Enhancing the focusing properties of a microwave radiometry imaging system with broadband phased array configurations

In this paper we present our recent progress towards the optimization of the focusing properties of a prototype hybrid microwave radiometry - hyperthermia system. The proposed system operates in a totally passive, non - invasive manner providing real time, in depth temperature and/or conductivity variation measurements. It uses an ellipsoidal conductive wall beamformer that provides the necessary focusing of the electromagnetic radiation. The system´s operating frequency range is 1-4GHz combining adequate detection depth with reasonable spatial resolution. With the view to manipulate the focusing area inside the medium of interest without its physical movement at the full operating range of our radiometric receivers, we investigated the use of phased arrays with wideband antennas. Specifically, two-element array setups were used to compute the electric field distribution inside the ellipsoidal beamformer and two human head models. The results at the lower frequencies confirmed previous findings, showing it is possible to manipulate the focusing point around the geometrical focus by varying the phase distribution of the array elements. At the higher frequencies of the operating range the lower penetration depth in the human brain tissues results to superficial focal areas. In this case the phase variation leads to a shift of the focusing area inside different regions of the head model.