US2955287A - Antenna - Google Patents

Description

Oct. 4, 1960 R. D. BOGNER 2,955,287

ANTENNA Filed Dec. 31, 1956 3 Sheets-Sheet 1 FIG. I

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AGENT United States Patent ANTENNA Richard D. Bogner, Bethpage, N.Y., assignor to Tyner Corporation, New York, N .Y.

Filed Dec. 31, 1956, Ser. No. 631,869

11 Claims. (Cl. 343-753) This invention relates to directional antennas.

In the design of directional antennas, the general considerations include as a goal the obtaining of high gain, narrow beam width and low side lobes. These desideratums are generally not achieved in full because of practical considerations of weight, size or mechanical limitations. An antenna design frequently requires compromise of both maximum desired side lobe level and maximum desired beamwidth at the half power level, in a given plane, for an antenna of a given maximum physical size. In some applications, the designer may be required to accept a more moderate gain in order to achieve lower side lobe levels, or compromise all characteristics because of size considerations.

It is often required in the design of antennas especially, for example, large rotating antennas, that the diameter of a circle which circumscribes the antenna in a plane normal to the rotation axis be minimized for a given radiation pattern half power beamwidth and side lobe level in that plane. This plane is often the plane of largest antenna linear dimension and is usually the azimuth plane.

An antenna structure is described herein which requires a smaller circumscribed diameter for a given half power beamwidth and side lobe level, than has previously been considered practical to obtain.

I have discovered that by properly arranging a number of end fire elements in an array I can achieve an antenna pattern of narrower beamwidth consistent with a given side lobe level, in a smaller antenna diameter than was previously considered practicable. Briefly stated, the antenna of this invention consists of an integral number of substantially identical end fire radiators arranged in an equally spaced array. The spacing between elements, the length of the elements, the number of elements and other critical dimensions are so chosen in accordance with the procedure stated more fully hereinafter that for a. given circumscribed diameter an antenna of surprisingly high gain, or surprisingly narrow beamwidth for a given low side lobe level, is obtained in a compact structure.

There follows hereinafter a mathematical analysis of the antenna which establishes a preferred range of configurations providing optimum performance.

It is a general object of this invention to provide a high gain directional antenna having a narrow half power level beamwidth and low side lobe level in relation to the diameter of a circumscribed circle.

It is another object of this invention to provide a directional antenna of small height and breadth for a given value of antenna gain.

It is still a different object to provide a high gain directional antenna of small weight.

A further object of this invention is to provide a high gain directional antenna characterized by very low side lobe levels.

A still different object of this invention is to provide an antenna of high performance characteristics susceptible of being embodied in a rigid mechanical structure.

A further object is to provide an antenna capable of being simply and quickly assembled and disassembled by relatively unskilled personnel.

These and other objects, the nature of the present invention, its various features and advantages, will appear more fully upon consideration of the various specific illustrative embodiments shown in the accompanying drawings and of the following detailed description of these embodiments.

In the drawings:

Figure 1 shows in plan an antenna array of this invention.

Figure 2 is a rectangular plot of a measured typical field strength pattern (in db) propagated by a four equally fed element antenna of this invention which is four wavelengths in diameter in the plane of the array.

Figure 3 is a pictorial representation of a polyrod element suitable for incorporation in the array of this invention.

Figure 4 is a section, shown pictorially, of a waveguide launched cigar element array.

Figure 5 is a general schematic showing in plan of a four element array of this invention employing a dipole launched cigar element.

As employed hereinafter the term degrees refers to electrical degrees. The linear dimensions are stated as relative values throughout, relative either to one wavelength or to 360 electrical degrees (which is equivalent to one wavelength) of the operating frequency. A length stated as 2, for example, means either two wavelengths or two (360) equal to 720 electrical degrees.

