US2945227A - Improvements in ultra short wave directive aerials - Google Patents

Description

July 12, 1960 BRQUSSAUD 2,945,227

IMPROVEMENTS IN ULTRA SHORT WAVE DIRECTIVE AERIALS Filed NOV. 4, 1957 3 Sheets-Sheet 1 July 12, 19 G. BRoussAuD 2,945,227

IMPROVEMENTS IN ULTRA SHORT WAVE DIRECTIVE AERIALS Filed Nov. 4, 1957 3 Sheets-Sheet 2 July 12, 1960 ouss u 2,945,227

IMPROVEMENTS IN ULTRA SHORT WAVE DIRECTIVE AERIALS Filed Nov. 4, 1957 3 Sheets-Sheet 3 FIG. 6

FIG. 7

radiating devices.

Generale de Telegraphic Sans Fil, a corporation of France Filed Nov. 4, 1957, Ser. No. 694,251

Claims priority, application France Nov. '21, 1956 l Claims. (Cl. 343-731) The present invention relates to directional energy More particularly it relates to energy radiating devices capable of use with any wavelength, ranging from U.H.F. to V.H.F., with their configuration remaining basically unaltered and only their dimensions changing in proportion to the wavelength used.

In this respect, it should be noted that it is extremely advantageous to provide high-gain, directional aerials displaying the above characteristic and thus making it possible to build, on a reduced scale, working models, operating in the U.H.F. wave range, of radiating systems which are destined to be operated, for example, in the V.H.F. wave range. As it is well known, this is not always possible. It is for instance hardly possible to obtain V.H.F. antennas by correspondingly increasing the dimensions of U.H.F. antennas comprising reflectors, since the size of such antennas would become prohibitory.

It is therefore an object of the present invention to provide aradiating device capable of use in the U.H.F. wave range as well as in the V.H.F. wave range simply by correspondingly changing the dimensions thereof and yet always preserving an excellent performance.

A radiating device according to the invention comprises a conductive strip, the width of which is small with respect to the working wavelength, combined with a helically shaped metal wire wound thereabout, means being provided at one end of this strip for feeding electromagnetic-wave energy to be radiated to the assembly thus formed. Preferably, the strip lies parallel to a conductive metal planar piece. The dimensions of this piece are large and the distance between the same and the strip is small with respect to the working wavelength. Under these conditions, the aerial radiates a wave polarized perpendicularly to said planar piece i.e. vertically, if this planar piece is horizontal.

. According to another embodiment of the invention, two strips, parallel to each other and normal to a conductwound thereabout, the two assemblies being energized in phase opposition. In this case there is obtained a wave which is polarized perpendicularly to both strips,

Patented July 12, 1960 of which is small with respect'to the operating wavelength )tvin free space. It is, for example, equal to A/ 10. This strip is parallel to a plane metal surface 2, the dimensions of which are large as compared with A. Strip 1 and plane 2 are spaced apart by a distance of approximately Al 10. An exciter system 3,- located at one end of the line, comprises a coaxial cable, the inner conductor of which is connected to strip '1 and the outer conductor to conductive surface 2.

The resulting ultra high frequency field is, as is known, nearly completely comprised between strip 1 and its projection on plane 2 and is perpendicular to both. Such a line thus behaves substantially like a wave-guide wherein propagation occurs according to the TEM mode. By providing along such a line radiating elements coupled therewith, an aerial can be obtained.

In the aerial according to the invention, such radiating elements are obtained as shown in Fig. 2. In addition to planar element 2, strip 1 and exciter 3, this aerial comprises a helical wire 4 wound about strip 1. The cylinder bounded by helix 4 is coaxial with or symmetrically disposed relative to the strip.

When an ultra high frequency wave propagates along a helix, isolated in space, the lines of force of the ultra high frequency electrical field, of which the helix is the seat, are at all points normal to the helix. The helix behaves like a delay line and the mode of propagation is quite different from the TEM mode.

It may be assumed that each strip-line section gives up a certain amount of the ultra high frequency energy to the helix portion facing this section, as shown in Fig. 3.

' The lines of force 5 of the electric field propagating along the helix are normal thereto and the lines of force 6 of the electric field propagating along the strip are normal to the strip. In the radiating assembly illustrated in Fig.

, 2, two propagation modes coexist. Now, it is known ing plane, are provided, each strip having a helical wire I that is, horizontally, if the strips are perpendicular to the ground.

The invention will be best understood from the following description taken in conjunction with the appended drawing wherein,

I, Fig. 1 diagrammatically illustrates a transmission line of the strip-line type;

Fig. 2 diagrammatically shows an aerial according to the invention;

Fig. 3 is a diagram explanatory of the operation of the aerial shown in Fig. 2;'

Fig. 4 is a diagrammatic view of a device for energizing the aerial of the invention;

Figs. 5, 6 and 7 are further embodiments of aerials according to the invention.

Fig. 1 shows a transmission line of the strip line type. Such a line comprises a metal strip 1 the width that'undersuch conditions, everything happens as though uniformly distributed radiating sources were coupled to strip-line 1.

One tested aerial of this type, for

7 example, had the following dimensions:

Length of strip 1 8% Width of strip 1 M10 Distance between strip 1 and plate 2 A/lO Diameter of helix 4 v.10

Pitch of helix 4 M .5

The performance was as follows: I

Frequency band 2700-4000 mc./s.

Radiating direction 10 above plate 2.

Gain 16 db.

Width of 3 db 16.

Level of side lobes, in altitude -10 db.

Level of side lobes, in azimuth -20 db.

