The feedhorn is a device that collects the signals at the focus of the satellite dish and channels them to the LNB (Low Noise Block Down Converter). The LNB amplifies the received signals (3.6 – 4.2 GHz for C-band or 12.25 – 12.75 GHz for Ku-band) and converts them to lower frequency in the range between 950 and 2150 MHz, and are then sent down a cable to the satellite receiver.
To receive both C-band and Ku-band signals, you need a dual band feedhorn with both C-band and Ku-band LNBs. If you want to receive programmes from both vertical and horizontal polarisations, you will need a feedhorn providing outputs for both polarisations. Furthermore, by installing a dual-band and dual-pol feedhorn, you can receive signals from both C and Ku bands and each band having signals from both vertical and horizontal polarisations simultaneously.
Ref: http://www.asiasat.com/asiasat/contentView.php?section=76&lang=0
The feedhorn is covered with a window of polystyrene fiberglass to prevent moisture and dirt from entering the open end of the waveguide. If a dry-air pressure exist in the waveguide system, ceramic materials or quartz glass is used as covering material.
