Slotted bifilar or quadrifilar helix antenna
View Patent ↗A slotted bifilar or quadrifilar helix antenna has a plurality of helical antenna elements. The antenna elements have an outer planar surface. A slot element is secured to an interior of the outer planar surface. The slot element extends radially inwardly to a slot element edge. At least two radially opposite slot element edges define a tapered slot. At a shorted point on the antenna, at least one radially opposite pair of slot elements are electrically shorted together. A feed point is axially offset from the shorted point along the antenna axis.
1. A slotted helix antenna, comprising:
a plurality of helical antenna elements, each helical antenna element comprising an outer planar surface which spirals around an antenna axis and a slot element secured to a central interior portion of said outer planar surface, said slot element extends radially inwardly from said outer planar surface, each slot element comprises a slot element edge, whereby at least two radially opposite slot element edges define at least one tapered slot therebetween;
a shorted point at which at least one radially opposite pair of said plurality of slot elements are electrically shorted; and
a feed point axially offset from said shorted point with respect to said antenna axis.
2. The slotted helix antenna of claim 1 , wherein said slot element edge is described by the following equations:
R
=
K
(
ⅇ
a
θ
-
1
)
and
K
=
R
max
(
ⅇ
a
θ
max
-
1
)
;
wherein θ is an angle that represents an angular distance between a slot axis and a given point on the slot element edge, where the center of the angle is at the shorted point of the plurality of helical antenna elements, and θ varies from zero at the shorted point to θ max at a further most end point of the slot element edge;
wherein R is a distance from the shorted point to a given point on the slot element edge for a given value of θ;
wherein R max is a maximum distance from said shorted point to a furthermost end point of said slot element;
wherein θ max is an angle where R max occurs;
wherein K is a constant determined by the conditions at R max and at the shorted end of the tapered slot where θ and R are zero; and
wherein a is a constant of exponentiation that determines the rate of exponentiation of said slot element edge.
3. The slotted helix antenna of claim 1 , further comprising a coaxial cable at said feed point electrically connected to a first of said plurality of slot element edges and to a radially opposite second of said plurality of slot element edges.
4. The slotted helix antenna of claim 1 , further comprising a feed pipe which extends through an axis of said tapered slot.
5. The slotted helix antenna of claim 4 , further comprising said slot elements being electrically shorted to said pipe at said shorted point.
6. The slotted helix antenna of claim 4 , further comprising at least two coaxial cables being connected to said pipe and to at least two radially opposite slot element edges at said feed point.
7. A method for making a slotted helix antenna, comprising the steps of:
providing a plurality of helical antenna elements with an outer planar surface that spirals around an antenna axis;
securing a slot element to a central interior portion of said outer planar surface;
providing that said slot element extends radially inwardly from said outer planar surface;
providing that each slot element has at least one slot element edge, whereby at least two radially opposite slot element edges define at least one tapered slot therebetween;
providing a shorted point at which at least one radially opposite pair of said plurality of slot elements are electrically shorted; and
providing a feed point axially offset from said shorted point with respect to said antenna axis.
8. The method of claim 7 , further comprising the step of:
providing that said at least one slot element edge is described by the following equations:
R
=
K
(
ⅇ
a
θ
-
1
)
and
K
=
R
max
(
ⅇ
a
θ
max
-
1
)
;
wherein θ is an angle that represents an angular distance between a slot axis and a given point on the slot element edge, where the center of the angle is at the shorted point of the plurality of helical antenna elements, and θ varies from zero at the shorted point to θ max at a further most end point of the slot element edge;
wherein R is a distance from the shorted point to a given point on the slot element edge for a given value of θ;
wherein R max is a maximum distance from said shorted point to a furthermost end point of said slot element;
wherein θ max is an angle where R max occurs;
wherein K is a constant determined by the conditions at R max and at the shorted end of the tapered slot where θ and R are zero; and
wherein a is a constant of exponentiation that determines the rate of exponentiation of said slot element edge.
9. The method of claim 7 , further comprising the step of providing that at said feed point a coaxial cable makes a connection to a first of said plurality of slot element edges and to a radially opposite second of said plurality of slot element edges.
10. The method of claim 7 , further comprising the step of providing a feed pipe which extends through an axis of said tapered slot.
11. The method of claim 10 , further comprising the step of providing that at said shorted point said slot elements are electrically shorted to said pipe.
12. The method of claim 10 , further comprising the step of providing that at said feed point at least two coaxial cables are connected to said pipe and to at least one radially opposite pair of slot element edges.