Abstract:
A method to feed antennas proximal to a monopole antenna is shown. A monopole antenna is fed through a ground plane by a conventional means. A transmission feed line for an antenna proximal the monopole antenna passes through the ground plane and makes contact with the monopole antenna at some distance from the ground plane, this contact being made by a non-signal carrying conductor of the transmission line. In the special case of a coaxial feed transmission line, this non-signal carrying conductor is the outside of the outermost conductor of the coaxial feed line. After making contact with the monopole antenna the feed line then passes through or along the side of a monopole antenna to reach the antenna proximal to the monopole.

Description:
This application claims benefit to U.S. provisional application Ser. No. 60/157,121, filed Oct. 4, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to antenna feed methods, and more particularly to antennas for transmitting and/or receiving electromagnetic energy. More particularly, the invention relates to a method to feed antenna(s) in close proximity to a monopole. 
     2. Description of the Prior Art 
     Monopole antennas are known in the art and described in numerous antenna texts. U.S. Pat. No. 4,814,777 issued to Monser teaches an antenna system comprising a vertical monopole antenna coupled to a first feed on a ground plane conductor and a dipole antenna comprising a plurality of horizontal dipole antenna elements coupled to a corresponding plurality of feeds on the ground plane conductor. The plurality of dipole antenna elements being disposed about the first feed. The vertical monopole antenna comprises a plurality of monopole antenna elements, the plurality of monopole antenna elements and the plurality of dipole antenna elements being alternately radially disposed about the first feed. 
     U.S. Pat. No. 3,739,390 issued to Poppe, et. al., teaches a dual antenna system including first and second antennas respectively capable of operating at first and second distinct frequency ranges. The antenna system taught comprises a coaxial transmission line having a central conductor and an outer conductor surrounding and insulated from the central conductor. The central conductor of Poppe has a section that extends axially beyond the outer conductor, at least a portion of which defines a radiating element of a first antenna. A pair of intersecting conductors coupled to the outer conductor of Poppe&#39;s antenna system extend radially for defining a first reference for element for a first antenna and also defining a radiating element of a second antenna. The pair of intersecting conductors serve as a load element for the outer element thus increasing the effective electrical length of the second antenna. A grounded sleeve surrounds and is insulated from the outer conductor and defines a second reference element for the second antenna. The inner conductor serves to feed one antenna and the outer conductor feeds the second antenna and the two antennas are fed from the same point from the ground plane. 
     U.S. Pat. No. 2,498,655 issued to Faymoreau, et. al. teaches an orientable antenna arrangement comprising a plurality of N superimposed antenna systems where N is the number of systems each rigidly mounted on a mast structure. The mast structure comprising in space a coaxially fixed relationship a vertical central conducting member and a plurality of coaxial tubular conducting members there being one more of the conducting members than there are antenna systems. The antennas taught by Faymoreau are each fed coaxially to each other through the same point in the ground plane. 
     SUMMARY OF THE INVENTION 
     A method to feed antennas proximal to a monopole antenna is shown. A monopole antenna is fed through a ground plane by a conventional means. A transmission feed line for an antenna proximal the monopole antenna passes through the ground plane and makes contact with the monopole antenna at some distance from the ground plane, this contact being made by a non-signal carrying conductor of the transmission line. In the special case of a coaxial feed transmission line, this non-signal carrying conductor is the outside of the outermost conductor of the coaxial feed line. After making contact with the monopole antenna the feed line then passes through or along the side of a monopole antenna to reach the antenna proximal to the monopole. 
     A feed method is defined herein as the method used to convey the signals from the transmitter to an antenna and to convey signals from an antenna to the receiver. 
     The feed method taught herein provides both a method of feeding antennas in the proximity of the monopole and helps a monopole to obtain a wider impedance bandwidth. This feed method is applicable to feeding any types of antennas that are in the proximity of a monopole. A balun and impedance matching circuit for the attached antenna, if needed, may be located either inside or outside the monopole. The specific type of monopole used is not pertinent, the monopole can be thin, thick, cage, conical, inverted conical, printed-circuit, or any other type of monopole. This method has been shown to work well with conical monopoles and inverted conical monopoles, both of solid and caged wire construction. For typical flared or conical monopoles the electrical contact point taught herein is typically located at more than 0.1 wavelength from the monopole feed point. At certain frequencies where a flared or conical monopole is approximately 0.15 wavelengths long, the presence of the electrical contact taught herein produces a higher input resistance for the monopole feed, hence assisting in impedance matching the monopole and allows the monopole height to be reduced. 
     The above brief description sets forth rather broadly the more important features of the present invention in order that the detailed description thereof that follows may be better understood, and in order that the present contributions to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject matter of the claims appended hereto. 
