A low-cost, high isolation, printed loop-antenna system for multiple-input multiple-output (MIMO) applications in the 2.4 GHz WLAN band is presented. By feeding the orthogonal eigenmodes of the array, port decoupling (S21< -20 dB) with tightly coupled elements (only 0.07λ separation) is obtained. The orthogonal eigenmodes are realized based on 180° coupler. Then decoupled external ports of the feed network may be matched independently by using conventional matching circuits. With this low-cost and high isolation characteristic, it is very suitable for being embedded inside a wireless access point (AP).
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