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An automatic tuning circuit for matching an antenna to a radio receiver. The automatic tuning circuit includes a tunable non-Foster circuit for coupling the receiver and the antenna; and sensing and feedback circuits for sensing the combined capacitance of the tunable non-Foster circuit and the ante

An automatic tuning circuit for matching an antenna to a radio receiver. The automatic tuning circuit includes a tunable non-Foster circuit for coupling the receiver and the antenna; and sensing and feedback circuits for sensing the combined capacitance of the tunable non-Foster circuit and the antenna and for tuning the tunable non-Foster circuit to automatically minimize the combined capacitance of the tunable non-Foster circuit and the antenna.

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1. An automatic tuning circuit for matching an antenna to a radio receiver, the automatic tuning circuit comprising: a tunable non-Foster circuit coupling the receiver and the antenna; andsensing and feedback circuits sensing the combined reactance of the tunable non-Foster circuit and the antenna a

1. An automatic tuning circuit for matching an antenna to a radio receiver, the automatic tuning circuit comprising: a tunable non-Foster circuit coupling the receiver and the antenna; andsensing and feedback circuits sensing the combined reactance of the tunable non-Foster circuit and the antenna and for tuning the tunable non-Foster circuit to automatically minimize the combined reactance of the tunable non-Foster circuit and the antenna without making the combined reactance of the tunable non-Foster circuit and the antenna equal to zero so that an absolute value of the reactance of the tunable non-Foster circuit is maintained at a slightly smaller value than an absolute value of the reactance of the antenna to maintain stability of the tunable non-Foster circuit. 2. The automatic tuning circuit of claim 1 wherein the tunable non-Foster circuit comprises an otherwise non-tunable non-Foster circuit with a variable capacitance added across a negative impedance output of the otherwise non-tunable non-Foster circuit to thereby render the otherwise non-tunable non-Foster circuit tunable. 3. The automatic tuning circuit of claim 2 wherein the variable capacitance is supplied by reverse biased varactor diodes coupled in parallel with the negative impedance output of the otherwise non-tunable non-Foster circuit, a junction point between the series coupled varactor diodes providing a control input to the tunable non-Foster circuit. 4. The automatic tuning circuit of claim 3 wherein the sensing and feedback circuits comprise: means for sensing an input impedance associated with the antenna and the tunable non-Foster circuit when a RF signal is applied to the antenna and the tunable non-Foster circuit via the means for sensing; andan operational amplifier whose output is coupled to the control input of the tunable non-Foster circuit. 5. The automatic tuning circuit of claim 4 wherein the sensing and feedback circuits further comprise a sample and hold circuit coupled between said operational amplifier and said control input of the tunable non-Foster circuit. 6. The automatic tuning circuit of claim 1 wherein the sensing and feedback circuits comprise: means for sensing an input impedance associated with the antenna and the tunable non-Foster circuit when a RF signal is applied to the antenna and the tunable non-Foster circuit via the means for sensing; andan operational amplifier whose output is coupled to a control input of the tunable non-Foster circuit. 7. The automatic tuning circuit of claim 6 wherein the sensing and feedback circuits further comprise a sample and hold circuit coupled between said operational amplifier and said control input of the tunable non-Foster circuit. 8. The automatic tuning circuit of claim 1 wherein the tunable non-Foster circuit emulates a variable negative capacitor and wherein the antenna is a dipole or a monopole. 9. A tuning circuit for matching an antenna to a variable frequency oscillator, the automatic tuning circuit comprising: a tunable non-Foster circuit coupling the variable frequency oscillator and the antenna; andsensing and feedback circuits for sensing the combined reactance of the tunable non-Foster circuit and the antenna and for tuning the tunable non-Foster circuit to minimize the combined reactance of the tunable non-Foster circuit and the antenna without making the combined reactance equal to zero and such that the combined reactance of the tunable non-Foster circuit is less than the reactance of the antenna and of the same sign. 10. The tuning circuit of claim 9 wherein the tunable non-Foster circuit comprises an otherwise non-tunable non-Foster circuit with a variable reactance added across a negative impedance output of the otherwise non-tunable non-Foster circuit to thereby render the otherwise non-tunable non-Foster circuit tunable. 