Design of a wideband multi-channel system for time reversal hyperthermia

Purpose: To design and test a wideband multi-channel amplifier system for time reversal (TR) microwave hyperthermia, operating in the frequency range 300 MHz–1 GHz, enabling operation in both pulsed and continuous wave regimes. This is to experimentally verify that adaptation of the heating pattern with respect to tumour size can be realised by varying the operating frequency of the antennas and potentially by using Ultra-wideband (UWB) pulse sequences instead of pure harmonic signals. Materials and methods: The proposed system consists of 12 identical channels driven by a common reference signal. The power and phase settings are applied with resolutions of 0.1 W and 0.1°, respectively. Using a calibration procedure, the measured output characteristics of each channel are interpolated using polynomial functions, which are then implemented into a system software algorithm driving the system feedback loop. Results: The maximum output power capability of the system varies with frequency, between 90 and 135 W with a relative power error of ±6%. A phase error in the order of ±4° has been achieved within the entire frequency band. Conclusions: The developed amplifier system prototype is capable of accurate power and phase delivery, over the entire frequency band of the system. The output power of the present system allows for an experimental verification of a recently developed TR-method on phantoms or animals. The system is suitable for further development for head and neck tumours, breast or extremity applications.