US3488657A - Low profile antenna - Google Patents

Description

United States Patent O M U.S. Cl. 343--708 13 Claims ABSTRACT OF THE DISCLOSURE A low profile antenna to show r-adiation and polarization characteristics similar to a simple monopoleva-n'tenna. The antenna of the present invention has anloverall length on the order of 1/2 or some multiple of 1/2 of the wavelength at the midband frequency of the antenna. The antenna is formed into two short stubs, one being a feed and the other a ground, placed close together and projecting perpendicularly from the ground surface. The stubs are connected by wire sections running generally parallel to the ground plane surface. These sections are folded so they are spaced near and run generally parallel to each other.

This invention relates generally to antennas and more particularly to a low profile antenna having radiation characteristics substantially similar to a monopole anten- Certain quasi-spherical satellites having a typical nominal circumscribing diameter of two or three feet` may require antennas which operate in the UHF and VHF bands with coverage as close to isotropic as possible. A monopole antenna sometimes referred to as a stub or whip antenna, extending radi-ally from the satellite provides a simple mechanical and electrical configuration and essentially meets the desired radiation characteristics. However, the physical length of such antennas may require that the antenna be mounted on the satellite for self-erection when it is to be operational. Although relatively simple procedures are available for erecting such antennas, a self-erecting antenna is more complicated and less reliable than a fixed antenna.

The objects of the present invention are to provide an antenna that is particularly suited for use on a quasispherical body; that is mechanically simple; that is fixed 'and does not require erection; that is compact and has a low profile; and that achieves effective quasi-isotropic coverage.

Other objects, features and advantages of the present invention will become apparent from the following description the appended claims and the accompanying drawings in which:

FIGURE 1 shows a quasi-spherical satellite on which is mounted an antenna element of the present invention with the satellite serving as a ground plane;

FIGURE 2 is a fragmentary section taken on 2-2 of FIG. l to further illustrate the antenna element and coaxial line which provides an unbalanced feed to the element;

FIGURE 3 is a fragmentary section illustrating a further embodiment of the present invention;

FIGURE 4 is a view showing a coordinate system for radiation patterns of the antenna illustrated in FIGS. 1 and 2;

FIGURE 5 is a principal plane radiation pattern of the antenna shown in FIG. 1; and

FIGURE 6 is an equatorial radiation pattern of the antenna shown in FIG. 1.

Referring to FIGS. 1 and 2 an antenna element 12 is mounted on a quasi-spherical satellite 14 which may have 3,488,657 Patented Jan. 6, 1970 a polyhedron shape as illustrated. Satellite 14 is formed with a conductive shell 16 having an exterior surface 18 which serves as a ground plane for element 12. Elcment 12 comprises a first conductor portion 20 fastened and electrically connected at one end to shell 16 and extending radially outwardly from satellite 14. Conductor portion 20 has its outer end joined to a second conductor portion 22 which extends laterally outwardly from conductor 20 in a direction circumferentially of satellite 14. Conductor portion 22 is bent radially inwardly as at 24 to extend substantially parallel to the surface 18. At the outer end of conductor portion 22, element 12 has return bent end portion 26 joined to a third conductor portion 30 which extends in the opposite circumferential direction, to the right as viewed in FIG. 2, and in generally parallel spaced relation to conductor portion 22 and surface 18. At the right end of conductor portion 30, element 12 has a return bent end portion 32 joined to a fourth conductor portion 34. Portion 34 extends in a direction circumferentially of satellite 14, toward the left as viewed in FIG. 2 in parallel spaced relation to conductor portion 30 and surface 18. Conductor portion 34 terminates closely adjacent the radial conductor portion 20 with element 12 being bent radially inwardly to form a radial conductor portion 36 parallel to portion 20. A coaxial feed line 38 has an outer conductor 40 fastened and electrically connected to shell 16 and an inner conductor 42 fastened and electrically connected to conductor por tion 36. Conductor 42 is supported in line 38 by an insulating bead 44.

In the preferred embodiment, element 12 has a length A between the end portions 26, 32 on the order of onequarter of a wave-length at the operating frequency. The total length of conductor portions 20, .22, 26, 30, 32, 34 and 36 is on the order of one-half of a wavelength. The length of conductor portions 26, 32 and the spacing B between conductor portion 30 and conductor portions 22, 34 is a nominal fraction of a wavelength, at least less than 0.06 wavelength. Conductor portions 20, 36 are also spaced apart a nominal fraction of a wavelength at least less than 0.06 wavelength. Conductor portions 20, 36 have a height C that is a small fraction of a wavelength, generally in a range of 0.02-0.06 of a wavelength. Preferably conductor portion 20 is fastened directly to shell 16 closely adjacent portion 36. However conductor portion 20 can -be fastened directly to conductor 40 of line 38. Conductor portions 22, 30, 34 are spaced from surface 18 a distance substantially equal to the height C of conductors 20, 36. Although element 12 resembles in appearance a folded dipole antenna the performance of element 12 is radially different from a conventional folded dipole. The length A is one-quarter of a wavelength as contrasted to onehalf of a wavelength for a conventional folded dipole. Additionally the feed to element 12 by'a coaxial line 38 is unbalanced as contrasted to a balanced feed for a conventional folded dipole and polarization is at right angles to that of a folded dipole.

