Design and test of a 434 MHz multi-channel amplifier system for targeted hyperthermia applicators

Purpose: For our head-and-neck hyperthermia (HT) applicator, an amplifier system with full amplitude and phase-control to deliver the radio-frequency signals, was not available. We therefore designed and tested a 433.92 MHz multi-channel amplifier system. System description: The design consists of a direct digital synthesizer (DDS) system that generates 12 phase-controlled coherent 433.92 MHz signals, which are amplified to maximum 200 W output per channel. Directional couplers are placed at the amplifiers to couple a small portion of both forward and reflected signals to gain-and-phase detectors. The power setting is applied with a resolution of 2 W and for the phase it is 0.1°. The channels are sequentially sampled at 100 Hz per channel. Methods: We tested the performance of the designed amplifier system by measuring the RF spectrum, power and phase accuracy, and by characterising the feedback control by using highly accurate power and phase meters. Results: The spurious emission is less than 60 dBc and the first two harmonic frequencies are suppressed more than 45 dB. The measurement accuracy for the power (±5%) is valid for at least 20 days after calibration and for the phase (±5%°) it is valid for at least 2 months. Conclusions: The amplifier system operates according to our design criteria to support targeted HT. It can be used for both our in-house developed superficial and head-and-neck HT applicators or any other HT applicator that works on the same frequency of 433.92 MHz.

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