Sensitivity in the measurement of microwave surface resistance of high-T-csuperconducting samples of different sizes by the cavity method

Cavity resonators are conventional devices for measuring the temperature an d frequency dependence of microwave surface resistance, R-s, of superconduc ting samples. The temperature dependence can provide information about the losses due to those conduction electrons that are not condensed into the su perconducting state. Since surface resistance characterizes the response to the electromagnetic field near the surface, it qualifies the suitability o f the superconducting material for microwave device applications. The measu rement of R-s by the cavity technique is performed by replacing the end pla te of TE0.11 mode cavity with the superconducting sample. The sensitivity o f measurement is restricted for the samples whose dimension is less than th at of the end plate. In this paper, we report the measurement of surface re sistance of bulk YBa2Cu3O7 samples of varying dimensions, using a lamina wi th a circular opening in the end plate. Sensitivity and the error in the me asurement of R-s is discussed with respect to the uncertainties in the Q-va lue and the R-s-value of the background copper cavity.