US2805415A - Microwave antenna system - Google Patents

Description

Sept 3, 1957 B. BERKOWITZ 2,805,415

' MICROWAVE ANTENNASYSTEM Filed Aug. z 1952 TTORNEY United States Patent tice Patented Sept. 3, 1957 MICROWAVE ANTENNA SYSTEM Bernard Berkowitz, Jamaica, N. Y., assignor to Sperry Rand Corporation, a corporation of Delaware Application August 2, 1952, Serial No, 302,401 8 Claims. (Cl. 343-777) This invention relates to a microwave antenna system, and, more particularly, is concerned with a horn structure for sequentially producing asymmetrical electromagnetic radio beams having space patterns which are mir-' ror images of one another.

Transmitting systems providing alternately energized overlapping lobes are employed in aircraft locators, direction finders, and instrument landing systems. Particularly in the latter case, it is desirable that the individual eld patterns of the overlapping lobes have an asymmetrical conguration to provide broad coverage in the offcourse region and to provide sharp cut-off in the oncourse region where the lobes overlap, the two lobes having space patterns which are substantially mirror images of each other.

It is a general object of this invention to provide an improved radiating system for producing overlapping lobes having asymmetrical space patterns.

Another object of this invention is to provid-e means, including a horn type radiator, which can be readily controlled and adjusted to modify the space pattern of each of the lobes.

Another object of this invention is to` provide a radiat ing system in which the shape of the farfeld pattern can be modified without physically altering the radiating structure by simply changing the phase relationship and power level of the energy components fed to the radiator.

Another object of this invention is the provision of a radiator capable of producing a pair of overlapping asym- Y metrical lobes from a continuously energized compoundtype horn.

These and other objects of the invention which will become apparent as the description proceeds are achieved by the provision of a radiator comprising a single sectoral horn mounted above a pair of adjacent sectoral horns, the apertures of these horns lying in a commonplane. The mouth of the single sectoral horn is joined to and feeds energy to a rst input wave guide section of a Y-junction. The mouths of the adjacent horns are joined as a pair and feed energy to a second input wave guide section of the Y-junction, the wave guide sections of the junction having the same cross-sectional dimensions as the mouth of the first horn and the combined mouths of the adjacent horns. The output Wave guide section of the Y-junction is connected to an output sectoral horn which is ared in a plane perpendicular to that of the above-mentioned horns. Microwave energy is fed to each of the pair of adjacent horns in phase opposition with respect to the other, and in phase quadrature with respect to the` microwave energy fed to the single horn. Switching means is provided which introduces a periodic phase reversal in the energy fed to the pair of horns in relation to the energy in the single horn to provide sequential mirror image asymmetrical space patterns.

For a better understanding of the invention reference should be had to the accompanying drawings, wherein,

Fig. l is a plan View of the radiating structure of the present invention;

Fig. 2 is a side elevational view of the radiator system;

Fig. 3 is a graphical plot of the `electric field intensity as a function of position across the aperture of the single horn and the pair of adjacent horns; and

Fig. 4 is a rectangular coordinate plot of the resulting far-field space pattern showing the energy measured in decibels as a function of angular deviation from a line perpendicular to the plane of the horn aperture.

With particular reference to the Vform of the invention as illustrated in the drawings, the numeral 10 indicates generally a source of microwave energy, such as, for example, the transmitter of an instrument landing system. Energy from the microwave source 10 is coupled to the input portion of an adjustable divider 11, which may be of any suitable type such as a hollow pipe wave guide Y-junction having a movable ap 12 for changing the ratio of energy transmitted through the two output portions. An adjustable phase shifter 15 and a rectangular hollow wave guide` 13 couple energy from the upper output portion of the divider 11 to a sectoral horn 14. The sectoral horn 14 is joined at its throat portion 16 to the wave guide 13.

Mounted directly below the sectoral horn 14 and in adjacent relationship to each other are a pair of sectoral horns 20 and 22 Whose respective apertures 24 and 26 lie in a common plane with the aperture 18 of the sectoral horn 14. The throat portions of sectoral horns 20 and 22, indicated at 28 and 30 respectively, are joined by a rectangular hollow wave guidesection 32. Energy from the lower output portion of the divider 11 is fed to the` sectoral horns 20 and 22 through a phase switch, indicated` generally at 19 (the form and function of which is hereinafter described), to an E-plane` T 36 in the wave guide 32 at a p oint mid-way between the throat portions 28 and 30 of the sectoral horns 20 and 22. By virtue of the additional path length, equal to a half wavelength at the operating frequency, provided by the loop 33, the electric field at any given point in the horn 20,. for example, at the aperture 24, is out of phase with the electric eld in the horn 2,2 at the corresponding point,` as at the aperture 26.

