Frequency Agility in Microwave Dielectric Resonators

At present. cellular mobile communication systems use input and output filters which are tuned to cover the whole band of interest. This is done because tuneable filters that have low enough loss or do not themselves produce significant unwanted signals do not exist. For example, filters can be tuned by using varactor diodes but these are nonlinear devices which produce unwanted signals that are too large for the filters to be used in commercial communication systems. They also have low unloaded 0 which result in filters with a high insertion loss. A low loss, low spurious interference, filter which could be tuned to a single communications channel would offer tremendous advantages in the design of the rest of the system. These are:The ability to exclude, at an earlier stage in the receiver to that currently possible, signals in the same band as your own. This would considerably ease the problems of spectrum planning and greatly improve spectrum efficiency and the information transfer capacity available to users (the public). Spectrum is. of course, a unique, limited resource, so any spectrum efficiency improvements are worthwhile.The ability to reduce greatly the amount of unwanted signals radiated from a transmitter. The design of power amplifiers for 3G communication systems is much more difficult than for GSM systems. For example, the amplifiers must have a linear transfer characteristic. which is not required for GSM.In order to achieve this frequency agility we intend examining two methods. These are1 Ferroelectric/paraelectric tuning - where a voltage will alter the relative permittivity of the material and hence the frequency.2 Piezoelectric tuning - where a change in the position of a tuning element will alter the frequency.In order to verify these ideas, a prototype device of each will be manufactured and tested.The prototype will comprise* a single resonator dual mode 2 pole filter* a a 2 resonator 2 pole filter and a 2 resonator dual mode 4 pole filter