A quarter‐mode (QM) substrate‐integrated‐waveguide (SIW) cavity is designed as a dual‐functional component. By etching three slots, four sub‐cavities are formed and then two of them with the same size are individually fed by a coaxial port. Three resonating frequencies are excited in the single QM SIW cavity. One of them can radiate cavity energy input by these ports into free space, implying a two‐element multiple‐input‐multiple‐output (MIMO) antenna, whereas the other two can transmit energy from one port to the other port, indicating a second‐order bandpass filter. Moreover, antenna isolation and filter bandwidth can be adjusted to a certain degree. A prototype with the overall size of 0.40λ₀ × 0.40λ₀ × 0.02λ₀ has been fabricated. The integrated bandpass filter demonstrates the measured center frequency of 3.8 GHz and operating bandwidth of 32 MHz while the integrated MIMO antenna exhibits the frequency of 3.4 GHz, bandwidth of 67 MHz, port isolation of 18.0 dB, radiation gain of 4.0 dBi, and envelope correlation coefficient of 0.25.

中文翻译：

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集成了两元素MIMO天线和二阶带通滤波器的双功能QM SIW腔

四分之一模（QM）基板集成波导（SIW）腔被设计为双功能组件。通过蚀刻三个槽，形成四个子腔，然后通过同轴端口分别馈入其中两个大小相同的子腔。在单个QM SIW腔中激发三个谐振频率。其中一个可以将这些端口输入的腔能量辐射到自由空间中，这意味着一个双元件多输入多输出（MIMO）天线，而另外两个可以将能量从一个端口传输到另一个端口，表示第二个阶带通滤波器。此外，天线隔离度和滤波器带宽可以调整到一定程度。原型与0.40的整体尺寸λ ₀  ×0.40 λ ₀  ×0.02 λ ₀已经被捏造了。集成的带通滤波器展示了3.8 GHz的测量中心频率和32 MHz的工作带宽，而集成的MIMO天线展示了3.4 GHz的频率，67 MHz的带宽，18.0 dB的端口隔离，4.0 dBi的辐射增益以及包络相关性系数为0.25。