Amana Refrigeration, Inc.

Raytheon Company

James E Simpson

Arnold M Bucksbaum

Buddy J Austin

A circularly polarized microwave oven. Microwave energy is coupled from a waveguide above the ceiling to the cavity by a rotatable vertical probe extending through a circular aperture in the cavity. A strip conductor closely spaced to the ceiling to limit radiation therefrom conducts the microwave current to an air dielectric patch antenna radially offset from the axis of the probe. A vertical section of the strip conductor spaces the patch antenna more than one-eighth wavelength from the ceiling which functions as a ground plane. The patch antenna is rectangular and the dimensions of its sides are selected to be respectively resonant above and below the operating frequency of the oven. More specifically, the dimensions are selected so that the orthogonal currents parallel to the rectangle sides produce orthogonal radiated components that are equal in magnitude and separated by 90.degree. in phase. Accordingly, the resonant patch or flag antenna radiates substantially circular polarization. The probe is supported on a vertical post of a support cradle suspended from the ceiling and the patch antenna is rotated about the axis of the probe.

Microwave oven having resonant antenna

A circularly polarized microwave oven. Microwave energy is coupled from a waveguide above the ceiling to the cavity by a rotatable vertical probe. A strip transmission line closely spaced to the ceiling to limit radiation therefrom conducts the microwave current from the probe to a helical strip antenna radially offset from the axis of the probe. The helical strip antenna has a cylindrical segment which has a downward slope from its feed end to gradually increase the spacing between the cylindrical segment and the ceiling which functions as a ground plane. The increase in radiative efficiency around the cylindrical segment caused by increasing the spacing to the ceiling offsets the magnitude of the current traveling wave diminishing as a result of radiation losses. Accordingly, the magnitude of the X and Y electric vectors are substantially equal over a relatively wide angle thus defining circular polarization. Connected to the opposite end of the cylindrical segment is a flat or horizontal segment of the helical antenna. Rotation of the probe about its axis moves the helical antenna in a horizontal circular path thus further enhancing the heating uniformity.

Microwave oven with circular polarization

A metal rod rack shelf for a microwave oven wherein extension support rods are substantially prevented from being excited with high electric currents. The rack is embodied with quarter wavelength choking structures in the regions where the extension support rods connect to the rack mainframe. Accordingly, the effective short circuits in those regions are transformed to open circuits at a distance of one-quarter wavelength along the support rods. As a result, the support rods do not rise to high temperatures or radiate intense microwave fields that could cause melting of or arcing to microwave transparent brackets which mount to walls of the oven cavity and engage the rods.

Microwave oven shelf

A microwave oven having a directional rotating antenna axially supported on an axis of one wall of a microwave oven cavity of the microwave oven which provides circularly symmetric uniform energy distribution of microwave energy within the microwave oven cavity and consistent heating of a product in the microwave oven cavity. The directional rotating antenna includes a two-by-two array of antenna elements where each element is an end driven half-wavelength resonating antenna element supported by a length of conductor perpendicular to the wall of the microwave oven cavity. A parallel plate transmission line connects to each of the supports, four of which join at a junction which connects to a cylindrical probe antenna. The probe antenna is excited by microwave frequency currents of a waveguide adjacent to the wall of the microwave oven cavity. The directional antenna is rotated by a moving stream of air circulated through the microwave oven cavity. A dome having a flattened conical shape extending outwardly in the wall of the microwave oven cavity provides a nearly circular recess partially surrounding the directional rotating antenna and provides uniform energy distribution in the product being heated. The dome returns microwave energy reflected from the product towards a circular area in the middle area of the microwave oven cavity. A transition section extends between the top of the dome and the one wall of the microwave oven cavity. The waveguide including three sides affixes to the outside wall of the dome, the transition section, and an extension of the wall extending beyond the microwave oven cavity which supports the microwave power source, all of which comprise the fourth wall of the waveguide. The microwave oven provides a consistent cooking pattern, especially for sensitive foods by utilizing high power of the microwave power source.

Microwave oven with improved feed structure

A microwave oven having a directional rotating antenna axially supported on an axis of one wall of a microwave oven cavity of the microwave oven which provides circularly symmetric uniform energy distribution of microwave energy within the microwave oven cavity and consistent heating of a product in the microwave oven cavity. The directional rotating antenna includes a two-by-two array of antenna elements where each element is an end driven half-wavelength resonating antenna element supported by a length of conductor perpendicular to the wall of the microwave oven cavity. A parallel plate transmission line connects to each of the supports, four of which join at a junction which connects to a cylindrical probe antenna. The probe antenna is excited by microwave frequency currents of a waveguide adjacent to the wall of the microwave oven cavity. The directional antenna is rotated by a moving stream of air circulated through the microwave oven cavity. A dome having a flattened conical shape extending outwardly in the wall of the microwave oven cavity provides a nearly circular recess partially surrounding the directional rotating antenna and provides uniform energy distribution in the product being heated. The dome returns microwave energy reflected from the product towards a circular area in the middle area of the microwave oven cavity. A transition section extends between the top of the dome and the one wall of the microwave oven cavity. The waveguide including three sides affixed to the outside wall of the dome, the transition section, and an extension of the wall extending beyond the microwave oven cavity which supports the microwave power source, all of which comprise the fourth wall of the waveguide. The microwave oven provides a consistent cooking pattern, especially for sensitive foods by utilizing high power of the microwave power source.

Microwave oven feed apparatus

Microwave ovens typically have an oven cavity and a feed system for supplying microwaves through a feed opening into the cavity. Such ovens are inproved by providing a field stirrer rotatably mounted over and covering the feed opening. The field stirrer is a single conductive plate having a single radiating slot in the plate exposing only a portion of the feed opening to the cavity through the slot at any position of the plate during its rotation. The slot is in the shape of an arc or other shape which is tangentially longer than it is radially wide. The plate also has a plurality of wings, fins, or vanes outside the feed opening. The vanes and slot are arranged so that electrically identical positions of the plate occur only every full circle of rotation by virtue of bilateral symmetry at most. The plate is spaced from the feed opening and into the cavity by a sufficient distance to permit flow of microwave energy beneath the plate for distribution around the periphery of the plate and by the vanes. The geometry and dimensions of the slot, plate periphery, and vanes can readily be adjusted for best cooking in actual practice. In an additional embodiment the plate periphery cooperates with the feed opening in the manner of a slot without need of slotting the plate itself.

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Coralville, IA, United States of America

James E Simpson