Underpinning mobile telecomm through advanced filters
Microwave data transfer links offer high-speed, high-performance communications over long ranges with low interference rejection and high reliability. In comparison to fixed links the use of frequency-agile wireless considerably improves the cost- and time-effectiveness of related infrastructure. Unfortunately bandwidth availability for mobile communications (up to a few GHz) limits link capacity. Addressing this need the TUF project focused on developing innovative tuneable microwave devices and technology for future mobile communication systems. This technology and its components can facilitate flexible allocation of frequency and bandwidth. The project work was centred on developing new materials for dielectric resonator filters that display extremely low dielectric loss. The key idea was to develop high Q-factor dielectric resonator ceramics aimed to be used in channel filters. In addition, suitable methods for electronic tuning of these filters were also required. In comparison to piezoelectric and ferrimagnetic, ferroelectric films are able to tune their relative permittivity via application of static electric fields. Therefore, a thin film of ferroelectric material, when coupled with a dielectric resonator results in effective tuning. For the proper characterisation of the dielectric properties of thin films two methods were developed. First, a 14GHz Split Post Dielectric Resonator (SPDR) was realised by the Warsaw University of Technology. This non-destructive method is suitable for the largest size on which films can be deposited. With the aid of a new generic mode matching code for complex film permittivity patterns, arbitrary radial geometries can be easily modelled and analysed. The second method that was developed was the Stripline Double Resonator (SDR) that is capable of measuring the change in complex permittivity of ferroelectric films under tuning. The resonators were designed to work in the same frequency range in order to allow the use of both techniques in tandem.
