An ideal feed for a dualband reflector would provide a rotationally symmetric radiation pattern with low side- and back-lobe levels, as well as good isolation between receiving ports for the 2 bands. The port isolation for low- and high-frequency operation bands is critical to allow the feed for each band to be optimized independently and to reduce complexity of the feed electronics.
The dualband coaxial horn antenna - consisting of two circular coaxial guides – can be designed to provide excellent port isolation and good radiation properties as a reflector feed. The outer guide of the construction is longer than the inner guide, and has a quarterwave choke and an iris at its aperture. The inner guide is filled with a dielectric material that extends beyond the aperture....Dualband coaxial horn: Geometry
The design of the antenna is geometrically constrained to ensure TE11 propagation. The choke, iris and dielectric inner material enable independent optimisation of the lower- and upper-band cut-off frequencies.
At the lower operating frequency (4 GHz for the example shown below) the outer guide is above cut-off and has a narrow passband. The inner guide is below cut-off. At the upper operating frequency (6 GHz for the example shown below) the inner guide is above cut-off and the coupling between the ports is low. The radiation pattern at the lower operating frequency is highly symmetric. The radiation pattern at the upper operating frequency is slightly asymmetric but still provides acceptable illumination for most cases.Typical reflection coefficient versus frequency Total typical gain 3D radiation pattern at frequency centre 1 and frequency centre 2