The instantaneous far-eld pattern generated by the multiple horn structure above described may be considered as made up of two components, hereinafter referred to as thesymmetric component and the anti-symmetric component. The symmetric component is radiated from the single horn 14 while the anti-symmetric component is radiated from the pair of adjacent horns 20 and 22 acting simultaneously. When the energy illuminating the single horn aperture 18 is in phase quadrature with respect to the energy illuminating the coplanar double apertures 24, 26, the far-field pattern generated is the algebraic sum of the component patterns. The phase quadrature relationship may be obtained by providing a difference in path length of a quarter of a wavelength between the transmission path from the source 10 to the aperture of the horn 14 and the transmission path from the source 10 to the apertures of the horns 20 and 22. The, phase shifter 15 provides additional adjustment to achieve theI desired phase relationship. By proper selection of horn shape, including the ilare angle, length of the horn, and formation of the throat portion where the horn is joined to the input wave guide, the energy distribution across` the aperture of any of the horns can be controlled. The

illumination that the far-field pattern of the horn follows` the same function. Thus, the` symmetric component of the far field is a Gaussian-like patter The horns 20 and 22 are preferably designed" so that,`

when energized 180 out of phase with each other, the illumination across the adjacent apertures 24 and 26 resembles approximately a Rayleigh function, which is the derivative of the Gaussian function; The illumination across the`combined apertures 24 and 26 is illustrated by curve 40 of Fig. 3. An aperture illumination' resembling the lRayleighfun-ction likewise produces a far-eld pattern -following the same function. Thus, t-he anti-symmetric component of the far-fieldV pattern is a Rayleighlike pattern. Moreover, the sum of these functions at the aperture of a horn, regardless of the ratioof energy levels therein, yields a space pattern resembling the algebraic sum of the components. With the horn apertures having an energy distribution according to the Gaussian and Rayleigh functions, the far-field pattern can be readily found by adding algebrai- 'callyrthe two curves 38 and l40ct Fig. 3, which also represent t-he far-field component patterns. The result is an asymmetrical space pattern, as Vshown by the curve 42 of Fig. 4, obtained vby the addition of the symmetrical and Aanti-symmetrical components which 'are derived respectively from the 4single horn 14 and the adjacent horns 20 and 22. u It will be appreciated -that the energy distrirbution in the far-eld Vpattern is partly affected by the power ratio of the symmetric and anti-symmetric components. Thus, the present invention provides a ready means for varying t-he shape of the pattern in space simply by regulating this power ratio, which can be accomplished by means of the adjustable divider 11.

By reversing the phase of the energy in the - horns 20 and 22, thealgebraic sign of the anti-symmetric component of the far-field pattern is changed, as indicated by therdotted curve 40', of Fig. 3. The dotted curve 42 of l'ig. 4 indicates the resulting pattern in space, and is a mirror image of t-he pattern 42 resulting from the antisymmetric component of curve 40. This 180 phase shiftl is periodically introduced by the switch 19, which alternately permits passage of energy through wave guide sections 44 and 46. These sections differ in path length by a half guide wavelength. One suitable switch for such purposes includes a motor 48 which drives a disc 50, the disc Ibeing provided around its periphery with a plurality of spokes. The spokes pass through gaps in each of the wave guide sections 44 and 46, and are so positioned that when a spoke intercepts one of the wave guidel sections, the other wave guide section is open to permit transmission of energy therealong. A switch of this type is described in detail in Patent No. 2,544,715 to R. B. Muchmore.

In order to avoid phase interferences in the elevational andthe horns 20 and 22 are combined and radiated from a single aperture. This is accomplished by the provision of a Y-junction wave guide section, indicated generally at 52, the branch arms 54 and 56 of which join the single lliorn14and the adjacent horns 20v and 22 at their respective apertures. The output portion 58 of the Y- junction 52 is narrowed in the E-plane to attenuate higher order modes which might be produced in the Y-junction. The output portion 58 is coupled to the throat of an output sectoral horn 59 which provides beam sharpness in elevation. The ilareV of the output horn 59 is perpendicular tothe flareV of thefsectoral horns 14, 20 and 22.

