Low-Profile Two-Port MIMO Terminal Antenna for Low LTE Bands with
Wideband Multimodal Excitation
Abstract
Multiple-input multiple-output (MIMO) is a key
enabler for high data rates in mobile communications. However, it is
challenging to design MIMO terminal antennas for LTE bands below 1 GHz,
due to the conventional chassis offering only one resonant
characteristic mode (CM). Recently, it was shown that minor structural
changes can yield up to two additional resonant modes for designing
two-port MIMO antennas. Nonetheless, the resulting bandwidth for the
second port is relatively small. To simultaneously meet bandwidth and
other practical requirements (including low profile and no off-ground
clearance), a step-by-step approach for structural changes and feed
design is applied in this work to exemplify the use of physical insights
from CM analysis to achieve a competitive wideband two-port solution.
The main novelty is that an entirely new mode is identified and
appropriately tuned by structural modification for creating an
additional resonance below 1 GHz. Moreover, two simple probe-feed ports
are designed to jointly excite different subsets of four modes over
frequency. In addition, far-field pattern orthogonality is guaranteed by
the different phase shifts of the characteristic electric fields at the
port locations. Furthermore, bulkier self-resonant antenna elements are
avoided. To show design flexibility, a three-port version is also
demonstrated.