Quasi-optical feeds and multiplexers

For frequencies above about 80 GHz a quasi-optical network, not a waveguide network, is necessary if the specified performances are to be achieved over a wide bandwidth. Each signal beam is transported from the receiver horn (it is convenient to adopt a time-reversed description) to the dual-reflector antenna´s feed-plane, by a train of lenses, or (preferably) focussing mirrors, through two or more dichroic plates. Some of the considerations arising in the design of such quasi-optical trains are indicated. Both beam control optics and dichroic plates are considered