Direct N-QAM multiport modulators utilizing butler matrices

In this paper, we present novel N-QAM multiport modulators utilizing a standard Butler matrix and a set of switchable terminations. The presented theoretical investigation reveals, that using a 4 × 4 Butler matrix one can design a 16-QAM modulator, whereas utilizing an 8 × 8 Butler matrix 64- and 256-QAM modulators can be realized. The presented theory has been verified by measurements of the developed multiport modulators, proving the developed concept.