A circularly polarized sequential-rotation 2 × 2 patch antenna array integrated with a 60-GHz Doppler radar system is implemented on the low-temperature co-fired ceramic (LTCC) substrate. The LTCC technology with multiple metal layers is able to satisfy the different dielectric thickness requirements of antennas and microstrip feedlines, and it also provides a compact millimeter-wave packaging option for the CMOS radar chip. Compared to linearly polarized single-patch antenna, the 10-dB bandwidth of the antenna array on LTCC increases from 1.3 (2.4%) to 7 GHz (12.8%) at 55 GHz, and narrow 50- Ω feedline is achieved to realize flip-chip transition. As the modeling and manufacturing variations are often present in the millimeter-wave systems, wide antenna bandwidth is able to cover the possible frequency drift and increase the yield of system-in-package. The circular polarization also provides better isolation against other sensors in multiple radars applications.
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Shen et al. (2012) studied this question.
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