A system comprising: a monolithic microwave integrated circuit (11, 111, 212) comprising an input pad, and an output pad, the monolithic microwave integrated circuit (11, 111, 212) having a first impedance; a waveguide having a second impedance; an interface (10, 110); and a structure surrounding the monolithic microwave integrated circuit (11, 111, 212) and the interface, wherein the interface comprises: a waveguide step launch (16, 115) having the first impedance at the first end and the second impedance at a second end, wherein the second end is connected to the waveguide; a first isolation wall placed above the monolithic microwave integrated circuit and located between the input pad and the output pad, the first isolation wall being part of the structure surrounding the monolithic microwave integrated circuit (11, 111, 212) and the interface; and a cavity defined by the waveguide step launch (16, 115), wherein the cavity has a different size at different points along the direction of a microwave pathway, and wherein the size of the cavity increases at different points along the direction of the microwave pathway from the monolithic microwave integrated circuit (11, 111, 212) to the waveguide (26, 120), wherein the output pad of the monolithic microwave integrated circuit (11, 111, 212) is connected by a wirebond to either the isolation wall or to the waveguide step launch (16, 115). a monolithic microwave integrated circuit (11, 111, 212) comprising an input pad, and an output pad, the monolithic microwave integrated circuit (11, 111, 212) having a first impedance; a waveguide having a second impedance; an interface (10, 110); and a structure surrounding the monolithic microwave integrated circuit (11, 111, 212) and the interface, wherein the interface comprises: a waveguide step launch (16, 115) having the first impedance at the first end and the second impedance at a second end, wherein the second end is connected to the waveguide; a first isolation wall placed above the monolithic microwave integrated circuit and located between the input pad and the output pad, the first isolation wall being part of the structure surrounding the monolithic microwave integrated circuit (11, 111, 212) and the interface; and a cavity defined by the waveguide step launch (16, 115), wherein the cavity has a different size at different points along the direction of a microwave pathway, and wherein the size of the cavity increases at different points along the direction of the microwave pathway from the monolithic microwave integrated circuit (11, 111, 212) to the waveguide (26, 120), a waveguide step launch (16, 115) having the first impedance at the first end and the second impedance at a second end, wherein the second end is connected to the waveguide; a first isolation wall placed above the monolithic microwave integrated circuit and located between the input pad and the output pad, the first isolation wall being part of the structure surrounding the monolithic microwave integrated circuit (11, 111, 212) and the interface; and a cavity defined by the waveguide step launch (16, 115), wherein the cavity has a different size at different points along the direction of a microwave pathway, and wherein the size of the cavity increases at different points along the direction of the microwave pathway from the monolithic microwave integrated circuit (11, 111, 212) to the waveguide (26, 120), wherein the output pad of the monolithic microwave integrated circuit (11, 111, 212) is connected by a wirebond to either the isolation wall or to the waveguide step launch (16, 115).