A reverse-diplexing RF chain architecture for space telecom antennas

A novel self-diplexing feed-system architecture, particularly suitable for high-power multicarrier operated space telecom antennas and conceived for dual/tri-band operation, is addressed in this paper. The proposed architecture is particularly effective in multiple frequency applications where a relatively large bandwidth is requested at the lowest frequency band. Common desirable features of space telecom feed-chains are: negligible passive intermodulation products (PIM-free design), multipaction-free operation, wide operative bandwidth, high isolation (in polarization and frequency), low losses, flexibility in polarization (i.e. dual linear or dual circular). The proposed system architecture is based on a reverse configuration, where the dual polarized high-frequency signals are extracted first from (routed to) the common waveguide of the feed-chain. The building block of this system configuration is a dual-polarization reverse-coupler integrated with a dual-polarization stop-band filter. The latter exploits a two resonant-element cell that exhibits high rejection levels in the stop-band and low reflection levels in the pass-band. A broad-band design of both the coupler and stop-filter is achieved by adopting a quasi-circular ridge common waveguide. The proposed solution is modular in design, providing enough flexibility and allowing customization to different antenna optics and frequency sub-bands. This feature is achieved by replacing specific components in tandem connected through customized PIM-free flanges, where high power signals are present. Hence, PIM avoidance, easy hardware manufacturing and higher tolerance accuracy are possible. Within this framework, different implementations will be highlighted with reference to the most common telecom applications in Ku/Ku+; Ku/K, K/Ka and K/Ka/EHF frequency bands, according to the following frequency plans: 1. Ku/Ku+: Ku-Tx [10.7, 12.75] GHz, Ku-Rx [13.7, 14.5], Ku+:Rx [17.3, 18.4] GHz 2. Ku/K: Ku Tx [10.7, 12.75] GHz, Ku-Rx [13.0, 14.5], K-Tx [17.7, 21.2] GHz 3. K/Ka: K Tx [17.7, 21.2] GHz, Ka-Rx [27.5, 31.0].GHz 4. K/Ka/EHF: K-Tx [19.5, 21.2] GHz, Ka-Rx [29.2, 31.0] GHz, EHF-Rx [43.5, 44] GHz.