To interconnect three or more adaptors in a wave digital filter, it is now typical to use a Binary Connection Tree (BCT) [152,364], in which only three-port adapters are needed. Three-port adaptors can handle any combination of parallel and series connections.
For example, suppose we wish two connect adaptors and in parallel using a new three-port parallel adaptor , as shown in Fig.F.6. Adaptors and are normally themselves three-port adaptors in a BCT, but they can be any kind of adaptor (scattering junction). All that matters from the point of view of adaptor is the connecting port wave impedances and . Then to make the top port of adaptor reflection free, we choose its wave impedance to be the parallel combination of all other connected adaptors, i.e., in this case. We mark the top outgoing port of as being reflection-free using the ` ' symbol.