Cyclotron emission from large magnetic polar caps in DQ Her binaries is calculated taking the magnetic field distribution and self-eclipses into account. The calculative method is based on the additivity of Stokes parameters for incoherent beams. The principal result obtained is that the large polar cap effectively leads to the averaging out of the emission from individual elements on it. Hence, relatively flat circular polarization light curves are obtained, compared to the uniform slab case, while the linear polarization which appears as a pulse in the latter case is smeared out and reduced, in some cases, to below the threshold of detection. The results are so qualitatively different that it should be possible to determine, from polarization light curves, whether the polar cap is extended or not and to estimate the polar magnetic field of the white dwarf. Comparison with the observations of 3A 0729 + 103 suggest that its B(0) is about 10 million G and that its polar cap is extended. 35 references.