Abstract: An apparatus includes a plurality of ports, a directional coupler transformer and an impedance circuit. The directional coupler transformer may be configured to (i) receive a forward input signal from a first port of the plurality of ports, (ii) generate a coupled signal at a second port of the plurality of ports, (iii) generate a forward output signal and receive a return signal at a third port of the plurality of ports and (iv) generate an internal signal at an internal node. The impedance circuit may be directly connected to the internal node and configured to direct the internal signal to a signal ground to control an isolation between the forward input signal and the return input signal. The isolation is controlled by an impedance of the impedance circuit.