US2398095A - Electromagnetic horn radiator - Google Patents

Description

a) 6 Q) \JUKMUII nuu-u April 9, 1946. M. KATZlN 2,398,095

="" L4 ELECTROMAGNETIC HORN RADIATOR Filed Aug. 31, 1940 3 Sheets-Shet 1 Qtml Ml mu 3 Sligets-Sheet 2 I l I III llll Ill IVENTQR v ATORNEY M. KATZIN ELECTROMAGNETIC P IORN RADIATOR -Filed Aug. 51. 1940 April 9, 1946.

p i .9, 19 6. M. KATZIN 2,398,095

ELECTROMAGNETIC HORN RADIATOR Filed Aug. 51, 1940 3 Sheets-Sheet 3 AT'ToiaNE Patented Apr. 9, 1946 team stai ELECTROMAGNETIC HORN RADIATOR Martin Katzin, Riverhead, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application August 31, 1940, Serial No. 354,954

8 Claims.

The present invention relates to ultra short wave antenna systems and, more particularly, to electro-magnetic horn structures and to means for efficiently coupling them to high frequency energy sources and/or transducer means.

An object of the present invention is to increase the power gain of electro-magnetic horn antenna structures.

A further object is the provision of an electromagnetic horn structure having a minimum front to back length for a given frontal or mouth area.

Another object is the combination of a plurality of electro-magnetic horns to obtain large effective apertures while at the same time maintaining a minimum over-all length.

A further object of the present invention is the combination of a plurality of electro-magnetic horn structures in such a way that distortions of the high frequency energy wave introduced by one horn are compensated for by similar distortions of opposite phase in another horn.

Still a further object of the present invention is to increase the efficiency of coupling between electro-magnetic horn radiators and their exciting sources.

Still another object is to prevent the radiation of undesired waves from horn structures generated as a result of curvature of the horn or energizing pipes.

A further object is the increase of efficiency of electro-magnetic horn radiating structures.

The present invention includes among its features the combination of a plurality of small horns of a predetermined ratio of length to frontal area in such a way as to obtain a composite structure having a large frontal area with a short over-all length. Furthermore, the horns thus combined may be straight horns or they may be curved or folded in order to still further decrease the over-all length of the structure.

Another feature of the present invention contemplates so designing the rate of taper of the horn structures and their connection to the exciting means in such a Way as to obtain a maximum efiiciency of coupling between the horns and their exciting means.

Further objects, features and advantages of the present invention may be more completely understood by reference to the following detailed description which is accompanied by drawings in which Figure 1 is an illustration of an electromagnetic radiating horn structure useful in explaining the present invention; Figure 2 illustrates-a modification of the structure of Figure 1 in accordance with a feature of the present invention, while Figures 3, 4, 5 and 6 illustrate ways in which the horn structures may be curved or folded in order to reduce their over-all frontto-back length; Figures 7 and 8 illustrate improvements in the horn structure whereby it is possible to obtain a desired amount of power gain with shorter over-all lengths, while Figures 9 and 10 illustrate modifications of a coupling pipe structure between the horn and its exciting means whereby spurious or undesired frequency components are eliminated or reduced.

Figure 1 shows a, single horn antenna H having a width x, a height y and an over-all length Z. To the small, or throat, end of the horn is coupled a short section of wave guide which acts as a resonant chamber and is indicated generally by reference numeral l2. Within the wave guide section I2 is located an exciting antenna [3 which is connected to a source of high frequency oscillations by means of transmission line TL. The length of antenna I3 is preferably of the order of a quarter of the operating wavelength. The simplest wave, that is, the one with the lowest critical frequency for rectangular hollow pipe transmission which gives a vertically polarized radiation in a single forwardly directed beam, is known as an 110,1 wave. This wave has a component of magnetic force in the direction of propagation and a component of electric field intensity directed parallel to the y axis and at right angles to the direction of propagation. There is no component of electric field intensity in the horizontal direction, i. e., along the x axis. The subscripts 0,1 denote the harmonic order of the wave in each coordinate. Since we are dealing, in the present case, with rectangular pipes one subscript is required for each coordinate, the first subscript denoting the number of half sine waves of electric field intensity along the a: axis and the second subscript thenumber of half sine waves of electric field intensity parallel to the y axis.

Th antenna system shown in Figure 1 is designed to radiate vertically polarized waves in a comparatively narrow beam, the sharpness of the beam being determined by the frontal area m, y and the over-all length Z.