Polarization Normal to plate 2.

For an understanding of the operation of the aerial described, the following facts should be considered: Helix 4 maybe considered as providing a great many radiating points along line 1, whereby the radiated beam is made highly directive.

'Since energy propagating in line 2 is radiated, the phase velocity of the wave in the line is increased. Now, it is known that in a strip-line the phase velocity of the wave is substantially equal to the wave velocity in free space: consequently, energy radiation by the aerial results in said phase velocity becoming higher than the velocity of light. It will therefore be appreciated that the elementary radiations, transmitted by the whole of the elementary sources comprised in the aerial, combine in a direction inclined over plane 2. Since all the components of the aerial have a wide pass-band, this will also be .true for the unit considered as a whole.

As to the polarization direction, it is due to the direction of the lines of force of the electric field in the strip line.

The exciter is illustrated in Fig. 4. It comprises a coaxial cable whose outer conductor 6 is connected to helix '4 and to planar element 2, its inner conductor 7 being connected to strip 1.

As a modification, a dielectric layer may be applied on planar element 2, resulting in a decrease of the phase velocity of the wave propagating in the line, thus compensating for the acceleration due to radiation. The aerial will then radiate in a direction nearer the horizontal and its band-width is increased.

The amount of energy radiated per unit of length by an aerial of the type described, depends on several parameters:

(a) Width of strip 1: the greater this width as compared with the wavelength, the lower the energy radiated per unit of length. A thread-like conductor may be used, having a square or circular cross-section.

(b) Diameter of helix 4: the nearer the diameter to the width of the strip, the closer helix 4 is coupled to line 1 and the greater the energy radiated.

(c) Helix pitch: for a zero pitch, the helix turns will be in contact with one another, and thus no energy will be radiated and, for an infinite pitch, no coupling will take place between the helix and the line; accordingly there is a certain pitch which provides a maximum coupling.

As a consequence of the above, to provide an aerial according to the invention, having predetermined radiation characteristics, it will be necessary to determine the above parameters by trial.

Fig. 5 shows another embodiment of the device according to the invention. This device is adapted for radiating horizontally polarized waves. It comprises two identical strips and 11, parallel to and facing each other. Strip 10 is surrounded by a helix 40 and strip 11 by a helix 41, both helices being identical but wound in opposite directions. The exciters 50 and 51, similar to exciter 3 in Fig. 1, are adapted to energize the two assemblies, respectively. Exciters 50 and 51 are fed in I phase opposition from a common source 52.

In fact, the two assemblies shown in Fig. 5 behave as electric images of one another. If the strips are vertical, the unit described is equivalent to the unit illustrated in Fig. 2, planar element 2 being assumed vertical, since if this element is perfectly conductive the radiation provided in Fig. 2 may be considered as emanating from the strips 1, symmetrical with respect to the planar element. The radiation will show substantially the same directional properties, although the polarization will be horizontal, the aerial radiating in its median plane.

For the device to operate correctly, it is necessary that it be at a substantial distance from the ground, this distance being for instance of the order of X.

As already mentioned, the aerial described may be used, provided it has adequate dimensions, as well in the U.H.F. as in the V.H.F. wave range.

When used in the V.H.F. wave range, the system according to the invention may be advantageously built up as shown in Fig. 6.

In this case, strip 21 will be formed of a grid, the

A. meshes of which have sides approximately equal for instance, to M20. Planar element 2 corresponds to the ground on which a grid may be spread. Helix 44 has a rectangular cross-section, and so does the mouth of the exciter 33 which may be placed on the ground. Helix 44 may, for instance, be supported on wooden posts 60.

The device illustrated in Fig. 7 corresponds to that shown in Fig. 5. It comprises two strips 45 and 46, similar to strip 44 of Fig. 6, and a single helix 30, wound about both strips. The strips are both energized from the secondary winding of a transformer 52 having its middle point grounded.

Both devices must be closed on a matched load according to the known technique common to a great number of endfire radiating devices, such as rhombic antennas.

What I claim is:

1. Directional ultra high frequency radiating device, comprising: at least one planar strip of conductive material, means associated with said strip for forming therewitha strip line in which ultra high frequency energy propagates in the direction of said strip a helically shaped metal wire wound about said conductive strip substantially over the whole length of the latter and means for feeding ultra high frequency energy to said strip and said wire.-

2. Directional ultra high frequency radiating device, comprising: a planar strip of conductive material, a conductive planar element parallel to said strip, a helically shaped metal wire wound about said conductive strip over substantially the whole length of the latter and means for feeding ultra high frequency energy to said strip and said wire.

3. Directional ultra high frequency radiating device, comprising: two identical parallel planar strips facing each other and of conductive material, a helically shaped metal wire wound about at least one of said conductive strips over substantially the whole length of the latter, and means for feeding ultra high frequency energy to said strips in opposite phase relationship.

4. Directional ultra high frequency radiating device, comprising: first and second identical parallel planar strips, facing each other and of conductive material, a first and a second helically shaped metal wire respectively wound about said first and said second conductive strips, over substantially their respective whole lengths, and means for feeding ultra high frequency energy in opposite phase relationship to said first strip and wire on the one hand and to said second strip and said second wire on the other.

5.. Directional ultra high frequency radiating device comprising: two identical parallel planar strips facing each other and of conductive material, a helically shaped metal wire wound about said conductive strips over substantially the whole length of the latter, and means for feeding ultra high frequency energy to said strips in opposite phase relationship.

References Cited in the file of this patent UNITED STATES PATENTS

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