US 3229297 A
Description (OCR text may contain errors)
Jan. 11, 1966 R L. BELL ET AL 3,229,297
WIDE-BAND DUAL CONICAL ANTENNA WITH lNTERMEDIATE IMPEDANCE TRANSITION COUPLlNG Filed Aug. 22, 1965 2 Sheets-Sheet l ca '1 m I Q 2 3 n: "'3 Q) N 9 l- 9\ t N) x l I &
1 Ir c\\l \l \i \I N N N N N N N N P k N N INVENTORS Ross Leon BeH Orville Lee McCIeIIand Jan. 11, 1966 R L. BELL ETAL 3,229,297
WIDE-BAND DUAL CONICAL ANTENNA WITH INTERMEDIATE IMPEDANCE TRANSITION COUPLING Filed Aug. 22, 1963 2 Sheets-Sheet 2 INVENTORS Ross Leon Be BY Orville Lee McCleHand Agents United States Patent 3,229,297 WIDE-BAND BUAL CONTCALANTENNA WITH INTERMEDIATE IMPEDANCE TRANSITION CGUPLING Ross Leon Bell, Dallas, and Orvilie Lee McClellanrl, Richardson, Tex., assignors to Collins Radio Company, Cedar Rapids, Iowa, a corporation of Iowa Filed Aug. 22, 1%3, Ser. N 303,740 4 Claims. (Cl. 343-722) This invention pertains to broadband antennas and particularly to antennas that have respective lower conical structures effective over wide frequency ranges and coupling means for effectively adding upwardly extending elements to convert the antennas to monopoles of substantial cross section for extending their ranges to lower frequencies.
A conical antenna that is mounted on its apex over a good ground plane provides sufficient omnidirectional horizontal radiation over a wide range of frequencies for communication with widely dispersed stations. If signal of frequencies still lower than the normal wide range is fed to the conical antenna, the predominate lobe of the antenna field pattern is no longer directed along the horizon. However, a vertical monopole of substantial diameter, a broad or fat monopole, effectively radiates signal horizontally with frequencies that have corresponding wavelengths several times the physical height of the antenna.
According to the present invention, the lower portion of an antenna structure functions as a conical antenna with its usual horizotaolly directive characteristics for a wide band of frequencies, and both the lower and upper portions function as a broad monopole for an extended lower range of frequencies. An antenna utilizing this principle is readily constructed for operation over a frequency range in which the ratio of the highest frequency to the lowest frequency is at least 9:1. According to this invention, an antenna comprises a lower simulated con ical antenna structure that has its apex directed downward and an upper structure that is coupled to the conical antenna through impedance matching stubs. The impedance of these stubs is high for the higher frequencies but becomes low for lower frequencies to couple the upper and lower structures as the frequencies become too low to be radiated effectively by the lower conical portion. To provide a simple, rigid structure, the upper structure of a preferred embodiment also resembles a cone. The apex of the upper cone is directed upward. Both conical structures are supported by a simple vertical tower and guy wires. The impedance matching stubs for coupling the upper and lower cones are conveniently spaced twowire transmission lines that appear as a hoop positioned coaxially about an intermediate point on the tower and as spokes that extend radially from that point to the hoop. Each conductor of the hoop is a circular edge of a respective cone. The radial lines cooperate with guy wires to position the hoop.
An object of this invention is to extend the frequency range of a conical antenna.
A feature of the invention is the utilization of two-wire transmission lines for coupling the upper and lower portions of the antenna and also for contributing mechanically to the support of the antenna.
The following description and appended claims may be better understood with reference to the accompanying drawings in which:
FIG. 1 is a top oblique view of the antenna of this invention; and
FIG. 2 is a fragmentary view of an intermediate portion of FIG. 1 to show in detail the means of coupling the upper and lower structures.
3,22%,297 Patented Jan. ll, M266 With reference to FIG. 1, the upper conical structure 10 and the lower conical structure 11 of the antenna are supported vertically by the central tower 12. In pracflee, the tower 12 is a trussed metal structure and the apices of the upper and lower conical antenna portions are connected respectively to the top and bottom of the tower. However, the antenna system would function effectively when a non conductive supporting tower is used.
The upper cone with its apex pointing upward comprises a plurality of equally spaced conductors 13 extending downwardly from a metal fastening plate 14 that is secured to the top of the tower 12. The number of conductors 13 is determined by the size of the antenna structure and by the range of frequencies of the signals that are to be radiated by the upper structure. A suflicient number of conductors must be used to support the lower conical portion and to appear as a substantial electrical radiating surface to the signals within its effective frequency range. Since both the upper and lower portions of the antenna function as a broad monopole for signals within the range of frequencies at which the upper portion is effective, the upper portion need not necessarily resemble a cone, but obviously the conical construction provides a simple, rigid structure. An antenna of FIG. 1 with the dimensions that are shown below performs very satisfactorily with six upper conductors 13. The lower end of each of the upper conductors 13 is connocted to the top end of a respective insulating spacer 15. The insulating spacers 15 are held outwardly by guy w' es 16 that extend from the centers of the insulators to the ground and that are broken electrically into passive short lengths by series of spaced insulators 17. Other than the guy wires, the wires or conductors that are fastened to the insulators are electrical parts of the antenna.
