US3541564A

US3541564A - Multiple channel zig-zag antenna array

Info

Publication number: US3541564A
Application number: US784114A
Authority: US
Inventors: Ronald E Fisk
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1968-12-16
Filing date: 1968-12-16
Publication date: 1970-11-17
Anticipated expiration: 1987-11-17

Description

Nov. 17, 1970 R. E. FISK MULTIPLE CHANNEL ZIG-ZAG ANTENNA ARRAY Filed Dec. 16. 1968 FIGB /l6 INVENTORZ RONALD E. FISK,

BY ms ATTORNEY.

United States Patent "ice 3,541,564 MULTIPLE CHANNEL ZIG-ZAG ANTENNA ARRAY Ronald E. Fisk, Syracuse, N.Y., assignor to General Electric Company, a corporation of New York Filed Dec. 16, 1968, Ser. No. 784,114 Int. Cl. H01q 9/16, 19/10 US. Cl. 343-793 3 Claims ABSTRACT OF THE DISCLOSURE This invention relates to antennas, and more particularly to an antenna of the zig-zag panel type.

In many metropolitan areas, suitable locations for transmitting antennas are limited. Therefore, a means for using the existing space most efficiently is highly desirable. A striking example of the lack of availability for suitable locations for transmitting antennas is that of the Empire State Building in New York City, where all television transmitter antennas are concentrated. In other areas costly antenna towers must be built even though they are able to provide only limited usable space for mounting antennas.

Accordingly, it is an object of this invention to provide an improved antenna array comprising two zig-zag antennas occupying the physical space normally required for a single zig-zag antenna.

Another object of this invention is to provide an improved multiple channel panel antenna array which comprises two zig-zag type antennas arranged in an extremely small spacial area.

Still another object of the present invention is to provide two interleaved zig-zag type antenna radiators which are arranged on a common panel and disposed in parallel spaced apart planes.

Further objects and advantages of my invention will become apparent as the following description proceeds.

Briefly, in carrying out one form of my invention, there is provided an interleaved zig-zag antenna array which comprises a generally rectangular, planar, electrically conductive reflector upon which is mounted in spaced insulated relationship an outer zig-zag radiator and an inner zig-zag radiator interleaved between the outer radiator and the reflector. The outer radiator transmits on a first operating channel frequency and the inner radiator transmits on a second, higher operating channel frequency. Each radiator is spaced from the reflector a distance equal to between one-tenth and fifteen onehundredths of the wave length at the mean operating frequency of that particular radiator. Thus the outer radiator, transmitting at a mean operating frequency lower than that of the interleaved inner radiator, will be spaced at a greater distance from the reflector than the inner radiator. Each radiator is comprised of a like number of zig-zag elements of a length L equal to onehalf wave length'at the mean operating frequency of the respective radiator. Because the operating frequency of the outer radiator is lower than that of the inner radiator, the length L of the elements of the outer radiator is greater than that of the elements of the inner radiator. The corresponding elements of the outer and inner radiators cross near the respective midpoints at approximately 90 in order to minimize the coupling effect between Patented Nov. 17, 1970 the radiators. Therefore, the pitch angle of the elements of the outer radiator is approximately the complement of the pitch angle of the inner radiator. By this invention, an antenna array is provided which occupies no greater space than did previous single zig-zag panel antennas, while also producing improved multi-channel broadcast capabilities.

The novel features believed characteristic of this invention are set forth in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood by reference to the following description, when taken in conjunction with the accompanying drawing, in which:

FIG. 1 is a front elevation view of a multiple channel zig-zag type antenna array embodying my invention in one form thereof;

F161. 2 is a side elevation view of the antenna array of FIG.

FIG. 3 is a section view taken on lines 33 of FIG. 1;

FIG. 4 is a front elevation view of a modified form of the antenna array of FIG. 1.

Referring to FIGS. 1-3 of the drawings, it will be seen that there is provided a zig-zag type panel antenna array comprising a generally rectangular, planar, electrically conductive reflector 6, and outer and

inner zigzag radiators

8 and 10, respectively, spaced apart and insulated from the reflector 6 by a plurality of standoff insulators, exemplified by the insulators designated with reference numeral 12. The

radiators

8 and 10, are each disposed in a separate plane, their planes of disposition being in parallel spaced apart relationship to each other and to reflector 6.

The outer radiator 8 comprises a number of zig-zag conductor elements 14 connected in seriatum, each element being joined to the next successive element at a predetermined angle, one-half of which angle is defined as the pitch angle A of the element. The pitch angle A of each element 14 (as shown in FIG. 1), may also be defined as the angle the element makes with a plane perpendicular to the longitudinal axis of the radiator 8.

Each zig-zag element 14 of the radiator 8 as measured from a corner to an adjacent corner has a nominal length L equal to one-half wavelength at the mean operating frequency f of the channel upon which the radiator 8 is operating. The radiator 8 is fed at a medial feed point 16 through a coaxial cable 18 delivering an RF voltage at operating frequency f Radiator 8 is spaced from the reflector 6 by a predetermined critical distance. Optimum performance of the radiator 8 has been found to obtain when the radiator 8 is spaced from the reflector 6 a distance within the range of one-tenth to fifteen one-hundredths wavelength at the operating frequency f of the radiator 8.

