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The design of a C-band phase shifter fabricated in a commercial 0.25 mum BiCMOS technology is presented. Phase shift is enabled by tuning the varactors of a lumped element, equivalent of a transmission line. Only one single control voltage is required. The circuit is optimised for adaptive antenna combining on the basis of the 802.11a standard and matched for 50 Omega terminations. Within a frequency band ranging from 5.2 to 5.8 GHz, the circuit yields a phase control range of higher than 195deg, an insertion loss of only 3.6 +1.5 dB, return losses higher than 12 dB and a 1 dB compression point above 10 dBm. The chip and circuit areas amount to 0.6 and 0.25 mm2, respectively. To the knowledge of the authors, at comparable phase control range, the lowest insertion loss for a passive phase shifter integrated in silicon reported to date is demonstrated.