     In this respect, before explaining the invention in detail, it is to be understood that the invention is not limited in its application to the details of the construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood, that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. 
     As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for designing other structures, methods, and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
     It is therefore an object of the present invention to provide a method to feed antennas proximal to a monopole antenna. 
     It is also an object of the present invention to allow that antennas in close proximity to a monopole can be used with minimum degradation of performance of either the monopole or the other antennas. 
     It is a further object of the present invention to improve the impedance bandwidth performance of the monopole. 
     It is another object of the present invention to reduce the overall dimensions of the volume occupied by the antenna system, including the monopole. 
     It is an another object of the present invention to provide a feed method that is relatively easy to construct and results in extremely broadband performance of the antenna system. 
     It is another object of the present invention to obviate the need for costly, narrowband concentric coaxial feed structures for plural antennas. 
     These together with still other objects of the invention, along with the various features of novelty which characterize the invention, are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be made to the accompanying drawings and descriptive matter in which there are illustrated preferred embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood and the above objects as well as objects other than those set forth above will become more apparent after a study of the following detailed description thereof. Such description makes reference to the annexed drawings wherein: 
     FIG. 1 is a block diagram of a method to feed an antenna system where the antenna system includes a first antenna in close proximity to a monopole antenna. 
     FIG. 2 is a close-up diagram of the method illustrated in FIG. 1 showing a cross-sectional slice through a two conductor coaxial feed transmission line, it&#39;s relation to a monopole and to a ground plane. 
     FIG. 3 is a close-up diagram of the method illustrated in FIGS. 1 and 2, showing a longitudinal slice through a two conductor coaxial feed transmission line, it&#39;s relation to a monopole and to a ground plane. 
     FIG. 4 illustrates an example of the instant invention employing a pair of crossed dipole antennas orthogonal to a conical monopole antenna and parallel to a ground plane. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference now to the drawings, a signal feed method for an antenna system including a first antenna in close proximity to a monopole antenna embodying the principles and concepts of the present invention will be described. 
     FIG. 1 is a block diagram showing an antenna system  10  comprised of a first antenna  16  in close proximity to a monopole antenna  18 . The antenna  10  is shown with the ground plane  20 . First antenna  16  is fed from first transmitter/receiver  12  by first transmission feed line  50  including a first signal carrying conductor  26 , a second signal carrying conductor  28   b  and a first non-signal carrying conductor  28   a.  Monopole antenna  18  is fed from second transmitter/receiver  14  by second transmission feed line  60  including a third signal carrying conductor  22  and a fourth signal carrying conductor  24 . Alternatively, monopole antenna  18  may be fed by any conventional means through the ground plane. First electrical conductor  30  connects the monopole antenna  18  to the surface of the first non-signal carrying conductor  28   a  which feeds the first antenna  16 . The first electrical conductor  30  is connected from first contact point  30   b  on the monopole antenna  18  to second contact point  30   a  on the first non-signal carrying conductor  28   a.  The non-signal carrying conductor  28   a  is connected to the ground plane  20  by electrical conductor  36 . The electrical conductor  36  is connected to the non-signal carrying conductor  28   a  at a third contact point  36   a  and to the ground plane  20  at a fourth contact point  36   b.  First electrical connector  30  and second electrical connector  36  need not be of visible length but may be solder or other convenient means of electrical contact. Circuits for baluns, impedance matching, and phasing may be inserted between first conductor  26 , second conductor  28   b  and first antenna  16  if needed for feeding first antenna  16 . 
     If the type of transmission line feeding antenna  16  does not provide a non-signal carrying conductor  28   a,  an additional conductor should be inserted to connect points  30   a  and  36   a.  This additional conductor does not need to extend to first antenna  16 . 
     FIG. 2 is an example of the antenna system  100  where the feed transmission line  500  to the first antenna is a coaxial cable  320 . The antenna system  100  includes a first antenna (not shown), a monopole antenna and a ground plane. A small portion of the monopole antenna is shown at  180  and a small portion of the ground plane is shown at  200 . The coaxial cable  320  is shown in cross section and shows how it is connected to the monopole antenna  180  and the ground plane  200 . The coaxial cable  320  includes a layer of insulation  340  intermediate an inner signal carrying conductor  260  and an outer conductor  280 . The monopole antenna  180  is fed by conventional means and is specifically not fed by feed transmission line  500 . Outer conductor  280  has a signal carrying inner surface  280   b  and a non-signal carrying outer surface  280   a.  The first electrical connector  300  connects the non-signal carrying outer surface  280   a  to monopole antenna  180 . The first electrical conductor  300  is connected from first contact point  300   b  on the monopole antenna  180  to second contact point  300   a  on the non-signal carrying conductor  280   a.  The non-signal carrying conductor  280   a  is connected to the ground plane  200  by a second electrical conductor  360 . The second electrical conductor  360  is connected to the non-signal carrying conductor  280   a  at a third contact point  360   a  and to the ground plane  200  at a fourth contact point  360   b.  First electrical connector  300  and second electrical connector  360  need not be of visible length but may be of solder or other conventional means of electrical contact. After contacting the monopole at  300   b  coaxial cable  320  may pass either into the monopole antenna  180  or it may pass along the outside of the monopole antenna  180 . 
