Miniaturized 90 degree hybrid coupler using high dielectric substrate for QPSK modulator

This paper describes miniaturized 90 degree hybrid coupler using edge-coupled microstriplines. A high dielectric constant substrate (K=38) and high-density coupled-line configuration are adopted to realize small chip size. A conventional meandered coupled-line type and a new spiral coupled-line type were discussed for a high-density configuration. A bandwidth from 1.8 GHz to 3.6 GHz with /spl plusmn/0.5 dB power dividing balance and 90/spl plusmn/3 degrees phase difference were achieved with a chip size of 1.5/spl times/1.5 mm.