Development of a wideband high power amplifier for cancer treatment.
Medical hyperthermia refers to heating of tumors to temperature levels which are lethal to the cells for sufficient periods of time or rendering the cancerous cells more sensitive to ionizing radiation or chemotherapy. In order to increase the temperature in cancerous tissues, high power solid state microwave amplifiers need to be used. Recently ultra wide-band and continuous wave microwave methods have received increasing attention. Using adaptive focusing annular phase array applicators the radiation pattern can be adjusted according to tumor size and seating depth. For this purpose power amplifiers operating across 300MHz-1000MHz having a minimum output power of 150W needed to be designed. By varying the operating frequency the penetration depth can be controlled. Since currently 12 (with plans to increase the number to 18) of these amplifiers will be operating simultaneously in the designed system, the power added efficiency of the amplifier will be important both to regarding the cost of electricity and also allow for easier cooling requirements and thus a more compact system. The aim in this project is to have an efficiency of 60% across the band. In this thesis a power amplifier working in a push-pull configuration, designed using an NXP LDMOS device (BLF-647P) capable of delivering 200W RF power is demonstrated. During this thesis, different power combining topologies were studiedusing a nonlinear model that was developed in ADS using basic data provided by NXP. Using the developed model, load pull simulations have been performed and the input, two output matching networks are designed based on results from the load pull simulations. The design was manufactured and mounted on a copper base plate designed for this work which allowed efficient water cooling as well as serving as a fixture to firmly attach the matching circuits to the transistor and connectors. The measurements show that the design is capable of delivering more than 125 W from 360-940 MHz in pulsed mode operation with a mean efficiency of 50% which was measured in continuous mode. This work has demonstrated a high power wideband amplifier with high efficiency needed to drive future hyperthermia systems. The high efficiency of the amplifier allows for modern hyperthermia systems to be built in a more compact configuration with lower operating cost, which would not be possible with commercially available amplifiers.
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