Referring to the coordinate system illustrated in FIG. 4 and the radiation pattern of FIG. 5, a principal plane pattern 50, corresponding to a g5 plane (=0) shows deep nulls along the radial axis, 0:0. A substantially true donut shape is achieved about the axis 6:0, with an equatorial radiation pattern 51 (0:90) being illustrated in FIG. 6. Thus the radiation pattern is substantially identical to that of an unloaded monopole projecting radially outwardly from satellite 14 on the axis: 0:0. Element 12 bears some similarity to a T antenna or an inverted L antenna since radiation appears to be primarily from the radial conductor portions 20, 36. By way of further example the radiation patterns illustrated in FIGS. 5 and 6 were obtained with a quasi-spherical satellite having a nominal circumscribing diameter in the order of 32 inches. For a frequency of 153 megacycles element 12 had the following dimensions: A=17 inches; B -2 inches; C=3 inches and was formed of number gauge wire. Conductor portions 20, 36 were spaced apart 1.5 inches. The coaxial line 38 had an impedance of 50 ohms and the antenna impedance was 23.5 ohms resulting in a voltage standing wave ratio of 2.1 to l. In general a voltage standing wave ratio on the order of 2 to 1 or less can be achieved over a narrow band of frequencies. The electric field polarization was E0. Although the ground plane formed by surface 18 and thus the diameter of the satellite 14 directly affects the radiation pattern of element 12, the effects are believed tO be substantially similar to those which would occur with a monopole antenna. Polarization properties also correspond to those of a monopole antenna.

It has also been found that an antenna of the present invention can achieve the desired radiation characteristics over a broader frequency range when operated at higher multiples of one-half of a wavelength, although the one-half Wavelength element described hereinabove is preferred where size and compactness are prime considerations. By way of further example on a 24 inch diameter satellite when element 12 was operated at substantially one full wavelength with a 50 ohm feed, a voltage standing wave ratio of less than 2 to l was achieved over a frequency range of 18S-190 megacycles. Element 12 had the following dimensions: A=29.25 inches; B=2.5 inches; C=3 inches; and the spacing between portions 20, 36 was 1.5 inches.

Referring to the embodiment illustrated in FIG. 3 of an antenna element 56 wherein elements similar to those shown in the embodiments of FIGURES 1 and 2 are identified by like reference numerals, the laterally outer ends of conductor portions 22, 34 are bent radially outwardly as at 58, 60 and joined to a conductor portion 62. Conductor portion 62 is bent at positions designated by numerals 64, 66 to be disposed above and in generally parallel spaced relation to conductor portions 22, 34 and surface 18. The antenna element 56 (FIG. 3) is substantially identical in operation to the element 12 (FlG. 1), with little, if any effect on the radiation pattern being realized by the change in position of the conductor portion 62. The embodiment illustrated in FIG. 1 is preferred since its profile is lower than the profile of element 56 (FIG. 3).

Although the antenna elements 12 (FIG. l) and 56 (FIG. 3) have been disclosed for use with a true and quasi-spherical ground plane, ground planes having other configurations are also contemplated where radiation corresponding to a conventional monopole is desired with a low profile antenna. It will be understood that the antenna which is herein described and disclosed is presented for purposes of explanation and illustration and is not intended to indicate limits of the invention, the scope of which is defined by the following claims.

What is claimed is:

1. An antenna comprising means forming a conductive ground surface and an antenna element attached and electrically conected at one end to a feed point situated substantially in the plane of said surface and attached and electrically connected at its other end to said ground surface, said element having a first portion etxending from one end generally perpendicular to said surface at said feed point, a second portion joined and electrically connected to the other end of said first portion and projecting laterally outwardly in one direction from said first portion in generally parallel spaced relation to said surface, a third portion joined and electrically connected to an outer end of said second portion and projecting an opposite lateral direction beyond said feed point in generally parallel spaced relation to said surface and in generally parallel spaced relation to said second portion, said element being return bent at a juncture of said second and third portions, a fourth portion joined and electrically connected to said third portion and extending in said one lateral direction toward said feed point and generally parallel spaced relation to said surface and said third portion, said element being return bent at a juncture of said third and fourth portions and a fifth portion joined and electrically connected at one end to said fourth portion and extending downwardly from said fourth portion generally perpendicular to said surface and generally parallel to said first portion.