Two conductors 1S and 19 are spaced apart by insulators l5 to appear as a hoop about an intermediate point on tower 12. The conductors tie mechanically the upper and lower cones ill and 11. In FIG. 2, the upper condoctor 18 is fastened to the lower ends of the conductors 13 of the upper cone at the respective insulators 15. The radius of the hoop that is formed by conductors 13 and 19 is determined by the length of each of the six shortcircuited two-wire transmission lines that comprise conductors 20 and 21. The conductors 20 and 21 of each of the transmission lines extend radially from a respective spacer 22 that is connected to the intermediate point of the tower 12 to a respective insulating spacer 15. At a required distance from each insulator is, a shorting bar 23 is connected across the conductors 2i and 21 to form an impedance matching stub for coupling the upwardly extending conductors 13 and opposite conductors of the lower cone. The upper conductor 20 of each radial line is connected to a respective upwardly extending conductor 13 and to the upper conductor 18 of the space lines that form the hoop.
The cage of the lower cone has more conductors than that of the upper cone for the lower cone must be effective to radiate signals over a range of frequencies that are higher than the range of frequencies of the signals that are radiated by the upper and lower structures together as a monopole. A lower radiating conductor 24 extends from a conductive fastening plate 26 at the bottom of the tower upward to each of the insulators 15. According to the specifications of a preferred embodiment of the antenna as given below, three conductors 25 are evenly spaced in each space between adjacent conductors 24. The conductors 24 for the lower cone that correspond to the upwardly extending conductors 13, are connected at respective insulators 15 to the lower conductor 19 of the transmission line that is in the form of a hoop and to the lower conductor 21 of the respective ductors extend radially from the base of the antenna.
radial transmission lines. At high frequencies, the portions of the transmission line near the insulators offer high impedance between the upper conductors 13 and the conductors 24' and 25 of the lower cone. The intermediate conductors 25 extend from the fastening plate 26 upward across both conductors 18 and 19 of the hoop so that the two conductors of the hoop are short-circuited where the conductors 25 are fastened. The conductors 18 and 19 of the hoop can be replaced by a single conductor that corresponds to the lower conductor 19. However in practice, a more uniform standing-wave ratio at the input of the antenna over a wide frequency range is provided by the coupling of the hoop that is in addition to the coupling provided by the impedance matching stub at the outer end of the radial lines.
The antenna must be mounted proximate a good ground plane in order that the lower inverted cone functions in cooperation with its image in a biconical mode to provide an omnidirectional, horizontally directed field pattern. The antenna is supported over its ground plane by mounting the apex of the lower cone on the mounting insulator 27. In a practical installation, 36 buried con- In the event that a small elevated antenna structure is used to radiate signal of still higher frequencies, a counterpoise can be utilized for the ground plane. Signal of a selected frequency over a wide frequency band is applied by feed cable 28 between the lower conductive fastening plate 26 and ground.
An antenna according to FIG. 1 with a height of 68 feet has a frequency range from 3 to 30 megacycles. At the lower frequency at which the antenna functions as a monopole, the effective height of the monopole is 0.2 wavelength. The 24 conductors that extend from the hexagonal hoop to the lower apex simulate a vertical cone for a range of frequencies from 3 to about 9 megacycles. The transitional range of frequencies at which the mode of operation of the antenna is transferred from that of an inverted cone to that of a broad monopole is 2 megacycles wide at about 9 megacycles. The direction of maximum radiation of the antenna is along the horizon except during transmission of signal having frequencies in the narrow transitional band. The input impedance of the antenna is about 59 ohms and the maximum voltage standing-wave ratio on the transmission feed line does not exceed 3:1. The shorting bars 23 on the radial transmission lines are placed so that the impedances of the stubs change from low to high values for frequencies in the transitional region. The upper structure is prevented from being an effective radiator for signals at the high end of the frequency range because the matching stubs offer a high impedance to eliminate radiation currents on the upper structure.
Although this invention has been described with reference to a single preferred embodiment, other equivalent antenna configurations that operate in a biconical mode over a wide range of high frequencies and have impedance matching means for coupling upwardly extending radiating elements to the top of the conical structure to convert the mode of operation to that of a monopole for extending the frequency range to lower frequencies, may be constructed by those skilled in the art and still be within the scope of the following claims.
What is claimed is: V
1. A broadband antenna having a lower structure that is electrically a right-circular conical configuration and an upper structure that is a plurality of upwardly directed radiating members, said conical structure being mounted on its apex with its axis vertical and its apex near a ground plane, transmission line means for applying signal voltage between said apex and said ground plane, means for mounting said upwardly directed members to extend upwardly from the upper circumferential edge of said conical structure, said members being spaced apart, the lower ends of said members being spaced slightly apart from said upper edge so that negligible direct coupling of the signal exists between said conical structure and said upwardly directed members, inductive-capacitive coupling means connected between the lower end of each of said upwardly directed radiating members and an adjacent point on said upper circumferential edge of said conical structure, the impedance of said coupling means being sufficiently high at frequencies higher than a transitional range of frequencies to prevent substantial transfer of signal energy between said conical structure and said upwardly directed members, said impedance of said coupling means being sufficiently low at frequencies lower than said transitional range of frequencies to permit said antenna to function as a broad monopole, said transitional range of frequencies being at the higher end of a frequency range over which said conical structure provides substantial radiation in a horizontal plane, and the operation of said coupled conical structure and upwardly directed members as a monopole substantially extending the frequency range of said antenna to frequencies much lower than the lowest frequencies that can be radiated effectively horizontally by said conical structure only.
