US2966678A - Multifrequency resonant antenna - Google Patents

Description

, Dec. 27, 1960 E. F. HARRIS 2,966,678

MULTIF'REQUENCY RESONANT ANTENNA Filed March 27, 1958 x 1% osc/zmr/on/s 1269/ 5i 2 2 J2 T326 55 2&5

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Z; 16/ @zzamw United States Patent P MULTIFREQUEN CY RESONANT ANTENNA Edward F. Harris, 4729 Farwell, Lincolnwood, Ill.

Filed Mar. 27, 1958, Ser. No. 724,466

7 3 Claims. 01. 343-809) My invention relates to an improved multifrequency resonant antenna in which a common conducting element coacts with a plurality of helices to provide resonance at a plurality of frequencies.

Antennas for radio use perform best when resonant at the frequency of operation, since reactive impedance components then disappear and efncient coupling is attained with respect to the connected transmission line or other circuit elements. However, since the antenna frequency of resonance is a function of length it is not normally possible to operate an antenna at more than one wavelength without loss of resonant action. Where multifrequency operation is required, the practice has normally been to use some form of complex antenna array having traps of one sort or another or to use a nonresonant array. These expedients are, however, undesirable because they degrade the electrical performance of the antenna by making it moredifficult to load, they frequently result in inactive antenna sections at some frequencies, and they introduce severe problems of maintenance. 7

The above problems are particularly acute in short antenna for mobile use, where each element of antenna length must be used for eflicient performance, the antenna is subject to adverse physical conditions, and quick shifts from one frequency to another without adjustment are necessary.

In the antenna herein described and claimed an elongated conducting element, preferably vertically oriented,

is of substantially less than a quarter wave length at the shortest wave length to be radiated, thus providing a short overall antenna height. A plurality of helical top elements are mounted on the free end of this first, or common, conducting element. Each helix is dimensioned to providein conjunction with the common conducting elementresonant operation at one of the selected frequencies. In operation of the antenna, each helix becomes active at its own frequency and serves to define a complete resonant antenna. out substantially aifecting the operation of the other helices, thus providing essentially the same operation that would otherwise be secured from a plurality of individual antennas of similar length and tuned individually to the respective frequencies. Preferably, one helix is mounted coaxially with the common element of the antenna and other helices are mounted at a substantial angle to this helix and to each other.

It is therefore a general object of the present invention M It is another object of the present invention to provide an improved multi-frequency antenna that operates with substantially the same effectiveness as a single frequency antenna of similar length.

Yet another object of the present invention is to pro- This is done with? ice vide an improved multi-frequency antenna having a common base element for all frequencies crowned by other elements which become active at their own separate frequencies to provide effective multi-frequency operation.

A still further object of the present invention is to provide an improved multi-frequency antenna which involves no switching elements, involves no complex circuit configuration, is readily manufactured, has small size and length, is of pleasing design and configuration and in other respects is particularly suitable for effective commercial operation.

The novel features which I believe to be characteristic of my invention are set forth with particularity. in the appended claims. My invention itself, however, will best be understood by reference to the following descrip-.

tion taken in conjunction with the accompanying drawing in which:

Figure 1 is a fragmentary elevational View, with parts broken away, of an embodiment of the antenna of the present invention;

Figure 2 is a fragmentary top-plan view of the antenna of Figure 1; V

Figure 3 is a fragmentary, cross-sectional view through axis 3-3, Figure 2;

Figure 4 is a top-plan view of an alternative embodiment of the present invention arranged for di-pole operation; and

Figure 5 is a fragmentary chart showing the VSWR characteristics of the antenna of Figures 1-4.

As shown in Figure 1 the antenna may be mounted on a fiat conducting plate 10 which may, for example,

be the flat top surface of the trunk of an automobile. This plate has an opening in which is disposed the insulating spacer 12 which in turn receives the metallic conducting socket 14, which may, for example, be of aluminum. The source of oscillations 16 is connected to plate 10 (which serves as a ground plate to define a ground plane) and to the socket 14, as shown.

The base portion of the antenna is indicated generally at 18. It consists of a lengthy tube 22 of conducting material, such as aluminum, which is received in base cap 20 and is secured therein by means of a friction fit or otherwise. Base cap 20 is of aluminum or other conducting material. Threaded stub 23 of cap 20 is thread edly received in the socket 14 as shown. Tube 22 of the base portion 18 is the principal radiating portion of the antenna. It may be in the form shown, that is a conducting tube, or may consist of a wire conductor in the form of a helix wound with a relatively large pitch on an insulating low-loss core.

