Microwave oscillator with reduced phase noise

• US 5,059,927 A
• Filed: 06/07/1990
• Issued: 10/22/1991
• Est. Priority Date: 08/28/1989
• Status: Expired due to Fees

• Current Assignee: AIL Systems, Inc. (L3Harris Technologies, Inc.)
• Original Assignee: AIL Systems, Inc. (L3Harris Technologies, Inc.)
• Inventors: Cohen, Leonard D.
• Primary Examiner(s): Grimm, Siegfried H.
• Application Number:
  US07/534,735
• Time in Patent Office: 502 Days
• Field of Search: 331/74, 331/76, 331/77, 331/96, 331/107 DP, 331/107 SL, 331/107 C, 331/107 G, 331/117 D, 331/177 V
• US Class Current: 331/77
• CPC Class Codes: H03B 2009/126 using impact ionization avalanche transit time [IMPATT] diodes
• CPC Class Codes: H03B 2201/0208 the means being an element with a variable capacitance, e.g. capacitance diode
• CPC Class Codes: H03B 9/141 and comprising a voltage sensitive element, e.g. varactor

Abstract

An oscillator operational in the millimeter wave and microwave range, including frequencies greater than 60 GHz, is provided with reduced phase noise by enhancing Q of the resonant circuitry by reactively terminating fundamental frequency oscillation and increasing stored fundamental frequency energy in the resonant circuitry. A two frequency system is provided with constructive reflection of energy at fundamental frequency back to the resonant circuitry, and with isolation of fundamental frequency energy from the output load. Energy to the output load is obtained from the in-situ generated second harmonic of the active element. Phase noise is reduced by enhancing Q by more than an order of magnitude.

Claims

1. A method for reducing phase noise in an oscillator operational in the millimeter wave and microwave range, comprising providing a lumped element active circuit including an active element with a negative resistance, providing a lumped element resonator circuit coupled to said active circuit and affording resonant circuitry in combination therewith, reducing phase noise by enhancing Q of said resonant circuitry by reactively terminating fundamental frequency oscillation and increasing stored fundamental frequency energy in said resonant circuitry.

2. The method according to claim 1 comprising reactively terminating fundamental frequency oscillation with sufficiently high reactance such that said resonant circuitry is the prime energy storing and frequency determining circuit.

3. The method according to claim 1 comprising providing means reactively terminating fundamental frequency oscillation with sufficiently high reactance such that said resonant circuitry is the prime energy storing and frequency determining circuit and such that said means reactively terminating fundamental frequency oscillation is not an oscillation frequency determining element nor a substantial energy storing element.

4. The method according to claim 2 comprising providing said resonator circuit with a tuning circuit, and comprising providing broadband reactive termination of fundamental frequency oscillation, and providing Q enhancement and phase noise reduction over the full tuning range of said oscillator.

5. The method according to claim 1 comprising reactively terminating fundamental frequency oscillation by high pass filtering to separate fundamental frequency from a higher order harmonic at least as high as the second order, and passing said higher order harmonic to provide an oscillator output.

6. A method for reducing phase noise in an oscillator operational in the millimeter wave and microwave range, comprising providing a lumped element active circuit including an active element with a negative resistance, providing a lumped element resonator circuit coupled to said active circuit and affording resonant circuitry in combination therewith, reducing phase noise by enhancing Q of said resonant circuitry by operating said oscillator in a two frequency mode by providing a high pass filter closely coupled to said active circuit and reactively terminating fundamental frequency oscillation and preventing propagation of fundamental frequency energy beyond said active circuit, and passing a higher order output harmonic at least as high as the second order to an output load and isolating fundamental frequency energy from said load.

7. The method according to claim 6 comprising generating said higher order harmonic in-situ in said active element, obtaining output power from said higher order harmonic generated in-situ in said active element, isolating fundamental frequency energy from said higher order harmonic output to said load by in-situ harmonic generation in said active element, providing said high pass filter with sufficiently large reactance to fundamental frequency such that the energy stored in said resonant circuitry is large compared to the energy delivered to said load at said higher order harmonic such that Q of said resonant circuitry at fundamental frequency is more than an order of magnitude larger than the Q of an oscillator loaded at fundamental frequency and delivering energy to a load at fundamental frequency.

8. The method according to claim 6 comprising providing said resonator circuit with a tuning circuit, and providing broadband reactive termination with said high pass filter and continuous phase noise reduction over the full tuning range of the oscillator without circuit adjustment.