The structure consists of an n number of substantially identical end fire radiators 2a, 2b, 2c, etc., of length L and end width w, arranged in an equally spaced array and inscribed in a circle 4 of diameter d. The spacing between the centerlines of the elements is s, and the distance from the center of the end radiator 2a to the furthest edge of the ground plane 6 is A. Since the width of the resulting radiation beam (Figure 2) is an inverse function of both the product ns, and the square root of the length L, this beam will be narrowest for a given d when both L and ns are made as large as possible. The circumscribed circle of diameter d referred to is defined by four points, the outside corners of the end radiators 2a and 2e and the edges of the ground plane. There exists simple plane geometry relationship as shown in Figure 1 which may be expressed as a mathematical relationship between L, d, w, A, n and s (or between L and the product (n-1)s for a fixed d, A, and w, the latter two values being small and relatively constant in a practical system), based on simple plane geometry relationships in conjunction with Figure 1 which relationship is w 2 L =d [(n1)s+A+ (1) A second and separate relationship can be set up between L and ns if the required condition of low side lobes is to be met with the minimum diameter d. In general, it is desirable to maximize ns within the circle consistent with an L just large enough to give the side lobe level required, since L must be larger, in most cases, for a given element factor beamwidth than the base length (nl)s for a given array factor beamwidth, base length is defined as the distance between center lines of end elements and is (nl)s for n elements.

I. Equal amplitude feed embodiment For the case in which each of the elements of the array is fed with substantially the same amplitude of signal, side lobe levels of the entire antenna in the order of 22 to 26 db below the beam peak level in the plane of interest can be obtained. For this situation, the required relationship between L and ns can be determined from the fact that the shortest value of L giving rise to 22-26 db side lobes has been found to occur when the angular displacement of the first element pattern null from the beam peak is between 63% and 84% greater than the displacement of the first array factor null (0 Adding to this the two known facts that (l) for close to optimally designed end fire elements, having 8-13 db first (maximum) side lobes, 0 lies between 40 and 50 times the reciprocal of the square root of L, and that (2) the array factor null occurs at 180 divided by ms for ns 2 /2, the required range of L in terms of ns can be found as follows:

N 1S N where ns 2 /z Substituting (3) and (4) in (2) and solving for the maximum and minimum simultaneous extremes of (2) and (3):

Equation 5 and the mathematical relationship previously described between L and (nl)s [Eq. 1] allow a mathematical determination of a range of the number of elements, their spacing and length required to make optimum use of the area of the circle of diameter d. The values of w and A, as well as the exact function between the length L of the end fire element and the position of the first end fire element pattern null 0 must be known in any particular case for an exact solution; since it is desirable to have a minimum w and A, and since also the range of the optimum relationship between L and 0 is well known as described, however, the structure may in general be determined within narrow and defined limits.

Simultaneous solution of Eq. 1 and Eq. 5 over the range of the latter show that this antenna design provides a distinct advantage over conventional techniques in terms of obtainable beamwidth for 22-26 db side lobe levels in a given diameter d. This advantage, however, is shown by the solutions to occur only in the ranges s between 160 and 320 degrees, and d between 2 and 12 wavelengths, which requires a range of n between 2 and 16.

Based on the foregoing relationships and experimental data, the following limitations have therefore been found critical; for the case of substantially equal amplitudes (or 22-26 db side lobe levels):

L shall be between and %(ns) (where L and s are in wavelengths) It shall be between 3 and 15 in number.

Example: A representative set of solutions for d=4 (wavelengths) E 3 are found from Eq. 1, 2, 3 and 4 to be:

(wavelength) The values of d, 0 0 A and w chosen above are only representative of choices in the allowable ranges of these parameters, showing that a discrete solution for n, s and L is then possible. Small variations in the relationships between 0 and 6 and 0 and L, required in any case will cause small changes in the values of s and L for a given d and n.