2. The antenna set forth in claim 1 wherein said antenna is arranged and adapted to operate at a predetermined frequency and said perpendicular portions have a height substantially less than one-quarter of a wavelength of said predetermined frequency.

3. The antenna set forth in claim 2 wherein said perpendicular portions have an effective electrical length in the range of from 0.02 to 0.06 of a wavelength of said predetermined frequency.

4. The antenna set forth in claim 1 wherein said first and said fth portions are spaced apart a distance substantially less than one-quarter of a Wavelength of said predetermined frequency.

5. The antenna set forth in claim 1 wherein said first, said second, said third, said fourth, and said fifth portions have a combined electrical length on the order of onehalf of a wavelength of said predetermined frequency.

6. The antenna set forth in claim S wherein said third portion has an effective electrical length on the order of one-quarter of a wavelength of said predetermined frequency and said second portion and said fourth portion have substantially equal effective electrical lengths.

7. The antenna set forth in claim 6 wherein said third portion is spaced from said second and said fourth portions a distance substantially less than one-quarter of a wavelength of said frequency.

8. The antenna set forth in claim 1 wherein said surface is a quasi-spherical surface, said first and said fifth portions extend radially of said surface and said second, third, and fourth portions extend circumferentially of said surface.

9. The antenna set forth in claim 1 further comprising unbalanced feed means electrically connected to said first and said fifth portions.

10. An antenna comprising a quasi-spherical member having a conductive exterior surface and an antenna element mounted on said member, said antenna element having first and second portions extending radially outwardly from said surface, one end of one antenna portion being attached and electrically connected to said surface, one end of the other antenna portion being electrically connected to a feed point situated substantially in the plane of said surface, and a third antenna portion connected at one end to the radially outer end of said first antenna portion and connected at its other end to the radially outer end of said second antenna portion, said third antenna portion having a generally rectangular configuration formed by two short sides and two long sides, and said first and said second antenna portions being connected to said third antenna portion substantially at a midpoint of one of said long sides.

11. An antenna comprising means forming a conductive ground surface and an antenna element, said element comprising first and second parallel and spaced apart conductors mounted normal to said surface, one of said conductors being grounded at one end to said conductive surface, the other of said conductors being arranged and adapted to be energized at a predetermined frequency by means of a coaxial feed line, said first and said second conductors being spaced apart a distance substantially less than one-quarter of a wavelength at said predetermined frequency, and a third conductor electrically connected at one end to said first conductor above said ground surface and at its other end to said second conductor above said ground surface, said third conductor being disposed generally parallel to and spaced from Said ground surface a distance substantially less than one-quarter of a wavelength of said predetermined frequency and said first, said second, and said third c011- ductors having a total electrical length on the order of la multiple of one-half of a wavelength.

12. An antenna comprising forming a conductive ground surface and an antenna element, said element comprising first and second parallel spaced apart conductors mounted normal to said surface, one of said conductors being grounded at one end to said surface and the other conductor being arranged and adapted to be energized at a predetermined frequency by means of a coaxial line, said first and said second conductors being spaced apart a distance substantially less than onequarter of a wavelength at said predetermined frequency, a third conductor attached and electrically connected to said first conductor above said ground Surface and extending laterally outwardly in one direction generally parallel to said ground plane in the opposite lateral ditached and electrically connected to said second conductor above said ground surface and extending generally parallel to said ground plane in the opposite lateral direction, and a lifth conductor connected at one end to the laterally outer end of said third conductor and at its other end to the laterally outer end of said fourth conductor, said fth conductor being a straight conductor and being disposed generally parallel to said third conductor and said fourth conductor.

13. The antenna set forth in claim 12 wherein said References Cited UNITED STATES PATENTS 2,370,628 3/1945 Alford 343-705 2,404,093 7/ 1946 Roberts 343-708 2,612,606 9/1952 Wehner 343-708 2,636,987 4/1953 Dorne 343-708 OTHER REFERENCES R. C. Fenwick: A new class of electrically small antennas, IEEE trans. on antennas and propagation, May 1965, pp. 379-383.

HERMAN KARL SAALBACH, Primary Examiner W. H. PUNTER, Assistant Examiner U.S. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,488,657 Dated January 6, 1970 Inventor(s) Paul I. Pressel and Allen J. Loudon It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

IN THE SPECIFICATION Column 2, lines 5l and 52 .radially. should read radically- Column 3, line ll .E6. should read -E 9- IN THE CLAIMS Claim l, line 3 .conected. should read -connected- Claim l2, line 1 -meansshould appear after "comprising".

Claim l2, lines l5 and 16, replace the phrase "said ground plane in the opposite lateral ditached" with -said ground surface, a fourth conductor EAL) Attest:

Edward M' Flache" In WILLIAM E summum .m nesting Officer Gomissioner of Patents

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