US Patent 7385461 Method of combining signals and device therefor

A bias T device (20) and a method for combining a first DC signal with a second RF signal is disclosed. The device (20) is provided with a first signal splitting means (30) in the form of a hybrid 90 degree (quadrature) coupler having at least two isolated transmission lines (34,40). The first signal splitting means (30) is adapted to receive said first signal at one input (22) and said second signal at another input (24). A second signal splitting means (32) having at least two isolated transmission lines (34′, 40′) is also provided. Said second signal splitting means (32) is coupled to said first signal splitting means (30) such that the respective sets of transmission lines (34, 34′, 40, 40′) comprise isolated signal routes (70, 72) through said device (20). An output (26) provides an output signal comprising a combination of said first DC signal and said second RF signal. A coupling effect between at least two of said transmission lines (34, 34′, 40, 40′) is used to combine said first signal with said second signal.