Tuning fractal antennas and fractal resonators

• US 6,104,349 A
• Filed: 11/07/1997
• Issued: 08/15/2000
• Est. Priority Date: 08/09/1995
• Status: Expired due to Term

• Current Assignee: Fractal Antenna Systems Inc.
• Original Assignee: Nathan Cohen
• Inventors: Cohen, Nathan
• Primary Examiner(s): Wimer, Michael C.
• Application Number:
  US08/967,372
• Time in Patent Office: 1,012 Days
• Field of Search: 343/702, 343/795, 343/806, 343/792.5, 343/787, 343/788, 343/741, 343/846
• US Class Current: 343/702
• CPC Class Codes: H01Q 1/246 specially adapted for base stations
• CPC Class Codes: H01Q 1/36 Structural form of radiating elements, e.g. cone, spiral, umbrella; Particular materials used therewithH01Q1/08, H01Q1/14 take precedence
• CPC Class Codes: H01Q 1/38 formed by a conductive layer on an insulating support patch antennas H01Q9/0407; microstrip dipole antennas H01Q9/065; microstrip slot antennas H01Q13/106; transmission line microstrip antennas H01Q13/206; manufacturing reflecting surfaces using insulating material for supporting the reflecting surface H01Q15/142
• CPC Class Codes: H01Q 21/205 providing an omnidirectional coverage turnstile aerials H01Q21/26
• CPC Class Codes: H01Q 21/28 Combinations of substantially independent non-interacting antenna units or systems multiple beam H01Q25/00
• CPC Class Codes: H01Q 9/0407 Substantially flat resonant element parallel to ground plane, e.g. patch antenna dipole H01Q9/285; monopole H01Q9/40

Abstract

A first fractal antenna of iteration N≧2 in free space exhibits characteristics including at least one resonant frequency and bandwidth. Spacing-apart the first fractal conductive element from a conductive element by a distance Δ, non-planarly or otherwise, preferably ≦0.05λ for non-planar separation for frequencies of interest decreases resonant frequency and/or introduces new resonant frequencies, widens the bandwidth, or both, for the resultant antenna system. The conductive element may itself be a fractal antenna, which if rotated relative to the first fractal antenna will alter or tune at least one characteristic of the antenna system. Forming a cut anywhere in the first fractal antenna causes new and different resonant nodes to appear. The antenna system may be tuned by cutting-off a portion of the first fractal antenna, typically increasing resonant frequency. A region of ground plane may be formed adjacent the antenna system, to form a sandwich-like system that is readily tuned. Resonator systems as well as antenna systems may be tuned using is disclosed methodology.

Claims

1. An antenna system comprising:

a first fractal antenna including a first element having a portion that includes;

at least a first motif selected from a family consisting of (i) Koch, (ii) Minkowski, (iii) Cantor, (iv) torn square, (v) Mandelbrot. (vi) Caley tree, (vii) monkey'"'"'s swing, (viii) Sierpinski gasket, and (ix) Julia;

and a first replication of said first motif and a second replication of said first motif such that a point chosen on a geometric figure represented by said first motif will result in a corresponding point on said first replication and on said second replication of said first motif;

wherein there exists at least one non-straight line locus connecting each said point;

wherein a replication of said first motif is a change selected from a group consisting of (a) a rotation and change of scale of said first motif, (b) a linear displacement translation and a change of scale of said first motif, and (c) a rotation and a linear displacement translation and a change of scale of said first motif, and wherein said first fractal antenna is characterized in space by at least one resonant frequency and by a bandwidth; and

a conductive element, spaced-apart from said first fractal antenna by a distance Δ

chosen to vary at least one characteristic of said antenna system, at a desired frequency c/λ

, where c is velocity of light, selected from a group consisting of (i) said resonant frequency, and (ii) said bandwidth.

