US2834013A - Plural antenna assembly - Google Patents

Description

May 6 1958 `F. x. BUCHER ETAL PLURAL ANTENNA ASSEMBLY Filed sept. 2. 1953 Risparmi/a MA TCH/Nq asv/ce TRANSPO//DR D/SNC'E PLURAL ANTENNA ASSEMBLY Francis X. Bucher and Richard J. Fahnestock, Nutley,

and Frank l. Lnndburg, East range, N. J., assignors .to International Telephone and Telegraph Corporation, Nutley, N. J., a corporation of Maryland Application September 2, 1953, Serial No. 377,995

12 Claims. (Cl. 343-726) No. 229,629, filed June 2, 1951, for Antennas, an antenna assembly is disclosed for use as an omnidirectional radio beacon. This beacon antenna assembly comprises a cage structure containing a rotating dipole antenna and a loop antenna disposed symmetrically with respect to the dipole to provide a rotating pattern in the form of a cardioid which is generally horizontally polarized. In this beacon antenna assembly the cage structure is extended vertically above the portion containing the two antennas, this extension being required to suppress the vertical polarization component rof the beacon radiation that would otherwise be present if it Were not for this upper extended section.

One of the objects of the present invention is to incorporate in the upper cage structure of this type of beacon antenna one or more additional antenna units without altering the beacon radiation characteristics thereof.

Another object is to provide a type of antenna within I having independent radiations, combined within a single j structure normally required for one of said antennas thus economizing in supporting structures and overall dimen- .sions otherwise required' by the three units when separated.

The above-mentioned and other objects of this invention will become more apparent upon reference to the following description taken in conjunction with the accompanying drawings, wherein:

Fig. l is a view in side elevation of an omnidirectional radio beacon with parts broken away illustrating the incorporation of two additional antenna units therein in accordance with the principles of this invention; and

Figs. 2 and 3 are cross-sectional views taken along lines 2-2 and 3 3, respectively, of Fig. l.

Referring to the drawing, Fig. l shows an omnidirectional radio beacon provided with a counter-poise 1 above which is disposed a small rotatable dipole 2. The dipole is driven by a motor 3 which is supported on a dielectric platform t. The dipole is rotated at 1800 R. P. M. to produce a rotating ligure-of-eight radiation. Above the dipole is a loop antenna 5 adapted to produce a circular radiation. Surrounding the antennas 2 and 5 is a first or outer cylindrical cage 6 having conductive pieces at the bottom and top thereof, such as indicated by the top piece 7. The cylindrical wall of the cage comprises a plurality of spaced conductive rods 8, as indicated more clearly in Figs. 2 and 3. This outer cage functions as a resonator energized by the antennas 2 and 5. The spacing of the en-d pieces at 1 and 7 is preferably selected slightly greater than a half wavelength of the lowest operating frequency. The rods 8 are spaced 2,834,013 Patented Mayv 6, 1 958 2 sulliciently close together to provide anetfective vertical polarization screen or filter -sothat only horizontally polarizedenergy-passes. Each two adjacent rods 8 -form effectively the boundaries of a short section'of waveguide which acts as the ultimate radiators. As it is longer than a half wavelength it will freely pass radiated energyin the TEN mode.

The structure so far described will provide-a rotating radiation field pattern in the shape -of a cardioid which will be generally horizontally polarized. Howevendue to the resonator yaction of the cage ya certain amount-of vertical polarization may be radiated from the'cage `structure due to radiation about -the upper end of the cage. This vertical polarization is substantially entirely overcome by extending the cagestructurerone or moreflengths vupwardly above the cage which contains the two antennas 2 and 5. -This upper structure is indicated by the -tw-o sections 9 and 10. From experience it is found that rthis upper structure should extend about yl2 feet above the cage section 6 in order to satisfactorily suppress undesired vertical polarization. lSince the 4dipole 2 is short with respect to the wavelength it would normally tend to have a low radiation resistance and an undesirable high capacitive reactance. The resonator formed bythe cage 6 does not fully Iovercome this deliciency of the short dipole. In order to load the dipole antenna properly to achieve a desired compensation, the loop antenna 5 -is mounted and formed as apart ofa second or inner cage 6a composed lof a plurality of circularly disposed vertical rods 8a. When the loop antennais properly adjusted vertically within the cage, the `spacingthereof `with respect to the lower end of the cage will be less than a half wavelength in the uppermost frequency so thatthe resonator action of the cage will be inductive.

