The GMRT reionization effort aims to map out the large scale structure of the Universe during the epoch of reionization ( EoR ) .
Removal of polarized Galactic emission is a difficult part of any 21 cm EoR program , and we present new upper limits to diffuse polarized foregrounds at 150 MHz .
We find no high significance evidence of polarized emission in our observed field at mid galactic latitude ( J2000 08h26m+26 ) .
We find an upper limit on the 2-dimensional angular power spectrum of diffuse polarized foregrounds of [ l ^ { 2 } C _ { l } / 2 \pi ] ^ { 1 / 2 } < 3 K in frequency bins of width \delta \nu = 1 MHz at 300 < l < 1000 .
The 3-dimensional power spectrum of polarized emission , which is most directly relevant to EoR observations , is [ k ^ { 3 } P _ { P } ( k ) / 2 \pi ^ { 2 } ] ^ { 1 / 2 } < 2 K at k _ { \perp } > 0.03 h Mpc ^ { -1 } , k < 0.1 h Mpc ^ { -1 } .
This can be compared to the expected EoR signal in total intensity of [ k ^ { 3 } P ( k ) / 2 \pi ^ { 2 } ] ^ { 1 / 2 } \sim 10 mK .
We find polarized structure is substantially weaker than suggested by extrapolation from higher frequency observations , so the new low upper limits reported here reduce the anticipated impact of these foregrounds on EoR experiments .
We discuss Faraday beam and depth depolarization models and compare predictions of these models to our data .
We report on a new technique for polarization calibration using pulsars , as well as a new technique to remove broadband radio frequency interference .
Our data indicate that , on the edges of the main beam at GMRT , polarization squint creates \sim 3 % leakage of unpolarized power into polarized maps at zero rotation measure .
Ionospheric rotation was largely stable during these solar minimum night time observations .