US3509573A - Antennas with loop coupled feed system - Google Patents

Description

April 28, 1970 K. G. BALMAIN ANTENNAS WITH LOOPCOUPLED FEED SYSTEM 2 Sheets-Sheet 1 Filed June 16, 1967 FIG. 2 PRIOR ART) F G. 7 (PRIOR ART) Attorney April 28, 1970 K. G. BALMAIN 3,509,573

ANTENNAS WITH LOOP COUPLED FEED SYSTEM Filed June 16, 1967 3 Sheets-Sheet 2 TO 7 E RMI NA Tl ON A ttorn e y I W /KM United States Patent 3,509,573 ANTENNAS WITH LOOP COUPLED FEED SYSTEM Keith George Balmain, Toronto, Ontario, Canada, as-

signor to The Governors of The University of Toronto, Toronto, Ontario, Canada Filed June 16, 1967, Ser. No. 646,675 Int. Cl. Hfllq 11/10, 21/12, 9/16 U.S. Cl. 343-7925 16 Claims ABSTRACT OF THE DISCLOSURE An antenna array comprising substantially coplanar and parallel unitary elements arranged in side by side relation and a feed or collector system therefor extending longitudinally of the array comprising a pair of conductors disposed to form in combination loops extending between and electrically insulated from adjacent elements; each of the loops being comprised of a portion of each of the conductors extending longitudinally of and contiguous each of the respective adjacent elements with the directions of such portions of each conductor being reversed at adjacent elements and with the direction of such portion of one conductor being opposite to the direction of such portion of the other conductor at each element when tracing the directions of such conductors from one end of the array.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to antennas for use in radiatedwave propagation communication systems and more particularly, to a novel system for feeding antennas from a source in the case of transmission or collecting signals from antennas in the case of reception resulting in more simplified and mechanically stronger antennas than heretofore possible, wherein the antenna elements or dipoles associated with the feed system are unitary elements rather than pairs of separate members.

The invention has, for example, particular application to the field of antennas such as are employed to provide unidirectional radiation patterns (or to provide unidirectional reception) that are essentially independent of frequency over wide bandwidths. An antenna of the type for which the invention has particular application is fully described in U.S. Patent 3,210,767, granted Oct. 5, 1965. Su'ch an antenna is known as a log-periodic antenna and involves the use of an array of substantially coplanar and parallel dipoles or elements of progressively, mathematically defined, increasing length and spacing in side by side relationship.

Description of the prior art In the prior art, as represented, for example, by U.S. Patent 3,210,767, the dipoles or elements are constituted by pairs of members which are fed in sequence by a common feeder which alternates in phase between successive elements or dipoles, the array being symmetrical about a line passing through the midpoint of each element or dipole constituted by the two separate members. Such an array has a backfire radiation being fed fro-m the smaller end and radiating toward the smaller end.

The necessity of forming each element or dipole of a pair of members so that the feed can be alternated in phase between successive dipoles gives rise to mechanical problems of supporting the elements in their proper orientation and leads to misalignment of the pair of members of each element.

SUMMARY OF THE INVENTION According to the'present invention the elements or dipoles of the antenna are single or unitary members and the coupling between the elements and the feed or collector system therefor is achieved by means of a novel conductor or feed system which is loop coupled to the elements to provide the required alternating phase relationship between adjacent elements without requiring the division of such elements into separate members thereby greatly simplifying the antenna structure, while providing important mechanical advantages and eliminating individual element or dipole misalignment.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood from the following detailed description taken in conjunction with the accompanying drawing in which:

FIGURE 1 is a schematic view of a prior art log-periodic dipole antenna array to which the present invention has particular application.

FIGURE 2 is a schematic view of the manner in which an antenna array of the type illustrated in FIGURE 1 is fed.

FIGURE 3 is a schematic view of a log-periodic antenna array of the class of FIGURES 1 and 2 but embodying the present invention.

