The present invention related to devices and methods that use returned power (RP) measurements during microwave energy delivery to perform one or more functions. For example, microwave devices and systems with one or more features to measure the returned microwave power. One or more measurements of the returned microwave power may be used to obtain information about one or more of: antenna shape, system status and system performance. One or more measurements of the returned microwave power shaping elements may also be used to obtain information about one or more properties of the target material. The invention also discloses devices and methods for delivering microwave energy to a variety of target materials to achieve a variety of desired microwave effects.