II. Tapered amplitude feed embodiment To obtain side lobe levels lower than 22-26 db below the beam peak, it is most expedient in this case to cause the relative power at each element to be different, and generally to taper symmetrically from the center element or elements to the end elements. It is further necessary in this case that separation between the position of the first array factor null and the first element null become smaller than the 63% to 84% of 6 referred to in the uniform case, and become approximately Zero in the limit. For any particular side lobe level desired, the general taper required, and from this a relationship between L and ns, can be established. This would allow in any case, using the mathematical relationships previously described plus other conventional array theory, a mathematical determination of the number of elements, spacing, length and other parameters. For this condition of amplitude taper the critical relationships (where the end elements are at least 10% in power below the center element(s)) become:

L between %(ns) and /z(ns) it between 3 and 18 s between electrical degrees and 320 electrical degrees d between 2% and 15h Suitable end fire radiators include helices, dielectric rods such as polyrods and ferrods, and cigars. This list is by way of illustration and is not intended to be limiting.

In general end fire elements which, at least in the plane of interest, are characterized by radiation patterns substantially symmetrical about the element axis, having a radiation maximum on the element axis, and having dimension between M5 and M 2, are suitable for use in this application.

The cigars as shown in Figures 4 and 5 are preferred for linearly polarized radiation. Experimentally, it has been found that the cigar-type elements alone allow metallic support along their lengths in the form of thin rods normal to the principal polarization electric vector, eliminating the need for long cantilevered structures and providing extremely rigid mechanical structures. Further, such an all metallic structure has been found lower in loss than structures involving use of dielectrics. The cigars, therefore, provide a distinct and incontrovertible advantage both in gain, weight and mechanical rigidity.

A typical structure is shown in Fig. 4 wherein the cigar elements consist of a cylindrical rod 20 and mounted thereon a plurality of discs 22. The discs 22 are spaced approximately /2). apart and are approximately /37. in diameter. When the radiator of length L (L is expressed in wavelengths at operating frequency) is energized by a launcher such as waveguide cavity 24, the electrical length L is measured from the feed 28 to the effective end (the end disc 46). A minor protrusion of rod 20 may be disregarded.

The structure is adapted to extremely simple and rigid mechanical construction. Pedestal 30 which may be of a rotating type supports the antenna by means of arms 32, 34 and 36. Beam 35, in turn, supports the other cigar elements by means of a similar arm arrangement.

The transmission line structure used to feed the elements may consist of a series of bilateral or other parallel splits, a series feed arrangement, or any other which provides the required amplitude, phase, and impedance with adequate decoupling.

The various elements or radiators 2a, 2b etc., shall be fed substantially in phase. The end elements may in certain cases be modified slightly from the other elements to reduce the diameter d, such a small alteration in certain cases not appreciably disturbing the performance.

In Figure 5 there is shown schematically a similar cigar element array fed by means of a dipole. In this instance the length L is measured from the dipole element 26 to the effective end (disc 48).

Septa, chokes, or metal plates may in some cases be placed around or between the bases of the elements to reduce or alter mutual coupling effects.

Typical uses for the antenna include object location, communication, scatter propagation, and object detection.

The array of this invention may be stacked in multiple to provide a battery of such arrays providing a desired pattern in the vertical plane, controlled by the relative pointing, phase or amplitude of the banks.

Figure 6 shows in plan the projection in a vertical plane of the elements of a four array antenna.

A typical antenna consisting of four arrays, 40, 41, 42, and 43 is shown in Figure 6. The number of elements in all arrays need not be identical but may be varied to shape the resulting pattern. In general, the beamwidth of each array should be approximately the same.

There is shown in Figures 7, 8, and 9 respectively, in schematic form, the side, front, and plan view of an antenna array in which the radiating elements 50 and 52 are tilted with respect to elements 51 and 53. In embodiments employing tilted elements it is important that the measurements of element length and spacing be that of the projection of the element onto the plane common to the elements.

