An 8-channel Ku band transmit beamformer with low gain/phase imbalance between channels

An 8-channel Ku band (12.5 GHz-14.7 GHz) transmit beamformer has been proposed and fabricated in a 0.18um SiGe BiCMOS technology, which has small phase variation over gain states and low gain/phase imbalance between channels. A current-steering variable gain amplifier (VGA) is proposed with constant current consumption for all gain states to maintain the input impedance, which achieves a small RMS phase variation of ±0.07°/dB. In addition to parasitics prediction from electromagnetic simulations, the layout of the 8-channel transmit beamformer is symmetrically designed to reduce gain/phase imbalance between channels. The RMS gain imbalance for channels 2-7 is ±0.14 dB and the RMS phase imbalance is ±0.71°, which, to the best knowledge of the authors, is the lowest compared to recently reported beamformers.