Dual-Band Dual-Polarized Omnidirectional MIMO Antenna With Ultra-Low Profile for Vehicular Communications

In this article, a dual-band dual-polarized (DP) omnidirectional multiple-input multiple-output (MIMO) antenna with ultra-low profile is proposed for vehicular communications. The vertically polarized element (VPE) is composed of a top-loaded metal disk, four bent arms and a round ground, which has a low profile of 0.049<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> represents the free space wavelength at the lowest operating frequency) and a broad band of 1.66 GHz to 4 GHz. It is evolved from a mono-conical antenna and eventually achieved an ultra-low profile while remaining the broad band by replacing the complete cone with four metal arms, adding a top-loaded metal disk and grounding structures, and the multiple bents of the four arms. After that, two horizontally polarized elements (HPEs) are meticulously designed and embedded in the ground and the top disk of the VPE, respectively. Benefiting from the low profile VPE, the planar HPEs and the compact embedding scheme, the proposed antenna has a profile of only 0.053<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub>. To verify the design, a prototype is manufactured and measured. The results indicate that the prototype has overlapping bands of 1.63–2.7 GHz and 3.22–3.82 GHz, gain variation in omnidirectional plane of below 2.4 dB, and isolation between ports of better than 25 dB.