Antennas and multiplexer structures are provided for establishing individual communication links with satellites that are located at geostationary positions in close angular proximity to one another. The antenna includes individual wave-guides where at least one of the wave-guides has a decreased dimension such that the wave-guides may be spaced in close proximity to each other to communicate with the satellites. For example, in one embodiment, the antenna includes at least one wave-guide that is a hollow metallic structure filled with a dielectric material. The dimensions of this wave-guide can be altered by changing the dielectric material used to fill the wave-guide. By using a dielectric material having an appropriate dielectric constant, the dimension of the wave-guide can be configured to allow the wave-guide to be spaced in close proximity to the other wave-guide.