A radio frequency (RF) heating apparatus and a microwave oven including an RF heating apparatus. The apparatus includes a cavity for receiving an object to be heated. The apparatus also includes a plurality of channels for generating RF radiation to be introduced into the cavity. Each channel includes a frequency synthesizer, a power amplifier and an antenna. Each channel is operable to use a common phase reference signal for generating the RF radiation. Each channel may be controllably operable to generate RF radiation having different, respective frequency spectra. Forward and reverse signal detection circuitry may be provided that is operable to determine amplitude, frequency and/or phase information relating to RF radiation in the cavity. This information may be used for adaptively controlling the RF radiation generated by each channel.