ABSTRACT To simultaneously cover the 700 MHz and 5G NR bands required by coal mine applications, this paper proposes a four‐band microstrip antenna on a single‐layer substrate using characteristic mode analysis (CMA). First, a meandering monopole structure is adopted to realize a 700 MHz operating frequency within a compact region. Then, an L‐shaped branch and a rectangular branch are loaded to cover the frequencies of 2.5 and 3.5 GHz successively. In the sequel, a slotted trapezoidal floor is adopted and optimized to further improve the impedance matching characteristics and generate another resonant frequency point of 4.9 GHz. With the help of CMA, the proposed antenna can satisfy the above requirement within a compact size of 0.11λ × 0.16λ and a large frequency ratio of 7:1, which makes it a good candidate to alleviate the issue of multiple‐system coexistence in coal mine applications.
Xu et al. (Wed,) studied this question.
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