US2434893A - Unidirectional antenna system - Google Patents

Description

A. ALFORD ET AL UNIDIRECTIONAL ANTENNA SYSTEM Jan. 27, 1948.

Filed July 9, 1943 2 Sheets-Sheet l INVEN TORS fl/VDREW 141 fO/PO CHESTER 5. 114477152119.

Janjz'z, 1948. A, ALFOR'D ETAL 2,434,893

UNIDIRE CTIONAL ANTENNA SYSTEM Filed July 9, 1943 2 Sheets-Sheet 2 IN VEN TORS l atented Jan. 27, 1948 2,434,893 UNIDIRECTIONAL ANTENNA SYSTEM Andrew Alford, New York, N. Y., and Chester B.

Watts, In, East Orange, N. J., assignors to Federal Telephone and Radio Corporation, Newark, N. J a corporation of Delaware Application July 9, 1943, Serial No. 494,060

6 Claims. (Cl. 250-11) This invention relates to directive antenna systems and in particular to antenna systems employing reflectors to determine the directivity.

An object of the invention is to provide a unidirectional antenna system which will produce a field pattern having a substantially uniform intensity over an arc of substantially 90.

Another object of the invention is to provide a unidirectional antenna system for a portable glide path transmitter.

Another object of the invention is to provide an antenna reflecting screen which in combination with an antenna will produce a predetermined field pattern.

These and other features of the invention will be best understood and appreciated from the following description of an embodiment thereof, described for purposes of illustration and shown in the accompanying drawings in which:

Fig. 1 represents an elevational view of the antenna and reflector combination of our invention.

Fig. 2 is a plan view of the antenna and reflector arrangement shown in Fig. 1.

Fig. 3 is a schematic diagram of our antenna and reflector arrangement to be used in describing the principl of our invention.

Figs. 4 and 4A show respectively arectangular screen with an antenna at its geometrical center and the field pattern which may result therefrom.

Figs. 5 and 5A represent a modified form of screen and the field pattern which may result from the modification, and

Figs. 6 and 6A represent respectively a still further modification of the reflecting screen and the field pattern which may result therefrom.

The antenna arrangement of our invention is particularly useful in connection with the establishment of a suitable glide path for the instrument landing of aircraft such as is described in Alford Patent No. 2,294,882. This patent describes an antenna arrangement in which two antennas are positioned one above the other in a manner such that their field patterns combine to produce a very satisfactory glide path. The antenna arrangement of our invention is particularly useful for establishing one of the field patterns of the glide path.

In the Alford patent above referred to, an antenna is provided which produces a conical field pattern radiating substantially uniformly in all directions from the transmitter. However, since only one segment of the field pattern is employed, radiation in thos directions which are not useful in forming a glide path, represents a waste of radiant energy. Furthermore, should there be obstacles in the field of the nonuseful radiated energy, reflected radiation therefrom may produce deleterious effects such as lobes of energy having maximum and minimum points in the field of the desired glide path. In accordance with our invention any re-radiation from such obstacles is prevented and a uniform field pattern results. This question of re-radiation from obstacles in the vicinity of an antenna is particu larly important in connection with portable equipment since an otherwise suitable location may be rendered undesirable due to the reflecting objects on one side only of the landing runway and the glide path transmitter.

The antenna arrangement of our invention is also suitable for mounting on the side of the truck employed for transporting the portable equipment from one location to another. In an actual installation, a reflecting member or screen having a predetermined shape is mounted vertically on the side of the truck and an antenna is positioned in front of the reflector in a manner such that the desired radiation pattern is obtained.

Referring now to the drawings in which is described a directive antenna system for establishing a horizontally polarized field and particularly to Figs. 1 and 2 reference character 2 represents the reflecting screen or shield whichis mounted on the side of the truck. The'screen may be a solid sheet of metal or a perforated or expanded metal sheet. The reference character 4 represents the antenna proper. It consists of two radiating elements 6 and 8 which are inclined at an angle of substantially with each other and insulatingly mounted from a hollow pedestal l0 and the reflector 2, the plane of said reflector being substantially perpendicular to the plane of said elements. the elements 6 and 8 are clamped between insulating supports H and I3 which in turn are mounted on the reflector 2. Other extensions from the radiating elements are clamped between insulators l5 and I! which in turn are mounted on the pedestal Ill. The detail construction of the antenna elements is completely illustrated in U. S. patent application of Alford et al., Serial No. 479,624, filed March 18, 1943, now Patent 2,372,651, issued April 3, 1945. In this application a loop comprising four elements arranged in a square is illustrated, whereas in accordance with our invention only two elements are employed. The antenna proper of our invention is the practical equivalent of one-half of the loop Extensions from one end of antenna of the Alford et al. application. If a plane is passed through one of the supporting structures at right angles to the plane of the radiating elements of the Alford et a1. application, that portion of the structure appearing on one side of the plane may be considered as the equivalent of the antenna structure 4 of our invention;

As described in the above referred to application, the length of the radiating elements 6 and 8 are quite short with respect to the wavelength,

the length preferably being substantially'ofth'e .nounced lobes of radiation occur.

- screen is modified so as to have a form reprefore characterized by having an operating-irequency band of considerable width and maybe classed as a broad band antenna. The elements, 8 and 8 are so disposed with"'respectt'o each other that considerable capacitiv reactance'exists between the ends of the elements at the apex of the V formed by the elements and 3 and between theremaining ends of 'the elements and the reflecting screen. This capacitance may be the inherent capacitance between the elementsfi and 8 or this capacitance may be augmented by additional capacitors located between the elements such as illustrated in Fig. 3 by reference characters l2 and i4.

