The quasi optical polarization separation principle is introduced. The new type of wire grid calibration source consisting of polarized wire grid

artificial black body

and cold sky signal is designed. Through the rotation of the polarized wire grid

the radiation energy of artificial black body and cold sky is mixed. The wire grid calibration source provides varying temperature signals

and solves the problem of low-frequency radiometer calibration. A measured reflectivity of 98.4% and transmittance of 99.9% at L-band is demonstrated. The brightness temperature dynamic range of wire grid calibration source is between 8K and 248K

which meets the design goal.