LengthenedH102cavity for electron spin resonance studies of aqueous samples

An H 102 cavity, constructed from waveguide size 16 for use with an X-band electron spin resonance spectrometer, may be increased in length to 12 cm by reducing the larger waveguide side. This allows the use of a flat sample cell 1 mm thick which is easier to make and to align than the flat cells in normal length H 102 cavities. If the empty cavity has been critically coupled, the minimum voltage standing wave ratio with a cell in position is obtained when the cell coincides with the electric field node. The voltage standing wave ratio in this case should be 1.5 for optimum sample volume.