A novel approach for higher-order mode extraction in communication satellite feed chains with tracking capability

This paper describes a novel higher-order mode extractor design, compatible with next-generation broadband satellite multiple beam antenna system requirements. This mode extractor, which is a key component in antenna pointing systems, has the advantage to be very compact and wide-band. This higher-order mode extractor is to be placed in between a feed horn and a user-link feed chain without affecting the design or performance of the user-link part. An improved design of the mode extractor, obtained thanks to a global optimization of the component, is presented in this paper. It fits in a cylinder of 25 mm in diameter and 24 mm in length. This improved design is well matched to the fundamental mode over the full transmit and receive frequency bands for broadband applications (17.7 - 20.2 GHz & 27.5 - 30.0 GHz), with a return loss better than 21 dB. The coupling coefficient for the tracking mode (TM01) is better than -0.4 dB over the full receive band (27.5 - 30.0 GHz), thus enabling a generic mode extractor design. Another important parameter for tracking purposes is the coupling between the fundamental mode and the tracking port, which affects the quality of the on-axis tracking null. Values below -68 dB were obtained in simulation for the proposed design.