Compact Doppler sensor operating at 31-32 GHz using a SiGe HBT MMIC and patch antennas

This paper describes a compact Doppler sensor consisting of a SiGe MMIC and patch antennas for transmitting and receiving. The MMIC has a differential oscillator operating at 31-32 GHz and a single balanced Gilbert cell mixer. For the differential oscillator lumped elements are used and the Gilbert cell mixer serves two purposes. First it generates the difference frequency of the transmitted and received signal, secondly it lets the RF-signal pass. This results in a total chip size of only 380 × 770 μm². On the microwave laminate substrate TMM3 patch antennas are realized, one for receiving and two for transmitting. The pads for the MMIC are prepared with solder bumps. This way the MMIC can be flip-chip mounted to the substrate of the patch antennas resulting in low losses at the interconnects.