A new technique for tuning the passband frequency of a microwave photonic bandpass filter is presented. It is based on controlling the polarization state of the signal in an amplified recirculating delay line loop with a polarizer at the output. A fixed wavelength laser can be used as an optical source. The filter has a sharp passband, which can be tuned continuously while maintaining the same passband width. Experimental results demonstrate continuous tuning capability of the high-resolution bandpass filter.