The horizontal dimension of the wave guide section I2 is chosen to be equal to, or greater than, a half of the operating free-space wavelength. The vertical dimension is not critical, but with horns of square aperture it is convenient to make it equal to the horizontal dimension.

The length of the wave guide section is at least long enough that a stable condition of the radiant wave energy is established within the wave guide section before the energy arrives at the small end of the horn. The distance between the exciting antenna l3 and the closed end wall I5 is on the order of a quarter wave-length. The exact distance is so chosen that the resultant impedance of the exciting antenna I3 is equal to the surge impedance of the transmission lin TL whereby reflections of energ back along the transmission line TL to the exciting source, not shown, are avoided. Since antenna systems of the type shown in Figure 1 must be mounted on tall towers in order to obtain as great a transmission range as possible, it is desirable to make the ratio of the over-all length to the frontal area as small as possible. One way in which this may be done is shown in Figure 2.

The single large horn structure ll of Figure 1 is, in Figure 2, substituted by a plurality of small horns 2|. Each of the small horns 2| may have a smaller ratio of length to frontal area than the single large horn of Figure 1. The total over-all frontal area m, y 0f the radiating structure of Figure 2 is the same as the frontal area ac, y of Figure 1, while at the same time the length l, as can readily be seen, has been shortened considerably. Each of the individual small horns 2| may be energized by exciting antennas within the short wave guide sections l2, [2 in the same way as described with reference to Figure 1. The separate antennas of Figure 2 are connected through equal length transmission line sections to the final transmission line TL which is energized from the exciting source. The radiation from all of the horns is thereby additive in an in-phase relationship. In some cases it may be desirable to still further decrease the over-all length of the antenna system shown in Figure 2, or it may be desirable to utilize a single large horn with a small over-all length instead of a, plurality of small horns. In such cases the radiating horn structure, or structures, may be constructed as shown in Figure 3.

The frontal area of the horn of Figure 3 is determined by the power gain desired and the over-all length is decreased by folding the horn over in a vertical plane. The horn shown in Figure 3 is shown as having a constant vertical dimension since this is a convenient form of construction where vertically polarized waves are to be radiated, though it is also effective for horizontally polarized waves or for both simultaneously where different directivity patterns are desired. As may be seen from the figure the horizontal dimension of the horn has a varying rate of taper. The advantages of this form of construction will be discussed in more detail hereafter with reference to Figures 7 and 8. The exciting means, which is not shown in this figure but which is similar to the wave guid and exciting antenna structure shown in Figures 1 and 2, is connected to the throat or small end 33 of the horn in any desirable fashion.

As in the case of Figure 1, an Ho,1 wave is applied to the horn having only a single electric field component parallel to the shorter side walls for waves of lowest critical frequency. An I-Ivo wave has its electric field component parallel to the horizontal axis. The general type of H w ve in a r ctan ular wave guide system ma be designated as 1-11, where m and n are positive integers, either one, but not both of which may have the value zero.

Any H wave of a higher order than the H0, (or Hm,0) class has components of the electric field parallel to both the vertical and horizontal axes. Furthermore, all E type waves, that is, those having a component of the electric field in the direction of energy propagation, also have electric field components parallel to both the long and short side walls. These properties ma be used to great advantage to control the type of wave radiated by the horn. A grid 34 of horizontal wires is placed across the opening of the mouth of the horn as shown in Figure 3. This grid is at right angles to the electric field component of the desired H0,1 wave and, therefore, forms no obstruction to the radiation of the desired wave. However, other types of waves, as pointed out above, have components of the electric field parallel to the wires of grid 34 and cannot, therefore, penetrate the grid 34. They are thus prevented from radiating whether the exist as a result of their generation in the exciting tube structure, or as a result of the refiection of the Hon wave from the curved surfaces of the horn. If desired, a smaller grid of horizontal wires may be placed before the bend in the horn, that is, at the small end 33 so that any E-waves generated by the bend may be prevented from traveling back to the transmitter as a reflection.

Other forms or folded horn structures are shown in Figures 4 and 5. These are similar to the one shown in Figure 3, except that the horn is tapered in both vertical and horizontal directions. With appropriate dimensioning of the small end of the horn, it may be used either vn'th horizontally, as well as vertically, polarized waves or both, as desired. The grid 34 shown in Figure 3 may be employed with either of these horns when only a single polarization is used, orienting the grid, as explained above, to pass only the desired wave.