.In the operation of the beacon, two transmitter units.12 I

i6 and thence through transmission line 17 to the dipole 2, and the other through a phaser 18 -to a second relay 19 for application through the adjustable matching device 20 and transmission line 21 to the loop antenna 5. The rotating antenna 2 is driven by motor 3 from a power source 22. The rotation of the dipole 2 producesv a reference signal by means of a tone-wheel 23 from the shaft of the motor 3. This reference signal, which is applied to the transmitter 14 through connection 24 is frequency modulated, for example, from about 9.48 to 10.44 kc. at a rate of 30 C. P. S. This reference signal modulates the V. H. F. signal tha't feeds the loop antenna. All modulation is removed from the portions of the V. H. F. signal that feeds the dipole. The rotation of the dipolealso produces a 30 C. P. S. variable phase signal which is in the form of a space modulation.

From the kforegoing description of the omnidirectional beacon it will be clear that an omnidirectional radiation pattern is obtained by means of the rotating dipoleZ,

the omnidirectional radio beacon, we also employ these cage sections for additional functions. In section 9 we provide an antenna 25 for distance measuring equipment (D. M. E.). The D. M. E. antenna 25 preferably cornprises a vertical stacked array of antenna units 26a whereby a vertical polarized omnidirectional radiation pattern is obtained, the array insuring a flat substantially horizontal lobe. The antenna units may be fed so as to tilt the radiation beam up or down with respect to the horizontal plane as may be desired. Such an array suitable for this purpose is disclosed in U. S. Patent 2,533,236. The cage section 9 is subdivided by a plate 27a thus dividing the section into two parts each less than one-half wavelength long at the omnidirectional beacon frequency to thereby render more uniform the wave front radiation of the D. M. E. antenna. While the antenna 25 does not atfect adversely the radiation pattern of the omnidirectional beacon, we find it necessary to incorporate a secon-d cage formed by an inner row of equally spaced conductive rods 26 circumferentially of the stacked array. The rods 26 may be of the same diameter as the rods 8a of the first or lower section 6. The two cages thus provided about the D. M. E. -antenna act as if they were a double-stub tuner and thereby serve to match the D. M. E. antenna to the free space about the outer cage. In other words, the D. M. E. antenna is a source of S-band energy which propagates through the openings between the adjacent rods of each of the concentric cages, the rods being spaced with openings equal to or greater than a half wavelength at the frequency of the energy propagated by this antenna. The openings or spaces between the adjacent rods of the cages impose dis' continuities to the radial propagated wave. The radius of the inner row of rods 26 is chosen so as to place the proper discontinuity in such a position that it will serve to match along with the discontinuity imposed by the outer row of rods 8a the wave impedance of the source to free space. This is similar in effect to the operation of a fixed double-stub tuner on a two-wire transmission line.

By locating the D. M. E. antenna 25 within the double cage section 9 the only influence of the cages observed is the suppression of minor lobes of the D. M. E. antenna. This tendency to suppress the minor lobes, however, operates to Yconcentrate more energy into the major lobes which results in increasing the effective range of the D. M. E. antenna. The D. M. E. radiation pattern is vertically polarized and has no adverse effect upon the radiation of the omnidirectional beacon of section 5.

The feed line cable for the antenna 25 preferably passes through one of the rods of the outer or inner cages of section 6. As shown it is extended up through a hollow rod 27 to the input connector 28 of the antenna 25.

in the top-most section l!) we provide microwave beacon antenna 29 which may be of the type disclosed in the Massachusetts Institute of Technology, Radiation Laboratory Series. volume l2, pages 325 to 328. The beacon antenna 29 is divided into a receiver section 30 and a transmitter section 31. By disposing these two sections on a common vertical axis the radiation pattern of each is substantially independent of the other. The radiation patterns of the beacon antenna sections are not affected by the conductors 8 since at the microwave frequencies used a half wavelength is very much shorter than the spacing between the conductors 8 and also than the distance between the upper and lower plates of the cage section 10. The waveguide feed lines for the two antenna sections Sti, 3l must be brought up along the cage without affecting the radiation patterns of the lower antennas. This is done by enlarging two fof the cage conductors in the form of rectangular waveguides as shown at 32 and 33. The waveguide 32 is coupled to the transmitter section 3l while the waveguide 33 is coupled to the receiving section 30. The lower end of the waveguide 32 is likewise coupled to a transponder E24 while the lower end of the waveguide 33* is coupled to a responder 35, the transponder and the responder units provided for two-way communication.