The discs 22 shown in the embodiment of Figure 4 need not be circular, but may be of any shape symmetrical about a plane through the axis of the radiating element and normal to the common plane of the radiators of a given array, e.g., equilateral triangle, ellipse, rectangle.

There has been disclosed herein the best mode of carrying out the invention presently contemplated and it is to be understood that various minor variations may be made without departing from the spirit of the invention.

What I claim is:

1. An end fire radiator, having a principal axis, adapted to be energized by a launcher at the non-radiating end of said radiator for the transmission of energy of wavelength A in the direction of the axis, the electrically active components of said radiator consisting of a plurality of substantially identical electrically conductive plates spaced between M8 and M2 apart, along said axis, with the plane of the plates normal to said axis, to form an elongated radiator fitting within a circumscribing cylinder, coaxial with said principle axis, having a diameter which is greater than M4 and less than M2.

2. The radiator of claim 1 wherein said electrically conductive plates are discs.

3. A low side lobe level antenna array comprising a plurality of the radiators of claim 1 each spaced from 4M9 to 8M9 away from the closest adjacent one of the other of said radiators.

4. The array of claim 3 in combination with means to feed said radiators in equal phase.

5. A low side lobe level antenna array adapted to transmit electromagnetic waves of wavelength A, comprising: an N number of end-fire radiators, each of said radiators having a principal axis and a plurality of substantially identical electrically conductive plates, spaced between M8 and M2 apart along said axis, with the plane of the plates normal to said axis, to form an elongated radiator fitting a circumscribing cylinder having a diameter which is greater than M4 and less than M2, wherein the projections of said radiators, into a common plane, are parallel to each other, are spaced a distance S, between 4M9 and 8M9 apart, center-to-center, and have a length L, in wavelengths, in the range where N is in the range 2 to 16, and means for exciting said radiators in equal phase.

6. A directional antenna comprising a plurality of ar rays as defined in claim 5, said arrays being electrically interconnected by means to excite said arrays in equal phase.

7. The array of claim 5 wherein said electrically conductive plates of said radiators are substantially equally spaced along the axis of the cylinder.

8. The array of claim 5 wherein said electrically conductive plates of said radiators are discs.

9. An antenna array adapted to transmit electromagnetic waves of wavelength A, said array being dimensioned to fit within a circle of diameter D, where D range from 2A to 12%, comprising: an N number of end-fire radiators, each of said radiators having a principla axis and a plurality of substantially identical electrically conductive plates, spaced between M8 and M2 apart along said axis, with the plane of the plates normal to said axis, to form an elongated radiator fitting a circumscribing cylinder having a diameter which is greater than M4 and less than M2, wherein the projections of said radiators, into the plane of the circle, are parallel to each other, are spaced a distance, S, from 4M9 to 8M9 apart, center-to-center, and have a length L in wavelengths, in the range where N is in the range 2 to 15, and means for exciting said radiators in equal phase.

10. The array of claim 9 wherein said electrically conductive plates of said radiators are substantially equally spaced along the axis of the cylinder.

11. An end fire radiator, having a principal axis, adapted to be energized by a launcher at the non-radiating end of said radiator for the transmission of energy of wavelength x in the direction of the axis, the electrically active components of said radiator consisting of a plurality of substantially identical electrically conductive plates substantially uniformly spaced between M8 and M2 apart, along said axis, with the plane of the plates normal to said axis, to form an elongated radiator fitting within a circumscribing cylinder, coaxial with said principal axis, having a diameter which is greater than M4 and less than M2.

References Cited in the file of this patent UNITED STATES PATENTS 2,556,046 Simpson June 5, 1951 2,624,002 BouiX Dec. 30, 1952 2,663,797 Kock Dec. 22, 1953 FOREIGN PATENTS 732,827 Great Britain June 29, 1955 OTHER REFERENCES Pub. (1), Kraus, Antennas, pp. 79, and 93 to 97, copyright 1950, by McGraw-Hill Book Co.

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