To improve the operation of the radiating system, impedan'celmatching-between the sectoral horns 14, 2i) and 22 and the Y-junction 52 is desirable. Thus matching irises formedby the projecting member '60 in each of the wave v'guide input portions 54 and 56 of the Y-junction 52 may be provided. Y A radio energy absorbent material 62 is preferably used asa lining for the inner surfaces of vthe,` sectoral horns to attentuate energy reected from the Y-junction 52 and to reduce intercoupling ,of'energy between the horns. Y e the `radiating system does; not require that the E-vector in ItV should be noted that theoperation of 4 the horns be aligned in any particular direction, i. e., the horns may be flared in either the E-plane or the H-plane.

While the horns 14, 20 and 22 have been described :as preferably generating aperture illuminations following Gaussian and Rayleigh functions, it should berunderstood that it is not essential `to lthe operation of the present invention that the energy distribution be limited tothese funcions only. They merely provide a ready basis for predicting the far-field pattern because of their self-reciprocal lproperties as above described. However, farifield patterns of various configurations can be generated by providing other aperture illuminationv functions from lthose described. Y

While the aperture 18 hasl been illustrated as having a width Ithat substantially equals that of the combined apertures 24 and 26, such relationship is not essential to the operation ofthe present invention, and in fact, a slightly narrower aperture in the single horn 14 may be desirable to limit side` lobe effect. be noted that lenses may be usedV in combination with the horn structure above described to provide additional shaping of the far-held pattern as may be required.

VFrom the above description, it will be appreciated that Ithe objects of the invention have been 'achieved by the provision of a radiating system which produces asymrnetricall overlapping lobes in space by the use of a coutinuously energized compound-type horn structure. Considerable latitude is provided in shaping the far-field pat- Y low pipe wave guide coupling the source -to said` pair of tern simply by modifying the power level and phase rela.

tionship of the energy components of the radiatingsystem by means of the divider 11 and phase `shifter 15.

It should be noted that, although the present invention has been particularly described as a radiating system, it may be readily adapted for use as a directional receiving system .as well. A the above construction and many aparently widely different embodiments of this invention Vcould be made without departing from the scope thereof,it is intended that all matter contained in the above description or Yshown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. Y

What is claimed is: t g

1. Ultra high frequency apparatus comprising a single sectoral horn, a vpair of sectoral horns having their apertures 'in a common plane with the aperture of said single sec-toral horn, Ithe apertures of said pairfof sectoral horns being in line and adjacent each other and parallel to the aperture of said single sectoral horn, a source of microwave energy, a hollow pipe wave guide coupling the source to said single sectoral horn, a Vbifurcated holsectoral horns, said bifurcated wave guide transmitting energy -to `the pair of sectoral horns in phase opposition to each other, means including a microwave Vswitch in series with'one of the wave guides for periodically Y shifting -the phase yof the energy in'one of the Vwave guides horn, the other of said input sections being joined to and coeXtensive with the-combined adjacent apertures of said pair of horns, the energy from said single sectoral?, horn being in phase quadrature with respect toy energy from said pair of sectoral horns-in the output wave guide.

section, and an `output sectoral horn ilared in a plane perpendicular to the flare-plane of said single and saidrpair of sectoral horns,.theroutput section ofthe Y-junction being joined to the throat portion of said output horn.

2. Ultra high frequency Vapparatus comprising a single sectoral horn, a pair of sectoral horns having their apertures in a common plane wi-th the apertureof said singlev sectoral horn, thenapertures of said pair of sectoral horns being in lline andV adjacent each other andV parallel to the,

In addition, it should n Since many changes could be made in aperture of said single sectoral horn, a source of microwave energy, means coupling the microwave source to each of said sectoral horns, said means coupling energy to said pair of horns in phase opposition with respect to each other, means for periodically changing the relative phase of the energy in said single lhorn and said pair of horns by 180, means including a pair of input hollow pipe wave guide sections and an output wave guide section joined in a Y-junction, one of said input sections being joined to and coextensive with the aperture of said single horn, the other of said input sections being joined to and coextensive with the combined adjacent apertures of said pair of horns, the venergy from said single sectoral horn being in phase quadrature with respect to energy from said pair of sectoral horns in the wave guide output section, and an output sectoral horn flared in a plane perpendicular to the areplane of said single and said pair of sectoral horns, the output section of the Y-junction being joined to the throat portion of said output horn.

