Tunable microwave filters using ferrites

• Main Author: Chitre, Nandkishore Mahadeorao
• Other Authors: Roberts, J.
• Published: Imperial College London 1962
• Subjects: 621.3815
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.602168

The need for tunable filters is discussed and a brief survey of tunable filter elements is given with emphasis on the magnetically tuned ferrite loaded elements. With the trend towards increasing bandwidth in communications systems the need for the development of tunable filters with medium Q's is shown The choice of a resonant element is discussed and a suitable structure - a thick resonant iris including a ferrite slab along sidewalls - is developed. It is shown that the thick iris may be characterized by three constants and the relations between the iris dimensions and the constants are derived and substantiated by measurement. The essential four pole representation of the iris requires the adaptation of the theory of filters and includes a study of optimum coupling and the results of non, optimum coupling. The theory of ferrite loaded apertures is developed and investigations made into the tuning range, the order of fields required and the choice of suitable ferrites. Lastly a two section tunable filter is described and the problems associated with multi-section filters are discussed.