We study a microwave superconducting stripline resonator made of NbN on a sapphire. substrate. A radiation detector (RD) having a thin meander shape is integrated into the resonator. We harness an extremely strong nonlinear instability occurring in the device in order to enhance its sensitivity to infrared radiation impinging on the RD. Characterization measurements yield a noise equivalent power of 34 fW/root Hz at a modulation frequency of 7.74 GHz. Such a device may be exploited for fast and sensitive radiation detection.