B16. Effect of mutual coupling on the performance of four elements microstrip antenna array fed by a Butler matrix

Detailed design of a four element microstrip antenna array fed by a Butler matrix is presented. The proposed structure represents a switched-beam smart antenna system working in the ISM band at 2.45 GHz. To compensate for mutual coupling effects, a four-arm spiral electromagnetic bandgap (EBG) structure is inserted between adjacent microstrip patches. The four-arm spiral EBG structure provides 40% reduction in size compared with the conventional mushroom EBG structure. The antenna gain with and without EBG substrate is evaluated taking into account the effect of mutual coupling. It is found that the use of four-arm spiral EBG substrate reduces the mutual coupling by (3-17) dB between the patches. This is useful in improving the accuracy of the direction of the main beam of the array. Moreover, this improves the gain by a small value of 0.25 dB. Simulation of the antenna system is carried out using Ansoft Designer software V4.