Compact series-fed microstrip patch array antenna in the 60 GHz band

Despite the inherent transmission-range limitations of 60 GHz band, it has applications in a wide variety of fields, notably in rear occupant alert (ROA) systems for monitoring vehicle occupants in rear seats. In-vehicle monitoring radar systems commonly utilize microstrip patch antennas for transmitting and receiving electromagnetic waves, which generally suffer from limited bandwidth. Although various techniques such as stub matching and single and multi-section quarter-wave transformers can be employed to widen the bandwidth of a microstrip patch antenna, they lead to an overall increase in the antenna size. This study proposes a compact 3 × 1 series-fed patch array antenna designed for operation in 60 GHz band. The proposed compact antenna achieves impedance matching by employing a symmetrical inset structure on both the top and bottom of the patches, with different patch sizes and interelement spacings. The overall antenna dimensions, using the RO4830 substrate (ε_r = 3.23, tan δ = 0.0033), are 1.41 mm × 7.04 mm × 0.125 mm. The impedance bandwidth ranges from 60.95 to 66.73 GHz, and the maximum realized gain is 10.24 dBi at 62.5 GHz. The half-power beam-widths (HPBWs) are 33.96 degrees in the E-plane and 76.19 degrees in the H-plane at 62.5 GHz.