Orthogonal properties of a set of 2-path filters
Arthur W. Keen, A.F. Comer · Electronics Letters · 1971
The known form of 2-path filter is shown to be one of a set of four structures which correspond to the sine and cosine of angular sum and difference formulas of elementary trigonometry. Two of these structures are shown to be components of the general orthogonal 2-port network and therefore useful for synthesis purposes.