A microwave tissue treatment device, comprising an antenna assembly enclosing an internal cavity housing an inner conductor, the antenna assembly including a baffle member dividing the internal cavity into a first cell and a second cell, at least a portion of the inner conductor being positioned within each of the first and second cells and a cooling system configured to circulate a cooling fluid through the antenna assembly such that at least a portion of the inner conductor is in fluid contact with the cooling fluid to thereby dissipate heat generated by the inner conductor during use of the microwave tissue treatment device. The cooling system includes a first inlet conduit and a first outlet conduit in fluid communication with the first cell to circulate the cooling fluid through the first cell, and a second inlet conduit and a second outlet conduit in fluid communication with the second cell to circulate the cooling fluid through the second cell. The baffle member is configured to substantially prevent comingling of fluid between the first cell and the second cell. The first cell defines a first volume, and the second cell defines a second volume different from the first volume, whereby the portion of the inner conductor positioned within the first cell is heated to a different extent than the portion of the inner conductor positioned within the second cell.