FIGURE 4 is a perspective view of a log-periodic antenna of the type schematically illustrated in FIGURE 3 embodying the invention and showing an optional supporting boom in dotted lines.

FIGURE 5 is an enlarged fragmented perspective view of a modified form of antenna embodying the invention.

FIGURE 6 is a view similar to FIGURE 5 but illustrating a modified form of loop coupled feed system.

FIGURES 7 and 8 illustrate uniform periodic and tapered periodic antenna arrays respectively constructed to embody the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to FIGURE 1 the antenna array illustrated comprises a plurality of dipoles or elements, 1, 2, 3, 4, etc. each formed of two elements lalb, 2412b, 3a3b and 4114b, etc., which have a length L L L and L etc., and are separated a distance d d 61 etc., in a mathematical relationship such that where K is a constant having a value less than I. As shown in FIGURE 2 the array is fed at its narrow end from a source 5 by a transmission line comprised by lines 6 and 7, the lines 6 and 7 being transposed or reversed between adjacent elements or dipoles being connected to the ends of the separate members lalb, 2a2b, etc. Such an antenna radiates in the backfire direction, that is, toward the source 5 and provides unidirectional frequency independent or log-periodic operation.

The portion of such an array which acts as the radiator is centered around those elements near resonance, that is, where Ln is approximately one-half a wave length, which elements absorb substantially all of the input power and convert it to a radiated electromagnetic field. As the frequency changes the portion of the array which serves as the radiator shifts along the array so that again such portion is centered around the elements whose length is approximately one-half wave length. Because of the backfire radiation the larger elements which are not excited do not interfere with the radiation pattern while the shorter inactive elements, because of their smaller size and spacing and alternate phasing, do not materially effect the radiation pattern.

For proper operation of the individual members of the dipoles, namely, the members 1a1b, 202b, etc. must be rigidly supported not only in relation to adjacent dipole elements but to each other giving rise to mechanical support problems.

With reference to FIGURES 3 and 4 there is illustrated a log-periodic antenna having the characteristics of the antenna of FIGURES 1 and 2 but embodying the present invention. In the antennas illustrated in FIGURES 3 and 4, it will be seen that the dipoles or elements instead of being formed of pairs of separate members are single unitary members 11, 12, 13, 14, etc. These elements 11, 12, 13, 14 have the same mathematically determined relative length and spacing as described in relation to the elements or dipoles of the array of FIGURE 1.

The feed system for the elements 11, 12, 13 etc. comprises a pair of feed conductors, wires or lines and 16 of suitable conducting material, such as copper, connected to a source 17. It will be understood that in the case of use of the antenna array for receiving such conductors, wires, or lines 15 and 16 then form collectors and will be connected to a suitable receiver input. The conductors 15 and 16 are insulated from but form, in effect, loops electromagnetically coupled to the elements 11, 12, 13, 14, etc. to excite and provide the appropriate phase reversal between adjoining elements or dipoles as hereinafter more fully described.

As illustrated in FIGURE 4, it will be seen that each of the feed lines or conductors 15 and 16 has a generally square Wave shape the length, and preferably also the amplitude, of the waveform progressively increasing corresponding to the progressive increase in the spacing and length of the elements 11, 12, 13, 14, etc. and with the waveform of one line being of opposite hand to the other. Thus, conductor or line 15 is being or shaped to provide portions or lengths 18 and 19 extending generally parallel to the axis of the antenna array between adjacent elements and portions or lengths and 21 of appreciable extent extending substantially parallel to and along or immediately contiguous to the antenna elements. The portions 20 and 21 thus provide electromagnetic coupling over their length between the line 15 and the antenna elements 11, 12, 13, 14 etc. to provide a relatively tight coupling between the line and the elements with the line to element coupling at adjacent elements being substantially reversed or approximately 180 out of phase.

