Electrosurgical forceps comprising: a pair of jaw elements pivotable relative to each other to open and close a gap therebetween; a first conductive element mounted in one of the pair of jaw elements adjacent to the gap; a second conductive element mounted in the other one of the pair of jaw elements adjacent to the gap opposite the first conductive element; a coaxial cable for conveying microwave energy having a specific frequency; and a signal transition portion at a distal end of the coaxial cable, the signal transition portion being arranged to connect the first conductive element to an outer conductor of the coaxial cable and to connect the second conductive element to an inner conductor of the coaxial cable, wherein the first conductive element and the second conductive element and the gap between the pair of jaws constitute a transmission line to support the microwave energy as a travelling wave, wherein the conductive elements on opposing surfaces of the pair of jaw elements are not in a uniform spatial relationship with each other along the length of the pair of jaw elements, wherein the transmission line formed by the first conductive element and the second conductive element is designed to couple electrical energy into biological tissue in the gap between the pair of jaw elements to prevent multiple reflections of the travelling wave, whereby the transmission line is non-resonant for the microwave energy along the travelling wave in the presence of biological tissue, and wherein the transmission line has a geometry selected to exhibit high loss at the specific frequency of the microwave energy when the biological tissue is present in the gap, whereby power received at the proximal end of the transmission line is deliverable into the biological tissue in the gap during a single transit of the travelling wave along the transmission line. a pair of jaw elements pivotable relative to each other to open and close a gap therebetween; a first conductive element mounted in one of the pair of jaw elements adjacent to the gap; a second conductive element mounted in the other one of the pair of jaw elements adjacent to the gap opposite the first conductive element; a coaxial cable for conveying microwave energy having a specific frequency; and a signal transition portion at a distal end of the coaxial cable, the signal transition portion being arranged to connect the first conductive element to an outer conductor of the coaxial cable and to connect the second conductive element to an inner conductor of the coaxial cable, wherein the first conductive element and the second conductive element and the gap between the pair of jaws constitute a transmission line to support the microwave energy as a travelling wave, wherein the conductive elements on opposing surfaces of the pair of jaw elements are not in a uniform spatial relationship with each other along the length of the pair of jaw elements, wherein the transmission line formed by the first conductive element and the second conductive element is designed to couple electrical energy into biological tissue in the gap between the pair of jaw elements to prevent multiple reflections of the travelling wave, whereby the transmission line is non-resonant for the microwave energy along the travelling wave in the presence of biological tissue, and wherein the transmission line has a geometry selected to exhibit high loss at the specific frequency of the microwave energy when the biological tissue is present in the gap, whereby power received at the proximal end of the transmission line is deliverable into the biological tissue in the gap during a single transit of the travelling wave along the transmission line.