Helical antenna and method of making same

• US 5,903,242 A
• Filed: 09/26/1996
• Issued: 05/11/1999
• Est. Priority Date: 10/24/1995
• Status: Expired due to Fees

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: Murata Manufacturing Co Limited
• Inventors: Asakura, Kenji, Kanba, Seiji, Tsuru, Teruhisa, Mandai, Harufumi, Shiroki, Koji
• Primary Examiner(s): Wimer, Michael C.
• Application Number:
  US08/718,967
• Time in Patent Office: 957 Days
• Field of Search: 343/873, 343/895, 343/872, 343/749, 343/788, 343/702
• US Class Current: 343/873
• CPC Class Codes: H01Q 1/362 for broadside radiating helical antennas
• 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

Abstract

A helical antenna is provided in which a predetermined resonance frequency can be determined at the design stage. The helical antenna includes a conductor which is formed from copper or a copper alloy inside a base in the shape of a rectangular parallelopiped formed from a dielectric material having barium oxide, aluminum oxide and silica as main constituents and which is wound in a helical shape along the length of the base. In such a case, the resonance frequency f0 of the helical antenna and the inductance components L of the conductor satisfy the relationship: ln (L)=A0+A1×ln (f0), where ln is a natural logarithm, and A0 and A1 are constants. One end of the conductor is extended onto the surface of the base and forms a power feeding terminal connected to a power feeding terminal formed on the surface of the base for applying a voltage to the conductor, and the other end thereof forms a free end inside the base.

Claims

1. A helical antenna comprising a conductor having a helical shape, the conductor having a resonance frequency f0 and an inductance L, the inductance L and resonance frequency f0 satisfying the following relation:

ln (L)=A0+A1×

ln (f0), where ln is a natural logarithm, and A0 and A1 are constants and further wherein the helical antenna comprises a substrate having a surface, the conductor being disposed spirally on the surface of the dielectric substrate or in the substrate;

a power supply terminal provided on a portion of the surface of the substrate for applying voltage to the conductors the conductor having one end coupled to the power supply terminal and a second end left unconnected, the substrate comprising a base comprising a plurality of layers stacked on top of each others the stacked layers establishing a direction normal to the stacked layers, the conductor disposed spirally such that the conductor has a spiral axis extending perpendicular to the direction normal to the stacked layers.

2. The helical antenna according to claim 1, wherein the antenna has a relative bandwidth defined as bandwidth W/resonance frequency f0 and a relative coil length defined as coil length a/wavelength λ

, the relative bandwidth and relative coil length of said conductor satisfying the following relation;

W/f0=B0+B1×

(a/λ

), where B0 and B1 are constants.

3. The helical antenna according to claim 1, wherein respective ones of said layers have a portion of the conductor disposed thereon, at least one of said layers having at least one conductive through hole therein, the conductive through hole adapted to electrically couple portions of said conductor disposed on respective ones of said layers when said layers are laminated together, thereby forming said helical conductor.

4. The helical antenna according to claim 1, wherein the conductor has a rectangular shape in cross section.

5. The helical antenna according to claim 1, wherein a relationship between the inductance L of the conductor and structural parameters of the conductor comprising a winding cross section S of the conductor, a number n of windings of the conductor and a coil length a of the conductor is L=K×

u×

S×

(n² /a) where K is the Nagaoka coefficient and u is the magnetic permeability of the base, the Nagaoka coefficient being defined as K=1/(1+0.9 r/a-0.02 (r/a)²) where r is the radius of the coil and a is the coil length.

6. A helical antenna according to claim 1, wherein the base comprises one of a dielectric material, a magnetic material and a combination of a dielectric material and a magnetic material.

7. A helical antenna according to claim 1 wherein the conductor comprises a conductor disposed in a helical groove on the surface of the base.

8. A helical antenna according to claim 1, wherein the conductor has a meander shape and said conductor is disposed on one of a surface of the base and inside the base.

9. A helical antenna according to claim 1 wherein the base comprises a dielectric material having barium oxide, aluminum oxide and silica as constituents.

10. A helical antenna according to claim 1, wherein the base comprises a dielectric material having calcium oxide, magnesium oxide, aluminum oxide and silica as constituents.

11. A helical antenna according to claim 1, wherein the base comprises a dielectric material having magnesium oxide and silica as constituents.

12. The helical antenna according to claim 1, wherein the conductor comprises a copper or copper alloy.

13. A helical antenna according to claim 1, wherein the base comprises a rectangular parallelopiped.

14. A method for making a helical antenna having a desired resonance frequency f0, the method comprising the steps of:

forming a conductor on or in a base in a helical shape and determining structural parameters of the conductor to obtain the desired resonance frequency f0, the structural parameters comprising a winding cross-section S of the conductor, a number n of windings of the conductor and a coil length a of the conductor based upon the following relationships;

L=K×

μ

×

S×

(n² /a), where K is the Nagaoka coefficient, μ

is the magnetic permeability of the base and L is the inductance of the conductor, the Nagaoka coefficient being defined as K=1/(1+0.9 r/a-0.02 (r/a)²) where r is the radius of the coil and a is the coil length; and

ln (L)=A0+A1×

ln (f0), where A0 and A1 are coefficients determined by the dielectric material of the base, and further wherein the base of the helical antenna comprises a substrate having a surface, the conductor being disposed spirally on the surface of the substrate or in the substrate;

a power supply terminal provided on a portion of the surface of the substrate for applying voltage to the conductor, the conductor having one end coupled to the power supply terminal and a second end left unconnected, the substrate comprising a plurality of layers stacked on top of each other, the stacked layers establishing a direction normal to the stacked layers, the conductor disposed spirally such that it has a spiral axis extending perpendicular to the direction normal to the stacked layers.