     FIG. 3 is a second view of the antenna system  100   a  where the feed transmission line  322  is a coaxial cable  320   a.  The antenna system  100   a  includes a first antenna (not shown) and a monopole antenna. A small portion of the monopole antenna is shown at  182  and a small portion of the ground plane is shown at  202 . The coaxial cable  320   a  or feed transmission line  322  has insulation intermediate an inner conductor  262  and an outer conductor  282 . Outer conductor  282  has an inner surface  282   b  and an outer surface  282   a.  First electrical conductor  302  makes connection with the outer surface  282   a  of the outer conductor  282  at first contact point  302   a.  First electrical conductor  302  is also connected with the monopole antenna  182  at second contact point  302   b.  Second electrical conductor  304  makes connection with the outer surface  282   a  at third contact point  304   a.  Second electrical conductor  304  is also connected to the ground plane  202  at fourth contact point  304   b.  First electrical connector  302  and second electrical connector  304  need not be of visible length but may be solder or other conventional means of electrical contact. After contacting the monopole at  302   b,  coaxial cable  322  may pass either into monopole antenna  182  or it may pass along the outside of monopole antenna  182 . 
     FIG. 4 is the antenna system of the instant invention employing a monopole  184  with a pair of crossed dipoles  400 ,  404  respectively. Monopole antenna  184  is fed via any conventional means by feed transmission line  224  from transmitter/receiver  144 . Monopole  184  is illustrated to be a conical monopole. In this example, the first antenna is chosen to be a pair of crossed dipole antennas  400  and  404 , these antennas being in close proximity to monopole  184 . The crossed dipoles in this example are orthogonal to each other and parallel to the ground plane  204  but this is not a requirement of the invention. Crossed dipole antennas  400  and  404  are fed from transmitter/receiver  124  via signal carrying feed lines at  264 , and non-signal carrying conductor  284 . Non-signal carrying conductor  284  contacts the monopole surface at electrical contact point  354  via solder or any convenient means. Feed lines  264  enter monopole  184  near contact point  354 . Non-signal carrying conductor  284  may also enter monopole near contact point  354 . Said contact point may be at a distance, on monopole  184 , from ground plane  204  of about 0.1 or more wavelengths of the lowest frequency to be employed. When monopole  184  provides sufficient interior space, then baluns, phasing, and impedance matching circuits  444  may be deployed inside the monopole as required to assist in feeding the dipoles,  400  and  404 . Circuits at  444  may or may not be needed and may also be located outside of monopole  184 . Transmission feed lines  264  from transmitter/receiver  124  connect to circuits  444  whence they are divided into separate feed lines. Feed line  294   a  feeds dipole element  190  of dipole  400 ; feed line  294   c  feeds dipole element  192  of dipole  400 ; feed line  294   d  feeds dipole element  194  of dipole  404 ; feed line  294   b  feeds dipole element  196  of dipole  404 . 
     It is apparent from the above that the present invention accomplishes all of the objectives set forth by providing a method to feed antennas close to a monopole such that antennas in close proximity to a monopole can be used with minimum degradation of performance of either the monopole or the other antennas and that the impedance bandwidth performance of the monopole is achieved whilst reducing the overall dimensions of the volume occupied by the antenna system, including the monopole. 
     With respect to the above description, it should be realized that the optimum dimensional relationships for the parts of the invention, to include variations in size, materials, shape, form, function and manner of operation, assembly and use, are deemed readily apparent and obvious to those skilled in the art, and therefore, all relationships equivalent to those illustrated in the drawings and described in the specification are intended to be encompassed only by the scope of appended claims. 
     While the present invention has been shown in the drawings and fully described above with particularity and detail in connection with what is presently deemed to be the most practical and preferred embodiments of the invention, it will be apparent to those of ordinary skill in the art that many modifications thereof may be made without departing from the principles and concepts set forth herein. Hence, the proper scope of the present invention should be determined only by the broadest interpretation of the appended claims so as to encompass all such modifications and equivalents.