11. The tuning circuit of claim 10 wherein the variable reactance is supplied by reverse biased varactor diodes coupled in parallel with the negative impedance output of the otherwise non-tunable non-Foster circuit, a junction point between the series coupled varactor diodes providing a control input to the tunable non-Foster circuit. 12. The tuning circuit of claim 11 wherein the sensing and feedback circuits comprise: means for sensing an input impedance associated with the antenna and the tunable non-Foster circuit when a RF signal is applied to the antenna and the tunable non-Foster circuit via the means for sensing; andan operational amplifier whose output is coupled to the control input of the tunable non-Foster circuit. 13. The tuning circuit of claim 12 wherein the sensing and feedback circuits further comprise a sample and hold circuit coupled between said operational amplifier and said control input of the tunable non-Foster circuit. 14. The tuning circuit of claim 9 wherein the sensing and feedback circuits comprise: means for sensing an input impedance associated with the antenna and the tunable non-Foster circuit when a RF signal is applied to the antenna and the tunable non-Foster circuit via the means for sensing; andan operational amplifier whose output is coupled to a control input of the tunable non-Foster circuit. 15. The tuning circuit of claim 14 wherein the sensing and feedback circuits further comprise a sample and hold circuit coupled between said operational amplifier and said control input of the tunable non-Foster circuit. 16. The tuning circuit of claim 9 wherein the tunable non-Foster circuit emulates a variable negative capacitor and wherein the antenna is a dipole or a monopole. 17. A tunable non-Foster circuit comprising: a conventional non-Foster circuit having an output where a negative capacitance is realized; anda variable capacitor coupled in parallel with the output of the conventional non-Foster circuit where the negative capacitance is realized, the variable capacitor having a capacitance less than the absolute value of the negative capacitance realized by the conventional non-Foster circuit, so that a variable negative capacitance is realized across the output of the conventional non-Foster circuit by varying the variable capacitor. 18. A method of matching an antenna to a radio receiver, the method comprising: coupling a tunable non-Foster circuit between the receiver and the antenna, the tunable non-Foster circuit and the antenna having a combined reactance;sensing the combined reactance of the tunable non-Foster circuit and the antenna in a sensing circuit; andtuning the tunable non-Foster circuit to minimize the combined reactance of the tunable non-Foster circuit and the antenna as sensed by the sensing circuit without making the combined reactance of the tunable non-Foster circuit and the antenna equal to zero so that an absolute value of the reactance of the tunable non-Foster circuit is maintained at a slightly smaller value than an absolute value of the reactance of the antenna to maintain stability of the tunable non-Foster circuit. 19. The method of matching the antenna to the radio receiver of claim 18 wherein the tunable non-Foster circuit comprises an otherwise non-tunable non-Foster circuit with a variable capacitance added across a negative capacitance output of the otherwise non-tunable non-Foster circuit to thereby render the otherwise non-tunable non-Foster circuit tunable. 20. The method of matching the antenna to the radio receiver of claim 19 wherein the variable capacitance is supplied by reverse biased varactor diodes coupled in series with the negative capacitance output of the otherwise non-tunable non-Foster circuit, a junction point between the series coupled varactor diodes providing a control input for the tunable non-Foster circuit. 21. The method of matching the antenna to the radio receiver of claim 20 wherein an input impedance is associated with the antenna, wherein the step of sensing the combined reactance of the tunable non-Foster circuit and the antenna includes applying a RF signal to the antenna and the tunable non-Foster circuit and wherein the step of tuning the tunable non-Foster circuit includes adjusting a negative capacitance of the tunable non-Foster circuit to minimize the the combined reactance of the tunable non-Foster circuit and the antenna while said RF signal is being applied to the antenna and the tunable non-Foster circuit. 22. The method of matching the antenna to the radio receiver of claim 18 wherein an input impedance is associated with the antenna, wherein the step of sensing the combined reactance of the tunable non-Foster circuit and the antenna includes applying a RF signal to the antenna and the tunable non-Foster circuit and wherein the step of tuning the tunable non-Foster circuit includes adjusting a negative capacitance of the tunable non-Foster circuit to minimize the the combined reactance of the tunable non-Foster circuit and the antenna while said RF signal is being applied to the antenna and the tunable non-Foster circuit. 