MULTI-AXIS CAVITIES FOR MICROWAVE SEMICONDUCTORS

• US 3,831,110 A
• Filed: 05/01/1972
• Issued: 08/20/1974
• Est. Priority Date: 05/01/1972
• Status: Expired due to Term

• Current Assignee: Lester F. Eastman
• Original Assignee: Lester F. Eastman
• Inventors: Eastman, Lester F.
• Primary Examiner(s): Kominski, John
• Application Number:
  US05/249,274
• Time in Patent Office: 841 Days
• Field of Search: 331/17R,17G,96
• US Class Current: 331/107.00G
• CPC Class Codes: H03B 9/141 and comprising a voltage sensitive element, e.g. varactor
• CPC Class Codes: H03B 9/145 the frequency being determined by a cavity resonator, e.g. a hollow waveguide cavity or a coaxial cavity H03B9/141 - H03B9/143, H03B9/147, H03B9/148 take precedence

Abstract

Multi-axis resonant cavities are provided in which a microwave semiconductor oscillator, e.g., an L.S.A. diode, operates in a below cut off mode with respect to the propagation characteristics of the cavity. An output coaxial transmission line extending into the cavity is radially spaced from the semiconductor and couples energy to a load by means of mutual inductance. In one arrangement, a flat circular cavity is formed in a block of electrically conductive material with a microwave semiconductor coaxially mounted at the center of the cavity having one face in electrical contact with a wave trap through which DC bias voltage is applied. The transmission line is offcenter, adjacent to the semiconductor. In a modification of this arrangement, the floor of the circular cavity forms a truncated cone and the side wall comprises a spherical section. The angle of the conical floor is used to determine the cavity inductance. A flat elliptical cavity is described in one arrangement wherein the semiconductor and the transmission line are located respectively at the two foci of the ellipse. The elliptical cavity forms a resonator as well as a means of coupling out energy. Other arrangements of the circular cavity are described in which a plurality of semiconductors are located symmetrically in the cavity. In another system a semiconductor is located at the center of a partial circular cavity connected to a ridge wave guide having a coaxial transmission line displaced from the semiconductor extending through the ridge. A special low impedence slug in the output line of a multi-axis cavity is designed to load the fundamental frequency of oscillation of the diode and reduce the loading at the second harmonic, thereby producing more power at the fundamental frequency. Varactor-tuned Gunn oscillator and Gunn effect amplifier embodiments are also presented.

Claims

1. A microwave oscillator circuit, comprising electrically conductive means for defining a microwave resonator cavity with a reflecting sidewall forming an approximately symmetrical radial transmission line, a microwave semiconductor device having a characteristic operating frequency operatively mounted in said cavity at a predetermined position such that the distance from said device to the sidewall is less than one-quarter wave length at said characteristic frequency and a localized resonance condition is established, means for applying DC bias voltage to said device, and means for coupling microwave energy out of said cavity.

2. A microwave oscillator circuit, comprising electrically conductive means for defining a microwave resonator cavity with a sidewall formed to reflect microwave energy and providing an approximately symmetrical radial transmission line, a microwave semi-conductor device having a characteristic operating frequency operatively mounted in said cavity at a predetermined spacing from said sidewall such that wave propagation from said device through said cavity is below cutoff, means for applying DC bias voltage to said device, and coaxial transmission line means operatively arranged in said cavity parallel to the axis of said device for coupling RF energy out of said cavity to a load by means of mutual inductance with said device.

3. A microwave oscillator circuit, comprising a body of electrically conductive material having a cavity formed therein bounded by a pair of opposing surfaces joined at their peripheries by a sidewall formed to reflect radiating microwave energy, a microwave semiconductor device having a characteristic operating frequency operatively mounted in said cavity at a predetermined spacing from said sidewall such that propagation of mirowave energy originating from said device through said cavity is below cutoff, means for applying DC bias voltage to said device to induce microwave oscillation therein, and output transmission line means extending from one of said opposing surfaces through the other surface and out of said cavity at a predetermined distance from said device for coupling oscillatory energy out of said cavity to a load by means of mutual inductance with said device.

4. The microwave oscillator of claim 3, wherein the distance between said device and the sidewall of said cavity is less than one-quarter wave length at said characteristic frequency.

5. The microwave oscillator of claim 3, wherein said upper and lower surfaces of said cavity are planar elliptical surfaces and are aligned in parallel, said sidewall being in the shape of an elliptical ring, said device being located coaxially with one of the focus lines associated with said sidewall and said transmission line means being located coaxially at the other such focus line.