2. The antenna system of claim 1, wherein said distance Δ

has at least one characteristic selected from a group consisting of (a) said first fractal antenna and said conductive element are spaced-apart in different planes by a distance Δ

≦

0.05λ

where λ

is wavelength at a resonant frequency of said antenna system in free space, (b) said first fractal antenna and said conductive element are spaced-apart in a common plane by said distance Δ

, and (c) at least one of said first fractal antenna and said conductive element is non-planar and said distance Δ

defines a closest distance separating said first fractal antenna from said conductive element.

3. The antenna system of claim 1, wherein said conductive element is selected from a group consisting of (a) a planar conductor, (b) a second fractal antenna defined by an iteration identical to said first fractal antenna, (c) a second fractal antenna defined by an iteration N identical to said first fractal antenna but having a different configuration, (d) a second fractal antenna defined by at least a third-order iteration, and (e) a second fractal antenna defined by at least a third-order iteration and having a configuration similar to a configuration of said first fractal antenna.

4. The antenna system of claim 1, wherein said conductive element is a second fractal antenna that includes a second element having a portion that includes at least a second motif and a first replication of said second motif and a second replication of said second motif such that a point chosen on a geometric figure represented by said second motif will result in a corresponding point on said first replication and on said second replication of said second motif;

wherein there exists at least one locus connecting each said point that does not define a straight line; and

wherein a replication of said second motif is a change selected from a group consisting of (a) a rotation and change of scale of said second motif, (b) a linear displacement translation and a change of scale of said second motif, and (c) a rotation and a linear displacement translation and a change of scale of said second motif;

wherein one of said first fractal antenna and said second fractal antenna is rotatable through a relative angle θ

therebetween to vary at least one characteristic of said antenna system.

5. The antenna system of claim 1, wherein said first fractal antenna includes a region that defines a cut such that at least one said resonant frequency of said antenna system is varied by said cut.

6. The antenna system of claim 1, wherein said first fractal antenna is formed non-planarly to vary at least one said resonant frequency of said antenna system.

7. The antenna system of claim 1, wherein said antenna system includes a ferrite core about which said first fractal antenna is formed.

8. The antenna system of claim 1, further including a feedline having a center conductor and a ground conductor;

wherein;

a portion of said first fractal antenna is connected to said center conductor of said feedline, and a portion of said conductive element is connected to said ground conductor of said feedline.

9. The antenna system of claim 4, further including a feedline having a center conductor and a ground conductor;

wherein;

a portion of said first fractal antenna is connected to said center conductor of said feedline, and said ground conductor of said feedline is connected to at least one region of said system defined by (a) a portion of said second fractal antenna, (b) a system ground, and (c) said conductive element and a system ground.

10. The antenna system of claim 1, further including:

a ground plane member;

said ground member disposed sufficiently close to said first fractal antenna so as to vary a characteristic of said antenna system.

11. The antenna system of claim 1, wherein said first motif has x-axis, y-axis coordinates for a next iteration N+1 defined by x_N+1 =f(x_N, y_N) and y_N+1 =g(x_N, y_N), where x_N, y_N are coordinates for iteration N, and where f(x,y) and g(x,y) are functions defining said first motif.

12. The antenna system of claim 1, wherein said first fractal antenna has a perimeter compression parameter (PC) defined by:

##EQU6## where;

space="preserve" listing-type="equation">PC=A·

log[N(D+C)]

in which A and C are constant coefficients for a given said first motif, N is an iteration number, and D is a fractal dimension given by log(L)/log(r), where L and r are one-dimensional antenna element lengths before and after fractalization, respectively.

