Design and Analysis of Dual Polarized Broadband Microstrip Patch Antenna for 5G mmWave Antenna Module on FR4 Substrate

This study presents a dual polarized broadband microstrip patch antenna for a 5G mmWave antenna module on an FR4 substrate. The proposed antenna was fabricated using a standard FR4 printed circuit board (PCB) process because of its low cost and ease of mass production. The electrical properties of the FR4 substrate in the 5G mmWave frequency band were also characterized. An air cavity structure was introduced to mitigate the high loss tangent of the FR4 substrate. Capacitive elements such as proximity L-probe feedings and parasitic patches are used to improve the impedance bandwidth of the patch antenna. For the polarization diversity of the massive multiple-input multiple-output (MIMO) capability, the antenna radiator was designed with a symmetrical structure, and the relative position of the L-probes excites the orthogonal resonant modes to enable dual linear polarization. The operation principle of the proposed antenna was thoroughly analyzed by characteristic mode analysis (CMA). The measured bandwidth of a single antenna was 23.1 % (23 ~ 29 GHz) and the gain value was 5 dBi. The measured cross-polarization suppression ratio of single antenna was 15 ~ 20 dB. The measured gain value of 1×4 antenna array was 10 ~ 11 dBi and the cross-polarization suppression ratio was about 20 dB. The size of the proposed single antenna is 0.41λ
₀
×0.41λ
₀
×0.1λ
₀
, and that of a 1×4 antenna array is 2.78λ
₀
×0.41λ
₀
×0.1λ
₀
. The envelope correlation coefficient (ECC) was calculated and was lower than 0.02 in the 5G mmWave frequency band.