6. The microwave cavity of claim 5, wherein the lesser distance along the major elliptical axis connecting the foci between said device and said sidewall of said cavity is less than one quarter wave length at said characteristic frequency.

7. The oscillator circuit of claim 4, wherein said cavity is approximately in the shape of a flat circular disc, said opposed surfaces being planar circular surfaces and said sidewall being in the shape of a circular ring.

8. The circuit of claim 7, wherein said device and said transmission line means are positioned in said cavity symmetrically about the geometric center thereof.

9. The circuit of claim 7, wherein said device and said transmission line means are located close to each other approximately at the center of said cavity to enhance mutual inductance output coupling.

10. The circuit of claim 7, wherein said device is located at the Center of said cavity.

11. The circuit of claim 10, wherein said transmission line means is located immediately adjacent to said device in said cavity.

12. The oscillator circuit of claim 7, wherein said transmission line means is located at the center of said cavity.

13. The circuit of claim 7, wherein at least one additional microwave semiconductor device is mounted in said cavity, and a separate means for applying bias voltage is present for each respective device.

14. The circuit of claim 13, wherein said transmission line means is located at the center of said cavity and said devices are symmetrically positioned about said center.

15. The circuit of claim 3, wherein said device is a Gunn diode and said transmission line means includes a variable capacitance means for tuning said Gunn diode.

16. The circuit of claim 15, wherein said capacitance means includes varactor means in said cavity and connector means external to said cavity for applying bias voltage to said varactor means and for simultaneously extracting microwave energy from said cavity.

17. The circuit of claim 16, wherein said connector means is in the form of a bias tee.

18. The circuit of claim 7, wherein said device is a Gunn diode and said output transmission line means includes varactor means for tuning the operating frequency of said Gunn diode.

19. The circuit of claim 5, wherein said device is a Gunn diode and said transmission line means includes varactor means for tuning the operating frequency of said Gunn diode.

20. A microwave oscillator circuit, comprising electrically conductive means for defining a cavity bounded by a planar circular surface, a conical surface having an axis perpendicular to said planar surface and having a geometrical vertex lying at the center of said planar surface, said conical surface being truncated in a plane parallel to said planar surface, and a circular ring-shaped sidewall joining the peripheries of said planar and conical surfaces for reflecting a microwave energy radiating from the center of said cavity, a microwave semiconductor device having a characteristic operating frequency operatively mounted coaxially in said cavity on the truncated portion of said conical surface, means for applying DC bias voltage to said semiconductor device for inducing microwave oscillations therein, and coaxial transmission line means radially adjacent to said device and parallel to the axis of said cavity extending through said cavity for coupling RF energy to an external load.

21. The circuit of claim 20, wherein said circular sidewall is a spherical section concentric with said planar surface.

22. The circuit of claim 20, wherein the radius of said cavity is less than a quarter wave length at said characteristic frequency such that propagation of waves radiating from said device through said cavity is below cutoff and output coupling is by virtue of effective mutual inductance between said device and said transmission line means.

23. The circuit of claim 20, wherein said device is in the form of a limited space-charge accumulation diode.

24. A microwave oscillator circuit, comprising electrically conductive means for defining a circular cavity having a radius of less than one quarter wave length at a characteristic frequency and of linearly increasing height in the radial direction from the center of the cavity, a microwave semiconductor device having said characteristic frequency operatively mounted at the center of said cavity, means for applying DC bias voltage to said device for inducing microwave oscillation therein, and output transmission line means radially adjacent to said device extending through said cavity parallel to the axis thereof for coupling RF energy to an external load.

25. The circuit of claim 24, wherein said device is a limited space-charge accumulation diode.

26. A varactor-tuned Gunn oscillator circuit, comprising electrically conductive means defining an elliptical cavity bounded by parallel planar elliptical surfaces joined at their peripheries by an elliptical ring-shaped surface, a Gunn diode mounted coaxially with one of the focus lines associated with said ring-shaped surface, means for applying DC bias voltage to said diode to induce oscillation, a coaxial transmission line extending into said cavity located coaxially with the other focus line associated with said cavity, varactor diode means positioned in said cavity along said coaxial transmission line, and connector means external to said cavity for applying DC voltage via said coaxial transmission line to said varactor diode means and for extracting microwave energy from said cavity via said transmission line.