13. A tunable fractal antenna system coupleable to a transceiver unit, the antenna comprising:

a first fractal antenna including;

a first element having a portion that includes at least a first motif selected from a family consisting of (i) Koch, (ii) Minkowski, (iii) Cantor, (iv) torn square, (v) Mandelbrot, (vi) Caley tree, (vii) monkey'"'"'s swing, (viii) Sierpinski gasket, and (ix) Julia;

and a first replication of said first motif and a second replication of said first motif such that a point chosen on a geometric figure represented by said first motif will result in a corresponding point on said first replication and on said second replication of said first motif;

wherein there exists at least one non-straight line locus connecting each said point;

wherein a replication of said first motif is a change selected from a group consisting of (a) a rotation and change of scale of said first motif, (b) a linear displacement translation and a change of scale of said first motif, and (c) a rotation and a linear displacement translation and a change of scale of said first motif; and

a conductive element, spaced-apart from said first fractal antenna by a distance Δ

chosen to vary at least one characteristic of said antenna system, at a desired frequency c/λ

, where c is velocity of light, selected from the group consisting of (i) resonant frequency of said antenna system, and (ii) bandwidth of said antenna system.

14. The tunable fractal antenna system of claim 13, wherein said conductive element is selected from a group consisting of (a) a planar conductor, (b) a second fractal antenna defined by an iteration identical to said first fractal antenna, (c) a second fractal antenna defined by an iteration identical to said first fractal antenna but having a different configuration, (d) a second fractal antenna defined by at least a third-order iteration, (e) a second fractal antenna defined by at least a third-order iteration and having a configuration similar to said first fractal antenna, (f) a second fractal antenna angularly rotated relative to said first fractal antenna, and (g) a second fractal antenna having a portion that defines a cut.

15. The tunable fractal antenna system of claim 13, further including a feedline;

wherein said antenna system is tunable by varying at least one parameter selected from a group consisting of (a) said distance Δ

, (b) relative rotation between said first fractal antenna and said conductive element, (c) location at which a center lead of said feedline is coupled to said first fractal antenna, (d) location of a cut in said first fractal antenna, and (e) size of a cut in said first fractal antenna.

16. The tunable fractal antenna system of claim 13, wherein said distance Δ

has at least one characteristic selected from a group consisting of (a) said first fractal antenna and said conductive element are spaced-apart in different planes by a distance Δ

≦

0.05λ

where λ

is wavelength at a resonant frequency of said antenna system in free space, (b) said first fractal antenna and said conductive element are spaced-apart in a common plane by said distance Δ

, and (c) at least one of said first fractal antenna and said conductive element is non-planar and said distance Δ

defines a closest distance separating said first fractal antenna from said conductive element.

17. A method of tuning a fractal resonator system, comprising:

disposing a first fractal member a distance Δ

from a conductive element;

said first fractal member including a first element having a portion that includes at least a first motif selected from a family consisting of (i) Koch, (ii) Minkowski, (iii) Cantor, (iv) torn square, (v) Mandelbrot, (vi) Caley tree, (vii) monkey'"'"'s swing, (viii) Sierpinski gasket, and (ix) Julia; and

a first replication of said first motif and a second replication of said first motif such that a point chosen on a geometric figure represented by said first motif will result in a corresponding point on said first replication and on said second replication of said first motif;

wherein there exists at least one non-straight line locus connecting each said point;

wherein a replication of said first motif is a change selected from a group consisting of (a) a rotation and change of scale of said first motif, (b) a linear displacement translation and a change of scale of said first motif, and (c) a rotation and a linear displacement translation and a change of scale of said first motif; and

tuning said fractal resonator system by modifying at least one parameter selected from a group consisting of (a) a magnitude of said distance Δ

, (b) an angular orientation between said first fractal member and said conductive element, (c) extent of curvature associated with at least one of said first fractal member and said conductive element, (d) size of at least one of said first fractal member and said conductive element, (e) shape of at least one of said first fractal member and said conductive element, (f) location of said conductive element relative to said first fractal member, (g) existence of a cut defined in at least one of said first fractal member and said conductive element, and (g) location of feedline coupling to at least one of said first fractal member and said conductive element.

18. The method of claim 17, wherein said system is an antenna system.