Fully Polarimetric Bistatic Radar Calibration With Modified Dihedral Objects

We introduce the design of dihedral reflectors that are used to calibrate an instrumented, dual-linearly polarized, wide-bistatic compact radar range operating at 160 GHz. The polarization scattering matrix of this bistatic calibration object may be tailored to rotate the incident linear polarization state to a slant polarization state in a fashion that is similar to the 90° dihedral that is used for calibrating monostatic polarimeters. The bistatic calibration object that we describe here is capable of introducing this polarization rotation while simultaneously steering the mainlobe of its specular reflection to the receiver. As we demonstrate, this characteristic of the mainlobe-steered dihedral (MSD) object can be achieved over a wide range of bistatic angles. The MSD object possesses a variety of desirable qualities for the calibration of bistatic polarimeters, but they are particularly useful for those systems that do not possess the capability to rotate their feed arrangement (e.g., millimeter-/ submillimeter-wave waveguide-based systems). Through both computational and experimental results, we demonstrate the capability of the MSD object to calibrate and characterize the accuracy (better than 0.5 dB) and polarization purity (~50 dB) of a 160 GHz dual-linearly polarized, bistatic compact radar range at 15°, 45°, and 75° bistatic angles.