The reason why the cage structure in the upper two sections suppresses some signals while passing others is apparent from the Well-known theory of structures such as waveguides and of slots in conductors. Electromagnetic waves lare propagated through such a structure if the dimension perpendicular to the direction of polariza` tion of the electrical field is a half wavelength or greater, and are suppressed if the dimension is less than a half wavelength. Thus, each dimension establishes a cutoi frequency for modes in which the electric field is perpendicular thereto. In cage section 9, the spacing of the rods is such that for vertically polarized signals the cutoff frequency is between the frequency of the omnidirectional antenna and the frequency of the D. M. E. antenna. ln the `cage section 1d, the frequencies of the microwave beacon are very high, and therefore the wavelengths are very short compared to all dimensions of the openings in the cage.

From the foregoing it will be clear that the three antenna sections of the assembly shown in Fig. l operate independently and without any adverse interference with the others. The omnidirectional antenna system of the lower section 6 requires the upper sections 9 and 10 of the cage structure to suppress the vertical polarized component of its radiated energy. The D. M. E. antenna of section 9 employs the outer cage 8 for its feed line leads and, in conjunction with the inner cage formed by conductors 26, as a tuned filter for the passage of vertically polarized radiation properly matched to the open space about the outer cage. While the D. M. E. antenna does not affect the operation of the cage as a suppressor of the vertical polarized `component of the omnidirectional antenna means of section 6, the cage structure thereabout enhances the radiation pattern of the D. M. E. antenna by increasing the range of the major lobes thereof. The beacon antenna of section 10 also employs certain of the conductors of the outer cage as leads for coupling the transmitter and receiver sections thereof to the corresponding ground equipment. The surrounding cage does not affect adversely the radiation patterns of section 3()V ably less than where such antennas are mounted inde.

pendently of each other.

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

We claim:

l. ln combination. an omnidirectional antenna assembly cornnrising a vertically disposed cylindrical cage structure divided by a conductive plate into lower and upper antenna sections, iirst antenna means disposed in the lower section to produce a radiation pattern horizontally polarized at a first frequency, second antenna means disposed in said upper section to produce a radiation pattern vertically polarized at a second frequency, the upper cage section being formed of a plurality of circumferentially spaced vertically disposed conductors with openings between them having a width of less than a half wavelength at said iirst frequency and at least a half wavelength at said second frequency to suppress the vertical polarized component of the radiation from said lower section and to pass therebetween vertically polarized radiation from said second antenna means.

2. The combination according to claim l, wherein the second antenna means comprises a stacked array of antenna elements and a second series of circularly spaced vertically disposed conductors with openings between them at least a half wavelength wide at said second frequency located concentrically about said second antenna means within said cage structure and constituting therewith a double tuned structure for impedance matching between the radiators of said array and free space.

3. In combination, an omnidirectional antenna assembly comprising a vertically disposed cylindrical cage structure divided by a conductive plate into lower and upper antenna sections, first antenna means disposed in the lower section to produce a radiation pattern horizontally polarized at a first frequency, second antenna means comprising a beacon antenna system including a transmitter section and a receiver section disposed along a vertical axis coaxially of said cage structure disposed within said upper section for radiation and reception of signals in a second frequency range, the upper cage section being formed of a plurality of circumferentially spaced vertically disposed conductors with openings between them having a width of less than a half wavelength at said first frequency to suppress the vertical polarized component of the radiation from said lower section, the dimensions of said openings being greater than a half wavelength in said second frequency range to pass therebetween radiation from said second antenna means.

4. The combination according to claim 3, wherein certain of the vertical conductors of said cage structure are in the form of waveguides, one of said waveguide conductors being coupled to the receiver section and the other waveguide conductor being coupled to the transmitter section of said beacon antenna.

