Optimization of axial RF field distribution in low-frequency EPR loop-gap resonators

A novel coupling method that optimizes the axial RF distribution of low-fre quency EPR loop-gap resonators is presented. It consists of a resonant coup ling loop positioned at the centre of a two-section loop-gap resonator. Thi s arrangement ensures a symmetrical distribution of the radio frequency fie ld along the axis of the resonator. The design of st central coupling syste m suitable for EPR resonators operating at about 220 MHz is described. Expe rimental results show that with the central coupling system the RF field is symmetrical and has a Very good axial homogeneity (100% of the resonator l ength).