In connection with microwave communication systems, such as those used in communication satellites, microwave channelizing filters are provided to separate the receive antenna beam signals according to frequency. In previous systems, polarization and spatial isolation of beams were employed to permit reuse of the assigned frequency spectrum. The systems were often designed with two sets of channelizing filters, where all of the receive antenna beam signals of given polarization are filtered by a set of filters corresponding to that polarization. To improve the isolation between adjacent filters within a filter set, the filters were separated into two groups, whereby one group contained all odd-numbered filters and the other group contained all even-numbered filters. However, as the number of isolated beams is increased, the interconnection of all the users becomes very complicated and is one of the factors that limits the number of reuses of the frequency spectrum.
The above-discussed filtering arrangement is unsuitable for new generations of communication satellites wherein it is desirable to reuse the assigned uplink and downlink frequency spectrums over a plurality of geographic zones and to interconnect small earth terminals in one zone with terminals in another zone. An example of such a communications satellite is disclosed in U.S. patent application Ser. No. filed as 896,983, owned by the Assignee of the present application. In the system disclosed in that application, a communication satellite interconnects large numbers of very small aperture earth terminals in a manner which maximizes satellite EIRP as well as the available bandwidth. The system employs highly directional contiguous beams on the downlink which substantially increases the EIRP and allows multiple reuse of the assigned frequency spectrum. As a result, the number of communications that can be provided for point-to-point service is maximized. The high multicarrier transmitter efficiency is achieved as a result of the dispersion of intermodulation products and the deleterious effects of rain on the downlink channels are easily overcome by the use of pooled transmitter power. The interconnection of the many users is achieved by a combination of a filter interconnection matrix and a highly directional addressable downlink beam.
The present filter interconnection matrix is intended to overcome the deficiencies of the prior art and may be employed with a satellite communication system of the type discussed above.