A Simple Method to Stabilize Radiation Pattern over a Large Bandwidth

An alternative radiation stabilization method has been presented for patch antenna. With this method, side radiation could be suppressed when a conductor ring and a circular slot both with the width of a quarter-wavelength are placed on the same layer and around patch antenna. An experimental structure has been simulated and the distance from antenna part to conductor ring is optimized using parametric function of HFSS software. Measured results given in this paper obviously indicate that not only the side radiation from the boundary of substrate could be suppressed effectively, but also the antenna directivity could be adjusted and enhanced after this method has been carried out. Both simulation and measurement indicate that when the distance is set to one guided wavelength ( ), side radiation could be suppressed the most effectively and the return loss of patch antenna is only slightly affected. 1. Introduction To meet the needs of designing a planar, wideband and dual-polarized antenna array for the reception of direct-broadcast satellite (DBS) system, a patch antenna which is composed of 7 patches arranged in a cross-shape, has been studied in [1] as the element of big array. After optimizing the size of patches and the width of gaps of cross antenna, the relative bandwidth reaches up to 38% with respect to the central frequency (band is from 10 to 14.7？GHz). But according to the radiation patterns shown in [1], the cross antenna has a disturbed omnidirectional pattern in the front side and its main beam is also steered due to the unsymmetrical structure. As an omnidirectional and stable radiation in front side is expected over all the bandwidth, a solution to correct these disturbances is required. The idea of using metamaterial to improve antenna directivity has been proposed in [2–4]. In [2] Turpin et al. have constructed a metalens for crossed-dipole feed antenna and the measured directivity was reported to have increased more than 6？dB. In [3, 4], two types of metamaterial structures composed of copper grids with lattices are introduced for patch antenna; not only directivity but also the front-to-back ratio is greatly increased as reported in their studies. But according to their methods, the metalens is a nonplanar structure which looks like a wall, and the copper grids methods are not suitable for broadband applications due to the relative narrow band of metamaterial structure. Reference [5] provides us with a single element antenna which uses freeformed cylindrical woodpile cavity; very good SLL (sidelobe level), narrow beam, and good