In Figure 4 the exciting means which may be similar to that shown in Figures 1 and 2, is connected to the small end of the horn 43. In some cases there may be insufficient space within the spiraled portion 44 for the exciting structure so the spiral may be extended to one side as indicated by 54 in Figure 5.. This frees the small end 43 so that either an exciting means such as shown in Figure 1 may be readily connected thereto even if it is of considerable length, or a long wave guide may be connected thereto reaching to the transmitter location which may be, for example, at the base of the supporting tower structure for the horn.

Figure 6 illustrates a further modification which in one aspect may be considered as embodying two horn structures, such as shown in Figures 3 or 4, arranged to be energized at 53 by a single energizing chamber. The wave guide structure is split as indicated at 64 and bent around to form two separate radiating horns 5| and BI. In this form of construction it will not, in all cases, be necessary to include a horizontal grating in front of the mouth of the horns 5| and BI in order to suppress the higher order l-I waves and any E waves generated as a result of reflections from the curved surfaces of the horns. Since waves emerging from the mouths of the horns travel an equal distance from the small end 53, and the curvatures, being in opposite relative directions, generate E waves of opposite instantaneous polarities, as the E waves emerge from the mouths of the horns 5|. 6| they combine in opposing phase relationship and cancel one another. While only two horns are shown in Figure 6 it is, of course, within the scope of the present invention to use banks of any multiple of two to obtain the desired frontal area.

In Figure 7 I have shown a modified form of horn which may be used either alone or in any of the combinations previously shown. In order to obtain the full power gain possible, it is necessary to reduce the rate of flare of a horn as the aperture of the horn is increased. Thus, when horn apertures are increased to obtain increased power gain, the length of the horn must be increased at a, greater rate. With linear tapering or flarin of the sides of the horn, the length of the horn must be increased for two reasons as the frontal aperture is increased: first, because of the increase in aperture, and second, because of the decreased rate of flare necessitated. It is therefore contemplated as shown in this modification to build the horn with a rate of flare which is initially large but decreases constantly with increasin distance from the throat as required by the increasing aperture. In this way the desired power gain may be obtained while the over-all length of the horn is less than would be the length of a horn of uniform taper. In Figure 7 the horn H is indicated as flaring only in the horizontal plane, the distance between walls 15 and 16 increasing at a more rapid rate nearer the throat, but at a decreasing rate as they approach the mouth of the horn. The walls 11 and 18 are indicated as being parallel since the particular example illustrated is to be used only with waves of a single vertical polarization. It is, of course, within the scope of the invention to likewise taper the distance between walls 11 and 18 in the same way as indicated for walls 15 and 16. While horns of square or rectangular cross section are preferred for linear polarization, it is, of course,

also within the scope of the present invention to utilize horns of circular or elliptical cross section, if desired.

Figure 8 shows a further modification of the form of the invention shown in Figure 7 in which a smoother transition from the exciting chamber [2 is obtained by forming the horn with an increasing rate of flare near the throat as indicated by 85 and 86 of the side walls and then reducing the rate of the flare as indicated by 15 and 16 in the way described above with reference to Figure 7. Thus reflections are avoided at the junction of the throat of the horn to the exciting chamber l2, and still the advantages of the constantly decreasing rate of flare as described with reference to Figure 7 are obtained.

In the previously described embodiments of the present invention the exciting chamber l2 has been described as being quite short, that is, just long enough to insure that stable wave guide conditions are obtained before the wave guide is coupled to the radiating horn. In some cases it may be desirable to connect the radiating horn to the transmitter by means of a wave guide or hollow pipe line a, number of wavelengths long. In some cases the radiating horns may not present a perfect impedance match to the hollow pipe line even when using the horn structure described with reference to Figure 8, so that some reflection will take place from the load end of the line, resulting in standing wave components in section [2 and, hence, affecting the frequency characteristic of the system for wide band operation. This may be overcome as shown in Figure 9 wherein a wave guide section 92 of substantial length is coupled to the throat of horn II. The energizing structure, which is not shown in this figure, is connected to end 93 of the wave guide 92. A branch section 94 of the hollow pipe line is joined to wave guide 92 near the load end where the wave guide joins the throat of horn II. The far end of the branch section 94 is closed by a metal sheet 95 so that there is obtained the equivalent of a shunt branch line short-circuited at its far end. This gives the equivalent in hollow pipe transmission line technique to a shunt section of shortcircuited transmission line such as is used for impedance matching in the ordinary two conductor transmission lines. By locating branch section 94 at the appropriate distance from the throat of the horn, and making it the proper length, reflections will be eliminated along the wave guide 93 from the branch section 94 to the transmitter. In the case of a curved horn this method of impedance matching may be used to serve a double purpose. In progressing around a curve in a hollow pipe through which there is transmitted an H type of wave, that is, a wave with no component of electric field in the direction of propagation, some portion of the H wave energy is automatically converted into E waves, that is, waves possessing a component of the electric field in the direction of propagation, by the bend in the hollow pipe line.

