Dielectric resonators. Materials and components

In the article [E1920], dielectric resonators were presented as resonant elements to replace metal cavities in microwave circuits. They are used in oscillators and filters, and in various electromagnetic modes such as TE, TM and TEM. This article describes the properties of dielectric resonators. This enables manufacturers to improve these properties for the benefit of the user: high permittivity for greater miniaturization, high quality factor for high spectral purity in an oscillator or minimum insertion loss in a filter, adjustable temperature coefficient. This is achieved by studying the chemical compositions and the ceramic process, including the intimate mixing of the elements, raw materials, oxides or powdered carbonates, usually by liquid means, followed by the sintering conditions, including temperatures and oxidizing atmosphere. The formulations presented here are based on simple oxides such as alumina Al₂O₃ or titanium oxide TiO₂, with permittivities of ~10 and ~100 respectively, and other oxides such as barium, zirconium, tin, tantalum, niobium and rare earths like samarium and neodymium. These non-trivial formulations provide a good compromise between improved thermal frequency stability, of some 10^–6/K, and sufficiently low dielectric losses, below 10^–3 or, equivalently, quality factors of over 1,000 up to tens of thousands. A few examples of circuit implementation are given.