| Summary: | Wideband self-decoupling of bandwidth-enhanced dielectric patch (DP) filtennas with stable filtering response are proposed in this letter. The TM101 and TE121 modes of the DP are combined to design a wideband antenna while its high-order TM111 mode is used to introduce an intrinsic upper radiation null, leading to a good filtering response. Sequentially, <inline-formula> <tex-math notation="LaTeX">$1\times 2$ </tex-math></inline-formula> DP filtennas have been taken as an example to verify that improving the isolation can keep the filtering performance of the filtenna array basically consistent with the original filtenna element, which is a design concept proposed for the first time in this paper. To maintain almost the same filtering response when the antenna elements are spaced closely, the wideband self-decoupling between the antenna elements is obtained by properly choosing the parameters (i.e. dielectric constants of the DP and substrate), without adding extra decoupling structures. For validation, <inline-formula> <tex-math notation="LaTeX">$1\times 2$ </tex-math></inline-formula> closely-spaced filtennas are fabricated and tested. The measured results denote that the prototype has impedance bandwidth (<inline-formula> <tex-math notation="LaTeX">$\vert S_{11}\vert < -10$ </tex-math></inline-formula> dB) of about 21.2% from 4.47 GHz to 5.53 GHz and in-band isolation is over 20 dB. Benefiting from the self-decoupling scheme, the difference of the in-band gain and stopband suppression between the element and <inline-formula> <tex-math notation="LaTeX">$1\times 2$ </tex-math></inline-formula> DP filtennas is reduced significantly, showing stable filtering response of the filtennas.
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