Dual-Frequency EHF Ground-Terminal Antenna

A design is presented for an EHF ground-terminal antenna in the form of a dual-frequency 2-ft dish. The 20 GHz receive horn is at the prime focus. The 44 GHz transmit feed is a focussed array of 32 square horns at the vertex of the dish illuminating a dichroic ellipsoidal Cassegrain sub-reflector. The sub-reflector is nominally transparent at 20 GHz and nominally a perfect reflector at 44 GHz. The directive gains at the two frequencies are estimated to be 39.0 dB and 44.9 dB, respectively. The dichroic surface is a single layer metal sheet whose periodic perforations are designed to exhibit a two-frequency resonant behavior giving near perfect reflection at 44 GHz and near-perfect transmission at 20 GHz. This design allows some 32 W of transmitter power to be generated by combining the power of 32 individual 1 W solid-state amplifiers. The combining losses (and the hardware) of a waveguide combining tree are avoided by space combining the fields radiated by the 32 individually fed horns. (Author)