A method of adjusting an ablation field radiating into tissue includes the initial steps of providing an energy applicator and providing one or more microwave field-detecting needle assemblies. Each microwave field-detecting needle assembly includes one or more rectifier elements capable of detecting microwave field intensity via rectification. The method includes the steps of positioning the energy applicator and the one or more microwave field-detecting needle assemblies in tissue, transmitting energy from an energy source through the energy applicator to generate an ablation field radiating about at least a portion of the energy applicator into tissue, and adjusting the ablation field radiating about at least the portion of the energy applicator into tissue based on at least one electrical signal transmitted by the one or more microwave field-detecting needle assemblies.