9. A method for reducing phase noise in an oscillator operational in the millimeter wave and microwave range, comprising providing a lumped element active circuit including an active element with a negative resistance, providing a lumped element resonator circuit coupled to said active circuit and affording resonant circuitry in combination therewith, providing a high pass filter closely coupled to said active circuit to prevent propagation of fundamental frequency energy beyond said active circuit to an output load, and to provide an oscillator output passing a higher order output harmonic at least as high as the second order, using said closely coupled high pass filter to limit energy circulation at fundamental frequency to the region of said active circuit to circulate fundamental frequency energy back to said active element to generate more higher order harmonic energy, to provide a two frequency system, including a fundamental frequency, and a higher order harmonic at the oscillator output, using said high pass filter to perform dual functions of (a) providing a large reactive load to the fundamental oscillation and constructively reflecting energy at fundamental frequency to generate more higher order harmonic energy, increase Q of said resonant circuitry and reduce phase noise, and (b) isolating the energy generated at fundamental frequency from the output load.

10. The method according to claim 9 comprising providing said resonator circuit with a tuning circuit, and tuning said fundamental frequency.

11. A method for reducing phase noise in an oscillator operational in the millimeter wave and microwave range, comprising providing a lumped element active circuit including an active element with a negative resistance, providing a lumped element resonator circuit coupled to said active circuit and affording resonant circuitry in combination therewith, providing an output waveguide coupled to said resonant circuitry and cut-off at the fundamental frequency of oscillation and constructively reflecting energy back to said resonant circuitry to enhance Q and reduce phase noise and passing a higher order harmonic at least as high as the second order to provide a resistively loaded oscillator output at said higher order harmonic.

12. The method according to claim 11 comprising providing reactive termination of fundamental frequency energy, generating said higher order harmonic in-situ in said active element, isolating said fundamental frequency from said resistive loading of said output waveguide by harmonic generation in said active element, and increasing stored fundamental frequency energy in said resonant circuitry by said reactive termination of fundamental frequency energy and providing a two frequency system including said fundamental frequency and said higher order harmonic which is output through said waveguide.

13. The method according to claim 12 comprising providing said resonator circuit with a tuning circuit, and tuning said fundamental frequency.

14. An oscillator operational in the millimeter wave and microwave range, comprising a lumped element active circuit including an active element with a negative resistance, a lumped element resonator circuit coupled to said active circuit and providing resonant circuitry in combination therewith, means for reducing phase noise by enhancing Q of said resonant circuitry comprising means reactively terminating fundamental frequency oscillation and increasing stored fundamental frequency energy in said resonant circuitry.

15. The oscillator according to claim 14 wherein said means reactively terminating fundamental frequency has sufficiently high reactance such that said resonant circuitry is the prime energy storing and frequency determining circuit and such that said means reactively terminating fundamental frequency oscillation is not an oscillation frequency determining element nor a substantial energy storing element.

16. The oscillator according to claim 14 wherein said resonator circuit comprises a tuning circuit, and wherein reactive termination of fundamental frequency oscillation is broadband, and Q enhancement and phase noise reduction is over the full tuning range of said oscillator.

17. The oscillator according to claim 14 wherein said means reactively terminating fundamental frequency oscillation comprises a high pass filter separating fundamental frequency from a higher order harmonic at least as high as the second order, and passing said higher order harmonic to provide an oscillator output.

18. An oscillator operational in the millimeter wave and microwave range, comprising a lumped element active circuit including an active element with a negative resistance, a lumped element resonator circuit coupled to said active circuit and providing resonant circuitry in combination therewith, means for reducing phase noise by enhancing Q of said resonant circuitry comprising means operating said oscillator in a two frequency mode comprising a high pass filter closely coupled to said active circuit and reactively terminating fundamental frequency oscillation and preventing propagation of fundamental frequency energy beyond said active circuit, and passing a higher order output harmonic at least as high as the second order to an output load and isolating fundamental frequency energy from said load.

19. The oscillator according to claim 18 wherein:

said higher order harmonic is generated in-situ in said active element;

output power is obtained from said higher order harmonic generated in-situ in said active element;

said fundamental frequency is isolated from said higher order harmonic output to said load by said in-situ harmonic generation in said active element;

the reactance of said high pass filter to said

y is sufficiently large such that the fundamental frequency energy stored in said resonant circuitry is large compared to the energy delivered to said load at said higher order harmonic such that Q of said resonant circuitry at fundamental frequency is more than an order of magnitude larger than the Q of an oscillator loaded at fundamental frequency and delivering energy to a load at fundamental frequency.

20. The oscillator according to claim 18 wherein said resonator circuit comprises a tuning circuit, and said high pass filter providing reactive termination is broadband and provides continuous phase noise reduction over the full tuning range of the oscillator without circuit adjustment.

