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Double Torsion Coil Feeding Structure for Patch Antennas

A new feeding structure for patch antennas is proposed in this paper. The feeding structure is formed by a double torsion coil (DTC) with one end electrically connected to the ground. The maximum stretch length of the coil is around half of the wavelength of the center frequency. The winding direction of the coil is reversed at the middle point of the coil. The DTC is able to produce two coaxial equivalent magnetic dipoles polarized in the same direction, which can not only excite the TM01 mode of a patch antenna but also create another resonance, leading to a wideband impedance bandwidth. The working mechanism is explained in this paper by physics intuition. To validate the new feeding structure, a linear-polarized and a dual-polarized patch antenna prototypes working in the 3.5 GHz band are designed, manufactured, and measured. It is found that the linear-polarized patch antenna can achieve a bandwidth of 25% standing-wave ratio (SWR < 2) and 9.5 dBi average gain with stable radiation patterns and low cross polarization over the impedance bandwidth. The new feeding structure has a high potential for wideband massive multiple-input and multiple-output (M-MIMO) arrays of 5G and future wireless communication systems.