The increasing consumer demand for high data rate wireless services, e.g. the 3G and emerging 4G networks, is resulting in high complexity supporting infrastructures. Radio base stations are responsible for transmitting signals to many simultaneous mobile users using sophisticated modulation formats and utilizing an increasing number of frequency bands. There is a desire to reduce the hardware complexity, costs and environmental footprint of these systems by making them reconfigurable. One potential solution is to integrate varactors, e.g. voltage controlled capacitors, into the circuit design. However, the high power conditions in, for instance, a radio base station puts tough requirements on the varactor technology. Silicon carbide (SiC) is a wide bandgap semiconductor material that enables the realization of low loss and high power devices at microwave frequencies. SiC Schottky diode varactors have been developed and fabricated in the Chalmers cleanroom facilities. These devices can handle high power conditions, while maintaining high capacitance tunability with reasonably low losses in the GHz frequency range. However, given the nonlinear nature of the devices, consideration must be given to the varactor port terminations at higher order harmonic frequencies. The goal of this proposed M.Sc. thesis is for the student to theoretically develop, computer design (microwave circuit and device simulation and CAD software), practically assemble (device mounting, soldering, and wire bonding), and measure (using advanced small- and large-signal microwave measurement equipment) reconfigurable circuits utilizing varactors at high power levels and microwave frequencies used in next generation wireless communication systems. Potential circuit designs could for instance include multipliers or frequency reconfigurable filters in an effort to evaluate the limits of the varactor technology relating to losses, power handling, tuning range and bandwidth. Systematic design procedures on how to properly handle or take advantage of the device nonlinearities should result. Throughout the work the student will be encouraged to pursue his or her specific research areas of interests.
Courses in high frequency and microwave electronics, knowledge of semiconductor device technology is a plus.
For more information please contact:
Supervisor: Christer Andersson