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This paper presents a dual-band RF front-end for WLAN low-IF receivers, operating in the 2.4 GHz ISM band and the three 5 GHz U-NII bands. The RF receiver uses an LNA with dual input stages, replacing the use of multiple independent LNAs operating at different bands, and one multi-band image rejecting mixer, which exploits the inherent broadband frequency response of multi-stage polyphase filters and singly-balanced active mixers. The chosen architecture avoids the use of switches in the RF path by means of a dual-band resonator at the LNA-mixer interface. Fabricated in a 0.25 μm 47 GHz-ft BiCMOS technology, the circuit exhibits 33.4 dB of conversion gain, 4.1 dB of NF and -16.6 dBm of iIP3 in the 2 GHz mode, while in the 5 GHz mode conversion gain is 27 dB, NF is 8.6 dB and iIP3 is -11.6 dBm. Power consumption is 14.9 mW for the low-frequency mode, and 18.7 mW for the high-frequency mode. Making use of no external components, this chip provides a good basis for the realization of low-cost receivers for dual-band operation.