5. In combination, a cylindrical cage structure, conductive plates dividing said cylindrical structure into three sections, the cylinder of said cage being formed by a plurality of circumferentially spaced vertically disposed conductors, first antenna means disposed in the lower section of said cage structure for radiation of horizontally polarized signals at a first frequency, second antenna means disposed in the intermediate section for radiation of vertically polarized signals at a second frequency, and third antenna means disposed within the uppermost cage section for radiation and reception of signals in a third frequency range, the vertical conductors of the other two sections disposed above said lowersection being spaced with openings of less than a half wavelength at said first frequency and at least a half wavelength at said second and third frequencies to suppress any vertically polarized energy of said first antenna means and to pass therebetween the energy of said second and third antenna means.

6. The combination according to claim 5, wherein said first antenna means comprises a rotating dipole and a loop antenna for radiation of a cardioid pattern.

7. The combination according to claim 5, wherein the second antenna means comprises a vertically stacked array of antenna units for radiation of an omnidirectional pattern; and said intermediate cage section includes an inner cage comprising a plurality of circumferentially spaced vertically disposed conductors with openings at least a half wavelength wide at said second frequency which cooperate with the vertical conductors of said intermediate cage section to provide a double tuned structure for impedance matching of the radiated energy of said second antenna means with respect to free space.

8. The combination according to claim 5, wherein the third antenna means comprises a transmitting antenna section and a receiving antenna section disposed axially of said cage structure; and certain of the vertical conductors of said cage are in the form of waveguides with means coupling one of said waveguide conductors to said transmitter section and means coupling the other of said waveguide conductors to said receiver section.

9. The combination according to claim 5, wherein said first antenna means comprises a rotating dipole and a loop antenna for radiation of a cardioid pattern; the second antenna means comprises a vertical stacked array of antenna units for radiation of an omnidirectional pattern; and said intermediate cage section includes an inner cage comprising a plurality of circumferentially spaced vertically disposed conductors with openings at least a half wavelength wide at said second frequency which cooperate with the vertical conductors of the cage section to provide a double tuned structure for impedance matching of the radiated energy of said second antenna means with respect to free space.

l0. The combination according to claim 5, wherein said first antenna means comprises a rotating dipole and a loop antenna for radiation of a cardioid pattern; the third antenna means comprises -a transmitting antenna section and a receiving antenna section disposed axially of said cage structure; and certain of the vertical conductors of said cage are in the form of waveguides with means coupling one of said waveguide conductors to said transmitter section and means coupling the other of said waveguide conductors to said receiver section.

1l. The combination according to claim 5, wherein said first antenna means comprises a rotating dipole and a loop antenna for radiation of a cardioid pattern; the second antenna means comprises a vertically stacked array of antenna units for radiation of an omnidirectional pattern; said intermediate cage section includes an inner cage comprising a plurality of circumferentially spaced vertically disposed conductors with openings at least a half wavelength wide at said second frequency which cooperate with the vertical conductors of the cage section to provide a double tuned structure for impedance matching of the radiated energy of said second antenna means with respect to free space; the third antenna means comprises a transmitting antenna section and a receiving antenna section disposed axially of said cage structure; and certain of the vertical conductors of said cage are in the form of waveguides with means coupling one of said waveguide conductors to said transmitter section and means coupling the other of said waveguide conductors to said receiver section.

l2. In combination, an omnidirectional antenna assembly comprising a vertically disposed cylindrical cage structure divided by a conductive plate into lower and upper antenna sections, first antenna means disposed in the lower section to produce a radiation pattern horizontally polarized at a first frequency, the upper cage section being formed of a plurality of eircumferentially spaced vertically disposed conductors with openings between them having a width of less than a half wavelength at said first frequency and at least a half wavelength at said second frequency to suppress the vertical polarized component of the radiation from said lower section and second antenna means disposed in said upper section to produce a radiation pattern vertically polarized at a second frequency, the vertical slots formed by the vertical conductors of said cage structure being at least a half wavelength wide at said second frequency to pass vertically polarized radiation from said second antenna means, said second antenna means comprises a stacked array of antenna elements and a second series of circularly spaced vertically disposed conductors with openings between them at least a half wavelength wide at said second frequency located concentrically about said second antenna means within said cage structure and constituting therewith a double tuned structure for impedance matching between the radiators of said array and free space, one of the vertical conductors of said cage structure being hollow and a feed line is contained therein for coupling to said antenna array.

References Cited in the file of this patent UNITED STATES PATENTS 2,533,236 Felsenheld Dec. l2, 1950 2,640,930 Lundburg et al June 2, 1953 2,726,388 Kandoian Dec. 6, 1955

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