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There are many orbital locations where linear and circularly polarised satellites are or could be in the future co-located. An LNB that can receive from both types of satellites could therefore significantly stimulate the use of space capacity for new services from existing locations through ease of reception for the consumer market.
1 Feed Horn
For reflectors designed to give high adjacent satellite isolation, the reflector profile is typically elliptic, and therefore an elliptic radiation pattern is required from the feed horn.
The alternative solution offered by other satellite operators is a service using two separate LNB's. This solution would require the design of an external IF switch network to combine the outputs of the two LNB's into four IF cables for routing to the Digital Video Recorder and any additional Set Top Boxes within the customer's home. There is a high risk in the implementation complexity and a significant increase in cost of the outdoor reception equipment.
The unit will be designed to receive circularly polarised signals of either polarity in the frequency band 12.2-12.7 GHz Ku band from current orbital locations and also receive linear polarised signals of either polarity in the frequency band 11.7-12.2GHz in the Ku band from co-located satellites.
However, the other two channels, one each from the horizontal and vertical probes, are combined in a hybrid coupler to produce Right Hand circular polarisation and Left Hand circular polarisation. The proposed block diagram is shown in figure 1 below.
The complete LNB will be manufactured with an integrated feed horn and waveguide.
The difficulty is in carrying this out while maintaining the necessary phase and amplitude balance required for the circular polarisation to be received. This is because circular polarisation is only perfectly achieved when horizontal and vertical polarisations are of exactly the same amplitude, and separated in phase by exactly 90 degrees.
These two channels
The project is divided into 10 Work Packages. These are :
All the aforementioned technical developments and design issues raised during the design phase were solved and project was completed within the required time-scales, however the original cost budgeted for the design portion of the project was exceeded. This cost over run being entirely supported by additional funds from Invacom. A number of unique inventive steps have been carried out and these have now been filed as patents to protect the technology.