Feed system for microwave oven

A microwave oven having, in combination, a source of linearly polarized electromagnetic waves, an oven cavity, and a feed system for radiating microwave energy into said oven cavity comprising:

• a rectangular waveguide coupled at one end to said source;
• a variable phase shifter and a short circuit at the other end of said waveguide;
• and
• a circular polarizer comprised of an aperture in the broad wall of said rectangular waveguide that radiates right-hand and left-hand circularly polarized waves into said oven cavity, one polarization for waves incident from the direction of said source and the opposite polarization for waves incident from the direction of said phase shifter;
• said phase shifter changing the phase of waves propagating toward the other end of said waveguide so that both polarizations of radiated energy interfere in said oven cavity and produce rotating elliptically polarized waves and therefore improved heating uniformity.

A microwave oven having, in combination, a source of linearly polarized electromagnetic waves, an oven cavity, and a feed system for radiating microwave energy into said oven cavity comprising:

• a rectangular waveguide 3-dB hybrid coupler having four arms, said source being coupled to a first arm;
• a pair of inclined radiating slots in the bottom walls of adjacent second and third arms which radiate right-hand and left-hand circularly polarized waves into said oven cavity;
• and
• a variable phase shifter in a fourth arm of said hybrid coupler for changing the phase of reflected energy that passes back through said inclined slots and is again reflected and reradiated;
• said opposite sense circularly polarized waves with varying phase relations interfering in said oven cavity to produce rotating elliptically polarized waves and therefore improved heating uniformity.

A microwave oven having, in combination, a source of linearly polarized electromagnetic waves, an oven cavity, and a feed system for radiating microwave energy into said oven cavity comprising:

• p1 a rectangular waveguide turnstile junction having four arms and a central aperture surrounded by a circular waveguide, said source being coupled to a first arm;
• short circuits at the ends of opposing second and third arms and at the end of a fourth arm which is opposite said first arm;
• and
• a variable phase shifter in said fourth arm for changing the phase of reflected energy which passes back through said circular waveguide;
• said circular waveguide radiating right-hand and left-hand circularly polarized waves with varying phase relations into said oven cavity which interfere to produce rotating elliptically polarized waves and therefore improved heating uniformity.