New Microwave Dielectric Resonator Materials for Wireless Communication – The Physics Congress 2003

A new group of ceramic materials could lead to more reliable and clearer microwave communication signals, according to engineers at South Bank University, London, speaking at the Institute of Physics Congress at Heriot-Watt University on Wednesday 26 March.

A small ceramic component made from a dielectric material is fundamental to the operation of filters and oscillators in several microwave systems, such as satellite TV receivers, military radar systems, Global Positioning System (GPS) devices, and mobile communications.

In microwave communications, dielectric resonator filters are used to discriminate between wanted and unwanted signal frequencies in the transmitted and received signal. When the wanted frequency is extracted and detected it is necessary to maintain a strong signal nevertheless. For clarity it is also critical that the wanted signal frequencies are not affected by seasonal temperature changes.

According to Dr Anna-Karin Axelsson, a member of the research team from South Bank University, the resonator materials for practical applications have to have certain key properties. A high relative dielectric constant is needed so that the materials can be miniaturised and a high quality factor (Q) is needed for improved selectivity. Low temperature variation of the material’s resonant frequency is also required so that the microwave circuits remain stable. “Everything from the electromagnetic properties to microstructure of the material is important for the final result” explains Dr Axelsson.

Although large numbers of ceramic dielectric materials have been developed, it has proven difficult to satisfy all these requirements in a single material at a reasonable cost. Dr Mailadil Thomas Sebastian, a member of the research team from the Regional Research Laboratory, in Trivandrum, India, is well known in the field of microwave ceramics and will address the Dielectrics for Emerging Technologies conference at Congress. According to Dr Sebastian: “The advantages of these new materials are that they are relatively cheap compared with some of the compounds currently used and in the future they can be improved even further by suitable additives and by optimizing the preparation conditions”

The new dielectric materials developed by Dr Axelsson and Dr Sebastian, working with team leader Professor Alford, are based on ceramics formed by baking the pressed powdered starting material mixture in a furnace at between 1200 and 1550 degrees Celsius. The researchers used X-ray diffraction studies, Raman spectroscopy and scanning electron microscopy to reveal the structure of the ceramics. The materials have the general formula Ce(M1/2Ti1/2)O3.5. Ce is the element cerium, Ti is titanium and O is oxygen. “M” represents any one of the metals magnesium, zinc, calcium, cobalt, manganese, nickel or tungsten. The numbers refer to the proportions of each element in the ceramic. “Further work is in progress to find the exact composition, internal structure and secondary phases in the ceramics,” says Dr Axelsson.