A method for upgrading a dual-band antenna assembly to a tri-band antenna assembly is provided. The dual-band antenna assembly includes a main reflector, and first and second antenna feeds arranged in a coaxial relationship and directed toward the main reflector. The first and second antenna feeds are for first and second frequency bands, respectively. The method includes positioning a third antenna feed through a medial opening in a center of the main reflector, with the third antenna feed directed towards the first and second antenna feeds. The third antenna feed is for a third frequency band. A subreflector is positioned between the main reflector and the first and second antenna feeds. The subreflector includes a frequency selective surface (FSS) material that is reflective for the third frequency band and transmissive for both the first and second frequency bands.