3. Ultra high frequency apparatus comprising a single sectoral horn, a pair of sectoral horns having their apertures in a common plane with the aperture of said single sectoral horn, the apertures of said pair of sectoral horns being in line and adjacent each other and parallel to the aperture of said single sectoral horn, a source of microwave energy, a hollow pipe wave guide coupling the source to said single sectoral horn, a bifurcated hollow pipe wave guide coupling the source -to said pair of sectoral horns, said bifurcated wave guide transmitting energy to each of said pair of sectoral horns in phase opposition, means in series with one of the wave guides for periodically shifting the phase of the energy in one of the wave guides relative to the phase in the other of ythe wave guides by 180, means including a pair of input hollow pipe wave guide sections and an output wave guide section joined in a Y-junction, one of said input sections being joined to and coextensive with the `aperture of said single horn, -the other of said input sections being joined to and coextensive with the combined adjacent apertures of said pair of horns, and an output sectoral horn joined at the throat portion thereof to the output section of the Y-junction.

4. Ultra high frequency apparatus comprising a single sectoral horn, a pair of sectoral horns having their apertures in a common plane with the aperture `of said single sectoral horn, the apertures of said pair of sectoral horns being in line and adjacent each other and parallel to the aperture of said single sectoral horn, a source of microwave energy, a hollow pipe wave guide coupling the source to said single sectoral horn, a bifurcated hollow pipe wave guide coupling the source to said pair of sectoral horns, said bifurcated wave guide transmitting energy to said pair of sectoral horns in phase opposition to each other, means in series with one yof the wave guides for periodically shifting the phase lof the energy in one of the wave guides relative to the phase in the other ofthe wave guides by 180, and an output sectoral horn ared kin a plane perpendicular to the Hare-planes of said single and said pair of sectoral horns, and means coupling energy to the throat portion of ythe output sectoral horn from the apertures of said single sectoral horn and said paid of sectoral horns.

5. Ultra high frequency apparatus comprising a single sectoral horn, a pair of sectoral horns having their apertures in a common plane with the aperture `of said single sectoral horn, the apertures of said pair of sectoral horns being in line and adjacent each other and parallel 4to the aperture of said single sectoral horn, a source of micr0- wave energy, a hollow pipe wave guide coupling the source to said single sectoral horn, a bifurcated hollow pipe wave guide coupling the source to said pair of sectoral horns, the energy at the aperture of said single sectoral horn being in phase quadrature with respect to energy at the apertures of said pair of sectoral horns, said bifurcated wave guide transmitting `energy to said pair of sectoral horns in phase opposition to each other, and means including a microwave switch in series with one of the wave guides for periodically shifting the phase of the energy in one of the wave guides relative to the phase in the other of the wave guides by 6. Apparatus for radiating asymmetrical mirror image lobes, said apparatus comprising a microwave source, a single horn, a pair of horns in side-by-side relationship and radiating from a single aperture, means coupling each of the horns to the microwave source, said means coupling energy to the single horn in phase quadrature with respect to energy coupled -to said pair of horns, said means further coupling energy to said pair of borns in phase opposition with respect to each other, and switching means in series with said coupling means and adap-ted to periodically change the relative phase of :the energy in the single horn and the pair of horns by 180.

7. Apparatus for generating consecutively a pair of asymmetrical overlapping radio beams, said apparatus comprising rst horn means radiating a symmetrical component, second horn means radiating an anti-symmetrical component, said first and second horn means radiating en ergy from a common aperture, the energy from said iirst horn means being in phase quadrature with respect to the energy from said second horn means at said common aperture, and means for periodically changing the relative phase of the energy from said rst horn means and from said second horn means at the common aperture by 8. Apparatus for generating consecutively a pair of asymmetrical overlapping radio beams, said apparatus comprising iirst horn means radiating a symmetrical component, second horn means radiating an anti-symmetrical component, and means for periodically changing the relative phase of the energy from said first horn means and from said second horn means.

References Cited in the le of this patent UNITED STATES PATENTS 2,415,242 Hershberger Feb. 4, 1947 2,438,735 Alexanderson Mar. 30, 1948 2,438,987 Bailey Apr. 6, 1948 2,461,005 Southworth Feb. 8, 1949 2,482,162 Feldman Sept. 20, 1949 2,514,678 Southworth July 11, 1950 2,540,839 Southworth Feb. 6, 1951 2,556,094 Lindenblad June 5, 1951 2,627,020 Parnell et al J an. 27, 1953

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