The inner radiator 10 is interleaved between the outer radiator 8 and the reflector 6 and is essentially like the outer radiator 8, being comprised of a plurality of zig- Zag conductor elements 20 with a pitch angle B and a length L, equal to one-half wavelength at the mean operating frequency f of the channel upon which the radiator 10 is broadcasting. The radiator 10 is fed at medial feed point 22 through a coaxial cable 24 delivering an RF voltage at operating frequency f The inner radiator 10 is also spaced from the reflector a distance within the range of one-tenth to fifteen one-hundredths wavelength at its operating frequency f The inner radiator 10 transmits at a higher operating frequency than the outer radiator '8, that is, f is greater than f Since both radiators -8, 10 are spaced from the reflector 6 the same distance, in terms of wavelengths at the respective operating frequencies, the inner radiator 10' will be located closer to the reflector 6 than the outer radiator 8 which transmits at a longer wavelength.

It is of crucial importance that the outer and

inner radiators

8, 10 be isolated from each other, viz, the mutual coupling between the radiators must be reduced to inconsequential proportions. If substantial coupling is present between the

radiators

8, 10, the radiation from one radiator will be picked up by the other radiator and reflected back through the feed line of the latter to and from its transmitter, producing a ghosting effect at the television receiver which picks up the signal. Other problems may be engendered by excessive coupling between the radiators, such as the generation of intermodulation components in the transmitter of the coupled radiator which would be broadcast from the coupled radiator in the form of spurious outerband radiation.

The desired degree of isolation between the

radiators

8, 10 is achieved in accordance with the present invention by aligning the radiators 8, -10 such that the element 14 of the outer radiator 8 crosses over the corresponding elements 20 of the inner radiator 10 at their respective midpoints and at approximately 90. It is evident that because the inner radiator 10 is transmitting at a shorter Wavelength than the outer dariator 8, the half-wavelength elements 20 of the inner radiator 10 will be shorter than the corresponding elements 14 of the outer radiator 8. Thus, in order for

corresponding elements

14, 20 of the outer and inner radiators 8, -10 to cross at their midpoints at approximately 90, the pitch angle A of the outer radiator 8 must be less than 45 and the pitch angle B of the inner radiator 10 must be greater than 45. In fact, a trigonometric analysis will show that if the corresponding elements of the outer and inner radiators cross at exactly 90, then the sum of the pitch angle A of the outer radiator 8 and the pitch angle B of the inner radiator 10 will be equal to 90. Thus for large differences in the operating frequencies f f of the outer and

inner radiators

8, 10 the pitch angle A of the elements 14 of the outer radiator 8 will approach whereas the pitch angle B of the inner radiator will approach 90. It will be understood then from the above discussion that isolation between the outer and

inner radiators

8, 10 can be achieved regardless of the operating frequencies of the radiators or the operating frequency difference between them.

A modified form of my invention is illustrated in FIG. 4. This modification of the basic antenna array is designed to achieve even greater isolation between the outer and inner radiators 8', 10' than is possible with the embodiment of FIGS. 1-3. This is accomplished by longitudinally shifting the position of one radiator along the axis of the panel with respect to the other radiator. In this arrangement the non-overlapping end portion of each of the radiators 'will broadcast with almost a total absence of coupling with the other radiator. This technique can be utilized where a slightly greater vertical space is available for mounting an array than is occupied by the embodiment of FIGS. 1-3 wherein the radiators are completely coextensive.

This invention is not limited to the particular details of the construction of the embodiment illustrated and I contemplate that various and other modifications and applications will occur to those skilled in the art. It is therefore my intention that the appended claims shall cover such modifications and applications as do not depart from the true spirit and scope of my invention.

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

1. A multiple channel zig-zag panel antenna array comprising:

(a) an electrically conductive reflector,

(b) a first zig-zag radiator comprising a plurality of zig zag elements and being mounted in insulated spaced relationship to said relflector, said first radiator being fed from a first source of RF voltage at a first operating frequency, and

(c) a second zig-zag radiator interleaved between said first radiator and said reflector, said second radiator comprising a plurality of zig-zag elements and being mounted in insulated spaced relationship to said reflector, said second radiator being fed from a second source of RF voltage at a second operating frequency,

((1) said first radiator elements and said second radiator elements crossing at approximately to minimize coupling between said first and second radiators.

2. A multi-frequency zig-zag panel antenna array comprising:

(a) an electrically conductive planar reflector,

(b) a first zig-zag radiator fed from a first source of RF voltage at a first operating frequency, said first radiator being spaced ten hundredths to fifteen hundredths wavelength at said first operating frequency from said reflector and insulated therefrom, and said first radiator comprising a plurality of zig-zag elements, said elements having a length equal to onehalf wavelength at said first operating frequency and a pitch angle A, and

(c) a second zig-zag radiator fed from a second source of RF voltage at a second operating frequency, said second radiator being spaced ten hundredths to fifteen hundredths wavelength at said second operating frequency from said reflector and insulated therefrom, and second radiator comprising a plurality of zig-zag elements, said elements having a length equal to onehalf wavelength at said second operating frequency and a pitch angle B, said second operating frequency being greater than said first operating frequency,

(d) said first radiator elements and said second radiator elements crossing near their respective midpoints, and the sum of said pitch angles A and B equaling approximately 90.

3. The antenna array defined in claim 2 wherein said first and second radiators are axially offset with all except an end portion of each of said first and second radiators in overlapping relationship.

References Cited UNITED STATES PATENTS 3,369,246 2/1968 Fisk et al. 343-806 3,375,525 3/1968 Fisk et al 343806 X 3,409,893 11/1968 Siukola 343-806 X HERMAN K. SAALBACH, Primary Examiner M. NUSSBAUM, Assistant Examiner US. Cl. X.R. 343-797, 806, 834