Development of linear amplifiers for radio communications at microwave and millimetre-wave frequencies based on modelling, linealization and baseband predistortion techniques

In collaboration with the RF research group of the University of Cantabria, the goal of this project was to development power linear amplifiers for communication applications working from microwave to millimetre-wave frequency bands. The work was carried out following two different lines on the basis of the techniques to be used as well as of the frequency band of the system. 1) Firstly, new nonlinear model amplifiers as well as new predistorting and linealisation techniques for low microwave frequency bands (L and C) were developed. To this end, a new system for measuring and characterising nonlinear amplifiers, based on direct conversion techniques (subsampling) was developed. The designed system acquired the input/output complex envelope measurements; therefore taking into account the special characteristics of multicarrier or OFDM modulations. Direct conversion techniques were also used to develop a base-band adaptive predistorter for L band applications. The potential extension of these predistorting schemes to higher frequency bands (C: 3,2.3,5 GHz and 5,1-5,2 Ghz) was explored. The new models obtained using the direct conversion measurement system were be used to develop linear amplifiers for several applications. 2) A second working line of the project is intended to the design of linear amplifiers without the need of external linearization systems. To get this goal it is necessary to have new nonlinear models for the traditional microwave active devices (LDMOS, MESFET, HEMT and HBT). Small and large signals models able to predict intermodulation products were developed for these devices. The developed models are based on splines and modular neural networks.