Capacitatively shunted quadrifilar helix antenna

• US 6,765,541 B1
• Filed: 04/24/2000
• Issued: 07/20/2004
• Est. Priority Date: 04/24/2000
• Status: Expired

• Current Assignee: United States Incorporated
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Josypenko, Michael J.
• Primary Examiner(s): Le, Hoanganh
• Assistant Examiner(s): CHEN, SHIH CHAO
• Application Number:
  US09/558,689
• Time in Patent Office: 1,548 Days
• Field of Search: H01/Q.136, 343/702, 343/745, 343/749, 343/751, 343/895
• US Class Current: 343/895
• CPC Class Codes: H01Q 11/08 Helical antennas

Abstract

A quadrifilar helix antenna is provided having a feedpoint for the antenna connecting to individual helical antenna elements. A capacitive network, distributed along the length of the antenna, constitutes a variable frequency shunting network. At each position a first capacitive structure, that may comprise a single capacitor or multiple capacitors in series, interconnects a first pair of opposite antenna elements; a second capacitive structure interconnects the second pair of opposite antenna elements. As an applied frequency increases, the capacitive structures progressively short the opposite antenna elements thereby electrically reducing the antenna length.

Claims

1. An antenna for operating over a range of frequencies about a cut-in frequency, said antenna extending along an antenna axis between a feed end and an other end comprising;

a plurality of pairs of diametrically opposed antenna elements wrapped helically about said axis from said feed end to said other end, each of said antenna elements having a length determined by the cut-in frequency; and

capacitive means spanning said antenna elements in each said pair of antenna elements a predetermined position from said other end for shorting said pairs of antenna elements at a characteristic frequency greater than the cut-in frequency.

2. An antenna as recited in claim 1 wherein said antenna includes additional capacitive means spanning said antenna elements in each said pair of antenna elements at other predetermined positions along the length of said antenna axis, each of said capacitive means at different positions having a different capacitive impedance.

3. An antenna as recited in claim 2 wherein said different capacitive means positions are evenly spaced along said antenna axis.

4. An antenna as recited in claim 2 wherein said capacitive means most proximate to said other end has a minimum capacitance and said capacitive means most proximate to said feed end has a maximum capacitance.

5. An antenna as recited in claim 4 wherein the differences between the capacitance of adjacent capacitive means are constant.

6. An antenna as recited in claim 4 wherein the differences between the capacitance of adjacent capacitive means vary.

7. An antenna as recited in claim 6 wherein the differences between the capacitance of adjacent capacitive means vary logarithmically.

8. An antenna as recited in claim 4 wherein each capacitive means includes conductors for connection to said antenna elements and said capacitance of each said capacitive means is determined by the capacitance required to short circuit said antenna elements at frequencies above the characteristic frequency for said capacitive means plus the capacitance required to compensate inductance in said conductors.

9. A quadrifilar helical antenna for operating over a frequency bandwidth defined by a minimum operating frequency and extending along an antenna axis between first and second ends thereof, said antenna comprising;

four equiangularly spaced helical antenna elements extending along said axis between said first and second ends, each said antenna element having a length of at least ¾

wavelength at a minimum antenna operating frequency and having a substantially constant thickness and width, said antenna elements constituting first and second element pairs consisting of a pair of diametrically opposed antenna elements; and

a plurality sets of capacitive elements connected between said antenna elements in said diametrically opposed pairs, each said set being connected at a different position along the antenna axis and each capacitive element in a set connected to said respective antenna element pair at the same position along the antenna axis.

10. A quadrifilar helical antenna as recited in claim 9 wherein said antenna is divided into n axially extending segments and includes n−

1 sets of axially spaced capacitive elements.

11. A quadrifilar helical antenna as recited in claim 10 wherein said antenna is divided into n axially extending segments and includes n−

1 sets of evenly axially spaced capacitive elements.

12. A quadrifilar helical antenna as recited in claim 11 wherein each capacitive element has a capacitance that short circuits said antenna elements at a different frequency, each of which is greater than said minimum frequency.

13. A quadrifilar helical antenna as recited in claim 12 wherein the difference between the capacitance in adjacent sets varies.

14. A quadrifilar helical antenna as recited in claim 12 wherein the difference between the capacitance in adjacent sets varies logarithmically.

15. A quadrifilar helical antenna as recited in claim 12 wherein each capacitance element includes at least one capacitor and conductors extending from said capacitor to said antenna elements, the capacitance of said capacitor being a function of the operating frequency at which said capacitance element shorts the attached antenna elements and the reactance of the conductors.

16. A quadrifilar helical antenna as recited in claim 15 wherein at least one of said capacitance elements includes first and second capacitors in series.

17. A quadrifilar helical antenna as recited in claim 16 wherein the difference between the capacitance in adjacent sets varies.

18. A quadrifilar helical antenna as recited in claim 16 wherein the difference between the capacitance in adjacent sets varies logarithmically.