This work presents the design of a dual band frequency modulated continuous wave (FMCW) radar receiver (RX) at the 2.4 and 5.8 GHz industrial, scientific and medical (ISM) bands. The designed low noise amplifier (LNA) has a single ended 50 Ω input stage followed by an active balanced-to-unbalanced (balun) stage. The radio frequency (RF) signal is then down-converted to a low intermediate frequency (IF) by a multi-tanh Gilbert cell mixer whose local oscillator (LO) port is driven by an integrated fractional-N phase locked loop (Frac-N PLL). After down-conversion, the resulting IF signal is low pass filtered and amplified by a baseband variable gain amplifier (VGA). Fabricated on an IBM 0.18 μm BiCMOS process, the measured RX performance is in good agreement with simulations achieving a measured maximum conversion gain (CG) of 82.0 and 77.2 dB and a noise figure (NF) of 7.3 and 8.0 dB at the 2.4 and 5.8 GHz bands respectively. The receiver consumes 22.3 mA from a 3 V supply and occupies a chip area of 0.32 mm2. When used as a primary FMCW radar transceiver (TRX), the designed chip achieves a ranging precision of 0.30 and 0.31 mm at the 2.4 and 5.8 GHz bands respectively. To the best of the author's knowledge, this dual band FMCW radar TRX has the highest level of integration reported in the literature.