radiator elements lying on a 360 surface of revolution and constituted by wires. The six sections are referenced 3 to 8 inclusive.

The wires in each section are shaped to follow the direct projection on the surface of revolution of the section to which it belongs, of a line which is 45 to the tangent to the mid-circular arc of that section at said line and which is in the common plane of said tangent and said line. Thus, for example, to take the section 6, the mid-circular arc of that sectiona complete circle since the arc is 360-is indicated by the broken line 10. If one imagines a plane which is tangential to the are It) at the point where a given radiator element crosses that are, said plane including the tangent to the are at that point, and if one imagines a line in that plane drawn at 45 to the said tangent, then the path followed by the radiator element on the surface of revolution constituted by the section 6 is chosen to be the direct projection of the said line on the said surface of revolution.

All the radiator elements for a typical practical case are shown in FIGS. 1 and 2 for the case of the section 6, but so as not to complicate the drawing only a few typical radiator elements are shown for each of the other sections 3, 4, 5, 7 and 8. In practice the radiator element spacing will be about the same in each section.

The shapes of the surfaces of revolution in which the various sections lie are so chosen that the said surfaces combine to make a single surface of revolution which, in the example illustrated in FIGS. 1 and 2, is parabolic in shape. If, therefore, a divergent radio beam is projected from an internal radio horn or like device represented at 9 so as to project a beam which spreads more or less over the full height of the aerial, that beam will be substantially totally reflected where it first strikes the inside of the aerial and will pass diametrically across the same to go substantially unimpeded through the diametrically opposite portion of the aerial. This is indicated by the arrow-headed broken lines in FIGS. 1 and 2. If as in the case illustrated, the shape of the aerial is parabolic, the emergent beam will be theoretically at any rate, a parallel sided beam. The shape of the aerial may be selected in dependence of the form of the emergent beam required: for example, if it is of major importance to keep aberration at a minimum an elliptically shaped aerial may be preferred to a parabolically shaped one.

FIG. 3 shows, in expanded form for the sake of simplicity in drawing, a woven cloth having parallel to one another at regular intervals, strips of wire (shown shaded) which are woven into the cloth. Strips of such cloth may constitute the strips, such as the strip 3, shown in FIG. 1.

The aerial just described has the advantage that it is a great deal easier to make than those described in the co-pending application Ser. No. 485,055, now abandoned. Thus a very close approximation to theoretical require ments (as regards radio reflection followed by transmission through the aerial) will be obtained if each section is constituted by bending a parallel sided strip of woven material shown in FIG. 3 consisting of wires 15 and insulating' (e.g. glass) threads 14 into the shape of the section, the wires in the woven material lying at 45 to the length of the step when flat. If such woven strips of widths substantially equal to the desired height dimension of the sections and of lengths substantially equal to the desired circumference dimensions of the sections are laid on a former shaped to the desired final barrel and made of suitable material, the wires in the woven cloth will take up, for all practical purposes, their required positions. An aerial as shown in FIGS. 1 and 2 may, therefore, be made by preparing a former of the required shape and simply sticking lengths of wire woven cloth shown in FIG. 3 in the former, impregnating the final structure to the required mechanical rigidity and strength in any convenient manner known in the art of making solid structures from woven glass materials.

If the element 9 is rotated round a circle having the axis of the aerial as center the emergent beam will be scanned in azimuth. For obvious optical reasons the 4 maximum radius of the circle is chosen as at about one half the maximum radius of the aerial in a case as illustrated in FIGS. 1 and 2 where the aerial is parabolic and a parallel sided emergent beam is required. It is, of course, not necessary to use a scanning source of radiation: for example, where the aerial is to be employed in a microwave link, one or more fixed sources pointing in different directions corresponding to the required directions of communication (more precisely at 180 to those directions) may be arranged inside the aerial. Again, although the described construction of wire elements constituted by wires woven into a cloth as shown in FIG. 3 is preferred, the individual radiator elements may take any form known per se, e.g. they may be constituted by more or less rigid wires or by material or by dipoles.

I claim:

An antenna system comprising a reflecting surface and a radiator positioned within said surface, said surface comprising a plurality of discrete coaxial ring-like sections, each of which includes a plurality of electrically isolated plane polarized radiator elements arranged on a single surface of revolution curved with respect to the axis of the ring-like sections and embracing an arc of 360, the planes of polarization of adjacent radiator elements being substantially parallel and the planes of polarization of radiator elements in the same section arranged diametrically opposite one another being mutually substantially perpendicular, the angle of each radiator element in each section being exactly relative to the mid-circular arc of that section only at the point where it crosses the mid-circular arc of that section and increasingly departing from the 45 angle with increasing distance from the point of intersection of the radiator element with the mid-circular arc, the surfaces of revolution adjoining one another on a common surface of revolution whose generatrix about the common axis is a conic section, the planes of polarization of the radiator elements of all the sections being in the same sense, said radiator elements being wires uniformly spaced throughout said surface.

References Cited in the file of this patent UNITED STATES PATENTS 1,855,155 Sampson Apr. 19, 1932 2,049,070 Mathieu July 28, 1936 2,412,562 Crawshaw Dec. 17, 1946 2,510,020 Iams May 30, 1950 2,528,667 Raabe Nov. 7, 1950 2,608,656 Korman Aug. 26, 1952 2,835,890 Bittner May 20, 1958 2,871,477 Hatkin Jan. 27, 1959 OTHER REFERENCES Pub. I, circularly-Polarized Biconical Horns, IRE Transactions on Antennas and Propagation, vol. AP-4, No. 4, October 1956, pages 592-596.