Apparatus and method for broadband matching of electrically small antennas

• US 6,121,940 A
• Filed: 08/03/1998
• Issued: 09/19/2000
• Est. Priority Date: 09/04/1997
• Status: Expired due to Term

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Original Assignee: AIL Systems, Inc. (ITT, Inc.)
• Inventors: Skahill, George, Pierro, John A., Rudish, Ronald M.
• Primary Examiner(s): LE, HOANGANH T
• Application Number:
  US09/128,168
• Time in Patent Office: 778 Days
• Field of Search: 343/701, 343/860, 343/850, 343/856, 455/291, 333/32
• US Class Current: 343/860
• CPC Class Codes: H01Q 9/00 Electrically-short antennas having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
• CPC Class Codes: H03H 11/30 Automatic matching of source impedance to load impedance
• CPC Class Codes: H03H 11/48 simulating reactances
• CPC Class Codes: H03H 11/481 Simulating capacitances

Abstract

A broadband impedance matching circuit employs active circuits featuring non-Foster reactance behavior, such as negative capacitor circuits and negative inductor circuits, to achieve extremely broadband matching of electrically small antennas. The matching circuit includes at least one non-Foster reactance circuit selected to neutralize the reactance exhibited by the antenna. The circuit further includes a dynamic dispersive impedance transformer circuit which compensates for the frequency dependent radiation resistance presented by the electrically small antenna. The dynamic dispersive impedance transformer is constructed using complementary Foster and non-Foster reactance circuits configured as an impedance transformer.

Claims

1. A broadband impedance matching circuit for interfacing an antenna to one of a signal source and a load, the antenna exhibiting a frequency dependent Foster reactance and a frequency dependent radiation resistance, the matching circuit comprising:

a non-Foster reactance circuit operatively coupled to the antenna, the non-Foster reactance circuit being selected to neutralize the Foster reactance of the antenna; and

a dynamic dispersive impedance transformer circuit, the dynamic dispersive impedance transformer circuit being operatively coupled to the non-Foster reactance circuit and effectively transforming the frequency dependent radiation resistance of the antenna into a substantially frequency independent resistance, the dynamic dispersive impedance transformer circuit being further coupled to one of the source and the load.

2. A broadband impedance matching circuit as defined by claim 1, wherein the dynamic dispersive impedance transformer circuit comprises:

a first reactance circuit having a first reactance value; and

a second reactance circuit, the second reactance circuit having a second reactance value, one of the first reactance circuit and second reactance circuit exhibiting non-Foster reactance with the second reactance value being selected to be substantially equal and opposite to the first reactance value, the first reactance circuit and second reactance circuit being operatively configured as an L-network.

3. A broadband impedance matching circuit as defined by claim 2, wherein the dynamic dispersive impedance transformer circuit further comprises a third reactance circuit, the third reactance circuit having a reactance value substantially equal to the reactance value of the first reactance circuit, the dynamic dispersive impedance transformer circuit being operatively configured as a T-network.

4. A broadband impedance matching circuit as defined by claim 2, wherein the dynamic dispersive impedance transformer circuit further comprises a third reactance circuit, the third reactance circuit having a reactance value substantially equal to the reactance value of the first reactance circuit, the dynamic dispersive impedance transformer circuit being operatively configured as a π

-network.

5. A broadband impedance matching circuit for interfacing an antenna to one of a signal source and a load, the matching circuit comprising:

a negative capacitor circuit;

a negative inductor circuit, the negative capacitor circuit and negative inductor circuit being connected as a resonant circuit having a first and second terminal, the first terminal being electrically connected to the antenna; and

a dynamic dispersive impedance transformer circuit, the dynamic dispersive impedance transformer circuit comprising;

a first reactance circuit, the first reactance circuit having a first terminal, a second terminal and a reactance associated therebetween, the first terminal being connected to the second terminal of the resonant circuit; and

a second reactance circuit, the second reactance circuit having a first terminal, a second terminal and a reactance associated therebetween, the reactance of the second reactance circuit being selected to be equal and opposite to the reactance of the first reactance circuit, the first terminal of the second reactance circuit being connected to the second terminal of the first reactance circuit and serving as an output terminal for the dynamic dispersive impedance transformer circuit for connection to one of the signal source and the load, the second terminal of the second reactance circuit being electrically coupled to circuit ground, the dynamic dispersive impedance transformer circuit receiving a first signal having a frequency dependent radiation resistance component from the antenna and transforming the first signal into a second signal having a substantially constant real resistance, the dynamic dispersive impedance transformer circuit providing the second signal at the output terminal.

