Accurate Modeling of Dichroic Mirrors in Beam-Waveguide Antennas

Frequency selective surfaces, also called dichroic mirrors, are usually analyzed assuming a uniform plane-wave excitation. However, when these devices are used within reflector antennas to combine/separate beams at different frequencies, they are often illuminated by corrugated horns, which generate a radiation pattern that cannot be approximated by a uniform plane wave. For this reason, it is important to properly analyze the interaction between the electromagnetic field generated by the horn and the transmission (or reflection) response given by the mirror. To carry out this task, this paper presents an approach based on the plane wave expansion of the field generated by the horn. The effectiveness of the proposed method, which is able to provide the degradation due to the dichroic mirror to the horn radiation pattern for both the co-polar and the cross-polar component, is validated versus measurements.