2. A broadband antenna having a lower structure that is electrically a right-circular conical configuration and an upper structure that is a plurality of upwardly directed radiating members, said conical structure being mounted on its apex with its axis Vertical and its apex near a ground plane, transmission line means for applying signal voltage between said apex and said ground plane, means for mountig said upwardly directed members to extend upwardly from the upper circumferential edge of said conical structure, said members being spaced apart, the lower ends of said members being spaced slightly apart from said upper edge so that negligible direct coupling of the signal exists between said conical structure and said upwardly directed members, a short-circuit transmission line as an impedance matching stub connected between the lower end of each of said upwardly directed radiating members and an adjacent point on said upper circumferential edge of said conical structure, the impedance of said stubs being sufficiently high at frequencies higher than a transitional range of frequencies to prevent substantial transfer of signal energy between said conical structure and said upwardly directed members, said impedance of said stubs being sufficiently low at frequencies lower than said transitional range of frequencies to permit said antenna to function as a broad monopole, said transitional range of frequencies being at the higher end of a frequency range over which said conical structure provides substantial radiation in a horizontal plane, and the opera tion of said ooupled conical structure and upwardly directed members as a monopole substantially extending the frequency range of said antenna to frequencies much lower than the lowest frequencies that can be radiated effectively horizontally by said conical structure only.
3. A broadband cage antenna comprising upper and lower radiating right-circular cones, said cones being coaxially mounted with a common axis perpendicular to a ground plane, said cones being oppositely disposed, the apex of said lower cone being mounted near said ground plane, the base of the upper cone being spaced a short distance above the upper circular edge of said lower cone, means for applying radio-frequency energy between said lower apex and said ground plane, a plurality of impedance matching stubs, each stub comprising a pair of spaced lines having a sho-rt-circuited end and an open end, the open end of each stub being connected between a point on the base of said upper cone and an adjacent point on the upper circular edge of said lower cone, said stubs being closely enough spaced around the adjacent peripheries of said' cones to provide close ooupling'therebetween for the lower frequencies within the overall frequency range of said antenna, said stubs having relatively high impedance for the higher frequencies that are Within the overall range of frequencies of the antenna, said lower cone functioning to provide radiation of said higher frequencies along the horizon, said stubs having a relatively low impedance for said lower frequencies within said frequency range to couple together the adjacent peripheries of said cones so that said antenna functions as a broad monopole to provide radiation for said lower frequencies along the horizon to extend the effective range of said antenna to frequencies lower than those effectively radiated horizontally by said lower cone only.
4. A broadband antenna comprising a supporting vertical tower, a plurality of radiating members aranged to form a lower cone and an upper cone coaxially supported by said tower, the base of each of said cones comprising a circular conductor, means for positioning said circular conductors about an intermediate point of said tower so that said conductors are parallel and positioned relative to said tower as a rim of a wheel is to its hub, the spacing between said circular conductors being appropriate for their use as short-circuited transmission lines to provide transition from low to high impedance within the frequency range of said antenna, a plurality of said radiating members of said upper cone extending from the top of said tower to uniformly spaced points on said circular conductor of said upper cone, an interconnecting conductive termination at the bottom of said tower, a plurality of said radiating members of said lower cone extending from said circular conductor of said lower cone to said termination at the bottom of said tower, said radiating members for said lower cone being more closely spaced than said radiating members of said upper cone, each of said members of said upper cone having an opposite corresponding member of said lower cone, each of said corresponding pairs of members being connected to opposite points on their respective circular conductors, a pair of radial parallel conductors connected from each opposite pair of said uniformly spaced points on said circular conductors to said intermediate point on said tower, each portion of said circular conductors and also said radial conductors that connect to each of said uniformly spaced points being short-circuited at required distances from said spaced points to provide low impedance coupling between said lower and upper cones for signal frequencies lower than a desired transitional frequency band of said antenna, input means for applying signal between said interconnecting termination at the bottom of said tower and a ground plane, said termination being proximate said ground plane, said lower cone predominating in the amount of radiation at frequencies higher than said transitional frequency band, and both of said cones effectively radiating together as a single monopole for frequencies lower than said transitional frequency band.
References Cited by the Examiner UNITED STATES PATENTS 2,508,657 5/1950 Teller-Bond 343-874 2,724,052 11/1955 Boyer 343 791 2,898,590 8/1959 Pichitino 343722 FOREIGN PATENTS 861,878 1/1953 Germany.
HERMAN KARL SAALBACH, Primary Examiner. A. R. MORGANSTERN, Assistant Examiner.