At its top end the base portion 18 is received in' header 24, shown in Figures 1, 2 and 3. This header is of a suitable conducting material, such as aluminum. It is of generally cylindrical shape, as shown. At its bottom end the header 24 has a bore 25, Figure 3, in which the rod 22 is loosely received as shown. Header 24 may be rotated around tube 22 and, when the desired orientation is attained, is secured thereto by set-screw 25. At

its top end the header 24 has a threaded socket 24a,-

The threaded opening 24a in cap 24 receives stub 27;

of the base cap 26 of the upper helical element indicated generally at 28, Figures 1, 2 and 3. As shown in Fig- Patented Dec. 27,1960

ures 1 and 3, this helical element is defined by the wire 30 which is wound about the fibreglass core 32 to form a helix. The helix so formed is covered and encased by the plastic jacket 34 as shown. This plastic jacket which may be of vinyl plastic is applied by the method described and claimed in my co-pending patent application Serial Number 687,286, filed September 30, 1957 and entitled Whip Antenna and Process of Fabricating the Same. In brief, the plastic 34 is initially in the form of a tube of smaller inner diameter than the outer diameter of the core and wire. The tube is dilated by application of a suitable chemical. It is then slipped over the assembled core 32 and helix 38 and base cap 26. The dilator then evaporates to restore the original character of the plastic and form a tight adherent sheath about the unit. It will be noted that the conductor 30 defining the helix extends through the center of core 32, Figure 3, to be received in the opening 262; of base cap 26 where it is soldered or otherwise joined to make a good electrical contact with the base. The element 28 has a plastic top cap 36, as shown, to protect the same from rain.

Each of the sockets 24d on faces 24c and 24b, Figures 2 and 3, receives an element constructed similarly to the element 28. That is, each includes an insulating core, a helix wound upon the core, and a suitable tought jacket, together with a base portion which is threadedly received in one of the sockets 24d of header 24. The element received in the flat 24b is indicated at 38 and its base cap is indicated at 40, Figures l-3. The element received in the face 24c is indicated at 42, Figures 1 and 2 and has base cap 44.

The helix 28 is wound with suflicient turns to cooperate with the base portion 18 to define an effective resonant antenna at one frequency range to be radiated. Preferably this is the lowermost frequency range, and for this the length of the element 28 is considerably greater than that of elements 38 and .2. In order to minimize antenna length and height and to provide maximum radiating efiiciency of the base element 18, it is desirable to wind the turns of element 28 as closely as conditions permit thereby making possible a maximum length of base 18 for any given antenna height.

The elements 38 and 42 are wound to define a resonant antenna system in connection with the common conductor or base 18 at the respective frequencies of the elements 38 and 42. Thus at one frequency of operation the element 38 cooperates with the base 18 to form a resonant antenna unit. At the other frequency the element 42 cooperates with the base 18 to form a like unit. These two frequencies are preferably higher than the frequency at which element 28 is active.

In a practical antenna constructed for use in the radio amateur 10, 15, and 28 meter bands, the following dimensions were employed:

Overcall antenna height (from support Length of helical elements 38 and 42 12 inches. Diameter of helical elements 38, 28

and 42 inch.

The conductor used on helical elements 28, 38 and 42 is number 20 AWG enameled copper wire. As indicated above the turns are as closely spaced as possible in the elements 28. In elements 38 and 42 they are spaced as required to provide the necessary resonant operation in the and 15 meter bands, respectively.

It will be observed from Figure 2 that'the helical elements 38 and 42 are approximately at right angles to each other as seen in top plan view. These elements are also disposed on a common plane with itself has a substantial angle to the axis of the element 18, although not Thus the elements 28, 38 and 42 have their axes at substantial angles to each other and there is minimum coupling between these axes. It has been found that with antennas constructed substantially in the form of Figures 1-3 that such coupling does not affect the operation of the unit and that actual operation is essentially that obtained with a single unit consisting of the base portion 18 and a coaxial helix adjusted for the specific frequency of operation.