23. The method of matching the antenna to the radio receiver of claim 18 wherein the tunable non-Foster circuit emulates a variable negative capacitor and wherein the antenna is a dipole or a monopole. 24. The method of matching the antenna to the radio receiver of claim 18 wherein the tuning the tunable non-Foster circuit to minimize the combined reactance of the tunable non-Foster circuit and the antenna as sensed by the sensing circuit occurs automatically. 25. A method of matching an antenna to a variable frequency oscillator, the method comprising: coupling the variable frequency oscillator to the antenna via a tunable non-Foster circuit which emulates a variable negative capacitor; andsensing the combined reactance of the tunable non-Foster circuit and the antenna; andtuning the tunable non-Foster circuit to minimize the combined reactance of the tunable non-Foster circuit and the antenna without making the combined reactance of the tunable non-Foster circuit and the antenna equal to zero so that an absolute value of the reactance of the tunable non-Foster circuit is maintained at a slightly smaller value than an absolute value of the reactance of the antenna to improve stability of the tunable non-Foster circuit. 26. The method of matching the antenna to the variable frequency oscillator of claim 25 wherein the tunable non-Foster circuit comprises an otherwise non-tunable non-Foster circuit with a variable capacitor added across a negative capacitance output of the otherwise non-tunable non-Foster circuit to thereby render the otherwise non-tunable non-Foster circuit tunable. 27. The method of matching the antenna to the variable frequency oscillator of claim 26 wherein the variable capacitance is supplied by reverse biased varactor diodes coupled in series with the negative capacitance output of the otherwise non-tunable non-Foster circuit, a junction point between the series coupled varactor diodes providing a control input to the tunable non-Foster circuit. 28. The method of matching the antenna to the variable frequency oscillator of claim 27 wherein an input impedance is associated with the antenna, wherein the step of sensing the combined reactance of the tunable non-Foster circuit and the antenna includes applying a RF signal generated by said variable frequency oscillator to the antenna via the tunable non-Foster circuit and wherein the step of tuning the tunable non-Foster circuit includes adjusting a negative capacitance of the tunable non-Foster circuit to minimize the the combined reactance of the tunable non-Foster circuit and the antenna while said RF signal is being applied to the antenna via the tunable non-Foster circuit. 29. The method of matching the antenna to the variable frequency oscillator of claim 25 wherein an input impedance is associated with the antenna, wherein the step of sensing the combined reactance of the tunable non-Foster circuit and the antenna includes applying a RF signal generated by said variable frequency oscillator to the antenna via the tunable non-Foster circuit and wherein the step of tuning the tunable non-Foster circuit includes adjusting a negative capacitance of the tunable non-Foster circuit to minimize the the combined reactance of the tunable non-Foster circuit and the antenna while said RF signal is being applied to the antenna via the tunable non-Foster circuit. 30. The method of matching the antenna to the variable frequency oscillator of claim 24 wherein the tunable non-Foster circuit emulates a variable negative capacitor and wherein the antenna is a dipole or a monopole. 31. The method of matching the antenna to the variable frequency oscillator of claim 25 wherein the tuning the tunable non-Foster circuit to minimize the combined reactance of the tunable non-Foster circuit and the antenna as sensed by the sensing circuit occurs automatically. 32. A method of automatically matching an antenna to a radio receiver, the method comprising: coupling a tunable non-Foster circuit between the receiver and the antenna;sensing the combined reactance of the tunable non-Foster circuit and the antenna;tuning the tunable non-Foster circuit to reduce the combined reactance of the tunable non-Foster circuit as sensed during said sensing step without attaining a zero value thereof;repeating said sensing and tuning steps until said combined reactance of the tunable non-Foster circuit and the antenna attain a small, non-zero, value thereof. 33. The method of automatically matching the antenna to the radio receiver of claim 32 wherein the tunable non-Foster circuit comprises an otherwise non-tunable non-Foster circuit with a variable capacitor added across a negative capacitance output of the otherwise non-tunable non-Foster circuit to thereby render the otherwise non-tunable non-Foster circuit tunable. 