15. The method for making a helical antenna according to claim 14, further comprising determining the coil length a of the conductor for obtaining a desired bandwidth W from the equation:

W/f0=B0+B1×

(a/λ

) where λ

is the wavelength and B0 and B1 are constants determined by the dielectric material of the base.

16. A method for forming a helical antenna having a desired resonance frequency f0 comprising forming a conductor into a helical shape on a base of dielectric material, the conductor having an inductance L wherein the inductance L satisfies a relationship ln (L)=A0+A1×

ln (f0) where A0 and A1 are constants determined by the dielectric material, and further wherein the base of dielectric material has a surface, the conductor being disposed spirally on the surface of the base or in the base;

a power supply terminal provided on a portion of the surface of the base for applying voltage to the conductor, the conductor having one end coupled to the power supply terminal and a second end left unconnected, the base comprising a plurality of layers stacked on top of each other, the stacked layers establishing a direction normal to the stacked layers, the conductor disposed spirally such that it has a spiral axis extending perpendicular to the direction normal to the stacked layers.

17. The method according to claim 16, further comprising determining a bandwidth W of the helical antenna based on the following equation:

W/f0=B0+B1×

(a/λ

) where a is the coil length of the conductor, B0 and B1 are constants determined by the dielectric material of the base and λ

is the wavelength.

18. The method according to claim 16, further comprising determining the inductance L of the conductor according to the following equation:

L=K×

μ

×

S×

(n² /a) where K is the Nagaoka coefficient, μ

is the magnetic permeability of the base, S is the winding cross-section of the conductor, n is the number of windings of the conductor and a is the coil length of the conductor, the Nagaoka coefficient being defined as K=1/(1+0.9 r/a-0.02 (r/a)²) where r is the radius of the coil and a is the coil length.

19. A method for determining structural parameters of a helical antenna given a desired resonance frequency f0, the method comprising:

determining a winding cross-section S, coil length a and number of winding turns n of a conductor of the helical antenna based on the formula;

space="preserve" listing-type="equation">n={(e.sup.A0 ×

f0.sup.A1)/(μ

×

S)}.sup.1/2 ×

(a/K).sup.1/2 where

A0 and A1 are constants determined by a dielectric material through which the conductor traverses, e is the dielectric constant of the dielectric material, μ

is the magnetic permeability of the dielectric material and K is the Nagaoka coefficient, the Nagaoka coefficient being defined as K=1/(1+0.9 r/a-0.02 (r/a)²) where r is the radius of the coil and a is the coil length; and

further wherein the helical antenna comprises a dielectric substrate having a surface, the conductor being disposed spirally on the surface of the dielectric substrate or in the substrate;

a power supply terminal provided on a portion of the surface of the dielectric substrate for applying voltage to the conductor, the conductor having one end coupled to the power supply terminal and a second end left unconnected, the dielectric substrate comprising a plurality of layers stacked on top of each others the stacked layers establishing a direction normal to the stacked layers, the conductor disposed spirally such that it has a spiral axis extending perpendicular to the direction normal to the stacked layers.

20. A method for making a helical antenna having a defined resonance frequency f0 and bandwidth W, the method comprising the steps of:

choosing a winding cross section S of the helical antenna, a number n of turns of the winding of the antenna and a coil length a of the helical antenna according to the equations;

L=K×

μ

×

S×

(n² /a) where K is the Nagaoka coefficient, n is the magnetic permeability of the material through what the winding traverses; and

L is the inductance the Nagaoka coefficient being defined as K=1/(1+0.9 r/a-0.02 (r/a)²) where r is the radius of the coil and a is the coil length;

ln (L)=A0+A1×

ln (f0) where A0 and A1 are constants determined by the material through which the winding traverses; and

W/f0=B0+B1×

(A/λ

) where B0 and B1 are constants determined by the material through which the winding traverses and λ

is the wavelength; and

further wherein the helical antenna comprises a substrate having a surface, the winding comprising a conductor disposed spirally on the surface of the substrate or in the substrate;

a power supply terminal provided on a portion of the surface of the substrate for applying voltage to the conductor, the conductor having one end coupled to the power supply terminal and a second end left unconnected, the substrate comprising a plurality of layers stacked on top of each other, the stacked layers establishing a direction normal to the stacked layers, the conductor disposed spirally such that it has a spiral axis extending perpendicular to the direction normal to the stacked layers.