While the present invention finds its major application in the case of vertical or whip type antennas, it may also be used with horizontal antennas, including dipole constructions. Figure 4 shows such a unit. In brief, an insulating support element indicated diagrammatically at serves to support in insulating fashion a pair of conducting sockets 114, each of which receives an element like that of Figures 1-3, each such element having a base portion 118, a helix 128 for one frequency, a helix 138 for the second frequency, and a helix 142 for the third frequency. A source of oscillations 116 provides the necessary power to operate the dipole unit.

The voltage standing wave ratio (VSWR) of the antenna described above of the entire frequency range of interest is shown in Figure 5. It will be noted that this ratio reaches essentially unity at the most favorable, or resonant point in each curve, and that in each instance the ratio is reasonably favorable within the band width involved.

In the appended claims the axes of the magnetic fields of the helices (or other inductance elements) are referred to as projecting outwardly from post 18 or extending away from the same to indicate that as the helix (or other inductance element) is traversed away from its point of connection to the post, the distance from the axis of the post increases.

While I have shown and described specific constructions of the antenna of the present invention it will be understood that other constructions may be used as well. Specifically, the unit may be arranged with only two helices, in which event operation is obtained on two separate frequencies. Alternatively, more than three helices may be used to obtain as many different resonant operating frequencies. Also, the orientation of the respective helices may be varied considerably without causing undesirable interaction and degradation of antenna performance. I therefore intend by the appended claims to cover all such modifications and alternative constructions as fall within their true spirit and scope.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A multifrequency antenna effective in relation to a plane of uniform potential in resonant action at a plurality of frequencies, comprising in combination: a conductor extending directly from said plane and having a linear base section and a top section connected thereto, said conductor as a whole being resonant at one of said wavelengths and the base section being less than one quarterwave length at the shortest of the wavelengths; and a plurality of inductance elements, one for each of the others of said wavelengths, connected respectively to the base section of the conductor at the point of connection of the top section, said inductance elements extending away from the base section and from each other, each of said inductance elements being resonant in conjunction with the linear base section of the conductor at one of the others ofsaid wavelengths to define a radiator in which radiation and reception occurs primarily from the base section of the conductor, whereby at said first wavelength the conductor is active as a whole to provide resonant operation and at each of the other wavelengths one of the inductance elements is active in conjunction with the base section of the conductor.

2. A multifrequency antenna effective in resonant action in relation to a plane of uniform potential at at least first and second wavelengths, comprising in combination: an elongated conducting element extending directly from said plane having length substantially less than a quarter wave at the shortest of said wavelengths; a first helix having its axis substantially coaxial with the elongated conducting element, said helix being physically disposed at the end of said conducting element and connected to said end, said helix being resonant in conjunction with the conducting element at said first wavelength to define a radiator in which radiation and reception occurs primarily from the elongated conducting element; a second hel.x having its axis oriented along a line projecting outwardly from said end of the conducting element and at a substantial angle to the axis of said first helix, said second helix being physically disposed at the end of said conducting element and connected thereto, said second helix being resonant in conjunction with the conducting element at said second wavelength to define a radiator in which radiation and reception occurs primarily from the elongated conducting element, whereby at said first wavelength the first helix is active in conjunction with the conductfng element to provide resonant antenna operation without substantial degradation due to the second helix and at the second wavelength the second helix is active in conjunction with the conducting element to provide resonant antenna operation without substantial degradation due to the first helix.

3. A multifrequency antenna effective in resonant action in relation to a plane of uniform potential at any one of a plurality of wavelengths, comprising in combination: an elongated conducting element extending directly from said plane having length substantially less than a quarter wave at the shortest of said wavelengths; and a plurality of helices, one for each of said Wavelengths, disposed at the end of said conducting element and connected to said end, said helices having their respestive axes differently oriented in relation to said conducLng element to locate the same in positions defining an inverted apex in relation to said element, the helices being respectively resonant in conjunction with the conductng element at the respective ones of said plurality of wavelengths, whereby at each of said wavelengths a single one of said helices is active in conjunction with the conducting element to provide resonant antenna operation without substantial degradation due to the other helices.

References Cited in the file of this patent UNITED STATES PATENTS 2,611,868 Marston et al Sept. 23, 1952 2,630,530 Adcock et a1. Mar. 3, 1953 2,673,931 Stevens Mar. 30, 1954 2,850,732 Kandoian et a1 Sept. 2, 1958 2,875,443 Kandoian Feb. 4, 1959 FOREIGN PATENTS 1,008,359 France May 16, 1952

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