34. The method of automatically matching the antenna to the radio receiver of claim 33 wherein the variable capacitor is supplied by reverse biased varactor diodes coupled in series with the negative capacitance output of the otherwise non-tunable non-Foster circuit, a junction point between the series coupled varactor diodes providing a control input to the tunable non-Foster circuit. 35. The method of automatically matching the antenna to the radio receiver of claim 34 wherein an input impedance is associated with the antenna, wherein the step of sensing the combined reactance of the tunable non-Foster circuit and the antenna includes applying a RF signal generated by a variable frequency oscillator to the antenna via the tunable non-Foster circuit and wherein the step of tuning the tunable non-Foster circuit includes adjusting a negative capacitance of the tunable non-Foster circuit to minimize the the combined reactance of the tunable non-Foster circuit and the antenna while said RF signal is being applied to the antenna via the tunable non-Foster circuit. 36. The method of automatically matching the antenna to the radio receiver of claim 32 wherein an input impedance is associated with the antenna, wherein the step of sensing the combined reactance of the tunable non-Foster circuit and the antenna includes applying a RF signal generated by a variable frequency oscillator to the antenna via the tunable non-Foster circuit and wherein the step of tuning the tunable non-Foster circuit includes adjusting a negative capacitance of the tunable non-Foster circuit to minimize the the combined reactance of the tunable non-Foster circuit and the antenna while said RF signal is being applied to the antenna via the tunable non-Foster circuit. 37. The method of automatically matching the antenna to the radio receiver of claim 32 wherein the tunable non-Foster circuit emulates a variable negative capacitor and wherein the antenna is a dipole or a monopole. 38. An automatic tuning circuit for matching an electrically small antenna having a capacitive reactance to a radio receiver, the automatic tuning circuit comprising: a tunable non-Foster circuit coupling the receiver and the antenna, the tunable non-Foster circuit generating a negative capacitance; andsensing and feedback circuits sensing the combined capacitance of the tunable non-Foster circuit and the antenna and for tuning the tunable non-Foster circuit to automatically reduce the combined capacitance of the tunable non-Foster circuit and the antenna to a near zero value without making the combined capacitance equal to zero so that an absolute value of the capacitance of the antenna is slightly larger than an absolute value of the negative capacitance of the tunable non-Foster circuit. 39. The automatic tuning circuit of claim 38 wherein the tunable non-Foster circuit comprises an otherwise non-tunable non-Foster circuit with a variable capacitance added across a negative impedance output of the otherwise non-tunable non-Foster circuit to thereby render the otherwise non-tunable non-Foster circuit tunable. 40. The automatic tuning circuit of claim 39 wherein the variable capacitance is supplied by reverse biased varactor diodes coupled in parallel with the negative impedance output of the otherwise non-tunable non-Foster circuit, a junction point between the series coupled varactor diodes providing a control input to the tunable non-Foster circuit. 41. The automatic tuning circuit of claim 40 wherein the sensing and feedback circuits comprise: means for sensing an input capacitance associated with the antenna and the tunable non-Foster circuit when a RF signal is applied to the antenna and the tunable non-Foster circuit via the means for sensing; andan operational amplifier whose output is coupled to the control input of the tunable non-Foster circuit. 42. The automatic tuning circuit of claim 41 wherein the sensing and feedback circuits further comprise a sample and hold circuit coupled between said operational amplifier and said control input of the tunable non-Foster circuit. 43. The automatic tuning circuit of claim 38 wherein the sensing and feedback circuits comprise: means for sensing the capacitance of the antenna and the tunable non-Foster circuit when a RF signal is applied to the antenna and the tunable non-Foster circuit via the means for sensing; andan operational amplifier whose output is coupled to a control input of the tunable non-Foster circuit. 44. The automatic tuning circuit of claim 43 wherein the sensing and feedback circuits further comprise a sample and hold circuit coupled between said operational amplifier and said control input of the tunable non-Foster circuit. 45. The automatic tuning circuit of claim 38 wherein the antenna is a dipole or a monopole.