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Abstract
Compact broadband microstrip rat-race couplers using microstrip/slotline phase inverters are proposed. A wide range of power-dividing ratio () is achieved by varying the impedance ratio of the transmission lines, while the dual-band impedance matching characteristic with frequency ratio (
) is obtained by varying the impedances of the transmission lines
only. For verification, a rat-race coupler with power-dividing ratio of
and operating at 1.0/2.5 GHz is designed, fabricated, and measured. The measured results are in good agreement with the simulated ones. The measured results show a bandwidth of 120% with better than 10-dB return loss and 31-dB isolation from 0.69 to 2.74 GHz.
Acknowledgement
This work is supported by the National Natural Science Foundation of China (61171029 and 61101017).