Impedance helical antenna forming Π-shaped directional diagram

Abstract

A quadrifilar helix antenna includes a cylindrical support extending along an antenna axis; a plurality of spiral antenna elements wrapped helically on the cylindrical support and along the antenna axis from a feed end to a remote end; a ground plane having a diameter of about 300 mm and perpendicular to the antenna axis; and each of the antenna elements including a plurality of breaks, with the breaks having capacitors between conducting portions of the antenna elements. All capacitors a positioned higher than 60 mm above the ground plane, and capacitance value varies inversely with height. The antenna exhibits a DU(10°)=−20 dB or better at an operating frequency f.sub.0=1575 MHz. The diameter of the cylindrical support is 30 +/−5 mm. A total height of the cylindrical support is 300 +/−50 mm. A winding angle of the helix is variable.

Claims

1. A helix antenna comprising: a cylindrical support extending along an antenna axis; a plurality of spiral antenna elements wrapped helically on the cylindrical support and along the antenna axis from a feed end to a remote end; a ground plane having a diameter of about 300 mm and perpendicular to the cylindrical support; and each of the antenna elements including a plurality of breaks, with the breaks having capacitors between conducting portions of the spiral antenna elements, wherein all capacitors are positioned higher than a height H.sub.1=90±30 mm above the ground plane, wherein values of the capacitors of each antenna element are $C_n=\{\begin{array}{cc}—,& z=0\mathrm{.Math.}{H}_1\\ \frac{1}{2\pi f_0\left(b*z+B\right)h},& z=H_1\mathrm{.Math.}{H}_2\end{array},$  where C.sub.n (in pF) is a capacitance of the n-th capacitor; z (in mm) is a vertical coordinate varying from zero at a beginning of the spiral antenna element and taking on discrete values z=nL, where n is the number of capacitor position, L=5 . . . 30 (in mm) is a constant representing distance (center to center) between adjacent capacitors, H.sub.2 is a total height of the cylindrical support, and b=0.04±0.01 (in Ohm/mm.sup.2), B=1.5±0.3 (in Ohm/mm), wherein a winding angle α of the helix is variable and calculated as α(z)=α*z+A, z=0 . . . H.sub.2, where α(z) (in deg) is the winding angle, and a=0.06±0.01 (in deg/mm), A=45°±5° are coefficients of an approximation equation for the winding angle, and wherein the antenna exhibits a Down-Up ratio of DU(10°)=−20 dB or better at an operating frequency f.sub.0=1575±40 MHz.

2. The helix antenna of claim 1, wherein the plurality of spiral antenna elements includes four antenna elements.

3. The helix antenna of claim 1, wherein a diameter of the cylindrical support is D=30±5 mm.

4. The helix antenna of claim 1, wherein a total height of the cylindrical support H.sub.2 is H.sub.2=300±50 mm.

5. A multifilar helix antenna comprising: a cylindrical support extending along an antenna axis; a plurality of spiral antenna elements wrapped helically on the cylindrical support and along the antenna axis from a feed end to a remote end; a ground plane having a diameter of about 300 mm and perpendicular to the antenna axis; and each of the spiral antenna elements including a plurality of breaks, with the breaks having capacitors between conducting portions of the antenna elements, wherein all capacitors are positioned higher than a height H.sub.1=90±30 mm above the ground plane, and wherein values of the capacitors of each antenna element are $C_n=\{\begin{array}{cc}—,& z=0\mathrm{.Math.}{H}_1\\ \frac{1}{2\pi f_0\left(b*z+B\right)h},& z=H_1\mathrm{.Math.}{H}_2\end{array},$  where C.sub.n (in pF) is a capacitance of the n-th capacitor; z (in mm) is a vertical coordinate varying from zero at a beginning of the spiral antenna elements and taking on discrete values z=nL, where n is the number of capacitor position, L=5 . . . 30 mm is a constant representing center-to-center distance between adjacent capacitors, H.sub.2 is a total height of the cylindrical support, b=0.04±0.01 (in Ohm/mm.sup.2), B=1.5±0.3 (in Ohm/mm), wherein a winding angle α of the helix is variable and calculated as α(z)=α*z+A, z=0 . . . H.sub.2 where α(z) (in deg) is the winding angle, and a=0.06±0.01 (in deg/mm), A=45°±5° are coefficients of an approximation equation for the winding angle, and f.sub.0 is an operating frequency.

6. The helix ante a of claim 5, wherein the plurality of spiral antenna elements includes four antenna elements.

7. The helix antenna of claim 5, wherein a diameter of the cylindrical support is D=30±5 mm.

8. The helix antenna of claim 5, wherein a total height of the cylindrical support H.sub.2 is H.sub.2=300±50 mm.

9. The helix antenna of claim 5, wherein the ground plane has a diameter of about 300 mm.

10. The helix antenna of claim 5, wherein the antenna exhibits a Down-Up ratio of DU(10°)=−20 dB or better at an operating frequency f.sub.0=1575±40 MHz.

