Reduction of mutual coupling between closely spaced patch antennas using dielectric stratification technique

The capabilities of multi-layer substrates to reduce mutual coupling between closely spaced (0.3-0.5 of the free-space wavelength) patch antenna elements in antenna arrays are investigated. The inhomogeneity is created in vertical direction by inserting relatively higher and lower permittivity layers on top of each other and to the appropriate positions inside the single-layer, homogeneous substrate. To validate the effectiveness at different operational bands, the technique is demonstrated for 3×1 E-plane X-band (centered at 8.47 GHz) and S-band (centered at 2.42 GHz) planar arrays. The reference antenna is chosen as a simple pin-fed rectangular patch printed on a thin substrate with a low relative permittivity of 2.2. For the X-band and S-band arrays, coupling reductions up to 4.3 dB and 3.2 dB are obtained, respectively, for inter element spacings around 0.38 of the free-space wavelength. Improvement in the scanning performance is also observed. The proposed technique validity for larger arrays is shown by simulations of infinite arrays. The proposed four-layer substrate is able to decrease the mutual coupling in E-plane while improving the scanning performance without any need to redesign the array topology. Therefore, it will be suitable for planar dual- or multi-band wide-angle scanning arrays that have high mutual coupling levels at the low frequency bands.