Direct quadrature phase shift keying modulation using compact wideband six-port networks

In this study, the operation of a compact six-port network operating as a quadrature phase shift keying (QPSK) modulator with a wide operational bandwidth is presented. The modulation has been accomplished using two types of single-layer six-port networks. The first six-port network uses a novel architecture that is newly introduced herein for use as a QPSK modulator, and employs broadband components previously developed by the same authors. The second six-port network employs the same types of broadband components in a conventional six-port architecture for comparison. The performance of the modulator using both six-port networks is tested using agilent´s advanced design system and its wideband operation is verified with measured results. It is shown that the proposed six-port modulator offers accurate QPSK symbol modulation at a symbol rate of 400 Msymbols/s across an octave bandwidth from 4.5 to 9´GHz (66´ operational bandwidth).