21. An oscillator operational in the millimeter wave and microwave range, comprising a lumped element active circuit including an active element with a negative resistance, a lumped element resonator circuit coupled to said active circuit and providing resonant circuitry in combination therewith, a high pass filter closely coupled to said active circuit to prevent propagation of fundamental frequency energy beyond said active circuit to an output load, and to provide an oscillator output passing a higher order output harmonic at least as high as the second order, said closely coupled high pass filter limiting energy circulation at fundamental frequency to the region of said active circuit to circulate fundamental frequency energy back to said active element to generate more higher order harmonic energy, said high pass filter providing a two frequency system, including a fundamental frequency, and a higher order harmonic at the oscillator output, said high pass filter performing the dual functions of (a) providing a large reactive load to the fundamental oscillation and constructively reflecting energy at fundamental frequency to generate more higher order harmonic energy, increase Q of said resonant circuitry and reduce phase noise, and (b) isolating the energy generated at fundamental frequency from the output load.

22. The oscillator according to claim 21 wherein said resonator circuit comprises a tuning circuit, and wherein said fundamental frequency is tuned.

23. An oscillator operational in the millimeter wave and microwave range, comprising an active circuit including an active element with a negative resistance, a resonator circuit coupled to said active circuit and providing resonant circuitry in combination therewith, an output waveguide coupled to said resonant circuitry and cut-off at the fundamental frequency of oscillation to constructively reflect energy back to said resonant circuitry to enhance Q and reduce phase noise, said waveguide passing a higher order harmonic at least as high as the second order to provide a resistively loaded oscillator output at said higher order harmonic.

24. The oscillator according to claim 23 wherein said higher order harmonic is generated in-situ in said active element, said fundamental frequency is isolated from said resistive loading of said output waveguide by harmonic generation in said active element, and said reactive termination of fundamental frequency energy increases stored fundamental frequency energy in said resonant circuitry and provides a two frequency system including said fundamental frequency and said higher order harmonic which is output through said waveguide.

25. The oscillator according to claim 24 wherein said resonator circuit comprises a tuning circuit, and said fundamental frequency is tuned.

26. A varactor tuned oscillator, VCO, operational in the millimeter wave and microwave range, comprising:

a lumped element active circuit including an active element with a negative resistance;

a lumped element tuning circuit coupled to said active circuit and providing resonant circuitry in combination therewith;

means for reducing phase noise by enhancing Q of said resonant circuitry comprising a high pass filter closely coupled to said active circuit to prevent propagation of fundamental frequency energy beyond said active circuit and to provide a VCO output reactively terminated at the fundamental frequency of oscillation and resistively loaded at a higher order harmonic at least as high as the second order, said high pass filter constructively reflecting fundamental frequency energy back to said resonant circuitry and increasing stored fundamental frequency energy in said resonant circuitry to generate more higher order harmonic energy, and also isolating fundamental frequency energy from the VCO output;

a first bias port for varactor tuning;

a second bias port for biasing said active element;

a first quarter wave choke at ≦

said higher order harmonic having first and second terminals, said first terminal of said choke being coupled to said first bias port;

a second quarter wave choke at ≦

said higher order harmonic having first and second terminals, said first terminal of said second choke being coupled to said second bias port;

said tuning circuit having first and second terminals, said first terminal of said tuning circuit being coupled to said second terminal of said first choke;

said active circuit having first and second terminals, said first terminal of said active circuit being coupled to said second terminal of said second choke and to said first terminal of said tuning circuit and to said VCO output, said second terminal of said active circuit being coupled to said second terminal of said tuning circuit;

said high pass filter providing a load circuit coupled to said VCO output at said first terminal of said active circuit, said load circuit reactively terminating said VCO output at said fundamental frequency and resistively loading said VCO output at said higher order harmonic and passing said higher order harmonic;

a first capacitor having first and second terminals, said first terminal of said first capacitor being connected to a node between said first bias port and said first terminal of said first choke, said second terminal of said first capacitor being connected to said second terminal of said tuning circuit;

a second capacitor having first and second terminals, said first terminal of said second capacitor being connected to a node between said second terminal of said first choke and said first terminal of said tuning circuit, said second terminal of said second capacitor being connected to a node between said second terminal of said second choke and said first terminal of said active circuit;

a third capacitor having first and second terminals, said first terminal of said third capacitor being connected to a node between said second terminal of said second choke and said first terminal of said active circuit, said second terminal of said third capacitor being coupled to said load circuit;

a fourth capacitor having first and second terminals, said first terminal of said fourth capacitor being connected to a node between said second bias port and said first terminal of said second choke, said second terminal of said fourth capacitor being connected to said second terminal of said active circuit.