A novel tunable microwave notch filter based on air-guiding photonic bandgap fiber (AG-PBGF) is proposed and experimentally demonstrated. The operational principle of the proposed filter is analyzed in detail. Using the character of wavelength-dependent high birefringence of AG-PBGF, the frequency response of the
polarization-dependent notch filter can be simply tuned by changing the incident optical wavelength, and its notch depth is dominated by the input azimuth angle. Moreover, the proposed filter is free from the coherence induced by the laser source. Therefore, the magnitude frequency response is robust. A piece of 20-m AG-PBGF is used in the experiment. As expected, the free-spectral range (FSR) changes from 22.4GHz to 8.74GHz when the wavelength from 1570nm to 1584nm and the largest notch depth is more than 40dB.