Fig. 3 illustrates the manner in which the radiating elements are energized. A source of radio frequency potential 16 delivers energy through transmission line It} to the elements 3 and 8 at the ends 2i} and 22 thereof. The transmission line passes through the hollow support it? which acts s a shield for the line. This shield is at screen potential. At any instant when the end 26 of element 6 is at a positive potential, the end 22 of element 8 is at a negative potential. This is illustrated by the dotted line 2 d showing the potential distribution along the radiating elements. It will also be clear that when the elements are energized in this manner that they ar radiating in phase coincidence. We have also illustrated in Fig. 3 the general manner in which the lines of electrostatic force extend from one end of the radiating elements to the other ends thereof. It will be seen that many of the lines of force extending for example, from end 22 terminate on the screen 2 rather than on the opposite end of the radiating element. Ifhese lines of force represent considerable coupling between the radiating elements and the screen, and considerable current is thereby induced in the screen. As electromagnetic waves are radiated outward from the elements, the screen currents likewis travel toward the boundary of the screen. These currentsupon reaching the screen boundary encounter an abrupt change in impedance with the result that some of the current is reflected backward toward the center of the screen and some of the energy from these currents is propagated into space where-it rcombines with thepenergy radiated from'the' elments to form a complex field pattern. We have found that unless special care is taken to properly shape the screen, undesirablelobes of radiation will occur and that the contour of constant field in tensity at a distance from the transmitter'will be irregular. This. of course, is an undesirable condition as anon-uniform glide pathwould result therefrom; P 1

To illustrate the above we have shown in Fig ures 4, 5 and .6. various shapes of reflecting'screens and :in'Figs. 4A, 5A; and 6A respectively corresponding, field" patterns in a plane passing sented by Fig. 5 and which has the same overall dimensions as the screen shown in Fig. 4 except that triangular portions are removed from the rectangle, the field pattern may take the form illustrated bythe curve 32 in Fig. 5A. It will be observed-that this field pattern is substantially uniform over an arc of approximately which is desirable. The shape of this pattern in space is similar to a quadrant of a pattern which would be produced if the radiating element forms a square loop such as is illustrated in the above mentioned Alford et a1. application wherein no reflecting screen was present. If larger triangular areas are removed from the reflecting screen, resulting in a screen shape such as is shown in Fig. 6, the field pattern illustrated by the curve 34in Fig. 6A might be obtained. It will be noticed that in this latter pattern there are three predominant lobes of radiation and that there is no longer a uniform field intensity over a quadrant of the field pattern.

The above analysis is illustrative only since it will be appreciated that manyfactors combine to produce the resultant field pattern. For example, if the length or the breadth of the rectangular reflector screen were changed, other forms of field patterns than those shown in Figs. 4A, 5A, and GA would result. However, after considerable experimentation in which both rectangular and triangular sections were removed from the corners of the screen, we have discovered that a simple solution consists in removing suitable triangular sections leaving th resultant screen of a shape approximately shown by the illustrations of Figs. 1 or 5. The shape of this screen or reflector may be described as having a rectangular portion M1 and two triangular portions 42 and i forming extensions on the ends of the rectangular portion as illustrated in Fig. 1.

Again referring to Fig. 3, it will be obvious that the support Hi substantially lies in an equal potential surface of the field produced by the elements 6 and 8. There is, thereforano tendency for the support to have current induced therein which might otherwise distort the field pattern or produce a loss of energy. A transmission line within the support is also so designed that its impedance matches the impedance of the radiating elements at thepoints where the line is connected to these elements.

While we have described above the principles of our invention in connection with specific apparatus it is to be clearly understood that this description is only by way of example and not as a limitation on the scope of our invention as set forth in the objects and the accompanying claims.

We claim:

1. A directive antenna system comprising a reflecting member, a hollow supporting member extending perpendicularly. from said reflecting member, two' radiating elements insulatingly mounted from said supporting member and said reflecting member, said elements being arranged to form a V, and a transmission line connected to said radiating elements and extending through said supporting member.

2. A directive antenna system in accordance with claim 1 wherein said reflecting member comprises a conducting sheet having a rectangular portion and two triangular portions, each triangular portion constituting an extension from an end of said rectangular portion.

3. A directive antenna system for establishing a horizontally polarized field of substantially uniform intensity over an arc of substantially 90 comprising tw horizontal antenna elements positioned to form substantially a right angled V, means for energizing said antennas for radiation in phase coincidence, a rectangular plane reflector positioned adjacent the diverging ends of said elements, the plane of said reflector being substantially perpendicular to the plane of said elements, said reflector being energized by radiation from said elements to produce standing Waves thereon, and means for defining over said are a predetermined radiation pattern due to said standing Waves, said means comprising additional triangular reflector means positioned at and conductively connected to each end of said rectangular reflector.

4. A directive antenna system in accordance with claim 3 wherein said plane reflector is p0- sitioned substantially at right angles to the plane of the earths surface whereby, due to reflection from said surface, said polarized field constitutes a segment of a substantially conical field pattern.

5. A directive antenna system comprising two radiating elements, said elements being arranged to form substantially a V, means for energizing said elements for radiation in phase coincidence,

and a reflecting member having a given con- I ments, the plane of said member being substantially perpendicular to the plane of saidelements, the length of each of said radiating elements being substantially 7% of a wave length at the operating frequency.

ANDREW ALFORD. CHESTER B. WATTS, JR.

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

UNITED STATES PATENTS Number Name Date 2,134,126 Hooven Oct. 25, 1938 2,065,787 Berndt et al Dec. 29, 1936 FOREIGN PATENTS Number Country Date 424,747 Great Britain Feb. 27, 1935

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