Miniaturised double-coaxial cavity resonator and duplexer with ZOR characteristic using air-core coils

A novel method of miniaturising the size of a coaxial cavity resonator by utilising zeroth-order resonance (ZOR) characteristics is presented. This miniaturisation has been achieved through the introduction of air-core coils inside a conventional coaxial cavity resonator. This structure possesses ZOR characteristics, which results in the miniaturisation of the resonator while still exhibiting a reasonable high unloaded Q factor. A duplexer was designed and fabricated using the proposed resonator. The measurement results verified that a 30% reduction in size was achieved compared with a traditional duplexer.