As shown in Figure 10, by placing the branch line 94 at the bend 96 of the wave guide 92 it is possible to equalize the E wave generated by the bend 96 in the main pipe line by an opposite E wave generated by the bend 91 in the branch line 94. The branch line thus is used for the double purpose of adjusting the termination of the feed line 92 for no reflection of the H wave which is being transmitted and for eliminating any E waves generated by the bend in the line.

While I have particularly shown and described several modifications of my invention, it is to be distinctly understood that my invention is not limited thereto but that improvements within the scope of the invention may be made.

I claim:

1. A horn radiator having rectangular mouth and throat apertures and being curved along its axis, means for energizing said horn with a wave of a polarization parallel to the plane in which the axis of said horn lies and means for suppressing radiant energy waves having a component of polarization normal to said plane caused by the curvature of said horn.

2. A wave guide having rectangular mouth and throat apertures of difierent sizes and its axis being curbed in a vertical plane, means for energizing said guide with a Wave having a component of electric field in a direction parallel to the axial plane of said guide and normal to the direction of travel of said wave within said guide and means for suppressing radiant energy waves having a component of electric field normal to said plane caused by the curvature of said guide.

3. A wave guide having rectangular mouth and throat apertures and being curved along its longitudinal axis, means for energizing said guide at its throat aperture with a wave having a component of electric field in a direction parallel to the plane in which the axis of said guide lies and normal to the direction of travel of said wave within said guide and means for suppressing radiant energy waves having a component of electric field normal to said plane caused by the curvature of said guide, said guide being tapered in a plane normal to the direction of the electric field component of said wave.

4. A tapered wave guide having rectangular mouth and throat apertures and being curved along its longitudinal axis, means for energizing said guide at its throat aperture with a wave having a component of electric field in a direction parallel to the plane in which the axis of said guide lies and normal to the direction of travel of said wave within said guide and means for suppressing radiant energy waves having a component of electric field normal to said plane caused by the curvature of said guide, said means comprising a grid transverse to the axis of said guide and conductive only in a direction normal to the direction of the component of electric field of said wave.

5. A horn radiator having rectangular mouth and throat apertures and being curved along its axis, means for energizing said horn with a wave of a polarization parallel to the plane in which the axis of said horn lies and means for suppressing radiant energy waves having a component of polarization normal to said plane caused by the curvature of said horn, said means comprising a grid transverse to the axis of said horn and conductive only in a direction normal to the direction of polarization of said wave.

6, A tapered wave guide having rectangular mouth and throat apertures and being curved along its longitudinal axis, means for energizing said guide at its throat aperture with a wave having a component of electric field in a direction parallel to the plane in which the axis of said guide lies and normal to the direction of travel of said wave within said guide and means for suppressing radiant energy waves having a component of electric field normal to said plane caused by the curvature of said guide, said means comprising a grid across the mouth of said guide and conductive only in a direction normal to the direction of the component of electric field of said wave.

'7. An electro-magnetic horn radiator comprising a plurality of curved tapered horns and means for supplying wave energy of desired characteristics to all of said horns in such relationship that the energy from all of said horns is additive in a predetermined direction, said horns being arranged in pairs with the curvatures of the horns of each pair being in opposite directions whereby waves of an undesired characteristic caused by said curvature are neutralized.

8. A wave guide having rectangular mouth and throat apertures and being curved along its longitudinal axis, means for energizing said guide at its throat aperture with a wave having a component of electric field in a direction parallel to the plane in which the axis of said guide lies and normal to the direction of travel of said wave within said guide and means for suppressing radiant energy waves having a component of electric field normal to said plane caused by the curvature of said guide, said means including a branch guide connected to said first mentioned guide and curved in the opposite direction along its longitudinal axis, said branch guide being closed at its free end and being of such length that energy reflected from said closed end combines with energy in the said first mentioned guide so that radiant energy waves having a component of electric field normal to said plane combine in a phase opposing relationship.

MARTIN KATZIN.

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