11. A helix antenna comprising: a cylindrical support extending along an antenna axis; a plurality of spiral antenna elements wrapped helically on the cylindrical support and along the antenna axis from a feed end to a remote end; a ground plane having a diameter of about 300 mm and perpendicular to the cylindrical support; and each of the spiral antenna elements including a plurality of breaks, with the breaks having capacitors between conducting portions of the spiral antenna elements, wherein all capacitors are positioned higher than a height H.sub.1=60 mm above the ground plane, wherein values of the capacitors of each spiral antenna element are given by $C_n=\frac{1}{2\pi f_0\left(b*z+B\right)L},$  where C.sub.n is a capacitance of the n-th capacitor; z is a vertical coordinate with discrete values z=nL, where n is the number of capacitor position, L is a constant distance (center to center) between adjacent capacitors of the spiral antenna element, and B and b are constants, wherein a winding angle α(z) of the helix is α(z)=E*z+A, where E and A are constants, and wherein the antenna has a Down-Up ratio of −20 dB or better 10° at an operating frequency 1535<f.sub.0 <1615 MHz.

12. The helix antenna of claim 11, wherein a total height of the cylindrical support H.sub.2 is 300±50 mm.

13. The helix antenna of claim 11, wherein L=5 . . . 30 mm.

14. The helix antenna of claim 11, wherein b=0.04±0.01 (in Ohm/mm.sup.2).

15. The helix antenna of claim 11, wherein B=1.5±0.3 (in Ohm/mm).

16. The helix antenna of claim 11, wherein the ground plane has a diameter of about 300 mm.

17. The helix antenna of claim 11, wherein E=0.06°/mm ±0.01°/mm, and A =45°±5°.

Description

BRIEF DESCRIPTION OF THE ATTACHED FIGURES

(1) The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

(2) In the drawings:

(3) FIG. 1 shows a conditional division of space into the upper and lower hemispheres.

(4) FIG. 2 shows an appearance of a prior art antenna.

(5) FIGS. 3A, 3B show a spiral turn of a prior art antenna.

(6) FIG. 4 shows a prior art antenna directional diagram.

(7) FIGS. 5A-5C show an embodiment of a design of a quadrifilar helix antenna.

(8) FIG. 6 shows a DD of the proposed antenna with a sharp drop to the horizon direction.

(9) FIG. 7 shows a Down/Up graph of the proposed antenna.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(10) Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

(11) The proposed invention according to FIGS. 5A-5C is a quadrifilar cylindrical spiral antenna with capacitors soldered into breaks in metal turns.

(12) The main features of the proposed antenna design are: 1. A quadruple spiral (FIGS. 5A, 5B) with capacitors soldered in-between breaks of spiral turns that is located onto a ground plane; 2. The diameter of the ground plane is selected such that a needed level of suppressing signals reflected from the ground in the nadir direction would be provided. In one of the embodiments, the diameter of the ground plane is 300 mm.; 3. The diameter of the spiral is D=30+/−5 mm.; 4. Total height of the spiral H.sub.2 is H.sub.2=300+/−50 mm.; 5. There is a free area with a height H.sub.1 where there are no capacitors H.sub.1=90+/−30 mm.; 6. A variable winding angle is equal to
α(z)=α*z+A,z=0 . . . H.sub.2, where   (1) α(z), [deg] is the winding angle; α=0.06±0.01[deg/mm];A=45±5[deg] are coefficients of the approximation equation for the winding angle; 7. Capacitors are loaded according to the following equation

(13) $\begin{array}{cc}{C}_n=\{\begin{array}{cc}—,& z=0\mathrm{.Math.}{H}_1\\ \frac{1}{2\pi f_0\left(b*z+B\right)h},& z=H_1\mathrm{.Math.}{H}_2\end{array},\mathrm{where}& \left(2\right)\end{array}$ f.sub.0 is the central frequency of the operational band; C.sub.n, [pF] is the capacitance of the n-th capacitor; z, [mm] is the vertical coordinate varying from zero at the beginning of the spiral and taking on discrete values: z=nh, where n is the number of capacitor position, h=5 . . . 30 [mm] is the pitch of arranging the capacitors along the vertical axis; b=0.04±0.01[Ohm/mm.sup.2]; B=1.5±0.3[Ohm/mm] are coefficients in the equation for calculating capacitors.

(14) These values are optimal values to provide required directional diagram drop at angles close to horizon. The values depend from each other and allow adjusting antenna performance.

(15) A PCB 509 is used for producing a spiral, with metallization areas 506 that can be manufactured by etching, for example. Between metallization areas there are breaks/slots 507. The produced PCB is then twisted to form a cylinder and fixed in this position.

(16) Capacitors 507 are soldered in breaks 508 between metallization areas 506. Spiral turns 501, 502, 503, 504 bare excited by pins (not shown in figures) passing through holes in the ground plane. The excitation circuit provides excitation of the right-hand circularly-polarized wave. FIG. 6 shows a directional diagram of the pilot antenna, which guarantees Down/Up ratio at least −20 dB at elevations θ≧10 degrees. At this, F(10°)=−11.5 dB. Similarly to FIG. 4, the angle zero is the zenith direction. The corresponding elevation angles read from the horizon (see FIG. 1) are in italics.

(17) FIG. 7 presents a graph of Down/Up ratio for the proposed antenna.

(18) Having thus described a preferred embodiment, it should be apparent to those skilled in the art that certain advantages of the described method and apparatus have been achieved. It should also be appreciated that various modifications, adaptations and alternative embodiments thereof may be made within the scope and spirit of the present invention. The invention is further defined by the following claims.