Frequency-agile Butler matrix with good interference suppression for multiple radio wireless platforms

In this study, a frequency-agile Butler matrix is proposed and designed to operate from 1.92 to 2.7 GHz, which can therefore be used in several different wireless applications, including the universal mobile telecommunications system, the wireless fidelity (WiFi) and the world interoperability for microwave access. Measured results show that the amplitude imbalance of this Butler matrix is less than 2 dB, while the average insertion loss is less than 2.7 dB. Meantime, the return loss is better than 15 dB, together with the isolation between input ports better than 17 dB. In addition, an antenna array fed by this frequency-agile Butler matrix is investigated. It exhibits good out-of-band suppression especially at the lower band, showing the advantages over other multiband and wideband counterparts. For example, when the multiple beam antenna operates at 1.95 GHz, the received power levels of 2.14, 2.35, 2.44 and 2.6 GHz are only 0.02, 0.46, 0.19 and 0.87%, respectively, compared with the reference received power level of 1.95 GHz.