It will be understood that the coupling between the line portions 20 and 21 and the antenna elements will be dependent upon the length of such portions and their proximity to the elements. In general, for closely associated feed line portions 20 and 21 and the respective antenna elements, acceptable coupling can be achieved with the length of such portions 20 and 21 ranging from about onetwentieth to one-third of the length of the associated element. Thus, while the length of the line portions, eg 20 and 21, preferably progressively increase proportionally to the increase of the length of the antenna elements along the array, they do not necessarily need to do so, as long as the above relationship obtains.

As a structure, it may be considered that the series of coupling portions 20 and 21 and connecting portions 18 and 19 of line 15 form, in effect, open sided loops with the open sides facing in opposite directions when moving from one such loop to the next adjacent loop.

Line or conductor 16 is similarly but oppositely bent or shaped to provide portions or lengths 23 and 24 corresponding to the lengths 18 and 19 of line 15 extending generally parallel to the axis of the antenna array between adjacent antenna elements and portions or lengths and 26 corresponding to the portions 20 and 21 of line 15 extending substantially parallel to and along or immediately contiguous to the antenna elements. Again the portions 25 and 26 of line 16 provide electromagnetic coupling over their length between the line 16 and the antenna ele- 4 ments 11, 12, 13, 14 etc. to provide a relatively tight coupling between the elements and the line with the coupling between the line and adjacent elements again being substantially reversed or approximately out of phase.

As before, the series of coupling portions 25 and 26 and connecting portions 23 and 24 of line 16 form, in effect, open sided loops with the open sides facing in opposite directions when moving from one such loop to the next adjacent loop. Between any pair of antenna elements the open side of the respective loop defined by either lengths 18, 19 and 20, or lengths 18, 19 and 21 of line 15 faces the open side of the corresponding loop formed by either lengths 23, 24 and 25, or lengths 23, 24 and 26 of line 16, and the two lines 15 and 16, thus, in combination form, in effect, closed loops to provide a feed or collector system which may be conveniently referred to as a loop coupled feed or collector system which couples the antenna elements to the source 17 in the case of transmission or to a suitable receiver input in the case of reception.

Because at any one antenna element the coupling portion 20 or 21 of line 15 extends along the element in the reverse direction to the corresponding coupling portion 25 or 26 of line 16 when tracing the lines 15 and 16 from one end of the array then the resulting coupling, due to the substantially 180 phase relation of the currents in the two lines will be additive at each such antenna element. While the coupling of the two lines are additive at each element, as above explained, the coupling is substantially reversed when moving from one element to the next adjacent element in either direction to provide the requisite unidirectional backfire field pattern in the case of transmission or to respond to a directional field directed at the small end of the antenna array in case of reception.

The lines 15 and 16 may conveniently be formed by conductors or wires having insulated coatings 27 so that they are electrically insulated from the antenna elements 11, 12, 13, 14 etc. or alternatively, if it is desired to use bare conductors or wires, it will be understood that suitable insulators may be employed between the lines and the antenna elements to preclude direct electrical connection therewith.

The feed lines 16 and 15 may also be shaped to cause the coupling line portions 20, 21, and 25 and 26 to lie alternately on opposite sides, that is, above and below adjacent elements 11, 12 etc., as shown in FIGURE 4. Alternatively, one line may run on one side of the elements and the other line may run on the other side of the elements as shown in FIGURE 6.

In such a feed system, as described in relation to FIG- URE 4, it will be understood that the impedance is substantially constant, independent of frequency, and may be readily matched with the source 5 in the case of transmission, or the receiver input in case of reception.

The feed lines 16 and 15 may be terminated with an impedance Z which conveniently may simply be a section of a shorted line.

The lines 16 and 15 may themselves be sufficiently rigid and the single elements 11, 12, 13 and 14 etc. clamped or otherwise secured by any suitable means (not shown) to the pairs of line coupling sections 20, 25, or 21, 26, to provide a rigid self-supporting antenna array without requiring further support, since only the spacing of the elements need be maintained.

