A miniaturized TM21 mode circular patch antenna is introduced. The miniaturization is realized by loading the patch with four symmetric radial slits, which facilitate elongating the current path and thus reducing the resonant frequency and the patch size. In particular, the eigenvalue of the proposed higher order mode is reduced to that of a conventional dominant TM11 mode antenna, resulting in about 40% reduction in the radius. The effects of the slit geometry on miniaturization and resonant frequency are studied. The measurement results are also presented, which are in good agreement with the simulation ones. Such miniaturized TM21 patch antennas with conical radiation patterns have manifold applications in phased array antennas for booming communication demands.
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