Mutual coupling in aperture-coupled microstrip patch arrays with a sequential feeding technique

Aperture-coupled microstrip patch antennas are very attractive candidates for many polarimetric phased array applications. They offer an excellent electrical performance and are easy to manufacture. Due to their multilayer design an optimum choice can be made for the patch and the feed substrate. Low-permittivity patch substrates yield a high bandwidth as well as high radiation efficiency. Dual linear polarization can be achieved by either crossed slot or offset slot configurations. Depending on the bandwidth the typical polarization isolation of dual polarized aperture-coupled antenna elements on low-permittivity substrates is about -25 dB. However, for several phased array applications a even higher polarization isolation is required. By sequential feeding techniques a significant improvement of the polarization purity at the array level with values of better than -45 dB is achieved. However, microstrip patch arrays with sequentially rotated antenna elements show a different coupling and scan behavior than arrays with unidirectional aligned antenna elements. This paper investigates microstrip patch arrays for phased array applications in the C-band with a sequential feeding technique.