Alternatively, as a further support, a central boom 31 may be employed as illustrated in dotted line in FIGURE 4 to give added strength and rigidity. Such a boom may be metal and the elements 11, 12, 13, 14 etc. may be secured or clamped directly to such boom by any conventional means.

FIGURE 5 illustrates a modified antenna array in the form of a printed circuit embodying the invention. In this array the antenna elements 32, 33, 34 etc. are printed on a supporting non-conducting sheet 3-5 and the feed system is comprised by the feed or collector lines 36 and 37 each of which again is of generally square wave formation to provide generally axially extending connecting portions or lengths 36a and 36b and 37a, 37b, respectively, extending between adjacent elements and coupling portions or lengths 38a38b, and 39a39b, respectively, which extend parallel and contiguous to but are insulated from such adjacent elements to provide a close electromagnetic coupling therewith. In the embodiment illustrated in FIGURE 5, each of the feed lines 36 and 37 alternates from one side of the sheet 35 to the other between the antenna elements being passed through the sheet at the intermediate points 40 with the result that the coupling portions 38a and 38b and 39a and 39b alternately lie on opposite sides of the adjacent antenna elements.

As before, it will be seen that the feed or collector system comprised by the conductors 36 and 37 provides, in efiect, a series of loops which are electromagnetically coupled to the elements 32, 33, 34 etc., the opposing directions of the coupling lengths 38a, 39a and 38b, 39b of the conductors 36 and 37 providing additive coupling at each individual antenna element, while the reversal of the directions of the coupling lengths 38a3'8b and 39a39b at adjacent elements provides a substantial reversal in phase between adjacent antenna elements. Thus, this arrangement gives rise to the unidirectional backfire radiation pattern in the case of transmission or renders the array unidirectionally responsive to arriving electromagnetic fields over a broad band of frequencies.

FIGURE 6 illustrates an antenna array generally similar to that illustrated in FIGURE 5, except that one of the feed lines or conductors 46 lies on one side of the antenna elements 42, 43, 44 etc. and the other of the feed lines or conductors 47 lies on the other side of the elements. Again the elements 42, 43, 44 may be printed in a non-conducting sheet 45 and the feed conductors may be formed as part of the printed circuit or may comprise stampings mounted on the sheet 45 the sheet serving to insulate the one feed conductor line 46 from the antenna elements 42, 43, 44 etc. the other line 47 being insulated from the said elements by an insulating coating 47 or any other insulating means which may comprise a sheet similar to sheet 45 so that the elements 42, 43 and 44 are sandwiched between two dielectric sheets.

Again the conductors or feed lines 46 and 47 are shaped to provide connecting portions 48a48b and 49a and 49b, respectively, and coupling portions 50a50b and SlaSlb, respectively, tightly coupled to the antenna elements. Each of the conductors 46 and 47 again thus forms, in eifect, a series of open sided alternately facing loops extending between adjacent antenna elements with the open sides of the loops of one conductor facing the open sides of the loops of the other conductor. Thus the conductors 46 and 47 again, in effect, provide in combination closed loops electromagnetically coupled to adjacent elements 42, 43 and 44 with the coupling between adjoining elements being substantially reversed to provide the desired unidirectional frequency independent antenna characteristics above described.

While the invention has been particularly described in relation to a log-periodic antenna the principle of the invention of antenna element feeding or collecting by means of a loop coupled feed or collecting system can also be applied advantageously to uniform periodic antenna arrays such as illustrated in FIGURE 7, or tapered periodic antenna arrays as illustrated in FIGURE 8. In each case the elements 52, 53, 54 etc. and 62, 63, 64 etc., respectively, can be formed as solid or one piece elements fed by the feed lines 56 and 57 and 66 and 67, respectively, and the structure may be made rigid with or without booms 70 and 71, respectively.

While specific embodiments of the invention have been described, it will be understood that many variations may be made in antenna arrays and the specific feed arrangements while still advantageously employing the principle of a loop coupled feed system with solid antenna elements without departing from the spirit or scope of the invention. In addition, it will be understood that while, for simplicity, the invention has been described and illustrated in relation to simple single antenna arrays, the invention is applicable to antenna systems which may comprice multiple or complex arrangements of antenna arrays.

