US2449999A - Antenna system for defining glide paths - Google Patents

Description

p 19430 L. .l. HEATON-ARMSTRONG 2, 9 I

ANTENNA SYS'I'EI FOR DEFINING GLIDE PATHS v Filed Oct. 15, 1943 2 smug-sum 1 Inventor p 28, 1948. L. J. HEATON-ARMSTRONG 2,449,999

ANTENNA sxsml FOR DEFINING cubs PATHS Filed Oct. 15. 1943 2 Sh e ets-Sheet a Invenlbr [oak Jain mhrpdnm/mz; y I I Patented Sept. 28, 1948 ANTENNA SYSTEM FOR DEFINING GLIDE PATHS Louis John Keaton-Armstrong, London, England, assignor to Standard Telephones and Cables Limited, London, England, a British company 7 Application October 15, 1943, Serial No. 509,300

In Great Britain October 30, 1942 6 Claims. (Cl. 343108) The present invention relates to antenna systems for defining a radio glide path for aircraft and of the kind in which the glide path is defined by a line of field or signal strengths of constant relationship produced by two overlapping fields in a vertical plane.

In one specific system one field comprises a plurality of directive lobes distributed angularly in a vertical plane and the other field comprises a single principal lobe, the glide path being defined by the overlapping of the lowermost lobe of the I multl-lobe pattern and single principal lobe. The single principal lobe not only overlaps the lowermost lobe of the multi-lobe pattern but encloses the .second higher lobe of the multi-lobe pattern which is also of field strength comparable with the single principal lobe and it is found that the ratio of dot to dash signal strengths produced in a receiver suitably located, by the second lobe and single principal lobe is not as great as desirable and in some cases might produce false constant radio or equi-signal glide paths.

The main object of the present invention is to provide an antenna system for defining a radio glide path in which these false courses are reduced or eliminated.

According to the present invention, in an antenna system for defining a radio glide path by a line of field or signal strengths of constant relationship produced by two overlapping fields in a vertical plane and comprising a first antenna unit The invention will be better understood from the following description taken in conjunction with the accompanying drawings, of one practical antenna system embodying. the invention.

In the drawings,

Figure 1 shows an antenna system by which false glide paths are obtained.

Figure 2 shows the radiation patterns produced by the. antenna units of the arrangement shown in Figure 1.

Figure 3 shows the modification of one of the units according to the present invention, and

Figures 4, 5, 6 and 7 show field distribution patterns for different conditions in the arrangement shown in Figure 3.

Referring to Figures 1 and 2 of thedrawings, the system for producing a glide path of the type hereinbefore specified comprises a horizontal dipole antenna i with parabolic reflector 2 located near to the ground to produce a distribution pattern having a principal lobe as shown at In, Figure 2. Minor lobes approaching the vertical may also be present but these are not shown as they are not troublesome as regards this invention. The other antenna unit comprises also a horizontal dipole 3 located before a plane reflector 4 so as to produce the multi-lobe pattern as shown by the broken line H in Figure 2. The number of lobes will depend, as is well known upon the height of the antenna 3 above the ground.

The transmitter power is keyed from one antenna to the other in dot-dash rhythm thus producing an equi-slgnal path 0A, Figure 2, one of the signals (dots or dashes) being received above 0A and the other signal below 0A. As already explained, since the lobe Iii encloses the second higher lobe i2, and the field strength of I0 is not very much greater than the field strength of i2, the-ratio between the dot and dash signals of Ill and [2, produced by a receiver located within the lobes i9 and I2, is not sufi'iciently great for practical purposes and may lead to false glide paths. Likewise other lobes of the multi-lobe pattern may produce with lobe I0, false paths. In the application of the present invention to this system, the dipole 3 is replaced by two dipole antennae 5, 6 one above the other as shown in Figure 3. These two dipoles 5 and 6 are fed in phase and are separated by such a distance as to reduce or eliminate the lobes near the lowermost lobe i I.

In Figures 4, 5, 6 and 7 the energy distribution curves are shown in full lines for the upper antenna unit A, 5, 6 and in broken line for the lower antenna unit l, 2.

Figure 4 shows the case of a single antenna unit 3, 6 located at a distance above the ground equal to 7.2). (wave-lengths of the operating frequency).

Figures 5, 6 and '7 show corresponding diagrams for two antennae 5, 6, Figure 3, whose mean distance above the ground is 7.2x but having different separating distances of 3.2x, 3.87\ and 4.8x respectively. From these curves it is apparent that as the distance between the antennae 5 and 6 is increased, the second lobes marked B and higher lobes marked C become smaller, so that theratio 3 of desired to undesired signals above or below the glide path is increased.

It might of course be possible in some cases to provide an auxiliary directive antenna system whose radiation pattern comprises a single lobe which may be directed'in the same .direction as the lobe it is desired to eliminate andied with current of the same frequency as the main unit 3, d but so phased that the radiated fields of the auxiliary system and the unit 4 are opposite in phase and keyed in the same manner and synchronously with the lobe it is to eliminate or reduce.

Whilst a specific embodiment of the invention has been described it will be understood that it is not limited to this embodiment but is capable of application to other systems utilising such radiation patterns as those specified. Furthermore in the embodiment described, the distance between the two antennae, 5, B may be selected and the relative strengths of currents fed to the two antennae adjusted accordingly and/or the phase relationship of the currents fed to the two antennae may be adjusted. Furthermore antenna systems other than the dipole and parabolic re= flector may be used for producing the single lobe radiation pattern.

What is claimed is:

1. An antenna system for defining a glide path resulting from the over-lapping of two field patterns in a vertical plane, said antenna comprising. a first dipole antenna, a parabolic reflector for said first antenna to provide a first antenna system having a vertical radiation pattern with a single principal lobe, a second dipole antenna disposed above said first, a third dipole antenna disposed above said second, plane reflecting means for said second and third antennas to provide a multi-lobe vertical pattern, said principal lobe overlapping the lower-most lobe of said multilobe pattern, means for feeding said second and third antennas in phase with each other, said second and third antennas together forming a composite antenna system having a mean height above ground and having a separation between 4 the second and third antenna of the order of one-half oi the mean height above ground whereby the lobes due to the composite antenna system overlapped by the principal lobe of the first antenna system are substantially reduced.

2. The system oi claim 1 wherein said reflecting means for the second and third antennas comprise a single plane reflector.

3. The system of claim 1 wherein the separation between the second and third antennas is between three and live wave lengths.

4. The system of claim 1 wherein the average height above ground is seven plus a fraction of a wave length.

5. The system of claim 1 wherein the average height is 7.2 wave lengths and wherein the separation between the second and third antennas is between three and live wave lengths.

6. The system of claim 1 wherein said reflecting means for the composite antenna system is a single plane reflector, wherein the average height above ground is between seven and eight wave lengths of operating frequency and wherein the separation between the second and third antennas. is between three and five wave lengths.

LOUIS JOHN HEATON-ARMBTRONG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,186,554 Pei-roux Jan. 9. 1940 2,189,283 Franz Feb. 6, 1949 2,213,859 Hahnemann Sept. 3, 1940 2,294,882 Alford Sept. 8, 1942 FOREIGN PATENTS Number Country Date 23,158/35 Australia July 2. 1936 438,900 Great Britain Nov. 26. 1935 546,021 Great Britain June 24, 1942 556,824 Great Britain Sept. 29, 1943

Images