US3521286A - Orthogonal array antenna system - Google Patents

Description

July 21, 1970 J. A. KUECKEN ORTHOGONAL ARRAY ANTENNA SYSTEM Filed April 21, 1967 IN VEN TOR. JOHN A; KUECKEN United States Patent Ice US. Cl. 343-730 Claims ABSTRACT OF THE DISCLOSURE An orthogonal antenna system having a plurality of distinct and separately tuned channels is described. The antenna comprises at least three mutually orthogonal radiating elements, with the first being a vertical radiator and the second and third being horizontal radiators.

The present invention relates to receiving and transmitter antenna systems, and more particularly the invention relates to antenna systems having a plurality of independent (decoupled) and separately tunable radiators.

There has long been a need for antenna systems which combine in unitary structure, means for simultaneously broadcasting or receiving non-interfering radio waves which are in the same frequency band.

In view of the foregoing, it is an object of the invention to provide an improved multichannel antenna system.

A further object of the invention is to provide an antenna system having at least three decoupled and separately tunable radiators.

A still further object of the invention is to provide a multichannel antenna system which may be mounted in limited space and which is substantially maintenance free.

Briefly described, an antenna system in accordance with the invention employs three mutually orthogonal radiators which are coupled together at an electrically balanced or neutral point. The first radiator is a vertical polarized radiator and the remaining two are horizontally polarized radiators which not only broadcast, but also provide a counterpoise for the vertical radiator.

Preferably, the horizontal radiators are folded dipoles, whereas the vertical polarized antenna is preferably a folded monopole antenna.

An important feature of this invention is the provision of the radiators in a mutually orthogonal relation. Because of the orthogonal relationship, the radiators are substantially decoupled and may be independently tuned over wide operating frequency ranges.

The invention itself, both as to its organization and method of operation, as well as additional objects and advantages thereof will become more readily apparent from a reading of the following description in connection with the accompanying drawings in which:

FIG. 1 is a diagrammatic perspective illustration of an antenna system in accordance with the invention, partially broken away for clarity of illustration, which shows, in schematic form, tuning elements for the various radiators;

FIG. 2 is a detailed view of one of the horizontal radiators shown in FIG. 1; and

FIG. 3 is a detailed view of the vertically polarized folded monopole element shown in FIG. 1.

It is preferable that a multichannel transmitting or receiving antenna system, having a series of radiators operable in a given frequency range, should include both vertical and horizontal polarized radiators. Moreover, it is preferable that the vertical radiator be provided with a good counterpoise or ground plane, especially if its radiating length is less than one-half of a wave length (A) at its operating frequency.

Turning now to the drawings, an antenna system is 3,521,286 Patented July 21, 1970 shown comprising three mutually orthogonal elements 2, 4 and 6 which are electrically coupled together at a balanced neutral point 7. The vertical element 2 is shown to be a folded monopole structure, whereas the horizontal elements 4 and 6 are folded dipoles. The term mutually orthogonal means that any selected radiator is substantially at right angles to the other two radiators. Both the horizontal radiators 4 and 6 are identical and are physically connected at the neutral point 7 so as to provide a counterpoise or ground plane for the vertical radiator 2. Actually, each radiator is provided with its own coaxial input line 9a, b and c, respectively, which may be coupled to separate transmitters or receivers, not shown. A single lead line 11 connects the outer conductors of each of the coaxial feed lines 9 to ground.

Each of the radiators sees the junction or neutral point 7 to be at zero volts by reason of symmetry if the radiators are physically balanced as will be discussed hereinafter. Because of this arrangement there will be substantially no interference between the radiators; this is especially true if the radiators are disposed in a mutually orthogonal relationship.

Each of the horizontal radiators 4 and 6 is the same and only one need be described. The radiator 6 (see FIG. 2) is in the form of a folded loop of a two wire transmission line which may, for example, be a coaxial cable and which terminates at two spaced free ends 10a and 10b. The free end 10a is shown coupled directly to its coaxial input line 9b. A capacitor C bridges the feed gap between the free ends 1011 and 10b and interconnects the inner conductor at the end 10a to the outer conductor at the 10b and a second capacitor C is shunt connected across the feed gap of the radiator and connects the outer conductor at the ends 10a and 10b. By adjusting the reactance of each of the capacitors C and C the radiator may be closely matched to the impedance of its input transmission line 9b.

In addition the dead leg 6a provides a near zero impedance connection for the vertical monopole 2 thereby providing a highly effective counterpoise connection without mutual impedance. Measured data for a set of /36A radiators yielded an isolation of 45 db with both units tuned to the same frequency and with complete independent tuning.

