By searching the IEEE JSSC you will find several papers for 5GHz 802.11a direct conversion receivers as well as the issues that they are facing like DC offset etc.
Some examples:
"A 5-GHz direct-conversion CMOS transceiver utilizing automatic frequency control for the IEEE 802.11a wireless LAN standard," Solid-State Circuits, IEEE Journal of , vol.38, no.12, pp. 2209-2220, Dec. 2003
"A 72-mW CMOS 802.11a direct conversion front-end with 3.5-dB NF and 200-kHz 1/f noise corner," Solid-State Circuits, IEEE Journal of , vol.40, no.4, pp. 970-977, April 2005
"A single-chip digitally calibrated 5.15-5.825-GHz 0.18-/spl mu/m CMOS transceiver for 802.11a wireless LAN," Solid-State Circuits, IEEE Journal of , vol.38, no.12, pp. 2221-2231, Dec. 2003