QPSK Modulation Using Multi-Port Device

This paper investigates digital modulation transmitter using multi-port device. The multi-port device is a 6-port replacing the high cost mixer in conventional transmitter. The main objective of this paper is to develop the digital modulator based on six-port network using Agilent ADS (Advanced Design Simulation) simulation tool. The S-parameters of a fabricated six-port network are measured using network analyzer. All the 2-port measured data of the six-port network are then mapped into matrix 6x6 by using MATLAB. The mapped 6x6 matrix is then used to model the six-port network in ADS simulation. The six-port network can be functioned as a digital modulation by connecting port 1 to local oscillator and port 3 to port 6 to either open and short termination. The RF modulated signal is going out from port 2 of the six-port network. The QPSK (Quadrature Phase Shift Keying) symbols are dependent on the combination of open and short terminations which are controlled by SPDT (Single Pole Double Throw) switches. The simulation and analysis of the output result are observed in terms of symbol rate and frequency of local oscillator.