Analysis of the effects of Absorptive Switch v/s Reflective Switch on the performance of Hybrid Coupler designed for Birdcage coil at 1.5T MR System

Birdcage coil when used as a transceiver coil for generating circularly-polarized fields must operate in Quadrature mode. This is done with the help of a Hybrid Coupler. Further to isolate the RF leakage signal in the receive path switches are introduced. However, introducing an RF reflective switch in the receive path changes the impedance at the receive port of the Coupler which causes impedance mismatch at the coil terminals. We have inserted an absorptive switch in the receive path of the coupler with an insertion of 0.45dB and isolation of 22.48dB which ensures no impedance mismatch.