Directional coupler cascading for signal enhancement

Claim 1

In a data transmission system of the type using directional couplers to couple information to a two way transmission line wherein said couplers are connected to enhance the desired backward coupled signal and minimize the parasitic forward coupled signal comprising; at least three directional couplers having fixed equal electrical characteristics and each having an input terminal, a backward coupled signal output terminal, a thru terminal and a forward coupled signal terminal; signal input means connected to said input terminal of the first directional coupler of said at least three directional couplers; a first minimum delay means connecting the thru terminal of each of said directional couplers except the last one to said input terminal of the succeeding directional coupler; a second minimum delay means connecting the backward coupled signal terminal of each of said directional couplers except the last one to the forward coupled signal terminal of the succeeding directional coupler; and means for terminating said forward coupled signal terminal of said first coupler and the thru terminal and the backward coupled signal output terminal of the last coupler in a characteristic impedance of the line to which said terminals are connected, the backward coupled signal of each directional coupler arriving simultaneously at said backward coupled signal output terminal to produce an enhanced backward coupled signal at the backward coupled signal output terminal of the last coupler of said plurality of couplers and said parasitic forward coupled signals arriving at said forward terminal of the first directional coupler out of coincidence thereby minimizing said parasitic forward coupled signal.