27. A microwave oscillator circuit, comprising electrically conductive means for defining a disc-shaped radial microwave cavity, a microwave semiconductor device having a characteristic operating frequency mounted in said cavity for producing radial microwave oscillations and spaced from the nearest point along the sidewall of said cavity by less than one quarter wavelength at the characteristic operating frequency of said device such that the characteristic operating frequency is below the wave propagation cutoff of said cavity, means for applying DC bias voltage to said device for inducing microwave oscillations therein, ridge wave guide means operatively connected to said cavity, and coaxial transmission line means extending through said wave guide parallel to the axis of said cavity and spaced a predetermined distance from said device, said ridge wave guide forming a transmission line from said device to said coaxial transmission line means.

28. The oscillator circuit of claim 27, wherein said ridge wave guide has a ridge which terminates approximately just beyond the location of said coaxial transmission line means away from said device.

29. The oscillator circuit of claim 27, wherein an additional disc-shaped radial microwave cavity is located at the opposite end of said ridge wave guide from the first said radial cavity, an additional microwave semiconductor device having the same said characteristic operating frequency similarly positioned in said additional cavity, said coaxial transmission line means being located approximately midway between said devices.

30. The oscillator circuit of claim 29, wherein the length of said ridge wave guide between said two devices is approximately one half wave length at the characteristic operating frequency of said devices.

31. A microwave oscillator circuit, comprising an elongated ridge wave guide having an internal ridge, a microwave semiconductor device operatively mounted on said ridge at a predetermined distance from one end of said wave guide, means for applying DC bias voltage to said device, and an output coaxial transmission line operatively positioned within said wave guide spaced along said ridge away from said one end and said device for coupling microwave energy out of said wave guide to an external load.

32. A microwave oscillator circuit, comprising electrically conductive means for defining a microwave cavity bounded by a pair of opposed surfaces joined at their peripheries by a sidewall formed to reflect microwave energy, a microwave semiconductor device having a characteristic fundamental operating frequency operatively positioned in said cavity such that the characteristic frequency of said device is below the cutoff of said cavity for wave propagation, means for applying DC bias voltage to said device for inducing microwave oscillations, a coaxial transmission line extending into said cavity parallel to the axis of said device for coupling out microwave energy, and means in said transmission line for loading the fundamental frequency output of said device and for separately unloading the second harmonic frequency produced by said device, whereby the proportionate power in the output at the fundamental frequency is increased.

33. The oscillator circuit of claim 32, wherein said loading mEans includes a low impedance section of said coaxial transmission line one-eighth wave length in length at the fundamental frequency and having low characteristic impedance at the fundamental frequency and second harmonic thereof, said low impedance section being located adjacent to said cavity.

34. The oscillator circuit of claim 32, wherein said low impedance section is one-eighth wave length in length at the fundamental frequency of said device and has low characteristic impedance at the fundamental frequency and second harmonic thereof, the end of said section nearer to said cavity being positioned in said coaxial transmission line at a distance from said cavity equal to an integral multiple of a half wave length at said fundamental frequency.

35. A microwave oscillator circuit, comprising electrically conductive means defining a disc-shaped radial cavity, a microwave semiconductor device positioned in said cavity such that the characteristic fundamental frequency of said device is below the cutoff for wave propagation in said cavity, means for applying DC bias voltage to said device, a ridge wave guide operatively connected to said cavity, a coaxial transmission line extending into said wave guide parallel to the axis of said cavity at a predetermined distance from said device along said wave guide for coupling out microwave energy from said cavity via said ridge wave guide, and means in said ridge wave guide for loading the fundamental frequency of said device and for separately unloading the second harmonic thereof such that the proportionate power at the fundamental frequency is increased.

36. The oscillator circuit of claim 35, wherein said loading means includes a low impedance section of said ridge wave guide one-eighth wavelength in length at the fundamental frequency of said device and having low characteristic impedance at the fundamental frequency and the second harmonic thereof, said section being positioned along said wave guide adjacent to said cavity.

37. The oscillator circuit of claim 35, wherein said loading means includes a low impedance section one-eighth wavelength in length at the fundamental frequency of said device and having low characteristic impedance at the fundamental frequency and second harmonic thereof, the end of said section nearer to said cavity being displaced from said cavity by an integral multiple of one-half wavelength at the fundamental frequency of said device.

38. The oscillator circuit of claim 4, wherein said cavity is formed to provide a radial transmission line approximately symmetrical about a midpoint.

39. The circuit of claim 38, wherein said output transmission line means is parallel to the axis of said device.

40. The circuit of claim 39, wherein said device and said output transmission line means are juxtaposed approximately at the midpoint of symmetry.

41. The circuit of claim 40, wherein the distance between said opposing surfaces is approximately the same as the axial height of said device.