In this paper, a high-order-mode (HOM) (TE330) cavity-fed 45° linear polarized 6×6 slot array antenna is proposed. The 45° linear polarization is achieved by introducing asymmetric cross slots on the HOM cavity, resulting in low profile and wide bandwidth. The antenna array was verified using standard printed circuit board technology. Measured results show that the impedance bandwidth ( $|S_{11}|\le$ −10 dB) is 13.9% (36.98–42.92 GHz), and the peak gain is 19.3 dBi with a 3-dB gain bandwidth of 13.6%. Attributed to its simple structure, low profile, and wide bandwidth, the presented antenna is a good candidate for 5G applications.