RF measurements with non-hysteretic SQUID

A theoretical analysis not restricted to the small-signal regime is given for the behavior of a nonhysteretic RF SQUID in RF measurements application. The modulation depth of the in-phase and out-of-phase components of the SQUID output voltage are calculated. It is shown that the DC magnetic flux bias should be adjusted to the value nΦ₀/2, where Φ₀ is the flux quantum. At that point it is possible to use a simple amplitude detector, and the SQUID input resistance does not affect RF power measurements. The necessary condition for the coupling between the SQUID ring and resonant circuit is found.