Asymmetric high isolation 6 dB microstrip couplers for load sensing applications

This paper proposes two new tightly coupled 6 dB microstrip couplers for two different frequency bands with high isolation and good load dynamic range. The couplers employ quadrature mode and odd mode suppression to achieve high isolation. The first proposed coupler uses modified three branch couplers, while the second coupler uses Wilkinson power divider and rat race coupler. The measured isolation of the first coupler is above 40 dB from 723MHz to 1.2GHz, and the second coupler has isolation better than 35 dB from 1.6 to 2.6 GHz. The couplers have load dynamic ranges of 28—45 dB and 21—32 dB, from 750MHz to 1.15 GHz, and 1.7 to 2.6 GHz, respectively. The high dynamic range of these two couplers make them suitable for load sensing applications.