Microwave heating apparatus with tuning means

Claim 1

In a microwave heating apparatus, comprising a microwave energy source, and a microwave heating means conected thereto for heating a material by exposure to microwave energy from the microwave energy source, a microwave tuning means forming the connection between the microwave energy source to the microwave heating means, the tuning means comprising a main waveguide section connecting the output of the microwave energy source to the input of the microwave heating means, first, second and third branch waveguides connected to the main waveguide section at spaced positions therealong from the microwave energy source, first, second and third adjustable tuning stubs attached to the first, second and third branch waveguides respectively, four signal sensing probes attached to the main waveguide section at spaced positions therealong between the microwave energy source and the first branch waveguide two further sensing probes attached to the main waveguide section as spaced positions therealong between the second and third branch waveguides, four microwave detectors each connected to one of said four sensing probes, two microwave detectors each connected to one of said two further sensing probes, a control circuit connected to said four micowe detectors and to said first and second adjustable tuning stubs to adjust, in response to said four microwave detector outputs, the effective electrical lengths of said first and second adjustable tuning stubs, and a control circuit connected to said two microwave detectors and to said third tuning stub to adjust, in response to the outputs of said two microwave detectors, the effective electrical length of the third tuning stub, whereby the microwave tuning means, in combination with the microwave heating means presents a substantially non-reflecting microwave load to the microwave energy source.