  In this paper we present a novel class of compact orthomode transducers which
use digital calibration to synthesize the desired polarization vectors while
maintaining high isolation and minimizing mass and volume. These digital
orthomode transducers consist of an arbitrary number of planar probes in a
circular waveguide, each of which is connected to an independent receiver chain
designed for stability of complex gain. The outputs of each receiver chain are
then digitized and combined numerically with calibrated, complex coefficients.
Measurements on two prototype digital orthomode transducers, one with three
probes and one with four, show better than 50 dB polarization isolation over a
10 C temperature range with a single calibration.