I claim:

1. An antenna comprising an array of substantially coplanar and parallel unitary elements arranged in side by side relation and means coupling said elements comprising a first conductor extending between said elements and having a coupling portion at each element of appreciable length extending parallel and contiguous to such element and insulated therefrom, the said portions at adjacent elements extending in opposite directions when traced from either end of the array, and a second conductor corresponding to the first conductor but of opposite hand having a coupling portion at each element of appreciable length extending parallel and contiguous to such element and insulated therefrom, the said portions-of said second conductor at adjacent elements extending in opposite directions when traced from said array end and with the directions of said portions of said first conductor being opposite to the directions of said portions of said second conductor at each element.

2. An antenna as claimed in claim 1 in which said first and second conductors constitute a feed or collector system extending longitudinally of the array and form in combination loops extending between and electrically insulated from adjacent elements.

3. An antenna as claimed in claim 1 in which said elements are of progressively changing length and spacing along the array to form a log-periodic antenna array.

4. An antenna as claimed in claim 1 in which said first and second conductors are rigid and form a support structure for said elements.

5. An antenna as claimed in claim 1 in which at least one of said element array and said conductors is formed by a printed circuit on a carrier sheet.

6. An antenna as claimed in claim '1 in which said coupling portions of said first and second conductors extend on opposite sides or adjacent elements of said array.

7. An antenna as claimed in claim 1 in which said coupling portions of each of said first and second conductors lies on opposite sides of adjacent elements of said array with the opposed coupling portions of said first and second conductors at each element lying on opposite sides of said element.

8. A broad band unidirectional log-periodic antenna comprising an array of substantially coplanar and parallel elements of progressively increasing length and spacing characterized in that each of said elements is a single member and the feed or collector system for said elements comprises a pair of conductors each of generally square Wave formation having portions extending generally parallel to the axis of the array between adjacent elements and coupling portions of appreciable length extending generally perpendicular to the array axis and parallel and contiguous to and insulated from said elements, the pair of conductors being of opposite hand with the coupling portions of one of said conductors extending in an opposite direction to the coupling portions of the other of said conductors when traced from an end of said array and the coupling portions of each of said conductors extending in opposite directions at adjacent elements when traced from an end of said array.

9. A broad band antenna as claimed in claim 8 in which the generally square Wave formation of each of said conductors has a progressively increasing amplitude and spacing corresponding to the increasing length and spacing of said elements.

10. A broad band antenna as claimed in claim 9 in which said conductors are rigid and form a support structure for said elements.

11. A broad band antenna as claimed in claim 9 in which said elements are mounted on a supporting boom extending axially of said element array.

12. A broad band antenna as claimed in claim 8 in which at least one of said element array and pair of conductors is formed as a printed circuit deposited on an insulating sheet.

13. A broad band antenna as claimed in claim 8 in which the coupling portions of one of said pair of conductors extend on one side of adjacent elements of said array and the coupling portions of the other of said pair of conductors extend on the side of adjacent elements of said array opposite to the coupling elements of the first mentioned conductor.

14. A broad band antenna as claimed in claim '8 in which said coupling portions of each of said conductors lie alternately on opposite sides of adjacent elements of said array and the coupling portions of said conductors at any one element lying on opposite sides thereof.

15. A broad band antenna as claimed in claim 8 in which said conductors are stampings.

References Cited UNITED STATES PATENTS 2,433,804 12/1947 Wolff 343-811 X 2,716,703 8/1955 Kane 343-814 X 3,056,960 10/1962 Wickersham 343-811 X 3,300,784 1/1967 Ervine 343-8l2 X HERMAN KARL SAALBACH, Primary Examiner T. VEZEAU, Assistant Examiner US. Cl. X.R. 3438l4, 822

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