Preferably, the vertical radiator 2 (see FIG. 3) is a folded monopole antenna formed in a U shaped member having two spaced arms 12 and 13 interconnected by means of a conductive merging section 14. The arm 12 is connected at its free end to ground. At point 15, the arm 13 is shown to be connected to the inner conductor of its two-wire transmission line 9c.

Preferably, the arms 12 and 13 should be substantially parallel and located at a small distance from each other as compared to the wavelength that is emitted. The antenna 10 may be formed from a strip of elementary wire, or, where ruggedness is required, from conductive metal pipe.

Experimentally, it has been determined that if the length of the grounded arm 12, which is designated by the dimension d, corresponds to greater than V 1 of the wave being emitted, then the radiation resistance will be a substantial quantity. On the basis of test data, the radiation resistance appears to increase as a function of the square of the frequency as d progressively corresponds to an. increasingly greater percentage of Put differently, after about x, the radiation resistance increases exponentially as the square of frequency. At the same time, the other resistance components of the antenna 10, namely the skin component R and the nominal resistance component R appear to respectively vary as a function of the square root of the frequency and linearly with the frequency. When the length of the grounded arm 12 is 3 less than x, these relationships do not hold true.

As viewed from the neutral point 7, when the dimension d corresponds to a range of from about /3 to VGA, the antenna will behave as though it were an element having a high inductive impedance. Accordingly, capacitive type tuning means may be employed to match the impedance of the radiator 2 to the transmission line 90 so that the radiator 2 and the transmission line 90 Will substantially be in resonance at any operating frequency in this range. The ability to tune with capacitive elements is especially advantageous inasmuch as inductive tuning elements interpose losses which degrade antenna system efficiency.

As shown in FIG. 3, an adjustable capacitor 19 is coupled between the junction 15 of the arm 13 and ground, in shunt across the transmission line 16, and a second adjustable capacitor 21 is disposed serially in one lead of the transmission line just before the feeding point 15. The capacitors 19 and 21 are so positioned in order to preserve line balance. With this arrangement, the greater portion of impedance matching tuning is accomplished by the capacitor 19, whereas a fine tuning adjustment is made by the capacitor 21.

The capacitors 19 and 21 may, of course, be mounted in sealed weatherproof containers, and it has been found preferable to have the capacitor 19 mounted immediately adjacent the ground location so that the arms 12 and 13 are substantially the same length. It has further been found that when the dimension d corresponds to'more than /6)\, the capacitive tuning shown in FIG. 3 is not effective to match the antenna to the transmission line. This match may be then accomplished by providing a shorting switch, which when closed provides a short circuiting path between the two antenna arms 12 and 13. With this configuration, by simply closing the switch, the antenna may be tuned beyond /6)\ of its overall length (viz dimension :1) until the radiator 2 begins to assume a capacitance reactance as viewed by the transmission line. Similar shorting switches may be used in the horizontal and vertical elements 4 and 6 both in their active and dead legs.

From the foregoing description it will be apparent that there has been provided an improved antenna system. Variations and modifications of the illustrated antenna system and components therefor will undoubtedly become apparent to those skilled in the art. Although the folded elements are preferred, other elements such as whips may also be employed in accordance with the invention. Moreover, the coupling to such whips may be What is claimed is:

1. An antenna system comprising a first element and at least two other folded dipole elements disposed in mutually orthogonal relationship and connected to each other at a neutral point, said folded dipoles being closed except for a feed gap, one side of each of said dipoles is a coaxial conductor, the outer conductor of which is connected to said first element at said neutral point and the inner conductor of which provides a feed line terminating at said feed gap, and means for coupling signals independently with respect to said neutral point whereby said elements are substantially decoupled from each other and can be independently tuned over Wide operating frequency ranges.

2. The invention as set forth in claim 1 including tuning means for each of said dipoles which comprises first and second capacitors connected across said gap, said first capacitor being in series with the feed line for its respective one of said dipoles.

3. An antenna system comprising a monopole element and a folded dipole element closed except for a feed gap, said dipole element and monopole element being disposed in mutually orthogonal relationship and connected to each other at a neutral point, one side of said dipole being a coaxial conductor, the outer conductor of which is connected to said monopole element at said neutral point and the inner conductor of which providing a feed line terminating at the feed gap.

4. The invention as set forth in claim 3 wherein an additional coaxial conductor is provided for feeding said dipole, the outer conductor of said additional coaxial conductor being connected to said dipole at said neutral point and the inner conductor of said additional coaxial conductor extending through the neutral point region and being connected to the inner conductor of the coaxial conductor which forms said one side of said dipole.

5. The invention as set forth in claim 3 wherein tuning means for said dipole comprises first and second capacitors connected across said gap, said first capacitor being in series with said feed line.

References Cited UNITED STATES PATENTS

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