Optimization and Performance Limits of a 64-QAM Wireless Communication Link at 220-260 GHz in a SiGe HBT Technology

We present a 1-meter wireless link based on Tx and Rx RF front-end modules working at a tunable LO frequency of 220-260 GHz with a channel BW of 13.5 GHz. The modules were manufactured in a SiGe HBT technology with f _T /f _max =350/550 GHz. The modulation scheme used was 64-QAM. This high spectral-efficiency modulation requires a higher degree of system purity than QPSK or BPSK. Therefore, an accurate correction of all error sources in the RF front-end, such as IQ imbalance, LO spectral purity, and linearity and intermodulation products, has been performed. After this, and together with a decision-directed feed-forward equalizer of 41 taps, a 81 Gbps 64-QAM with an EVM of 8.7% was achieved at 235 GHz. using a BW of 11.5 GHz. The full available channel BW could not be exploited at 1-meter distance because of AWGN SNR and phase noise constrains which scale linearly with the modulation BW.