6. A broadband impedance matching circuit for an antenna as defined by claim 5, wherein the dynamic dispersive impedance transformer circuit further comprises:

a third reactance circuit, the third reactance circuit having a first terminal, a second terminal and a reactance associated therebetween, the first terminal of the third reactance circuit being connected to the junction of the first reactance circuit and second reactance circuit, the second terminal of the third reactance circuit serving as an output terminal for connection to one of the signal source and the load.

7. A broadband impedance matching circuit for an antenna as defined by claim 6, wherein the reactance of the first reactance circuit is a positive inductive reactance.

8. A broadband impedance matching circuit for an antenna as defined by claim 6, wherein the reactance of the first reactance circuit is a negative inductive reactance.

9. A broadband impedance matching circuit for an antenna as defined by claim 6, wherein the reactance of the first reactance circuit is a positive capacitive reactance.

10. A broadband impedance matching circuit for an antenna as defined by claim 6, wherein the reactance of the first reactance circuit is a negative capacitive reactance.

11. A broadband impedance matching circuit for an antenna as defined by claim 5, wherein the antenna is a dipole and wherein the resonant circuit is in the form of a series resonant circuit.

12. A broadband impedance matching circuit for an antenna as defined by claim 5, wherein the antenna is a monopole element extending substantially perpendicularly over a ground plane and wherein the resonant circuit is in the form of a series resonant circuit.

13. A broadband impedance matching circuit for an antenna as defined by claim 5, wherein the antenna is a loop antenna and wherein the resonant circuit is in the form of a parallel resonant circuit.

14. A broadband impedance matching circuit for an antenna as defined by claim 5, wherein the antenna is a slot antenna and wherein the resonant circuit is in the form of a parallel resonant circuit.

15. A dynamic dispersive impedance transformer circuit, the dynamic dispersive impedance transformer circuit comprising:

a first reactance circuit, the first reactance circuit having a first reactance associated therewith; and

a second reactance circuit, the second reactance circuit having a second reactance associated therewith, one of the first reactance circuit and second reactance circuit being a non-Foster reactance circuit, the reactance of the second reactance circuit being selected to be substantially equal and opposite to the reactance of the first reactance circuit, the first reactance circuit and second reactance circuit being operatively configured as an L-network having an input terminal and an output terminal, the dynamic dispersive impedance transformer circuit receiving a first signal having a frequency dependent resistance component on the input terminal and transforming the first signal into a second signal having a substantially frequency independent resistance, the dynamic dispersive impedance transformer circuit providing the second signal at the output terminal.

16. A dynamic dispersive impedance transformer circuit as defined by claim 15, further comprising:

a third reactance circuit, the third reactance circuit having a third reactance associated therewith, the first, second and third reactance circuits being operatively coupled as one of a T-network and a π

-network.

17. A method of broadband impedance matching an antenna with one of a signal source and a load, the antenna exhibiting a frequency dependent Foster reactance and a frequency dependent radiation resistance, which comprises the steps of:

neutralizing the Foster reactance of the electrically small antenna by operatively coupling thereto a circuit exhibiting a non-Foster reactance;

transforming effectively the frequency dependent radiation resistance of the antenna into a substantially frequency independent resistance by operatively coupling a dynamic dispersive impedance transformer circuit to the circuit exhibiting a non-Foster reactance; and

operatively coupling the dynamic dispersive impedance transformer circuit to one of the signal source and the load.