Miniaturized FSS and Patch Antenna Array Coupling for Angle-Independent, High-Order Spatial Filtering

A new filter-antenna array design is presented in this article. This design approach can be employed to simplify the vertical integration of array beamformers. Basically, by placing a high-order filter, whose response is not sensitive to angle of arrival, in front of the array elements, the need for integrating bulky RF filters behind each element is eliminated. A new method for design of such phased-arrays is provided here in which the bandpass filters are removed, and instead, a metamaterial-based frequency-selective surface is placed directly over the antenna to perform the necessary filtering. The small spacing between the frequency-selective surface and the antenna, which is as low as similar to lambda/10 results in creation of a compact filter-antenna deign. The close proximity of the surface and the antenna is utilized to achieve a proper coupling between the selective surface and the array for high-order filtering without adversely affecting the gain or scan characteristics of the array. To test the performance of this approach, a 9 x 9-element patch-array is fabricated and measured at X-band. The array is then loaded with a 0.003 ''-thick, single-pole frequency-selective layer at a close distance on top. The measured received power as a function of frequency exhibits an improved frequency selectivity (better than the frequency-selective surface or the array alone). An improvement of about 50% reduction in the bandwidth and significantly higher frequency roll-off rate is observed once the array is covered with the metamaterial surface.