The effects of microwave current and dc magnetic field on quality factor and resonant frequency at 3 GHz of planar resonators, which were differently coupled to hysteretic microwave SQUIDs, are discussed. The dissipative response is analyzed in terms of a single-junction SQUID, and its coupling to a resonant tank circuit. The temperature dependences and field periodicities of all relevant parameters are discussed, and conditions for optimized operation are deduced. The results indicate potential for further improvement of the performance of microwave SQUID magnetometers.

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