A Shaped-Beam Hybrid Coupling Microstrip Planar Array Antenna for X-band Dual Polarization Airport Surveillance Radars

A novel dual-polarized microstrip patch array with a low-loss hybrid feed network suitable for X-band polarimetric airport surveillance radars (ASRs) is presented. A waveguide feed is used to excite a number of linear subarrays consisting of aperture-coupled microstrip cross-patch elements connected in series. The microstrip radiating part implements the dual polarization capability with low cross polarization, while the very reduced microstrip transmission line runs implied in the series-type feeding keep ohmic losses at a minimum. As a further major advantage of this antenna, the radiation pattern can be independently shaped in the two principal planes. In particular, the microstrip subarray is designed to produce a cosecant-squared pattern in the vertical plane, whereas the waveguide provides a Taylor-like illumination distribution to have low side lobes in the horizontal plane. As a result, the proposed array antenna is expected to stand out for high efficiency, polarization purity, simplicity of fabrication, light weight and compactness.