Polarization Properties of A Multi-Moded Concentrator
  We present the design and performance of a non-imaging concentrator for use
in broad-band polarimetry at millimeter through submillimeter wavelengths. A
rectangular geometry preserves the input polarization state as the concentrator
couples f/2 incident optics to a 2 pi sr detector. Measurements of the co-polar
and cross-polar beams in both the few-mode and highly over-moded limits agree
with a simple model based on mode truncation. The measured co-polar beam
pattern is nearly independent of frequency in both linear polarizations. The
cross-polar beam pattern is dominated by a uniform term corresponding to
polarization efficiency 94%. After correcting for efficiency, the remaining
cross-polar response is -18 dB.
