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.

中文翻译：

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具有宽带多模态激励的低LTE频段的薄型两端口MIMO终端天线

多输入多输出（MIMO）是移动通信中实现高数据速率的关键因素。然而，由于常规机架仅提供一种谐振特征模式（CM），因此为低于1 GHz的LTE频段设计MIMO终端天线具有挑战性。最近，研究表明，微小的结构变化可产生多达两个额外的谐振模式，以设计两端口MIMO天线。但是，第二端口的最终带宽相对较小。为了同时满足带宽和其他实际要求（包括低轮廓和无离地间隙），在这项工作中采用了逐步进行结构更改和进料设计的方法，以举例说明利用CM分析中的物理见解来实现竞争性的宽带两端口解决方案。主要的新颖之处在于，可以识别出一种全新的模式，并通过结构修改对其进行适当的调整，以在1 GHz以下产生额外的谐振。此外，两个简单的探针馈送端口设计为在整个频率上共同激发四种模式的不同子集。另外，通过端口位置处的特征电场的不同相移来保证远场图案正交性。此外，避免了笨重的自谐振天线元件。为了显示设计的灵活性，还演示了三端口版本。远场模式正交性由端口位置处的特征电场的不同相移来保证。此外，避免了笨重的自谐振天线元件。为了显示设计的灵活性，还演示了三端口版本。远场模式正交性由端口位置处的特征电场的不同相移来保证。此外，避免了笨重的自谐振天线元件。为了显示设计的灵活性，还演示了三端口版本。