Microwave oscillator

A box-shaped metal microwave oscillator is provided having two pairs of substantially parallel, confronting inner surfaces, the second pair perpendicular to the first pair to define an oscillator cavity. The forward end of the cavity is walled off with a slotted wall to permit only a portion of the oscillator energy to be emitted. The spacing of certain of the walls and the location of the oscillator components to the wall is described.

This invention relates to microwave oscillators, and more particularly to microwaveoscillators for use in police radar warning receivers.

A police radar warning receiver is an electronic assembly mountable in a vehicle, such as a passenger car or truck, motorcycle, boat or the like, which travels on land or water in areas subject to speed-monitoring radar surveillance by police,and functions to detect the presence of the police radar and provide the driver or user with an audible and/or visual indication that his speed is being checked by radar.

Typically, a police radar warning receiver includes an antenna, a printed circuit board, the circuitry needed to determine whether the received signal is a police radar signal and to provide appropriate indications and alarms, and a powerregulator device which regulates the energy received from a vehicle battery to power the circuitry. These components are located within a box-like housing having four side walls and front and rear end panels. The front panel which, when the receiver ismounted in the vehicle, faces the user, has indicators and control knobs. The rear wall has extending from it a power cord terminating in an appropriately configured plug to be received into the vehicle cigarette lighter.

Police radar units operate in either the X-band or the K-band of the frequency spectrum, as discussed in U.S. Pat. No. 4,313,216. Typical radar warning receivers are adapted to detect police radar signals in either band. Accordingly, policeradar warning receivers are sometimes referred to as dual frequency radar warning receivers.

One illustrative form of prior art receiver is the ESCORT radar warning receiver currently marketed by the assignee herein, Cincinnati Microwave Inc. of Cincinnati, Ohio. The ESCORT radar warning receiver contains circuitry permitting it todetect and indicate the presence of both X-band and K-band police radar signals. That circuitry is disclosed in aforesaid U.S. Pat. No. 4,313,216. Briefly, the oscillator generates dual frequency signals which are quasi-harmonically related. Thesesignals mix with the incoming signal and provide an output or mixed signal (the IF). The IF signal is evaluated to determine whether a police radar signal is present in which case an alarm is activated. This process is referred to as heterodyning, orsuper-heterodyning where the IF is mixed again with another local oscillator signal before evaluation.

Improved versions of the circuitry disclosed in U.S. Pat. No. 4,313,216 are described in U.S. patent application Ser. No. 575,422, filed Jan. 31, 1984, and U.S. patent application Ser. No. 656,026 entitled "Police Radar Warning ReceiverWith Mute Function," invented by Richard L. Grimsley, and filed concurrently herewith. Both of the aforesaid patent applications are also assigned to Cincinnati Microwave, Inc.

Police radar warning receivers of the heterodyne or super-heterodyne type utilize a microwave oscillator. Accordingly, an object of the present invention has been to provide an improved microwave oscillator for use in a police radar warningreceiver.

That objective has been achieved by providing a box-shaped oscillator section having a first pair of substantially parallel, confronting inner surfaces and a second pair of substantially parallel, confronting inner surfaces, the latter beingperpendicular to the former to define an oscillator cavity. The oscillator also has a slotted wall perpendicular to the four inner surfaces and positioned at one end of the oscillator section to preferentially permit only a portion of the oscillatorgenerated microwave signals to pass out of the oscillator cavity, whereby oscillation can be maintained in the oscillator cavity.

The oscillator further includes a Gunn diode having a central axis and being mounted within the oscillator cavity. The Gunn diode central axis is equidistant from both the second pair of inner surfaces and is spaced rearwardly of the slottedwall a predetermined distance L. The second pair of inner surfaces are spaced apart a predetermined distance W as determined by the formula: ##EQU1## wherein C=velocity of light;

L>W; and

12.0 Ghz

Other References

• Reference Data for Radio Engineers--p. 23-19
• Foundations for Microwave Engineering, pp. 322-323
• "Proven Procedures Guide Cavity VCO Design" Microwave (May, 1981)
• Microwave Engineer's Handbook, p. 26
• Foundations for Microwave Engineering, p. 96