US2783467A - Ultra-short wave aerials - Google Patents

Description

Feb. 26, 1957 n- EI-AL 2,783,467

ULTRA-SHORT mm: mam-s Filed June 25, 1952 United States Patent Oflice Patented Feb. 26, 1957 This invention relates to ultra-short wave aerials.

Radio aerial systems suitable for use on ultra-high radio frequencies, and having one of the two perpendicular dimensions very different from the other, are of course well known. A typical example of such a known aerial .5 Pal-lemusystem is the so-called cheese aerial, commonly emplayed for radar and which comprises a cylindro-parabolic reflector of small height, but much greater width, fed by a small horn ending a wave guide.

In practice the cylindrical height of a cheese aerial must be greater than half a wavelength. In many cases,

however, it would be advantageous to be able to reduce this dimension below the half wavelength, as for example in the case of an aerial for mounting on a very high speed vehicle such as a fast aeroplane.

The present invention seeks to provide improved aerials.

wherein one dimension may be made extremely small but which will nevertheless provide a radiation diagram comparable with those of known aerials of considerably larger dimensions.

According to the invention, an aerial is constituted by 35 a wave guide, one wall of which is extended in the axial direction by a substantially flat metal plate which is covered with a substantially uniform layer of dielectric material which also penetrates into a part of the wave guide where its thickness diminishes progressively. With 40 a rectangular guide the plate extension is preferably trapezoidal with the shorter of its two parallel edges common with one of the longer edges of the guide mouth.

The layer of dielectric outside the guide is preferably pierced with holes suitably disposed and having suitable diameters to maintain the wave front plane at the outlet of the plate.

The invention is illustrated in the accompanying drawings which show schematically one embodiment, Figure 1 showing the aerial as a whole and part-of the wave guide,

of the arrow A-will continue to be propagated in the direction Oz at the guide outlet if the thickness a is greater than a minimum value where K is the constant of propagation in the undefined space (beyond the guide mouth) and is given by the relation 2 where A is the wavelength. If the value of K is substituted in the above equation, it becomes:

442 1 If a is raised from the value an the theoretical limit 'of infinity, the speed of propagation rises from K to VZK.

The plane xOy constitutes a radiating mouth along 6 which the wave has a constant phase.

From a study of the radiation diagram in the plane of symmetry yOz, it may be shown that the field at any point M is a function of the angle The radiation diagram is symmetrical around Oz and the width of the diagram at half-power is a functio'n of the thickness of the dielectric a and of its constant e.

In order to avoid excessive losses in the dielectric, the latter is preferably made of a thickness between as and 1.4 an (as having the value defined above). conditions it is found, for a value of e equal to 2, the

radiation diagram at half-power forms afn angle of about If it is desired to reduce the width of this diagram, the thickness of the dielectric is given a value closer to ao. For a=ao, the wave slides along the dielectric, no energy penetrates (theoretically) into the latter and there is no radiation properly speaking, no distinction being made between the initial wave and the diffracted wave.

Thus, by suitably selecting the thickness a and the constant e of the dielectric, it is possible to obtain in the. vertical plane (plane 302) a diagram having the desired width. The diagram in the horizontal direction (plane xOz) is defined by the length of the plate 3 aldng Oz, and it may be made as fine as desired.

The dielectric layer 3 is extended by a bevelled tongue 4, which progressively transforms a H01 wave in the guide into a wave propagated at the speed of light in the space beyond the guide mouth.

If the wave guide is disposed on a metal surface, for example, the outer shell of an aircraft wing, the dielectric layer may be disposed directly on said surface.

In order to obtain at the outlet end of the dielectric a wave front perpendicular to the axis of the guide, it is necessary to compensate for the different effective lengths in the different directions in relation to the axis direction. For this purpose the dielectric layer is pierced with holes having vertical axes and disposed in such 'manher as to advance the wave in the direction under consideration. The diameters of the holes, which are smaller than onequarter of the wavelength in the dielectric, vary according to the direction, the size of the, holes increasing for directions more and moi e inclined to the axis of symmetry of the whole arrangement. Figure 2 illustrates one example of such perforation.

We claim:

1. An ultra-short wave antenna comprising an elo'ngated tubular wave guide having a substantially uniform rectangular cross section along its axis; a'flat metal plate extending from one wall of said wave guide in direction of the axis of said wave guide arid having a width sub stantially larger than the thickness thereof; a substantially uniform layer of dielectric material covering said flat metal plate and penetrating into a portion of said wave guide in which its thickness diminishes progressively, the width of said layer being substantially larger than the thickness thereof.

2. An ultra-short wave antenna comprising-an elongated tubular wave guide having a substantially uniform rectangular cross section along its axis; a flat metal plate extending from one wall of said wave guide in direction In these of the axis of said wave guide and having a width sub-' stantially larger than the thickness thereof; a substantially uniform layer of dielectric material covering said flat metal plate and penetrating into a portion of said wave guide in which its thickness diminishes progressively, the width of said layer being substantially larger than the thickness thereof, said layer of'dielectric material outside said wave guide being formed with holes having their axes perpendicular to the surface of said dielectric layer, said holes being disposed and dimensioned to maintain a planar wave front at the outlet of said plate.

3. An ultra-short wave aintenna comprising an elongated tubular rectangular wave guide having a substantially uniform cross section along its axis; a trapezoidal shaped large flat metal plate extending from one of the edges of said tubular rectangular wave guide, the smaller parallel side of said trapezoidal shaped metal plate being,

common with said one of the edges of said tubular recs tangular wave guide; a substantially uniform layer of dielectric material covering said flat metal plate and penetrating into a portion of said wave guide in which its thickness progressively diminishes; the portion of said 4 dielectric layer located outside said thickness comprised between where A is the wavelength of the radiated wave, and e the dielectric constant of said dielectric material.

References Cited in the file of this patent wave guide having a UNITED STATES PATENTS 2,425,336 Mueller Aug; 12, i947 2,473,446 Riblet June 14, 1949 2,577,158 Rosencrans Dec. 4, 1951 2,594,871 Chu et el. Apr. 29, 1952 2,596,190 Wiley May 13; 1952 2,605,416 Foster July 29, 1952 2,605,419 Atta July 29, 1952 2,605,420 Jatfe July 29, 1952 2,617,029 Plummer et a1. Nov. 4, 1952 2,648,002 Eaton Aug. 4, 1953 2,684,445

Eaton June 20, 1954

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