Very compact TM01 mode extractor for enhanced RF sensing in broadband satellite multiple beam reflector antenna systems

This paper describes a novel, very compact and broadband TM₀₁ mode extractor, which may be used as part of an RF sensing system in multiple beam antennas. Broadband satellite missions require multiple beam antennas with always smaller beamwidth, resulting in demanding pointing accuracy. The higher-order mode extractor (either TM₀₁ or TE₂₁) embedded in one feed chain of a multiple beam reflector antenna is a key component to provide enhanced RF pointing. The proposed TM₀₁ mode extractor combines two back-to-back turnstile junctions and a coaxial probe. This configuration is found to have several advantages in comparison to existing solutions. It is compatible with a generic user-link feed chain thus reducing development cost. It has broadband performance, thus enabling a generic mode extractor design compatible with any beacon signal frequency within the receive band. And it is very compact both in diameter and length, thus being compatible with currently targeted next-generation feed designs (less than two wavelengths in diameter). The simulation results of a specific design at Ka-band are reported in this paper. It provides a port matching for the fundamental modes better than -21 dB over the full transmit and receive Ka-band (17.7-20.2 GHz & 27.5-30 GHz) and the coupling coefficient for the TM₀₁ mode is better than -0.6 dB over the full receive band (27.5-30 GHz). The resulting design fits in a cylinder of 32 mm in diameter and 23 mm in length.