An Investigation on Electromagnetic Fields and Properties of the Loop-Gap Resonator, a Lumped Mode Microwave Resonant Structure

Methods of test and analysis have been developed for electromagnetic field configurations of loop-gap (split-ring) resonators, which are recently developed microwave resonant structures, devices now in use as sample structures for magnetic resonant spectroscopy. Perturbation methods have been used to investigate the field distributions, and a theoretical analysis have been performed using an expansion of Maxwell\u27s equations for the boundary conditions of the resonator. Mathematical methods such as separation of variables, and the method of weighted fitting have been used to match the internal modes of the resonator to the fringe evanescent modes, and the expressions found for the field distribution are used to derive expressions for the resonant characteristics of the device. The resonant frequency calculated by this method gives an average accuracy of about one percent when compared with experimental data. The coupling of the loop-gap resonator to external circuits was studied, and again theoretical analysis gave good agreement with measured results. Different methods of tuning the resonator were analyzed and tested, and it was found that the structure is tunable over a range of more than one octave. Further, its behavior as an element in microwave filter structures was investigated, leading to the design of a banpass [sic] filter with equal ripple type response for the 3 GHz band. A unique coupling method of the resonator to a transistor circuit is used for stabilization of a microwave oscillator in the 1.5 GHz range