Ka-Band Miniaturized 90 nm Complementary Metal Oxide Semiconductor Wideband Rat-Race Coupler Using Left-Handed and Right-Handed Transmission Lines

The traditional rat-race coupler comprises a quarter-wavelength transmission line and a three-quarter-wavelength transmission line. In this design, the slow-wave structure transmission line is employed to replace the conventional quarter-wavelength transmission line, and the three-quarter-wavelength transmission line is substituted with the left-handed transmission line. By using the TSMC CMOS 90 nm fabrication process, a circuit is created with a chip size of 300 mu m x 200 mu m, corresponding to the electrical size at 39 GHz of 0.039 lambda 0 x 0.026 lambda 0. The measured results demonstrate that the operating bandwidth is 35 to 43 GHz, with an amplitude imbalance of around 0 dB, a phase error within 1 degrees, a return loss of less than 26 dB, and an isolation better than 40 dB.