Increased use of wireless technologies for communications and sensing results in spectral overcrowding in the lower GHz range. Spectrum allocations in the upper microwave and in the millimeter-wave ranges are available, yet realizing low-cost circuits, e.g. for the 24 GHz ISM band remains a challenge. We are investigating the use of two Si/SiGe hetero-junction bipolar transistor technologies at Atmel Germany (the commercially available SiGel and the emerging SiGe2 processes), combined with compact circuit design and back-end micromachining techniques, for the realization of cost-efficient RF frontend solutions at frequencies above 20 GHz. Results presented here include a fully monolithic receiver IC for 24 GHz, and a 33 GHz oscillator module combined with a thin-film antenna structure using wafer-level integration. (C) 2003 Elsevier B.V. All rights reserved.